Hi
I am using Pololu High-Power Motor Driver 36v20 CS.
I tested driver using 40 volts and it was working. I turned off the power supplies and I am quite sure that the drivers were operational when I turned off the power. I later comeback
to continue with the driver, but as soon as I turned on the power supply, the short circuit safety of power supply got activated and every thing stopped working.
After inspecting the driver with multi meter, I see that the VIN and GND and DIR pin are shorted together. Also every mosfet is shorted.
This is the second driver that such thing is happening to it.
Why is that?
P.S: I am using this driver to run a Helmholtz coil. I already used the vhn5019 @ 24V and driven the coils for a while successfully. Now I need to increase the strength of coils by increasing voltage.
Thanks
Were the drivers connected to your supply when you turned the supply on? Does the driver start supplying current to the coil right away when the system is turned on? Could you post pictures of the setup that show all connections including the wires between the supply and driver, and the solder joints on the driver? How much current do you expect your coil to draw at 40V?
Thanks for your response.
When powering the power supply on or off, I always make sure that the PWM command is set to zero, so the driver is at neutral state in those moments.
The coils draw 10.25 Amp at peak voltage (42V).
The connections are secure as it can be seen in the below figure. I have disconnected the driver from the corresponding coil, but it is connected with the similar wire. Also the solders are strong and through. Capacitor was soldered to the driver during operation and I only disconnected after failure to check the underneath.
I have tested the current setup at its peak for 5 minutes to check heat dissipation and each part of the circuit (the driver, connection wires and coil itself) was normal (no hot I mean). Further, I have worked with my current set up using the VNH5019 drivers for a while (operating at 24 V), and everything was OK, so I do not think the problem is in soldering, connection, or circuit problem.
As far as I know the current driver does not have built-in fly-back diodes and maybe that’s the source of the problem. If that’s the case do you have any recommendation regarding that?
Best
Farshid
Thanks for the pictures and additional information. The MOSFETs in the driver have built-in body diodes that act as flyback diodes.
Rather than a connection issue I suspect voltage spikes on the driver’s input. They could come from unpredictable behavior when your power supply is turning on or current flowing back from the coil. Since the driver seemed to die at power up and your wires do not seem too long, spikes from the supply are more likely. You could use an oscilloscope to look at the supply’s turn-on behavior. If that is the issue, you could wait to connect your system to power until after the supply is on or try adding some transient protection like a TVS diode. Using a larger external capacitor than the ones supplied might also help.
Thanks for your response.
I checked the power supplies power up and down behavior and there was no overshoot/undershoot.
I am using mean-well power supplies series SE.
As a quick note, I am having 3 coils each powered by their own driver and power supply.
one run by your vhn5019 @24V@15Amp
one run by your your G2 High-Power Motor Driver 24v21 @31V@13Amp
and one that failed with the driver in discussion.
I checked the other two drivers input/outputs during operation and in startup and shutdowns with oscilloscope and everything was normal too. So I think it is unlikely that the other pieces of the setup is causing the issue.
Thanks
Farshid
I still suspect a voltage spike, since the main difference between the setup where things are breaking and the others is the higher input voltage and higher current draw from the coil (which would make any inductive spikes from the motor worse). I recommend using your scope to look at your setup when you start and stop delivering power to the coil as well. Could you also post pictures that show how the damaged drivers were connected to your full setup (please show all connections)?
Thanks for your reply.
The coil connections are similar to the input voltage connections and they are secure.
I think the issue with my biggest coil is that it has relatively high inductance (~115 mH) and the freewheeling current in high voltage is exceeding surge current rating of fly back diodes when commanding the coil to zero. Probably I have not noticed it during that process. I will measure this current in lower voltages with a new driver to make sure about it. If this is the case, then I should use a high current rating bidirectional TVS diode on motor output of the driver to handle that.
Thanks.
