battery-bike.md

battery-bike.md

Here's a comprehensive overview of ebike battery designs — especially relevant for your Omera frame project.

Cell Types: 21700 vs 18650

The industry has largely moved to 21700 cells for new builds. They're 50% larger in volume than 18650s but pack up to 45% more energy density, meaning more range with fewer cells and better heat management. em3ev

Spec	18650	21700
Diameter	18mm	21mm
Height	65mm	70mm
Max capacity	~3,500 mAh	~5,000 mAh
Weight	~48g	~70g
Best for	Compact builds, legacy packs	New builds, higher range batterydesign

Battery Placement Approaches

Downtube Integrated (Most Relevant for Omera)

The battery pack sits inside an oversized downtube, typically accommodating 40–60 cells. This is the cleanest look — the battery is invisible. Modern frames like Giant's EnergyPak use a removable cartridge that slides in/out through the bottom of the DT. This is why we discussed going to a 50mm DT for Omera — a standard 42mm DT can't fit 21700 cells (21mm diameter × 2 rows = 42mm bare minimum, no room for BMS/wiring). myvelo

Downtube External Mount

Battery bolts to the outside of the downtube using rivnuts or braze-on bosses. Common for conversions. Looks less clean but simpler to engineer. A 48V 25Ah pack with 65× 21700 cells comes pre-shaped in a downtube profile. yosepower.co

Triangle Bag/Pack

A custom-shaped battery fills the front triangle, held by a frame bag or custom cradle. Maximizes capacity (85+ cells possible) but looks bulky. Good for range-focused builds. twowheellifestyle

In-Tube Stealth

Cells are packed directly inside the frame tubes — split across top tube, seat tube, and down tube. Extremely stealthy but hard to service, limited capacity (~20 cells), and structurally risky since you're drilling access holes. forums.electricbikereview

What This Means for Omera

For a clean fixed-gear-style ebike, the best approach is downtube integrated with a removable cartridge:

• DT outer diameter: 55–60mm (up from Detroit's 42mm) to fit 21700 cells in a 2-wide or 3-wide arrangement
• Configuration: 13S3P (48V, ~15Ah, 720Wh) = 39× 21700 cells — fits in a ~55mm × 400mm downtube cavity
• BMS: 40A continuous, UL 2271 certified for US/California compliance bev-intl
• Access: Bottom-load at BB junction or side-load panel
• Weight: ~2.8kg for the pack alone

The 2026 California regulation (SB 1271) now requires UL 2849 or UL 2271 certification on all ebike batteries, so designing around a certified battery pack from the start avoids costly redesigns later. bev-intl

Want me to calculate the exact cell layout dimensions for the Omera downtube, or look into specific off-the-shelf battery packs that could fit?

You're right — if cells stack end-to-end and slide in from one opening, there's no way to insert a washer between them without breaking the drop-in flow.

So: skip per-cell fusing entirely. At 3.5A per cell, the BMS handles everything. No washers, no fuse strips, nothing between cells.

Each channel is literally:

[spring] → [cell][cell][cell][cell][cell] → [pad]

Cells touch each other directly, positive nub to flat negative, just like loading batteries into a flashlight. Drop in 5 cells, spring compresses the stack, done.

The only safety layer is the BMS — overcurrent, overvoltage, undervoltage, short circuit, temperature — all handled at the pack level, not per cell. That's completely fine at your power draw. [neogy](https://neogy.fr/en/news/news-nf-en-506041-standard-ebikes/)

yeah. each battery tube just has a flashlight cap. just like a maglight. you screw it in. Tighten it with a coin so it goes flush. can be all plastic I suppose? silicon ring in the plastic cap would keep it in place even under vibration over long time. also works as a weather seal. you only access this hatchet every 5 years or so when you change bats. its not something you open every day. we could add a thin teflon like tape inside each bat tube, that would reduce rattling, but not make the bats so tight that they would not slide out with gravity when needing to be replaced. wiring could go into the center of the cage in a long hole. I added a render of the scad you made earlier. I think we could iterate that design. just add screw-in caps and seal the bottom and add the pads there. and add a hole in the center that connects it all. the spring caps would connect to touchpoint just like a maglight. injection molding could have screw cap moulding part. that unscrew when mold is done. so groves are made when molding. the rest is just cylinder that goes with the mold cap sort of.

Here's the updated scaffold . Here's what changed from v1:

What's in v2

4 channel tubes (2×2 grid, same as your render):

• Thin-walled cylinders, bore sized for 21mm cell + 0.3mm PTFE liner + sliding clearance = ~21.9mm ID.
• Cells slide in/out with gravity. PTFE liner reduces rattle without gripping.

Bottom plate (sealed base):

• Solid plate that hulls around all 4 tubes — closes the bottom.
• 4 spring contact pad recesses (10mm diameter, 2mm deep) — this is where the flat contact pads sit, just like the bottom of a Maglite.
• Central wire hole passes through.

Screw-in caps (Maglite style, print 4×):

• Threaded plastic cap that screws into the top of each channel.
• Coin slot on top — tighten flush with a coin, no tools.
• O-ring groove on the skirt — silicone ring seals against moisture and holds under vibration.
• Spring contact nub on the inside face — presses against the positive terminal of the top cell, compresses the stack downward onto the bottom pad.

Central wiring channel (6mm hole):

• Runs the full length through the center of the 2×2 grid.
• Carries bus wires and BMS balance taps from the contact pads/springs to the electronics below.

Cross ribs at every 70mm (cell boundary):

• Structural bridges between adjacent tubes — keeps the scaffold rigid without being solid.

Assembly sequence

1. Slide PTFE liner into each channel (friction fit, stays permanently).
2. Drop 5 cells into each channel from the top, positive-nub up.
3. Screw in the 4 caps — spring nub compresses stack onto bottom pad.
4. Tighten flush with a coin. O-ring seals it.
5. Whole scaffold slides into the DT as one unit.

Injection molding notes

• The screw cap threads are made with an unscrewing core in the mold — standard technique for bottle caps, Maglite bodies, etc. [richfieldsplastics](https://richfieldsplastics.com/blog/considerations-for-battery-pack-mold-making/)
• The main body pulls straight out of a two-part mold along the tube axis — channels are just core pins.
• The bottom plate is the parting line — mold splits there.
• Only the O-ring groove on the cap is a minor undercut, easily handled by the unscrewing core.

Drop it into OpenSCAD and send me a screenshot — the thread profile is simplified (stacked rings instead of true helix), so it'll look approximate but the dimensions are correct for printing.

That's a really smart approach — using the scaffold's own structural rings as sliding rails. Let me make sure I understand the full system:

Three-layer assembly

1. Frame (upper half-oval) — welded permanently to the bike. Has longitudinal grooves machined on the inner edges.
2. Battery scaffold — the end rings and mid rings are shaped as full ovals matching the DT inner profile. These oval rings slide along the frame's grooves like a drawer on rails.
3. Cover (lower half-oval) — also has matching grooves on its inner edges. Clips onto the scaffold from below, completing the oval and locking the battery inside.

How it works

• Insert: slide the scaffold into the frame from one end. The oval rings ride in the grooves — self-aligning, always snug, no wobble.
• Retain: spring ball detents on the insertion end click into a dimple once the scaffold is fully seated. Keeps it from vibrating out during riding. globalspec
• Lock: a keyed lock on the opposite end (or the cover) secures everything. Anti-theft + safety.
• Remove (every ~5 years): unlock, push against the spring balls, slide the whole scaffold out as one unit. Unscrew the cork caps, swap c

Three-layer assembly

1. Frame (upper half-oval) — welded permanently to the bike. Has longitudinal grooves machined on the inner edges.
2. Battery scaffold — the end rings and mid rings are shaped as full ovals matching the DT inner profile. These oval rings slide along the frame's grooves like a drawer on rails.
3. Cover (lower half-oval) — also has matching grooves on its inner edges. Clips onto the scaffold from below, completing the oval and locking the battery inside.

