BAC 8000 Troubleshooting

Electric Motors and Controllers
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xenodius   1 kW

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BAC 8000 Troubleshooting

Post by xenodius » Feb 18 2020 1:40pm

This is a longshot, as I don't think many others are using these controllers right now. But even if nobody has advice, I'll update when I hear back from ASI and maybe it can help someone else too. And perhaps, this may serve as a cautionary tale for an apparently excellent but troublesome controller.

I am building my endgame ebike with a modded QS205, Fox 40 fork, Hope 4 V3's, 18650.lt snap-fit pack of 21s14p 30Q cells, and ASI BAC8000 on a Qulbix 140 frame. 4th >10kW build. Been spending the last 4 months trying to get this controller working, unfortunately. First bench test, I realized I could not connect via USB or bluetooth... it was DOA. 3 months after the RMA, I have a new replacement BAC8000. I used Alan's "Ebike Master Switch" design as a precharge/killswitch, which worked excellent on the first controller and brought the controller terminals up to battery voltage in ~2 seconds.

I tried to bench test the new controller, and now I can connect to it fine via USB or bluetooth, but it blew up my master switch when trying to precharge the battery connections. So I made a dumb 80-ohm, 80-watt ceramic resistor grid precharge line that I expected to be overkill, only to find that even ~1 amp will not precharge the controller-- it only brings the positive terminal to 1.2 volts! No wonder my master switch poofed! First time I tried to use this precharge, I definitely made a big arc and got a puff of smoke from one of my three 100-amp breakers.
  • Has anyone else ever had a controller fail in such a way that they cannot precharge the battery connections? Disconnecting the hubmotor phasewires or throttle connections does nothing.
  • How do I know if I need to replace my breaker now that I've almost certainly damaged the contacts by arcing? Check resistance?
Thanks for your time and any input.

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amberwolf   100 GW

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Re: BAC 8000 Troubleshooting

Post by amberwolf » Feb 18 2020 11:50pm

for a typical 3-phase bldc controller, when either the battery wires are reversed (which may or may not permanently kill whatever is connected to the battery positive and negative), or the phase fets are shorted across both halves of a bridge, the entire battery input is shorted.

the only thing that would prevent the first short is a diode in series with the battery input.

i can't think of anything that would prevent the second.


a third problem that can do this is if the main electrolytic caps are installed backwards, or otherwise internally shorted. in both of those cases, they usually explode after a fairly short time of current flow thru them. (if not explode, then rupture)

flat tire   1 MW

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Re: BAC 8000 Troubleshooting

Post by flat tire » Feb 19 2020 1:25am

21S is a little on the edge for ASI. 20S is the max they recommend. Voltage is low enough there you don't really need to precharge.

A 4000 is a much better match for a 205 since the power will be equivalent for almost the entire rev range. In other words you won't be able to pull max battery amps ever on a 4000 with QS205 and max phase current will be more than enough unless you have a very exotic long wheelbase heavy bike or something. The 8000 is very big.

Also Alan gets a lot of complaints and is inconsistent and dishonest. I wouldn't use him for anything better to buy straight from ASI. Once you order a single "eval kit" from ASI you can buy from them with dealer pricing. They don't need any actual verification you just need to say you have a company.

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