Faulty BMS?

[EmSeeDee]

I have a conversion kit fitted to my utility bike; it has a new Tongsheng motor and a 5 year old Hailong battery pack. All works well, except when I first set off, after between 5 and 10 seconds, the power cuts out for a moment. If I'm pedalling, the motor drops out and I have to turn it on again. After that, it's fine until I stop for a break (10 mins plus). If I'm coasting, I can see the battery charge state indication drop to zero and then recover almost immediately, but the motor doesn't drop out.

It's a 36V system and it's all set up to UK legal speeds & power, etc.

I'm suspecting that the BMS is the culprit, since it seems to happen just as the BMS wakes up and never again until after the BMS has gone to sleep. Is that feasible, and is it feasible to fit a new generic BMS to the battery - it seems to look like the ones displayed on eBay.

FWIW, the battery pack has a bluetooth module, from which I can see that all the cells seen to be the same voltage, but the lag in the bluetooth connection & app mean that It doesn't see the power dip. Also, once its over its initial hiccup the range seems OK, so I don't think there's a problem with the cells.

TIA

Mike

 

[Nealh]

Might be a dry solder joint onthe bms wiring , worth trying to wet the joints again and possibly use a bit of fresh solder in to the mix to see if it cures the issue. If not then one could try a new bms.

Though before a new BMS, one needs to see what is happening with the voltage sag before the cutting out, if the BT lags and is slow, temporary try and rig up another voltage mointor for real time voltage to see what is occurring.

 

[Bikes4two]

If after trying the things recommended by @Nealh and you've delved into the battery's inards and you feel confident in trying something else, then before buying another BMS (and avoid cheap BMS BTW - NealH could probably recommend a good source of supplier), look into how to bypass the BMS on the discharge side of life.

I have a TSDZ2 as well and the cheapo BMS in my battery was playing up and so I used a technique often used in the ESK (electric skateboard) world whereby the BMS discharge function is bypassed (see this YT piece HERE to get an understanding of this ploy).

Your battery pack likely has a fuse in the discharge cable and of course the TSDZ2 controller limits current in software/firmware to something like 15 amps, so no big deal to try out - but you do need to understand the potential risks about soldering around lithium ion battery packs.

You can get the idea of this ploy from the pic below - as you can see the thick black wire from the negative pole of the battery goes straight to the -P discharge port rather than to the normal BMS connection point, -B

BTW, a 'loop key' is just like an emergency 'pull switch' if for some reason you think you might want to disconnect the battery quickly.