How it works

• Insert: slide the scaffold into the frame from one end. The oval rings ride in the grooves — self-aligning, always snug, no wobble.
• Retain: spring ball detents on the insertion end click into a dimple once the scaffold is fully seated. Keeps it from vibrating out during riding. globalspec
• Lock: a keyed lock on the opposite end (or the cover) secures everything. Anti-theft + safety.
• Remove (every ~5 years): unlock, push against the spring balls, slide the whole scaffold out as one unit. Unscrew the cork caps, swap cells.

Design advantages

• No bolts or brackets — the grooves and oval profile do all the alignment and load-bearing.
• Cover doubles as structural — once clipped on, the full oval cross-section is incredibly stiff (closed tube vs open channel).
• Weatherproof — the oval-to-oval fit with the cover leaves minimal gaps; add a rubber gasket strip along the groove edges and it's fully sealed.
• Mold-friendly — the scaffold's oval rings are just a different 2D profile on the same linear_extrude, easy change in the SCAD.

What needs to change in the SCAD

• End rings and mid rings: change from the current hull() of 4 circles to an actual oval/ellipse profile matching the DT inner dimensions.
• Add rail lips: small protruding ridges on the oval rings that sit in the frame's grooves.
• Spring ball pocket: a small cylindrical recess on one end ring to house a standard spring ball plunger (M5 or M6 size, off-the-shelf from norelem or similar). [reidsupply](https://www.reidsupply.com/en-us/industry-news/how-detent-pins-work)
• Lock boss: a flat on the opposite end ring with a hole for a barrel lock cylinder.

Want me to update the scaffold SCAD with oval rings sized to your DT inner profile? I'll need the inner width and height of the downtube cross-section to get the ellipse right.

maybe not. they might get worn out over time. the edges etc. lets try a mechanical way instead. we fasten the scaffold to the cover with screws instead. the screw holes are welded on to the body of the cover. its an outside clip from the scaffold. because we need to access it with a screwdriver also the oval has limited space so that way we dont add to that narrow space. the places its fasten becomes apart of the design. anyways ill sketch this and experiment with design a bit. next. for the usb charging part. the place where we connect the battery when we insert it. like tracks that touches another grove that connects to the motor cable and other wiring etc. the usb charging will need to work with 65w. I think we also discussed support for 45w apple charger usbc. so we will need that part on the end of the battery. what parts do we need for the charging art and the connector track/grove contraption?

Good call on moving to screws for the scaffold-to-cover attachment — simpler and more durable than rails. Let me break down the two electrical systems you need.

USB-C Charging System (65W / 45W Apple)

Your pack is 20 cells (4×5). The series/parallel config determines what charging hardware you need, but assuming 10S2P(36V nominal, 42V full — the most common ebike voltage for 250W):

Component | What it does | Example/Price -- | -- | -- USB-C PD trigger board | Negotiates 20V @ 3.25A from any 65W charger (including 45W Apple) | ~$2–5 on AliExpress [aliexpress]​ Boost converter (20V → 42V CC/CV) | Steps up the 20V PD output to your pack's charge voltage, with adjustable current limit | ~$5–10, XL6019 or similar [youtube]​ 10S BMS with balance leads | Protects cells, balances during charge, handles over/under-voltage, over-current, temp | ~$8–15 for 10S 20A common-port BMS [aliexpress]​ USB-C port (panel mount) | Waterproof panel-mount USB-C receptacle on the battery end cap | ~$3–5, IP67 rated

The pogo pins mount on a small PCB at one end of the scaffold. When you slide the battery in, the spring-loaded pins compress against flat pads fixed in the frame — self-aligning, vibration-tolerant, and weatherproof when mated.scribd+1

Parts summary for the battery end

On the insertion end of the scaffold you'll have a small PCB or bracket holding:

1. USB-C panel-mount port (user-facing, accessible from outside)

2. PD trigger board + boost converter (tiny, fits behind the USB-C port)

3. 2 power pogo pins + 2–4 signal pogo pins (facing into the frame dock)

On the frame side (fixed permanently):

4. Matching flat contact pads (PCB or gold-plated copper strips)

5. Wiring from pads → motor controller, lights, display

The wiring from the BMS and USB-C board runs through the central 6mm wire hole in the scaffold to reach the pogo pin PCB at the end.

Before I spec exact parts, do you have a preferred series/parallel configuration for the 20 cells? 10S2P (36V) is most common for legal 250W ebikes in Norway, but 13S (~48V) is another option if the motor supports it.

Good call on moving to screws for the scaffold-to-cover attachment — simpler and more durable than rails. Let me break down the two electrical systems you need.

USB-C Charging System (65W / 45W Apple)

Your pack is 20 cells (4×5). The series/parallel config determines what charging hardware you need, but assuming 10S2P (36V nominal, 42V full — the most common ebike voltage for 250W):

Component	What it does	Example/Price
USB-C PD trigger board	Negotiates 20V @ 3.25A from any 65W charger (including 45W Apple)	~$2–5 on AliExpress [aliexpress](https://www.aliexpress.com/item/1005005298357571.html)
Boost converter (20V → 42V CC/CV)	Steps up the 20V PD output to your pack's charge voltage, with adjustable current limit	~$5–10, XL6019 or similar [youtube](https://www.youtube.com/watch?v=Pt1mnSqBO5U)
10S BMS with balance leads	Protects cells, balances during charge, handles over/under-voltage, over-current, temp	~$8–15 for 10S 20A common-port BMS [aliexpress](https://www.aliexpress.com/w/wholesale-bms-21700-4s.html)
USB-C port (panel mount)	Waterproof panel-mount USB-C receptacle on the battery end cap	~$3–5, IP67 rated

The signal chain is: USB-C charger → PD trigger (20V) → boost converter (42V) → BMS → cells. [bigyanproject](https://bigyanproject.com/en/type-c-module/pd65w-usb-c-fast-charging-module)

Why this works with Apple 45W

Apple's 45W charger outputs 20V @ 2.25A via USB-C PD. The PD trigger board negotiates whatever the charger offers. At 45W you'd charge at ~1A into the pack (after boost losses), which is perfectly fine for a pack you charge overnight. [electrek](https://electrek.co/2022/06/23/electric-bike-usb-c-battery-chargers/)

Battery-to-Frame Connector (the dock)

When you slide the battery into the frame, you need electrical contact. The cleanest solution is spring-loaded pogo pins on one end:

Component	Spec	Purpose
2× high-current pogo pins (power)	10A rated, gold-plated, ~4mm diameter	Pack positive + negative to motor controller scribd
2–4× signal pogo pins	2A rated, ~2mm diameter	BMS communication, thermistor, enable line [connectors-cables](https://www.connectors-cables.com/e-bike-pogo-pin-charging/)
Matching PCB pads (frame side)	Gold-plated copper pads on a small PCB	Fixed inside the frame at the mating end

The pogo pins mount on a small PCB at one end of the scaffold. When you slide the battery in, the spring-loaded pins compress against flat pads fixed in the frame — self-aligning, vibration-tolerant, and weatherproof when mated. connectors-cables

Parts summary for the battery end

On the insertion end of the scaffold you'll have a small PCB or bracket holding:

1. USB-C panel-mount port (user-facing, accessible from outside)
2. PD trigger board + boost converter (tiny, fits behind the USB-C port)
3. 2 power pogo pins + 2–4 signal pogo pins (facing into the frame dock)

On the frame side (fixed permanently):

4. Matching flat contact pads (PCB or gold-plated copper strips)
5. Wiring from pads → motor controller, lights, display

The wiring from the BMS and USB-C board runs through the central 6mm wire hole in the scaffold to reach the pogo pin PCB at the end.

Before I spec exact parts, do you have a preferred series/parallel configuration for the 20 cells? 10S2P (36V) is most common for legal 250W ebikes in Norway, but 13S (~48V) is another option if the motor supports it.

yeah. 10S2P (36V) sounds right.one question. does the support for 45w charger add complexity versus just supporting 65w and up? there is also 100w and up even 240w usbc.

