Hard Shock on Unknown 52v Battery - Diagnosis?

[nickD2012]

I've got a used 52v unknown triangle battery pack mounted in a soft case powering a BBSHD mid drive on a Giant Talon frame. My kid took the bike off a big jump because his friend with a Talaria XXX (why a 14 year old in a suburban area has one is beyond me), cracked a rim, and tore the bag off its mounts and walloped the battery quite hard on the down tube. The wrapping is intact and appears undamaged, though the BMS metal plate is dented and the on/off switch on the BMS no longer cuts power to the leads. This pack also is ~3-5 years old (acquired used). The battery did come in a hard case which split a while back.

I tested the output leads at the battery (which was fully charged when he went out), and am only seeing ~28v, though I see 58.8v across the P- and P+.

One hypothesis is that a bus bar may have broken, causing the leads to only pick up voltage from some of parallel packs, or the BMS damaged and impacting output leads.

Is there a safe way to diagnose whether this pack may still be good, or should it just go to the hazardous waste recycler? If I'm looking at a new battery, are there any that would handle some mountain bike activities?

 

[bananu7]

Is there a safe way to diagnose whether this pack may still be good

If the cells themselves are okay, then it might just have damaged wiring or BMS, as you mentioned. I'd start with an independent measurement of the individual groups, but if the entire packet has full 58.8V, it's very likely that they're all fine, and it's just the BMS that's misbehaving. Replacing it and putting everything in a nice solid case could very well bring it back to operation.

 

[nickD2012]

If the cells themselves are okay, then it might just have damaged wiring or BMS, as you mentioned. I'd start with an independent measurement of the individual groups, but if the entire packet has full 58.8V, it's very likely that they're all fine, and it's just the BMS that's misbehaving. Replacing it and putting everything in a nice solid case could very well bring it back to operation.

Thank you - are there any guides you’d recommend on how to take off the wrap, as well as reputable BMS suppliers?

 

[amberwolf]

The wrapping is intact and appears undamaged, though the BMS metal plate is dented and the on/off switch on the BMS no longer cuts power to the leads.

The most likely thing is that the wires from the switch to the board, or the switch itself, have brokn. Next, the dent is shorting something out, or did so momentarily before deforming away from it, and causing the FETs to be permanently turned on, or damaged and shorted, or they are stuck off and you're just seeing ghost voltage.

I tested the output leads at the battery (which was fully charged when he went out), and am only seeing ~28v, though I see 58.8v across the P- and P+.

Put a load on the battery, even just turning the bike on, while you are measuring. If the voltage drops to zero, that's because the BMS FETs are turned off because of a problem with either the BMS itself, or because of it reading a problem with the cells.


If the voltage stays exactly the same, then there's something else wrong that is dropping voltage across some component (almost certainly the BMS FETs; other than connectors there's not really anything else in series with the cells to drop voltage across)...but that should only happen under load when current is being drawn, and you'd see more voltage drop the higher the current was. No load should still read the full pack voltage.

 

[nickD2012]

Appreciate it - the bike won't turn on with the current battery. I did order a replacement BMS that gets here in the next few days since it I can't imagine a scenario where the current one will remain viable and will report back.

 

[amberwolf]

Even if the bike won't turn on, you should still do the test as described, and report the results. It will tell you something about the condition of the pack and what's going on.

Then you can begin testing cells, etc.

 

[nickD2012]

Even if the bike won't turn on, you should still do the test as described, and report the results. It will tell you something about the condition of the pack and what's going on.

Then you can begin testing cells, etc.

When I had a gen 1 Honda insight, I used an incandescent bulb to discharge the NiCad pack - would that be the recommended approach here?

 

[amberwolf]

You could use that as a load for further testing, but I'd still just first try the easy way, with the bike itself and do the test, because it's a tiny load that won't hurt the cells even if something is damaged in the battery, and you can still tell if the BMS is turning off it's output when the bike is turned on from an off condition.