I have a motor controller for a large dc motor that seems to have an internal problem causing it to shut itself down.
The controller has an output driver that energizes a contactor or (solenoid) by sinking the negative side of the solenoid coil. The controller has a safety feature that “senses” the current draw on this output driver pin. If the current is over 2A, the controller recognizes this as a fault and shuts the controller down.
My controller is giving this error and shutting down sporadically although I am measuring only about 200mA on the driver output wire when it shuts down.
I think I have created an external work around for this problem, but I am not sure it is the best way. I have connected 2 1N1448 diodes and a 1M Ohm resistor in parallel together. I then added these in series with the output driver wire to the solenoid coil. The idea was to use the diodes to allow the current to flow in one direction to energize the solenoid coil, but not allow the current to flow back to the controller. The resistor allows a reduced amount of current to go back to the controller so that the controller recognizes it is connected to a solenoid coil (else it will give an error).
It seems to be working fine. However, I’m not sure if my logic makes sense or if it is just a fluke… Does this make sense?
Also, I chose these values basically at random. I think the diodes I chose will allow 200-300mA of current and two in parallel seem to be plenty enough to energize my solenoid coil. The 1M resistor apparently gives enough current back flowing to the controller for it to work.
However, are there better values to achieve this? How do I calculate that? I am energizing the solenoid coil with 48v nominal. The solenoid coil as about 110-120 ohms measured across the coil.
You need a flyback diode in parallel with the solenoid coil for protection, like a 1N4007. That way you can absorb the reverse voltage that occurs when you switch off the coil.
The 1N4148 (which I guess you're using) is not suitable for this use. Series diodes don't do anything useful in this circuit.
It's a fluke.
A series diode or several parallel diodes in series won't stop 2A from flowing.
At 48V and 110 ohms, you should measure about 436ma not 200mA
Ok. I’m dumb. So help me understand. It is allowing enough current to allow the solenoid to energize. I know it is. It’s working and going through the diode.
But what y’all are saying is it wouldn’t allow the 2A of current that the motor driver is capable of?
The idea won't work.
If the controler is actually detecting an overcurrent, then maybe there actually is an overcurrent and you should try to find out why.
I have tried. I can’t. There is a feature on this controller that allows you to turn the “current sense” off. So that it will not detect an over current or protect the solenoid, but I can’t seem to access it through programming. It says in the manual that you can turn this off because there can be faulty readings due to emi. However I can’t turn it off. When it has triggered and I’ve measured the current when it triggered it was no where near the 2A.
Why would it be working with my current setup? Just luck?
What you need is a TVS (Transient Voltage Suppressor) diode.
Connect it between the controller output and ground. The end with the band connects the the controller ouput
Not knowing what is actually causing the controller to detect an overcurrent, I can't say that it will definitely fix the problem but it will suppress large voltage spikes.
Yep , need to see the motor controller .
If it’s a motor controller , then it should have protection internally to stop false tripping .
Fixes for it are really just sticking plasters .
The controller is a Curtis 1268-5403. I’m not sure why it is working correctly with my setup, but it is. I can remove the diode/resistor combo and just put the wire directly to the solenoid as it is supposed to be, but it is working… I kinda hate to mess with it.