No extra complexity at all. Supporting 45W, 65W, 100W, and even 240W chargers is automatic — it's literally the same single PD trigger board.

How USB-C PD negotiation works

The charger advertises what it can supply (voltage/current profiles), and the device (your PD trigger board) requests what it wants. Your trigger board asks for 20V. Then:kytchargers+1

• 45W Apple charger → offers 20V @ 2.25A → trigger gets 20V @ 2.25A (45W)

• 65W charger → offers 20V @ 3.25A → trigger gets 20V @ 3.25A (65W)

• 100W charger → offers 20V @ 5A → trigger gets 20V @ 5A (100W)

• 240W PD 3.1 charger → offers 20V, 28V, 48V → trigger asks for 20V, gets 20V @ 5A (100W)

The trigger board always negotiates the same 20V, regardless of what the charger is rated for. A bigger charger just means more current headroom — the boost converter behind it takes whatever it gets and charges the pack at whatever rate makes sense.reddit+1

So what does this mean for your design?

Zero added complexity. The parts list is identical whether someone plugs in a 45W Apple brick or a 240W GaN charger:

Part | Function -- | --

The boost converter's current limit is the real safety valve — you set it to whatever the cells can handle (e.g. 2A for a gentle 0.5C charge on your 2P pack). Even if someone plugs in a 240W monster, the converter only draws what it needs.[youtube]​

The 240W PD 3.1 bonus

There's actually an interesting future option: PD 3.1 chargers can output 48V @ 5A. Your 10S pack charges to 42V. So with a PD 3.1 trigger board (they exist now), you could skip the boost converter entirely — 48V stepped down to 42V is a simple buck, much more efficient than boosting from 20V. But that's an optimization for later; the 20V boost path works with every charger made in the last 5 years.[reddit]​

Bottom line: design for one USB-C port + one PD trigger board. Every wattage from 18W to 240W just works, automatically, with zero additional components.[kytchargers]​

No extra complexity at all. Supporting 45W, 65W, 100W, and even 240W chargers is **automatic** — it's literally the same single PD trigger board.

How USB-C PD negotiation works

The charger advertises what it can supply (voltage/current profiles), and the device (your PD trigger board) requests what it wants. Your trigger board asks for 20V. Then: kytchargers

• 45W Apple charger → offers 20V @ 2.25A → trigger gets 20V @ 2.25A (45W)
• 65W charger → offers 20V @ 3.25A → trigger gets 20V @ 3.25A (65W)
• 100W charger → offers 20V @ 5A → trigger gets 20V @ 5A (100W)
• 240W PD 3.1 charger → offers 20V, 28V, 48V → trigger asks for 20V, gets 20V @ 5A (100W)

The trigger board always negotiates the same 20V, regardless of what the charger is rated for. A bigger charger just means more current headroom — the boost converter behind it takes whatever it gets and charges the pack at whatever rate makes sense. reddit

So what does this mean for your design?

Zero added complexity. The parts list is identical whether someone plugs in a 45W Apple brick or a 240W GaN charger:

Part	Function
PD trigger board (~$3)	Always requests 20V, gets whatever current the charger offers [aliexpress](https://www.aliexpress.com/w/wholesale-usb-pd-trigger-board.html)
Boost converter 20V → 42V (~$8)	Steps up to pack charge voltage, you set max current (e.g. 2A)
10S BMS (~$10)	Balances cells, protects against overcharge/overdischarge
USB-C port (panel mount)	One port, works with every USB-C charger on earth

The boost converter's current limit is the real safety valve — you set it to whatever the cells can handle (e.g. 2A for a gentle 0.5C charge on your 2P pack). Even if someone plugs in a 240W monster, the converter only draws what it needs. [youtube](https://www.youtube.com/watch?v=02T9TVr0Vf8)

The 240W PD 3.1 bonus

There's actually an interesting future option: PD 3.1 chargers can output 48V @ 5A. Your 10S pack charges to 42V. So with a PD 3.1 trigger board (they exist now), you could skip the boost converter entirely — 48V stepped down to 42V is a simple buck, much more efficient than boosting from 20V. But that's an optimization for later; the 20V boost path works with every charger made in the last 5 years. [reddit](https://www.reddit.com/r/ebike/comments/1r31cv1/do_you_want_usbc_charging_on_your_ebike_why_why/)

Bottom line: design for one USB-C port + one PD trigger board. Every wattage from 18W to 240W just works, automatically, with zero additional components. [kytchargers](https://kytchargers.com/what-is-usb-c-pd-3-1/)

Good question. Yes, 48V has real benefits even when speed-limited to 25 km/h.

48V vs 36V (same 250W legal limit, same 25 km/h cap)

The speed limit is enforced by the sine wave controller, not the voltage. So a higher voltage doesn't make you faster — but it changes how the motor delivers power within that limit.reddit+1

  | 36V (10S2P) | 48V (13S1P or ~14S) -- | -- | -- Top speed | 25 km/h (software limited) | 25 km/h (software limited) Torque/acceleration | Good | ~10% more — motor pulls harder from standstill, feels snappier [jskuake]​ Hill climbing | Adequate at 250W | Better — motor draws less current for same power, stays cooler under load [pedelecs.co]​ Efficiency | More heat loss at higher current | Lower current for same wattage (P=V×I), less resistive loss in wires, controller, motor windings reddit+1 Motor noise | Slightly more | Slightly quieter [jskuake]​ Range | Baseline | Potentially 5–15% more range from reduced I²R losses [ouxi-ebike]​ Cell config (20 cells) | 10S2P → 2 parallel = good redundancy | Not possible with 20 cells (13S needs 13+ cells per series string)

The real issue: cell count

This is the dealbreaker. You have 20 cells in a 2×2×5 scaffold:

• 10S2P = 10 series × 2 parallel = 20 cells ✓ — fits perfectly, 36V nominal, 42V full charge

• 13S would need 13 cells in series, leaving only 7 for a partial second parallel string — doesn't divide evenly into 20[ebikerepairfactory]​

To do 48V (13S) properly you'd need 26 cells (13S2P), which means either a longer scaffold (6.5 cells long — awkward) or a wider one (3 wide — won't fit the downtube).

Verdict for Omera

Stick with 10S2P (36V). Here's why:

• 20 cells divide perfectly into 10S2P — clean, symmetrical, simple BMS wiring.

• You still get the full legal 250W with smooth sine wave control.

• The 36V efficiency penalty is minimal at 250W (you're only drawing ~7A vs ~5.2A at 48V — both are low current for 21700 cells).

• Simpler BMS (10S boards are cheaper and more available than 13S).[aliexpress]​

• The PD 3.1 future path (48V charger → direct charge) aligns neatly with a 42V pack anyway.

The 48V advantage is real for high-power ebikes (750W+), but at your legal 250W limit the difference is marginal and not worth the cell-count headache.[hd-ebike]​

Good question. Yes, 48V has real benefits even when speed-limited to 25 km/h.

48V vs 36V (same 250W legal limit, same 25 km/h cap)

The speed limit is enforced by the sine wave controller, not the voltage. So a higher voltage doesn't make you faster — but it changes how the motor delivers power within that limit. reddit

	36V (10S2P)	48V (13S1P or ~14S)
Top speed	25 km/h (software limited)	25 km/h (software limited)
Torque/acceleration	Good	~10% more — motor pulls harder from standstill, feels snappier [jskuake](https://www.jskuake.com/36v-vs-48v-ebike/)
Hill climbing	Adequate at 250W	Better — motor draws less current for same power, stays cooler under load [pedelecs.co](https://www.pedelecs.co.uk/forum/threads/48-volt-battery-or-36-volt-battery.48406/)
Efficiency	More heat loss at higher current	Lower current for same wattage (P=V×I), less resistive loss in wires, controller, motor windings reddit
Motor noise	Slightly more	Slightly quieter [jskuake](https://www.jskuake.com/36v-vs-48v-ebike/)
Range	Baseline	Potentially 5–15% more range from reduced I²R losses [ouxi-ebike](https://ouxi-ebike.com/blogs/news/what-is-better-a-36v-or-48v-ebike)
Cell config (20 cells)	10S2P → 2 parallel = good redundancy	Not possible with 20 cells (13S needs 13+ cells per series string)

The real issue: cell count

This is the dealbreaker. You have 20 cells in a 2×2×5 scaffold:

• 10S2P = 10 series × 2 parallel = 20 cells ✓ — fits perfectly, 36V nominal, 42V full charge
• 13S would need 13 cells in series, leaving only 7 for a partial second parallel string — doesn't divide evenly into 20 [ebikerepairfactory](https://ebikerepairfactory.com/blogs/news/36v-vs-48v-e-bike-battery-which-one-is-best-for-you)

To do 48V (13S) properly you'd need 26 cells (13S2P), which means either a longer scaffold (6.5 cells long — awkward) or a wider one (3 wide — won't fit the downtube).

