I have been using the 18V15 for over a year with a robot base (not shown) with great success and it’s time to build a bigger robot (see picture). Now, I think that I have killed two 18V15 high-power motor drivers using 3.6 A, 24 volt, 350 W motors from a power wheelchair, which I am operating at 12V from a car battery charged to 12.71 V. See the labels that is attached.
I do not know the stall current on these motors because I am not setup to measure that. My meter only goes up to 20A. I guess I could set up a shunt resistor and measure voltage accross that with my scope, but I don’t know how accurate that will be since I do not have any high power resistors. In fact, stalling these motors is going to be really hard because they are geared down from 3300 RPM to 120 RPM and I would really rather not take the assembly apart. I measure the DC resistance of the motor as 0.3 ohms. This results in a calculated stall of 80 A. Assuming that my measurment is a little high, a 0.15 ohm DC resistance would give us 160A. Now, assume that the stall current is between 100 A and 160A. With the motor running, reversing it would likely give us double (or more) of the stall current.
Here is what I did and what happened. I connected the motor leads and the power. I used a 480 ohm resistor to connect the 5V output to the PWM pin. The motor spins and I can leave it there for quite some time with no real heat generated on the 18V15 board. I can start and stop the motor, sort of pulsing it (not really PWM because I am doing it with my hand really fast; maybe 10 Hz). Then if I reverse the motor by tying the the DIR pin to 5V through another 480 ohm resistor, all works fine and the motor spins in reverse.
With this setup, the 480 ohm resistor connected to the DIR pin lost contact and everything stopped. I have not been able to restart the driver. I disconnected and reconnected power, tied the reset high, and let it cool off (even though it was not hot). I took off everything, reapplied power, measured the 5V output and it is in the millivolt range (between 10 and 20). So the 5 volt regulator is not coming on and providing an external 5V to this pin does not help. None of the FETs are shorted and their gates are not shorted to ground.
O.K. so I figured that the 18V15 driver chip is dead and I proceed to the other side. This is another new 18V15 and a different motor. I ended up doing the same thing to this one, but this time the DIR pin was on a toggle switch, which provides a very small delay, and I intentionally flipped the switch (ensuring that I was not shorting something out). This killed this 18V15 (I know… but I didn’t do it a third time).
So this was a long description leading up to the question. Is there a specific amount of time required before the motor can be reversed? I would like to use the motors to provide a balancing effect and I may need to rapidly reverse them. By the way, this works with motors that are 12V, 1.75 A, 60 W stall because that is what is on my other robot and this is how I use them (although the mass that is moving is much smaller, making the momentum much lower). Any suggestions for a motor controller that would work for this? I can probably spend about $200-250, but I really do not want to spend $400 or $500 dollars though.