I was working on a little self balancing robot and I needed a little more oomph so I increased the voltage from 12v to 18v (It’s a 24v motor out of an old printer). Within about 3 seconds I saw some magic smoke escape from the 18v15 motor driver so I disconnected power.
It appears the bottom right mosfet has a crack across it. I hooked up the fault lines to LED’s and connected my original 12v and nothing seems to be getting hot anymore on the board. Both LED’s are flashing about every second. It appears that every pin except for the ground is synced with the LED’s, they are all low and when the LED’s flash, all the other pins also go high, including the motor output - The motor is still, except every second or so it pulses for a split second.
The only thing I have connected to the driver when I am trying this is 12v input, ground pin goes to my breadboard so the LED’s will function, and the outputs to the motor. I am not trying to drive any kind of input signal to it at all.
Would a fried mosfet cause all these problems or is the driver chip itself probably bad? Is there a way I could test the mosfets while they are still on the board?
Oh and by the way, I measured the current draw of my motor, and it was only pulling about 150mA free wheeling, and if I held the wheel so the motor was stalled, it would pull about 800mA.
I realized, the reason why everything was flashing was because the 12v power supply I connected to it was shorting out, and it was going into automatic shutdown, over and over, about once a second. I desoldered the mosfet that had a crack and now the power supply is not going into automatic shutdown and the two fault LED’s stay lit. But now the driver chip is getting very very hot after a few seconds. The PCB under the bottom right mosfet made a tiny heat bubble, and I see the same thing under the top left mosfet, it had also gotten very, very hot.
Before I desoldered the bottom right mosfet, I measured the resistance between source and drain on all 4 mosfets and got the following results:
Top Left: 65.6 Ohms
Top Right: 13.8 Ohms
Bottom Left: 275 Ohms
Bottom Right: 224 Ohms
After desoldering the bottom right mosfet I got the following:
Top Left: 2.38M
Top Right: 14.1 Ohms
Bottom Left: 2.42M
I was also getting 10v out of the 5v out line (and the driver chip was getting really hot).
But now things are looking better, The two left mosfets are giving me the results I would expect if they were off and not conducting.
So I desoldered the top right mosfet, and now when I hook up power I get a little over 5v out of the 5v out line, and the driver chip is not getting hot anymore. I still have both LED’s on, but thats probably because it’s missing both mosfets so the bootstrap voltage is too low.
I have replacement mosfets I bought for a different project that I think I am going to try to solder on. They are the same exact make/model.
I am sorry you are having trouble with your driver. What is the stall current of your motor at 18V? Did you have the large electrolytic capacitor installed?