Verdict for Omera

Stick with 10S2P (36V). Here's why:

• 20 cells divide perfectly into 10S2P — clean, symmetrical, simple BMS wiring.
• You still get the full legal 250W with smooth sine wave control.
• The 36V efficiency penalty is minimal at 250W (you're only drawing ~7A vs ~5.2A at 48V — both are low current for 21700 cells).
• Simpler BMS (10S boards are cheaper and more available than 13S). [aliexpress](https://www.aliexpress.com/w/wholesale-bms-21700-4s.html)
• The PD 3.1 future path (48V charger → direct charge) aligns neatly with a 42V pack anyway.

The 48V advantage is real for high-power ebikes (750W+), but at your legal 250W limit the difference is marginal and not worth the cell-count headache. [hd-ebike](https://hd-ebike.com/36v-vs-48v-electric-bikes-whats-the-difference-and-which-one-should-you-choose/)

Great news: the whole charging system is tiny. Here's what each part actually measures:

Physical dimensions

Part | Dimensions (L×W×H) | Notes -- | -- | -- PD trigger board (ZY12PDN) | 31 × 15 × 4.3 mm [make.net]​ | Tiny, about the size of a thumbnail Boost converter (XL6019) | 50 × 28 × 13 mm ifuturetech+1 | The biggest piece — about a matchbox 10S BMS (small ebike type) | 80 × 60 × 6.5 mm [m.aliexpress]​ | Flat board, fits along the scaffold wall USB-C panel mount port | ~12 × 9 mm (face), 25 mm deep | Standard panel-mount connector

Want me to sketch how these boards stack at the bottom end of the scaffold, or should we first nail down the pogo pin connector layout for the frame dock?

Great news: the whole charging system is tiny. Here's what each part actually measures:

Physical dimensions

Part	Dimensions (L×W×H)	Notes
PD trigger board (ZY12PDN)	31 × 15 × 4.3 mm [make.net](https://make.net.za/product/8me1200/)	Tiny, about the size of a thumbnail
Boost converter (XL6019)	50 × 28 × 13 mm ifuturetech	The biggest piece — about a matchbox
10S BMS (small ebike type)	80 × 60 × 6.5 mm [m.aliexpress](https://m.aliexpress.com/i/32923031578.html)	Flat board, fits along the scaffold wall
USB-C panel mount port	~12 × 9 mm (face), 25 mm deep	Standard panel-mount connector

Total space needed

All of this stacks into roughly 80 × 60 × 25 mm — about the size of a credit card, 25 mm thick. That's easily smaller than the cross-section of your downtube oval.

Where it fits in the scaffold

There are two logical places:

Option A — Bottom end of the scaffold (behind the sealed bottom plate):

• The BMS lies flat against the bottom plate (80×60×6.5mm — fits within the scaffold's ~48×53mm footprint if oriented diagonally or trimmed to a custom PCB).
• PD trigger + boost converter stack on top of it.
• USB-C port faces outward from the bottom end cap of the DT.
• Pogo pins also face outward from this same end.
• All wiring stays short.

Option B — Separate end-cap module:

• A small 3D-printed enclosure bolted to the end of the scaffold.
• Houses all electronics + USB-C port + pogo pins.
• Slides into the frame with the battery as one unit.

Option A is cleaner — everything hidden inside the DT. The 6mm central wire hole in the scaffold carries the BMS balance leads from the cell connections down to the BMS board at the bottom.

Custom BMS consideration

Off-the-shelf 10S BMS boards at 80×60mm are designed for generic ebike cases. For your tight oval, you could order a custom-shaped BMS PCB that matches your scaffold's cross-section exactly — Chinese PCB houses do this for ~$15–30 in small batches. That way the BMS becomes a structural layer at the bottom of the scaffold rather than a separate board to squeeze in. [pswpower](https://www.pswpower.com/products/small-bms10s-36v-30a-or-13s-48v-30a-li-ion-battery-bms-for-18650-cell-hailong-dolphin-shark-case-ebike-battery-bms-141)

Parts cost summary

Part	Est. cost
PD trigger board	~$3–5
XL6019 boost module	~$5–8
10S BMS 20A	~$8–15
USB-C panel mount	~$3–5
Pogo pins (2 power + 4 signal)	~$5–10
Total electronics	~$24–43

Want me to sketch how these boards stack at the bottom end of the scaffold, or should we first nail down the pogo pin connector layout for the frame dock?

That changes the architecture in a good way — everything lives on the battery, nothing smart needed in the frame.

Self-contained battery: all electronics on-board

Since the battery charges standalone on your kitchen table, the entire charging system is inside the battery pack, not split between frame and battery:

What's inside the battery

Part | Size (mm) | Function -- | -- | -- USB-C panel port | 12 × 9 face, 25 deep | Plug your MacBook charger in here PD trigger (ZY12PDN or STUSB4531) | 31 × 15 × 4 | Negotiates 20V from any charger make+1 Boost converter (20V → 42V) | 50 × 28 × 13 | Steps up to pack charge voltage [ifuturetech]​ 10S BMS | 60 × 45 × 6.5 | Balances, protects, manages charge/discharge [m.aliexpress]​

The frame just needs matching flat pads — zero electronics, zero cost essentially.

What this means for the scaffold design

The bottom end of the scaffold gets a small electronics bay between the bottom plate and the end cap:

• BMS flat against the bottom plate (wired through the central 6mm hole to each cell group's balance taps)

• PD trigger + boost converter stacked on top

• USB-C port facing outward through the end cap (accessible when battery is removed from frame)

• Pogo pins also on the end cap (face into frame when inserted)

When the battery is in the bike: pogo pins connect to frame pads → motor runs. When removed: plug USB-C into the exposed port → charges on the kitchen table.

That changes the architecture in a good way — everything lives *on the battery*, nothing smart needed in the frame.

Self-contained battery: all electronics on-board

Since the battery charges standalone on your kitchen table, the entire charging system is inside the battery pack, not split between frame and battery:

What's inside the battery

Part	Size (mm)	Function
USB-C panel port	12 × 9 face, 25 deep	Plug your MacBook charger in here
PD trigger (ZY12PDN or STUSB4531)	31 × 15 × 4	Negotiates 20V from any charger make.net
Boost converter (20V → 42V)	50 × 28 × 13	Steps up to pack charge voltage [ifuturetech](https://ifuturetech.org/product/xl6019-dc-dc-5a-adjustable-boost-power-supply-module/)
10S BMS	60 × 45 × 6.5	Balances, protects, manages charge/discharge [m.aliexpress](https://m.aliexpress.com/i/32923031578.html)

Total volume: roughly a stack of 60 × 45 × 25 mm — fits in the bottom end of the scaffold behind the sealed plate, or in a small end-cap compartment.

