srn said:I dont understand the issue with cable length. I understand that long cables have high resistance, but how about the current peaks at long cables from battery to controller ? Can someone explain this ? And is it really better to have longer cable from controller to motor than from battery to ESC ?
Thank you for further explanation and best regards,
Soeren
Yes, the longer the battery wires the higher the resistance, but thats not the problem. The problem is the inductance.
The Mosfet's can be seen as a switch that turns on and off very quick.
Lets say one bank of FET's is in on stage and 200A are flowing into the motor at 60V.
At the moment when this bank of FET's turns off (and another bank turns on eg), there will occur voltage spikes which can be much higher as the battery voltage itself.
The higher the inductance of the battery wires incl. the bus bars in the controller, and the higher the motor current (which will be always abruptly interrupted by the FET's), the higher the voltage spikes will be.
The caps are now there to smooth out those spikes keeping them below a level which would be dangerous for other electronic components.
If you now have very long battery wires, the caps have lots of work (current ripple) and they can get hot and swell.
If the caps (partial)fail, the voltage spikes will kill the FET's.
Longer motor wires are absolutley no problem assuming the cross section is large enough so they can handle the amps :wink:
Twisting the battery wires or put them as close as possible beside each other helps to reduce the inductance in the supply line.