BMS with discharge bypass - or not?

[Bikes4two]

• There are a surprising number of 'lost power' issues reported on the forum where the BMS turns out to be the culprit.
• I have experienced the same with my TSDZ2 and 10Ah bottle battery and whilst I await a replacement BMS, I am running the battery with the discharge function bypassed.
• I've OSF on the TSDZ2 so I can set the motor current draw and controller Low Voltage Cut off and the battery output is fused at 20 amps
• So most of the BMS discharge functions are catered for - or so it seems to me?
• What are members thoughts on continuing to run with BMS discharge bypass (a common practice in the e-skateboard world), i.e. potential pitfalls and how might they be mitigated?

 

[soundwave]

dont do any of that with my bosch batts tho if the bms does die it is a bin job bar salvaging the cells in it.

now this is a real bms

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[wheeliepete]

I've been using a pack like this for 2 years now with no ill effect, it still charges and stays in balance. As long as you don't try to pull more amps than the cells can supply, I can't see a problem. You have the LVC of the controller to stop the voltage dropping too low.

Edit
Just to be clear, I am only advocating bypass for discharge wilst still charging through the BMS.

 

[matthewslack]

I've been using a pack like this for 2 years now with no ill effect, it still charges and stays in balance. As long as you don't try to pull more amps than the cells can supply, I can't see a problem. You have the LVC of the controller to stop the voltage dropping too low.

With a good battery used within its comfort zone it'll be ok, and unlike charging without bms, if anything goes wrong it will be a 'right side failure' I.e. safe, in the sense that a weak cell group will be destroyed by under voltage before the lvc kicks in, but there should not be a fire.

Unlike charging without bms, where a weak group will be pushed to overvoltage and possible fire before the fully charged voltage is reached.

 

[Nealh]

If charging without BMS one must be able to monitor all cell groups manually, which means a lot of patience and watching.
For 36v one can buy and use a 10s balance charger in place of a BMS but would need external balance connector, the main problem is knowing the weakest cell during discharge or stopping any discharge at a predetermined voltage so a voltage display or reading of some kine is required.

 

[Bikes4two]

dont do any of that with my bosch batts tho if the bms does die it is a bin job bar salvaging the cells in it.

Is that 'dont' or 'can't'? I've not owned Bosch batteries but from friends who have and from the forums, I get the impression that even if you can get to the BMS and diagnose it, you couldn't get a replacement BMS let alone get it to work with the rest of the Bosch system.

I may be wrong on that, but the limitations of proprietary systems vs more generic kits and their repair by the end user, are one of the advantages of the latter over the former.

 

[soundwave]

bosch use can bus so as soon as the power is cut to most of there bms boards it kills them as want you to buy another batt than have them recelled

not very green is it lol