What's in the frame

Now the frame side becomes dead simple — just dumb copper contacts (pads or rails). No electronics. The battery's BMS handles everything:

• 2 power contacts (V+ and V−) → motor controller
• Optionally 1–2 signal contacts (enable line, thermistor)

Charge time math

Your 10S2P pack with 5000mAh 21700 cells: [battsysbattery](https://www.battsysbattery.com/pro/21700-battery-5000mAh)

• Pack capacity: 2P × 5Ah = 10Ah at 36V = 360Wh
• With a 45W Apple charger: PD negotiates 20V @ 2.25A = 45W in, after boost losses (~85% efficient) ≈ 38W into the pack. Charge time: 360Wh ÷ 38W ≈ ~9.5 hours [manlybattery](https://manlybattery.com/battery-tools-and-resources/battery-charge-time-calculator/)
• With a 65W charger: 20V @ 3.25A = 65W in, ~55W net. Charge time: 360Wh ÷ 55W ≈ ~6.5 hours
• With a 100W charger: 20V @ 5A = 100W in, ~85W net. Charge time: 360Wh ÷ 85W ≈ ~4.2 hours ✓

So for your 4–5 hour target, a 65W+ charger gets you there. The 45W Apple brick works too, it just takes longer (~overnight). imrenbatteries

Simplified parts list

Since everything is self-contained on the battery:

Part	Est. cost	Notes
USB-C panel mount (IP67)	$3–5	On the exposed end of the battery
PD trigger board	$3–5	Requests 20V from any USB-C charger
Boost converter 20V→42V	$5–8	Set max current to 2A (safe 0.2C charge)
10S BMS 20A	$8–15	Common-port, handles charge + discharge
2× power pogo pins (battery side)	$3–5	Dock contacts for motor power
Total	~$22–38

The frame just needs matching flat pads — zero electronics, zero cost essentially.

What this means for the scaffold design

The bottom end of the scaffold gets a small electronics bay between the bottom plate and the end cap:

• BMS flat against the bottom plate (wired through the central 6mm hole to each cell group's balance taps)
• PD trigger + boost converter stacked on top
• USB-C port facing outward through the end cap (accessible when battery is removed from frame)
• Pogo pins also on the end cap (face into frame when inserted)

When the battery is in the bike: pogo pins connect to frame pads → motor runs. When removed: plug USB-C into the exposed port → charges on the kitchen table.

Good question. Your current design has smooth-bore tubes. Here's how the two options compare for your specific goals:

Circular Smooth Bore (what you have now)

This is actually the better choice for Omera. Here's why:

• Gravity drop-in: A smooth bore gives zero friction points. Tilt the frame, cells slide out by gravity alone. Any internal feature (ribs, honeycomb) adds contact points that can catch or slow the cell. ensinger-pc
• Low rattle: The current bore is pocket_d = 21.5 mm for a 21 mm cell — that's only 0.25 mm radial clearance per side. At that tolerance, the cell barely moves laterally. Rattle comes from axial movement (cell bouncing end-to-end), which you solve with the cork caps pressing down, not with wall texture. facebook
• Airflow: Smooth bore lets air flow freely along the cell length through the gap. Any wall texture disrupts laminar flow and creates dead spots where heat builds up. [sciencedirect](https://www.sciencedirect.com/science/article/pii/S2666202725000321)
• Moldability / printability: Smooth cylinders are trivial to injection mold or 3D print. Internal ribs or honeycomb add draft angle complexity and potential print artifacts. [ensinger-pc](https://www.ensinger-pc.com/resources/blog/a-guide-to-injection-molding-plastic-battery-components/)

Honeycomb / Internal Ribs

• Anti-rattle: Longitudinal ribs (3–4 thin fins running the tube length) do reduce radial rattle by creating point contacts that spring slightly. But with 0.25 mm clearance, you don't have a rattle problem to solve.
• Insertion friction: Every rib is a friction ridge. Cells won't drop in/out freely — you'd need to push them. Defeats your tool-free gravity requirement.
• Heat trapping: Honeycomb walls between tubes would block cross-flow cooling entirely. [sciencedirect](https://www.sciencedirect.com/science/article/pii/S2666202725000321)
• Complexity: Adds thin features that are hard to print cleanly and complicate mold tooling. [ensinger-pc](https://www.ensinger-pc.com/resources/blog/a-guide-to-injection-molding-plastic-battery-components/)

Recommendation

Keep smooth circular bores. Your 0.25 mm radial clearance is already tight enough to prevent meaningful rattle. For the small remaining axial rattle (cell bouncing lengthwise), the cork caps + bottom plate handle it. If you later find rattle is an issue in testing, the cheapest fix is a thin silicone O-ring inside each cap face (manufacturing detail, not modeled in SCAD) rather than redesigning the tube walls. patents.google

The one thing worth considering: a single shallow chamfer at the tube entry (top 1–2 mm flared by 0.5 mm) to make cell insertion easier when you're loading by hand. But again, that's a manufacturing annotation, not something to model now.

Here's the full file with the electronics backpack added at the bottom .

What's in the electronics bay

The bay sits at the bottom end of the scaffold (opposite the cork caps), rendered in SteelBlue so you can distinguish it. It extends 30mm below the bottom plate:

• Outer shell — same clover profile as the end rings, 2mm wall, so it matches the scaffold cross-section exactly.
• BMS pocket — 60×45×7mm recess at the top of the bay (right against the cell-side plate). Wired through the central 6mm hole to the balance taps.
• Boost converter pocket — 50×28×14mm below the BMS.
• PD trigger pocket — 31×15×5mm tucked beside the boost converter.
• USB-C port hole — 12×9mm hole through the front wall of the bay. This is where you plug in your MacBook charger when the battery is on the table.
• Pogo pin holes — through the bottom face: 2× large (4.5mm, power) on the outer positions, 4× small (2.5mm, signal) in the center. These face into the frame when the battery is inserted.
• Central wire hole — continues straight through from the scaffold above.

Orientation when in use

CORK CAPS (top)     ← you face this end upward on the table
│                      to access USB-C port on the bottom
│  cells cells cells
│  cells cells cells
│
ELECTRONICS BAY     ← USB-C port on side, pogo pins on bottom face
                      pogo pins dock into frame when bike-mounted

Render it and let me know if the proportions look right — the bay might need to be deeper or shallower depending on how the boards actually stack.

The oval (1-2-1 diamond) uses less space — but only by about 6%.

• Circle (2×2 grid): Ø 52.1 mm → 2,133 mm²
• Oval (1-2-1 diamond): 43 × 59 mm → 1,996 mm²

The oval is taller and narrower (43 × 59 mm) because the 1-2-1 stacking nests the top and bottom cells into the valleys of the middle pair. The circle is wider in all directions because it has to wrap a square. Practically though, the difference is small — only ~137 mm².

Here's just the electronics bay, isolated .

What you're looking at

The bay is oriented with z = 0 at the bottom (pogo pin face / frame-facing end) and z = bay_h (30mm) at the top (where it mates to the scaffold bottom plate):

• Top layer — BMS pocket (60×45×7mm), sits right against the scaffold plate. Balance wires come through the 6mm central hole.
• Middle layer — Boost converter pocket (50×28×14mm) + PD trigger pocket (31×15×5mm) beside it.
• Front wall — USB-C port hole (12×9mm) punched through the Y+ face.
• Bottom face — 2 large pogo pin holes (4.5mm, power) on the outer edges, 4 small pogo pin holes (2.5mm, signal) in the center.
• Central wire hole — 6mm, runs full height.

The outer shell matches the scaffold's clover profile exactly so it mates flush. Render it and let me know what needs adjusting — height, pocket positions, USB-C port placement, pogo pin layout, etc.

Yes, exactly. The 6 holes in the bottom face are where the pogo pins mount. Here's how it works:

Pogo pin placement

• 2 large outer holes (4.5mm) — these hold the power pogo pins (V+ and V−). They carry the main current to the motor controller (~10A rated).
• 4 smaller inner holes (2.5mm) — these hold the signal pogo pins. For BMS communication, thermistor reading, and an enable/wake line.

Each pogo pin is a small spring-loaded cylinder. You press-fit or solder it into its hole from the inside of the bay. The spring-loaded tip pokes out through the bottom face by a few mm.

