Motenergy 86v E-Kart ME1306 Build

[journeyman846]

Did you check your battery voltage? Did you charge those cells individually or in parallel with a bench power supply? Be very careful with using the battery without a BMS. Overcharging and over-discharging can easily damage individual cells, but individually charging the cells for assembly and testing is safe; just don't go too long and risk over-discharge when you aren't monitoring the cell voltage.

I have been waiting on the BMS for over a month now (stupid AliExpress) so I haven't had a chance to really charge the pack. I've also only done a couple short test drives and have monitored the voltage after every one so I am not too concerned with cell damage. I am going to try and charge the cells using what I have for now and see if the RPM's come up.

 

[EpsilonZero]

It looks like it was probably pretty low with one cell reading 2.91v while charging. Hopefully just charging gets your max RPM up. Were you seeing 3000rpm max under load or with wheels up off the ground?

 

[journeyman846]

It looks like it was probably pretty low with one cell reading 2.91v while charging. Hopefully just charging gets your max RPM up. Were you seeing 3000rpm max under load or with wheels up off the ground?

Yeah on the last run I bumped the battery limit up to 100 (bad idea) and quickly discharged the batteries, but still never got over 3000 RPM. And I also noticed that one cell wasn't charging correctly because I didn't add a bar between like the others so I had to fix that. I haven't really done much testing off the ground yet because the torque and power is pretty scary on these things. I will probably remove the chain once I get the batteries charged and give it a good test.

 

[EpsilonZero]

Yeah on the last run I bumped the battery limit up to 100 (bad idea) and quickly discharged the batteries, but still never got over 3000 RPM. And I also noticed that one cell wasn't charging correctly because I didn't add a bar between like the others so I had to fix that. I haven't really done much testing off the ground yet because the torque and power is pretty scary on these things. I will probably remove the chain once I get the batteries charged and give it a good test.

The limit doesn't alter your effective voltage; it just limits the current, so you shouldn't see any RPM difference anyway unless you were climbing a steep hill or something. Did the misconfiguration lower your total voltage or did you just lose capacity on that bank?

 

[journeyman846]

The limit doesn't alter your effective voltage; it just limits the current, so you shouldn't see any RPM difference anyway unless you were climbing a steep hill or something. Did the misconfiguration lower your total voltage or did you just lose capacity on that bank?

It very quickly depleted the pack. It went from 76ish volts to 60 (my controller lower limit) in a matter of seconds.

 

[EpsilonZero]

It very quickly depleted the pack. It went from 76ish volts to 60 (my controller lower limit) in a matter of seconds.

You mean it dropped to 60v while in operation or dropped and stayed there at rest? Too much current would definitely drop the pack voltage in operation (especially if one bank was operating at 1P) but you shouldn't lose 16v (at rest) from a few seconds. At 24s, a LiFEPO4 configuration is basically dead at 60v (2.5v per cell) at rest. If they were operated at the low charge level they were at for transport, that would explain some problems too.