nogrin said:
hi, sorry if this isn’t the place to ask questions i am new. i am in the process of purchasing an ebike/moped type thing and i had some questions i wasn’t able to find help with elsewhere. the bike im looking at getting has space to mount 3 hailong e bike battery cases. im planning to replace the controller and motor on the bike to make it relatively powerful. my issue is most places i can find hailong batteries they are limited at the bms to 40 amps at max. so my question is if i run 3 of these batteries in parallel would the max current output be 40 amps or 120 amps? and do you guys think that would be a good solution?
If in parallel, the current (and capacity) adds.
However--when any of them shuts down, for any reason, the system as a whole is now only as capable as the remaining packs--if the load exceeds what they can do, *and* they have protection against this, they'll shutdown leaving you without power.
But if they have no protection against overload, the BMS in them may simply fail...and this failure is usually the FETs, and those often fail shorted. If they do, then the result is that the BMS will *try* to turn them off when a condition (LVC (battery empty), etc) comes up that needs protection against, but the FETs won't respond; they're like a switch stuck in the on position. When that happens, you can then overdischarge the cells, and damage them. SUch a FET failure is "silent" meaning you won't even know it has happened, unless/until the batteries are damaged by the results and show obvious symptoms of this....
If the controller has LVC protection higher than the battery's, this is less likely...but can still happen in some scenarios.
To mitigate the possibility of this, you can run a wattmeter that keeps an Ah / Wh tally of usage during a ride, and when you get within some percentage of having used most of the total 3-pack capacity, start riding in a way that uses the batteries more gently. It's better for the batteries in general, and makes it less likely for most of the potential problems to occur.
Regarding the rest of the project, if you list the specific riding style, speed, etc., rider/bike/etc weight total, along with your riding conditions like hills (incl actual slopes), weather, road conditions, etc., desired range at what speed, and any other info possible, it will help us help you figure out how much motor, controller, and battery you will need to do the job you want the bike to do for you. Then you don't either have to just overbuild and overspend to be sure it can, or end up buying the wrong insufficient stuff first and having to buy a completely different "bigger" set of stuff later when the first doesn't do what you want.
Or you can go to the http://ebikes.ca/tools/simulator.html and simulate your proposed setup in your specific conditions, and see if it will work.