How it connects when in the bike

When you slide the battery into the downtube:

Battery slides in →

[CORK CAPS] ——— [SCAFFOLD + CELLS] ——— [ELECTRONICS BAY] →
                                              ↓
                                        pogo pin tips
                                              ↓
                                     compress against flat
                                     copper pads in frame

The bottom face of the bay is the insertion end. As the battery reaches its final position, the spring-loaded pins compress against matching flat pads (a small PCB or gold-plated copper strips) fixed permanently inside the frame. Spring pressure keeps solid contact even with vibration.

The USB-C port

The rectangular slot on the side wall (visible near the top of your render) is where the USB-C panel-mount receptacle sits. That hole lines up with a matching cutout in the alu cover, so when you pull the battery out and set it on the table, you can plug in your charger from the side.

Want me to adjust anything — pin spacing, hole sizes, USB-C port position?

Here's v2 . Two changes:

1. Fins gone — those were leftover thin walls between the individual board pockets (BMS, boost, PD trigger cavities overlapping awkwardly). Now the interior is just one clean hollow cavity. You drop all three boards in there and secure them with standoffs or adhesive. Much simpler.

2. USB-C goes through the side — the port hole is on the Y+ wall of the bay, positioned at 15mm up from the bottom. When assembled, this aligns with a matching hole drilled/CNC'd in the alu cover. So the charging workflow is:

• Battery in bike → USB-C port hidden inside the downtube, not exposed to weather.
• Pull battery out → USB-C port on the side of the alu shell, plug in your MacBook charger, done.

The alu cover just needs a 12×9mm cutout in the right spot to let the USB-C receptacle poke through or sit flush.

Render it and let me know how it looks — should be a clean box with no weird internals this time.

What you're describing is essentially the Shimano STEPS / Bosch PowerTube internal battery connector pattern — and it's the industry standard for good reason. connectors-cables

How It Works (Your Design Matches)

The mechanism has two halves:

Frame side (fixed):

• A plastic rail/fin block with parallel ribs that acts as an alignment guide. Pogo pins (gold-plated, spring-loaded) sit recessed between the fins, impossible to touch from outside. connectors-cables
• A ball-spring detent (spring-loaded steel ball in a housing) that clicks into a matching dimple on the battery when fully seated. [si.shimano](https://si.shimano.com/en/pdfs/dm/BT0001/DM-BT0001-05-ENG.pdf)

Battery side (removable):

• Matching parallel grooves that only accept the frame fins in one orientation (keyed/polarized). Slide in, no rotation possible. [si.shimano](https://si.shimano.com/en/pdfs/dm/BT0001/DM-BT0001-05-ENG.pdf)
• Flat gold-plated contact pads that the pogo pins press against when seated. No exposed pins on the battery — just flush pads recessed between the plastic ribs. connectorsupplier
• A detent pocket (small dimple or notch) for the ball-spring to snap into.

Why This Pattern Works

• Anti-rattle: The parallel fins create a tight sliding fit with zero lateral play. Ball-spring detent eliminates axial play. connectors-cables
• Safety: Pogo pins are recessed on the frame side; pads are flush on the battery side. No exposed live contacts on either half when separated. connectorsupplier
• Blind-mate friendly: Slide in along the rails, feel the click, done. One direction only, no alignment guesswork. si.shimano
• Vibration-proof: Pogo pin springs maintain constant contact pressure even under road vibration — rated for 100K+ cycles. jiatelcn

Typical Pin Count

Pin	Function
2 × power	B+, B− (high current, 10–25A capable)
1 × signal	Communication / CAN bus to BMS
1 × temp	NTC thermistor sense
1 × ground	Signal ground (separate from power ground)

For Omera you'd likely need 4–5 pogo pins: 2 power (sized for ~15A), plus signal/temp/ground. The power pins should be larger diameter (2.5–3 mm) with higher spring force than the signal pins. jiatelcn

Where to Source

Off-the-shelf pogo pin connector blocks (5-pin, 2.54 mm pitch, gold-plated, magnetic or friction-mount) are available from suppliers like Jiatel, CCP, and Higo — many already designed for e-bike battery applications. You'd design the plastic fin housing around these standard pins. ccpcontactprobes

This is exactly the right approach for Omera. The connector block would sit at the bottom of the downtube (inside the BB area), and the battery scaffold slides down from the top, rails engage, click.

Exactly — that's IP2X / finger-proof by geometry, the same principle used in EV battery packs and industrial blade connectors.

How It's Finger-Safe

The IEC 61032 "test finger" is 12 mm diameter, 80 mm long. If your fin gap is under 8 mm, no adult or child finger can enter. Put the contacts deeper than 10 mm inside that gap and nothing can touch them — not a finger, not a key, not a coin.jiatelcn+1

Your design:

text
       Gap: 5mm (finger can't enter)
         ↕
   ┌───┐ ┌───┐ ┌───┐ ┌───┐ ┌───┐
   │   │ │   │ │   │ │   │ │   │  ← fins, 2mm thick, 15mm tall
   │   │ │ ● │ │   │ │ ● │ │   │  ← pogo pins at ~10mm depth
   │   │ │   │ │   │ │   │ │   │
   └───┴─┴───┴─┴───┴─┴───┴─┴───┘
         frame block (fixed in downtube floor)

• Fin thickness: 2 mm

• Gap between fins: 5 mm (finger-proof)

• Fin height: 15 mm

• Contact depth: 10 mm down from fin top (unreachable)

When the battery scaffold drops in, its matching fins slide into the gaps. The pads on the scaffold fins meet the pogo pins at depth. From the outside, both halves just look like plastic combs — no visible metal, no exposed contacts, nothing to short with a tool or touch accidentally.

The Two Halves

Frame block (lives at downtube floor):

• 5 fins pointing up

• Pogo pins press-fit into the inner face of fins, facing inward across the gap

• Wired down through the block into the frame harness

Scaffold bottom (battery side):

• 4 matching fins pointing down, interleave between the frame fins

• Gold-plated flat pads on the fin faces, flush with the plastic

• No springs, no moving parts on the battery side

Pin Assignment (4 contact pairs across 4 gaps)

Gap | Left face | Right face | Function -- | -- | -- | -- 1 | pogo → | ← pad | B+ power 2 | pogo → | ← pad | B− power 3 | pogo → | ← pad | Signal / CAN 4 | pogo → | ← pad | Temp + ground

Power pins in the outer gaps, signal in the inner gaps — even if moisture gets in, the low-voltage signals are furthest from the high-current contacts.

This whole block is maybe 30 × 15 × 15 mm. You buy standard pogo pins and flat pads, press them into a small 3D-printed or moulded housing, and mount it at the downtube floor. Want me to add this to the scaffold SCAD as the bottom connector block?

Exactly right. What you're describing is called IP2X finger-safe design — it's an actual engineering standard.[gt-engineering]​

The rule

The IEC 60529 standard says: if a 12mm diameter test finger (simulating a human fingertip) cannot reach the live contact, it's IP2X finger-safe. So your fin gap just needs to be less than 12mm wide, and the contacts need to be recessed deep enough inside.ledphotometer+1

Your interleaved fin connector

text
Cross-section (looking down into the battery bottom):

FRAME SIDE (fixed in DT):          BATTERY SIDE (electronics bay):

    ┌─┐  ┌─┐  ┌─┐                    ┌──┐┌──┐┌──┐┌──┐
    │ │  │ │  │ │                    │  ││  ││  ││  │
    │ │  │ │  │ │                    │  ││  ││  ││  │
    │█│  │█│  │█│  ← pads            │●││●││●││●│ ← pogo pins
    │ │  │ │  │ │    on fins          │  ││  ││  ││  │   on inner
    │ │  │ │  │ │                    │  ││  ││  ││  │   slot walls
    └─┘  └─┘  └─┘                    └──┘└──┘└──┘└──┘

         3 fins                          4 slots

Battery drops in → slots interleave over fins:

              ┌──┐     ┌──┐
              │  │┌─┐  │  │┌─┐
              │  ││ │  │  ││ │
              │● ││█│  │● ││█│  ← pin meets pad
              │  ││ │  │  ││ │     inside ~4mm gap
              │  │└─┘  │  │└─┘     finger can't reach
              └──┘     └──┘

Design parameters

Parameter | Value | Why -- | -- | --

Why this is perfect for your design

• Vertical drop-in: battery falls straight down, slots slide over fins naturally with gravity.

