Did I Burn Up My Hbridge?

 
#1

Well, I spent the afternoon wiring up the 2.5 amp H-Bridge I bought from the store here to my dc motor. The motor pulls about 1 amp and runs on 24vdc. So, needless to say I have external power running to the H Bridge to power the motor. I do have a common ground between my external power supply, EZB and the H Bridge. After I wired it according to DJ's example and video I had a little trouble getting the motor to start to move. After fiddling with the PWM slider it started to turn at different speeds but only one way. Then it just quit. I decided to move the wires over the other side of the board and there I got the motor to move both ways but then after a very short time the motor stopped responding and just kept running on one direction. There is a light that stays on next to that port (Numbered D8). I fear one of the little transistors are shorted shut. I'm not sure I had that little white button up or down while I was doing all this. Could having this button in the wrong possession supplying external power cause my problems? Any ideas what happened? Am I SOL and time to get a new H-Bridge? Crap.

Another odd thing, I set up 4 Digital "Set" controls and assigned them to the comtrol ports the H-Bridge is plugged into. When I turn each one on and off, two different arrows will engage at the same time on the H-Bridge control (1&3, 2&4, 2&3, and so on). Odd.

Thanks, Dave Schulpius *eek*

#2

No Correction on the last oddity. When I click on a different arrow in the H-bridge control two different of the Digital port "set" controls will go off at the same time (2&4, 2&3, 2&4, 1&4) but the motor wont move when hooked to the left side port.

#3

Before connecting your motor and using high voltage, simply use a volt meter in place of the motor. That way you can verify before drawing a bunch of current. I doubt there is anything damaged, because as long as you didn't short the l298 and see a puff of smoke, it should be okay Smile

You can also witness the behaviour of the white switch by using the volt meter in place of the motors. Try that and see waht you get Smile

#4

Thanks for the words of wisdom. I wish I was as confidant as you on there being no damage. What about that stuck on light at D8 next to the poet that wont turn off? The light stays on with everything removed except the power. I fear the worst and I'm usefully optimistic about most things.
I saw no smoke so maybe your right. However I'm going to order a few more of these H-Bridges and take the precautions you suggest. Are the Chinese back from holiday yet and shipping? If not are there any suppliers here in the USA that carry these little workhorses?

Thanks, Dave Schulpius

#5

OK, I think I've come up with why I'm destroying h-bridges. I installed another working one and got things working properly with the H-Bridge movement control in EZ Builder. Push an arrow, push Stop, push the other arrow and the motor would reverse nicely. I did that a few times and all went well until....... I decided to switch the motor direction back and forth without pushing the "Stop" button. Well, it did change direction a few times nicely but then it just locked on in one direction again and would not respond. Remember, I'm supplying 24vdc through the H-Bridge to the DC motor (which is OK).

The problem happens when I reverse the motor quickly and it sends a serge back into the H-Bridge causing damage. I read that this is normal and dammage happens when there is no protection diodes to block the back shock. Seems that the back voltage ( counter-electromotive force also known as back electromotive force) can be as high as twice the supply voltage. So the answer is to surround the motor with Protection Diodes and a of course a fuse. The best type of diode to use is a very quick switching diode and they recommend a Shottky diode rated just above (not below) the value of the supply voltage and rated above the current you will pull. In my case I need a 30v, 3 amp diode sense my supply voltage is 24vdc and my motor pulls just above 2 amps under load (a 1N5821 is just right). Well, now to build the circuit and see if it helps. They also suggest adding caps to save the motor and add more power smoothing. Here is a drawing of how it should look:

User-inserted image

On a side note I also lost the neutral coming out of my 24vdc motor while I was testing and the main chip on the H-Bridge went up in real flames! About 4" high until I was able up unplug the power supply. What a night. *sick* At least I've learned some good lessons. Good thing I didn't burn up my B9. Can some onesay "fuse".

I'll keep posting my progress. Any comments are welcome (even if you call me dum as*) *eyeroll*
Thanks for listening,
David Schulpius