Hello,
I purchased a few of these:
https://www.pololu.com/product/799
and after using it on a project to power a small motor driver, V_in appears to be shorted to ground causing my power supplies to fault when trying to power it on. I’m guessing I either fried the IC switch, or need to reset it somehow to open the switch, but as the chip is not disclosed, its fairly hard to guess how to do this without causing more trouble.
Is there anything I can intentionally pull-up/down to manually reset the IC to force the switch open? If not all my smarter power supplies are complaining about the short (likely a good idea), so I’m weary to just plug it in unprotected to see if it works itself out.
In the meantime, I’ll try to figure out if I inadvertently exceeded the voltage or current specs somehow.
Best regards,
Christopher
As an update, I just replaced this module with a bench power supply to measure how much current I was drawing via the motor driver and found it to peak at around 1.3A when intentionally stalling the motor with normal working loads well below 500mA. I am only boosting a 5V USB-C supply to 6V to power the motor driver. Any idea what could have fixed the switch on the IC open under such operating conditions? I don’t want to burn another module to test it out so hoping someone can verify if these operating conditions are acceptable as they appear to be according the info I’m seeing on the product page.
Hello.
There is no way to “reset” the regulator; if that input is truly shorted to the output, it is damaged. How did you verify that the regulator is shorted? If your bench-top power supply has current limiting protections, you might try using it to supply the regulator with 5V separately from the rest of your system (i.e. nothing else connected to the input or output of the regulator). Could you post pictures of both sides of your regulator as well as some of your setup that show all of your connections?
By the way, if your motor draws 1.3A when stalling at 6V, then the current at the input of the regulator with a 5V input would be closer to 1.6A (or higher depending on efficiency), which is getting close to the limits of the regulator. Please note that starting up at full speed from a stop can cause your motor to draw upward of it’s stall current, and switching directions at full speed can briefly draw upwards of twice the stall current. So depending on how your motor was being driven, that could have caused problems. If you are not doing so already, I suggest taking some measures to reduce these sudden bursts of current, such as acceleration limiting.
Brandon
Hi Brandon,
I verified it is shorted by testing the resistance over the pins. The module was attached to a breadboard via the pin headers, so isolating the module was very easy simply by removing it from the breadboard.
Thanks for the tips on the stall current. It is possible my max/min multi-meter recordings do not register these very fast spikes when testing sudden reversals in motor direction, but I did test under such circumstances and didn’t find a max value larger than I quoted before.
I was using it in conjunction with one of Pololu’s dual motor drivers:
https://www.pololu.com/product/2130
but had not yet installed any current limiting resistors. I’ll be sure to do that prior to the next round of testing. Do you have any recommendations for safety factors when selecting the sense resistor on the 2130 module for this particular case? I was planning to I_chop to something around 750mA, i.e. a total of 1.5A max between the two channels. Do you think there is a need to reduce this more due to any latency between chopping and the current spikes you mentioned?
I do not have any specific recommendations for safety factors, but setting it to around 750mA like you described sounds reasonable. If your application allows for it, I would still recommend acceleration limiting as a way to help prevent sudden bursts of current.
You might also try using a scope to look at the voltage at the output of the regulator (i.e. the input of the motor driver) to make sure there aren’t any unusually large voltage spikes, since motors can create a lot of electrical noise and some of that could go back to the regulator.
Brandon
Thanks for your reply Brandon. As we’re working with a balancer robot, we need to allow for pretty rapid back and forth motion, so although possible, acceleration limiting would likely limit the performance of the balancer.
I will check the spike like you mentioned.