• Self-centering: the interleave guides the battery into exact alignment during the last 15mm.

• Finger-proof by geometry: 3–4mm slot gap is physically impossible to stick a finger into. Meets IP2X without any extra covers or caps.[ledphotometer]​

• Rattle-free: tight fin-slot fit + ball spring detent = zero play.

• No magnets needed: gravity + ball spring is enough.

Off-the-shelf or custom?

Werner Wirth (German company, supplies Bosch/Shimano tier) makes exactly this kind of interleaved blade battery connector for ebikes — IP67 rated, up to 30A power pins, finger-safe, keyed. Their modular system lets you pick pin count and current rating. Alternatively, you 3D-print the fin/slot housings yourself and press-fit standard pogo pins or blade contacts into the walls.[wernerwirth]​

Want me to model the interleaved fin connector as a SCAD piece — both the frame-side fins and the battery-side slots?

Exactly right. What you're describing is called **IP2X finger-safe** design — it's an actual engineering standard. [[gt-engineering](https://www.gt-engineering.it/en/insights/electrical-hazard-and-arc-flash-mitigation/protection-from-direct-contacts-ipxxb-or-ip2x/)](https://www.gt-engineering.it/en/insights/electrical-hazard-and-arc-flash-mitigation/protection-from-direct-contacts-ipxxb-or-ip2x/)

The rule

The IEC 60529 standard says: if a 12mm diameter test finger (simulating a human fingertip) cannot reach the live contact, it's IP2X finger-safe. So your fin gap just needs to be less than 12mm wide, and the contacts need to be recessed deep enough inside. ledphotometer

Your interleaved fin connector

Cross-section (looking down into the battery bottom):

FRAME SIDE (fixed in DT):          BATTERY SIDE (electronics bay):

    ┌─┐  ┌─┐  ┌─┐                    ┌──┐┌──┐┌──┐┌──┐
    │ │  │ │  │ │                    │  ││  ││  ││  │
    │ │  │ │  │ │                    │  ││  ││  ││  │
    │█│  │█│  │█│  ← pads            │●││●││●││●│ ← pogo pins
    │ │  │ │  │ │    on fins          │  ││  ││  ││  │   on inner
    │ │  │ │  │ │                    │  ││  ││  ││  │   slot walls
    └─┘  └─┘  └─┘                    └──┘└──┘└──┘└──┘

         3 fins                          4 slots

Battery drops in → slots interleave over fins:

              ┌──┐     ┌──┐
              │  │┌─┐  │  │┌─┐
              │  ││ │  │  ││ │
              │● ││█│  │● ││█│  ← pin meets pad
              │  ││ │  │  ││ │     inside ~4mm gap
              │  │└─┘  │  │└─┘     finger can't reach
              └──┘     └──┘

Design parameters

Parameter	Value	Why
Fin thickness	3–4 mm	Structural, holds the copper pad
Gap between fin and slot wall	3–4 mm	Way under 12mm → finger-proof [gt-engineering](https://www.gt-engineering.it/en/insights/electrical-hazard-and-arc-flash-mitigation/protection-from-direct-contacts-ipxxb-or-ip2x/)
Fin height	12–15 mm	Enough engagement depth for stable contact
Contact point depth	8–10 mm down from top of fin	Even a child's finger (test probe is 12mm Ø) can't reach
Number of fins	3 (frame side)	Gives 4 contact channels: V+, V−, signal, signal
Fin keying	Center fin is wider/offset	Prevents wrong orientation

Why this is perfect for your design

• Vertical drop-in: battery falls straight down, slots slide over fins naturally with gravity.
• Self-centering: the interleave guides the battery into exact alignment during the last 15mm.
• Finger-proof by geometry: 3–4mm slot gap is physically impossible to stick a finger into. Meets IP2X without any extra covers or caps. [ledphotometer](https://www.ledphotometer.com/blogs/ip-code-finger-safety-testing/)
• Rattle-free: tight fin-slot fit + ball spring detent = zero play.
• No magnets needed: gravity + ball spring is enough.

Off-the-shelf or custom?

Werner Wirth (German company, supplies Bosch/Shimano tier) makes exactly this kind of interleaved blade battery connector for ebikes — IP67 rated, up to 30A power pins, finger-safe, keyed. Their modular system lets you pick pin count and current rating. Alternatively, you 3D-print the fin/slot housings yourself and press-fit standard pogo pins or blade contacts into the walls. [wernerwirth](https://wernerwirth.com/en/connector-solutions/e-bike-connectors/)

Want me to model the interleaved fin connector as a SCAD piece — both the frame-side fins and the battery-side slots?

There are two solid ready-made options that match your blade-interleave, finger-proof concept:

Amphenol DuraEV™

This is the closest match to what you described. It's purpose-built for battery packs:amphenol+1

• 2 power + 4/6 signal pins in a blade-style housing with IP2X finger protection on both halves when unmated.

• First-mate-last-break (FMLB) — ground connects before power, power disconnects before ground. Safety by design.

• IP67 rated mated and unmated (with cap).

• Up to 70A continuous, 10,000 mating cycles.

• Keyed, CPA locking, compact.

• Buyable on Mouser Norway as single units.[no.mouser]​

Anderson SB50

The original blade-interleave battery connector, since 1953:mariner-sails+1

• Genderless — both halves are identical, flip one 180° to mate.

• Contacts sit deep inside parallel plastic blades — finger-proof by geometry.

• Stainless steel springs retain contacts, extremely low resistance.

• Up to 50A UL-rated (120A peak), 600V.

• Colour-coded mechanical keying prevents cross-mating.

• ~$5–10 per pair, available everywhere (Amazon, 12VoltPlanet, eBay, Biltema).

Which for Omera

  | DuraEV™ | Anderson SB50 -- | -- | -- Power pins | 2 (70A) | 2 (50A) Signal pins | 4–6 built in | None (power only) Finger-proof | ✅ IP2X both sides | ✅ by geometry Keyed | ✅ | ✅ colour-coded Price per pair | ~$15–25 | ~$5–10 Signal for BMS/temp | ✅ included | ❌ need separate connector Availability | Mouser (ships to Oslo) | Everywhere

DuraEV™ is the better fit — it has power + signal in one block, so you don't need a second connector for BMS comms and temp sensing. One connector does everything. Mount the socket half at the downtube floor, put the plug half on your scaffold bottom plate, and you're done.futureelectronics+1

The Anderson SB50 works too if you only need power and run signal wires separately — it's cheaper and more available, but means two connectors instead of one.

There are two solid ready-made options that match your blade-interleave, finger-proof concept:

Amphenol DuraEV™

This is the closest match to what you described. It's purpose-built for battery packs: amphenol

• 2 power + 4/6 signal pins in a blade-style housing with IP2X finger protection on both halves when unmated.
• First-mate-last-break (FMLB) — ground connects before power, power disconnects before ground. Safety by design.
• IP67 rated mated and unmated (with cap).
• Up to 70A continuous, 10,000 mating cycles.
• Keyed, CPA locking, compact.
• Buyable on Mouser Norway as single units. [no.mouser](https://no.mouser.com/new/amphenol/amphenol-fci-duraev-battery-connectors/)

Anderson SB50

The original blade-interleave battery connector, since 1953: mariner-sails

• Genderless — both halves are identical, flip one 180° to mate.
• Contacts sit deep inside parallel plastic blades — finger-proof by geometry.
• Stainless steel springs retain contacts, extremely low resistance.
• Up to 50A UL-rated (120A peak), 600V.
• Colour-coded mechanical keying prevents cross-mating.
• ~$5–10 per pair, available everywhere (Amazon, 12VoltPlanet, eBay, Biltema).

