Controller Shunt Experiments

[d8veh]

I measured the voltage drop across the shunt in my controller when 10 amps was flowing from the battery. It was 44mV, so the shunt is about .0044 Ohms, which sounds about right.

I cut the shunt and soldered on a 44cm loop of 14g wire, which would have approximately the same resistance.

Like that, the controller didn't want to run. It would only kick the motor. I found out that if I was really careful on the throttle, I could get the motor to run slowly. One time, by opening the throttle very, very slowly, I got the motor up to speed and was able to load it to 10 amps, which showed a voltage drop of 42mV across the wire, which is close enough to what I had before. I couldn't get it to run like that again. I tried the same experiment on another controller, and got the same result. A couple of times, a CPU error came on the display.

My thinking is that there is some capacitance or inductance in the wire that's causing some effect. Does anybody have any ideas what's going on?

I tried bending the wire into double reverse loops to cancel out inductance, but it still didn't work. When I bridge the original shunt it works immediately, but with much higher current available (probably double).

 

[wesnewell]

Too much resistance in the long wire? What are you trying to do? The reason you get double power when you bridge it is because with the wire bypass added, the shunt resistance is lower, basically doing a shunt mod.
http://endless-sphere.com/forums/viewtopic.php?f=2&t=31643

 

[d8veh]

Too much resistance in the long wire? What are you trying to do? The reason you get double power when you bridge it is because with the wire bypass added, the shunt resistance is lower, basically doing a shunt mod.
http://endless-sphere.com/forums/viewtopic.php?f=2&t=31643

It has less resistance than the original shunt. The wire is .0042 Ohms, and the original shunt is .0044 Ohms. When you combine them by bridging the original shunt,the resistance is 0.0021 Ohms.

 

[fechter]

That's pretty strange. Inductance in the loop is about the only thing that comes to mind. With inductance, the voltage across the shunt may be allowed to rise fast enough to trigger the overcurrent protection.

You might try hanging a large capacitor across the shunt.

 

[wesnewell]

Timing issue? Looks like you have ~2ns delay in that loop. 1ns=9 3/4" iirc.