Bafang Battery Charge Port: Whoopsie

The Bafang mid-drive e-bike kits I installed on Mary’s Tour Easy recumbent and a friend’s Terry Symmetry used the “Ultra-Slim Shark” lithium battery, a rectangular lump with a tapered snout:

Bafang BBS02 - Terry Symmetry full assembly
Bafang BBS02 – Terry Symmetry full assembly

The battery has a key lock on its left side:

Bafang battery - lock
Bafang battery – lock

The lock might deter casual thievery, but really prevents the battery from bouncing out of its mounting plate while riding.

The right side has a charge port closed with a rubber plug:

Bafang battery - charge port - closed
Bafang battery – charge port – closed

The cover protects a coaxial jack with a 5.5 mm OD and a 2.1 mm center pin:

Bafang battery - charge port
Bafang battery – charge port

My friend in Raleigh generally removes the battery before hoisting the bike into the back of her car to haul it to a friend’s house for their companionable rides: not lifting an additional seven pounds is a Good Idea™.

A momentary distraction in the middle of that process caused her to insert the brass key into the charging port, rather than the lock. The key put a very short circuit between the coaxial jack’s side contact and the center pin, melting the key tip and welding a brass nugget onto the side of the pin:

Bafang battery - damaged charge port
Bafang battery – damaged charge port

The charger plug normally sits almost flush to the port’s surface:

Bafang battery - charge plug
Bafang battery – charge plug

The nugget keeps the plug out the damaged port, preventing the plug from making electrical contact:

Bafang battery - damaged port - plug
Bafang battery – damaged port – plug

She owned the problem and immediately bought another battery, which tells you the value she places on riding her e-bike.

Verily it is written: let someone who is without whoopsie cast the first shade.

Any takers? Yeah, the way I see it, someone who says they’ve never done anything quite like that is either not doing anything or not telling the complete truth. For sure, I’ve done plenty of inadvertent damage!

Here’s the problem:

  • The damaged battery is the better part of 600 miles away from my shop
  • Civilians cannot ship 560 W·hr lithium batteries through any parcel delivery service
  • Civilians cannot fly or take the train with such a battery, either
  • Driving 1200 miles twice is out of the question for either of us

How would you proceed?

More to come …

For reference:

Basically, it is possible to ship lithium batteries up to 100 W·h.

16 thoughts on “Bafang Battery Charge Port: Whoopsie

  1. I have a friend who’s technically savvy and an EV enthusiast, who lives in Apex, not far away.

  2. Perhaps using Mary’s battery as a model, send step-by-step instructions with photos for disassembling the pack and removing the battery. Then ship the now harmless (and lighter) pack/frame/carcass to the Shop for rehabilitation.

    1. I took our battery apart: it’s a glued assembly with the connections deep inside the glue. Worse, disconnecting the charge port requires Cutting The Red Wire, then reconnecting it.

      I’m willing to do that, but disembowling and snipping wires inside a lithium battery is not a task for the inexperienced!

  3. No ideas, but a silly question. How was the complete kit shipped? Is that option available to the unwashed public?

    There’s a junction box in a house I used to live in–I thought I had removed the appropriate fuse. The sparks and resulting divots out of the box and screwdriver proved me wrong.

    1. We’ve burned up enough trucks and cargo airplanes, plus killing enough aircrew in the process, that they’re taking lithium battery safety very seriously nowadays. Large batteries can be shipped only by a real company with trained personnel and a call-for-info hotline; the mandatory on-the-box stickers are not available to civilians.

      The post now has linkies to the relevant rules for future reference.

      1. OK, that makes sense. Let the specialized pros do it. Even my Alinco handheld had lots of warnings about its relatively small LiPo battery.

        I encountered the wonders of Haz-Mat shipping when I got 4 428AH Rolls-Surette batteries for a solar system. There was a fair amount of electrolyte sloshed on the tops, with some clothing destroyed when I unwrapped the pallet and moved the batteries. The next move, I wore a plastic apron, and only ruined the legs of those pants. [Sigh] At least no skin contact.

        IIRC, the Boeing 787 was using LiPo batteries in bulk with (in hindsight) predicable results. I think that was when folks started to notice that such batteries are a wee bit riskier than older technology.

        1. Ewwww!

          I’m definitely not a pro, but I do have a morbid fear of dying …

  4. I once shorted a 12v-55 ampHr sealed lead/acid battery for a fire alarm panel, which involved triggering two simultaneous alarms, one supervisory from the backup battery charger giving up the ghost and the other from the smoke detector in the mechanical room being triggered by the burning insulation.

    1. It’s amazing how fast you can heat up a conductor using an essentially unlimited amount of current!

      1. The nature of the conductor will affect the consequences of said rapid heating….
        Back when I was young & foolish, I carelessly shorted a NiCd pack (which will give you some idea of how long ago this was) with a metal watch band. Owwwwww!

        Regarding the original whoopsie, how common is it for battery charge ports nowadays to double as rapid-discharge ports? Is this a consequence of the charge controller using a single FET to control charging current, with the parasitic diode acting as a discharge path?

        1. Replacement BMS modules (perhaps just the cheap ones?) have a single connection for either the battery or the charger, plus a sheaf of per-cell balancing connections. This battery has a similar BMS, apparently with both the battery and the charge connector wired in parallel. Nothing wrong with that, but it dumps the battery’s full ooomph into the charging connector during a whoopsie.

          The negative terminals go to separate points on the PCB, so the short-circuit current must pass through some active component; your thoughts on a FET body diode seem reasonable. Ouch!

    2. My old Belkin UPS uses two of the 6V 7(?) AH batteries. I discovered that doing R&R on them offers a risk of the metal case contacting the PCB. Merely a ground trace, and it was fixable. [mutter]

      There’s now a sheet of PVC atop the circuit board. OTOH, power has been fairly reliable, and the desktop computer is robust enough to deal with a power outage and will come back fine. I love me a journaling file system.

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