Which for Omera

	DuraEV™	Anderson SB50
Power pins	2 (70A)	2 (50A)
Signal pins	4–6 built in	None (power only)
Finger-proof	✅ IP2X both sides	✅ by geometry
Keyed	✅	✅ colour-coded
Price per pair	~$15–25	~$5–10
Signal for BMS/temp	✅ included	❌ need separate connector
Availability	Mouser (ships to Oslo)	Everywhere

DuraEV™ is the better fit — it has power + signal in one block, so you don't need a second connector for BMS comms and temp sensing. One connector does everything. Mount the socket half at the downtube floor, put the plug half on your scaffold bottom plate, and you're done. futureelectronics

The Anderson SB50 works too if you only need power and run signal wires separately — it's cheaper and more available, but means two connectors instead of one.

Critical point. When the battery is out charging in your apartment, the downtube is open at the top and the connector at the bottom is exposed to rain. It needs to survive that unmated and uncapped — because you won't always remember to plug a dust cap in.

This actually changes the recommendation:

The Problem with DuraEV / Anderson

Both achieve IP67 only when mated or with a protective cap. Frame-side socket exposed to rain with no cap = not rated. Water pools at the downtube floor (lowest point), sits right on the connector pins. That's a corrosion and short-circuit risk over time. futureelectronics

Better Approach: Pogo Pins Are Inherently Weather-Proof

This is where pogo pins actually win over blade connectors for your use case:

• Spring-loaded pins retract flush into the housing when unmated — no exposed cavities for water to pool in. connectorsupplier
• Gold-plated contact surfaces don't corrode even with repeated wet/dry cycles. [jiatelcn](https://www.jiatelcn.com/pogo-pin-design-guide-specifications/)
• Recessed inside the finger-proof fins, rain would have to travel sideways and upward between 5 mm gaps to reach the contacts — water doesn't do that.

The Real Solution: Fin Block + Pogo Pins + Drain

Design the frame-side fin block with:

• Pogo pins recessed 10 mm deep between fins (finger-proof + splash-proof).
• Open bottom / drain slots in the fin block so any water that enters runs straight out, never pools.
• Conformal coating (silicone spray) on the PCB/wiring behind the pins — cheap insurance.
• The downtube itself should have a drain hole at the very bottom (1–2 mm) so water that enters from the top opening exits and doesn't sit on the connector.

What to Buy

Go back to the custom pogo pin block approach, but with off-the-shelf pins:

• High-current pogo pins (3 mm barrel, 10A rated, gold-plated): ~$1–2 each from Jiatel or AliExpress. jiatelcn
• Signal pogo pins (1.5 mm barrel, 2A): ~$0.30 each. aliexpress
• Press them into a 3D-printed fin housing you design yourself — the fins provide finger safety and weather shielding in one part.
• Total cost: under $10 for pins + printed housing.

This way there are no cavities, no sockets, no places for water to collect on the frame side. Just gold pins between plastic fins that drain freely. When the battery drops in, the fins interleave and pogo pins compress against pads. When the battery is out charging, rain hits plastic fins and gold pins — nothing to damage.

Want me to source specific pogo pin part numbers from Jiatel or AliExpress that fit your current/signal requirements?

Spot on. This is a critical design point — the bike lives in Oslo weather, battery goes inside, frame stays out in the rain. The frame-side connector will get wet.

Three layers of protection

1. Fin geometry = self-draining

The interleaved fins are vertical — water doesn't pool, it runs straight down and out the bottom of the DT. No trapped puddles. This is actually better than most horizontal ebike connectors that can collect water.[bedeconnector]​

text
Rain enters open DT top
        ↓ ↓ ↓
    ┌─┐  ┌─┐  ┌─┐
    │ │  │ │  │ │   ← water runs DOWN
    │█│  │█│  │█│     the fin surfaces
    │ │  │ │  │ │
    └─┘  └─┘  └─┘
        ↓ ↓ ↓
    drains out bottom of DT

2. Contact material = corrosion-proof

Gold-plated contacts are standard for outdoor battery connectors — they don't oxidize, corrode, or build resistance even after years of rain exposure. Even if water touches them, nothing happens because:alibaba+1

• Gold doesn't corrode.

• 36V DC at open circuit won't arc or short through rainwater across a 3–4mm gap between pins.

• When battery is removed, there's no voltage on the frame-side pads at all — they're just passive copper/gold surfaces.

3. Optional: drain + dummy cap

For extra Oslo winter protection:

Feature | Purpose -- | -- Drain hole at bottom of DT cavity | Water never sits, always exits [bedeconnector]​ Snap-on dummy cap (like Giant does) | Plastic cover that clips over the fin area when battery is out. Takes 1 second [forums.electricbikereview]​ Dielectric grease on contacts | Thin coating repels moisture, doesn't affect conductivity [alibaba]​

What this means for the design

The frame-side fin connector needs:

• Housing: glass-filled nylon or PETG — UV and water resistant.

• Contact pads: gold-plated phosphor bronze — welded/soldered to wires, rain-proof by material.

• Open bottom: fins don't sit in a closed box — the bottom is open so water drains through.

• No electronics: frame side is 100% passive — just metal pads on plastic fins. Nothing to break, nothing to short.

The battery side is always dry (it's inside with you when charging), so standard pogo pins + PCB are fine there.

Want me to model the full interleaved fin connector now — both the frame-side fin piece and the battery-side slot piece?

Spot on. This is a critical design point — the bike lives in Oslo weather, battery goes inside, frame stays out in the rain. The frame-side connector **will get wet**.

Three layers of protection

1. Fin geometry = self-draining

The interleaved fins are vertical — water doesn't pool, it runs straight down and out the bottom of the DT. No trapped puddles. This is actually better than most horizontal ebike connectors that can collect water. [bedeconnector](https://www.bedeconnector.com/news/guide-to-waterproofing-xt60-connectors-for-outdoor-safety-284496.html)

Rain enters open DT top
        ↓ ↓ ↓
    ┌─┐  ┌─┐  ┌─┐
    │ │  │ │  │ │   ← water runs DOWN
    │█│  │█│  │█│     the fin surfaces
    │ │  │ │  │ │
    └─┘  └─┘  └─┘
        ↓ ↓ ↓
    drains out bottom of DT

2. Contact material = corrosion-proof

Gold-plated contacts are standard for outdoor battery connectors — they don't oxidize, corrode, or build resistance even after years of rain exposure. Even if water touches them, nothing happens because: alibaba

• Gold doesn't corrode.
• 36V DC at open circuit won't arc or short through rainwater across a 3–4mm gap between pins.
• When battery is removed, there's no voltage on the frame-side pads at all — they're just passive copper/gold surfaces.

3. Optional: drain + dummy cap

For extra Oslo winter protection:

Feature	Purpose
Drain hole at bottom of DT cavity	Water never sits, always exits [bedeconnector](https://www.bedeconnector.com/news/guide-to-waterproofing-xt60-connectors-for-outdoor-safety-284496.html)
Snap-on dummy cap (like Giant does)	Plastic cover that clips over the fin area when battery is out. Takes 1 second [forums.electricbikereview](https://forums.electricbikereview.com/threads/is-there-a-cover-for-the-battery-connections-when-battery-is-not-installed.29335/)
Dielectric grease on contacts	Thin coating repels moisture, doesn't affect conductivity [alibaba](https://www.alibaba.com/supplier/waterproof-battery-connector.html)

What this means for the design

The frame-side fin connector needs:

• Housing: glass-filled nylon or PETG — UV and water resistant.
• Contact pads: gold-plated phosphor bronze — welded/soldered to wires, rain-proof by material.
• Open bottom: fins don't sit in a closed box — the bottom is open so water drains through.
• No electronics: frame side is 100% passive — just metal pads on plastic fins. Nothing to break, nothing to short.

The battery side is always dry (it's inside with you when charging), so standard pogo pins + PCB are fine there.

Want me to model the full interleaved fin connector now — both the frame-side fin piece and the battery-side slot piece?