H-Bridge shorting out??

Hi,
I have used the tronicgr H bridge but I blew it. So then I bought a pololu and its doing the same thing (hasn't blown yet). The light on the circiut indicates the motor should be moving but when I connect the motor the light goes out. Basically if I put load on the motor connection of the motor controller I get no current flowing at all. I have put a multimeter on it and there is 1 couple of volts until I connect a motor, then it drops to zero.

When I blew the DMSHb I had a smaller motor connected and spun it by hand, after a few spins it started to move. Then I connected the wiper motor and it started to move. Then the mosfets popped...

Does anyone know what is happenning here and why the motors won't turn?

thanks in advance

You probably assembled the circuit wrong. Check the polarities of diodes, transistors. I remember Senator, a member here mentioning that on one of the DSMhb diagrams the Source and Drain of the transistors is mixed up.

If you wan't to troubleshoot and fix the problem, prepare for some research.

thanks, I have already gone through that painful process.... and its all working. I spent hours getting my AMC circuit working checking that the pcb was all connected right, nothing a forum can fix. Fortunately that's not the problem I am having. Both the H bridge and the Pololu VNH3SP30 I am using now don't seem to allow the current through. Its like the circuit breaks down when load goes in. I'll post a picture to explain, I'll just go shoot it.
cheers

ok here is my circuit. On the left side I have the green and red wires which go to the motor. in the middle are the two black wires, the one with the stripe is positive. on the other side I have 1 side of the motor controller, ie 1 motor, connected to the AMC. The LED is showing all the right numbers and I can move the joystick and get the numbers to move properly. I just can't get either of the motor controllers to move the motors. Then both showed 12 v coming out of the red and the green wires until you put a load on it. Then the led on the pololu goes out and the meter reads 0v!

I feel like a noob about this as if I have forgotton something REALLY Simple. If you want any more photo's, I am happy to oblige.

cheers.

What motor are you using? Did you connect the VNH3SP30 properly?

You don't have to feel like a noob because everyone is having problems with the circuit... There should have been revisions to the one that is up so newcomers don't make the faulty boards and then try to track down the problems.

Maybe tronicgr could give you more information as he designed and tested the DSMhb.

OK I worked out what was happenning...I got this to work by putting 5v on teh PWM connection from the AMC. I think the circuit isn't handling the PWM speed. by shorting it out like this there is a full speed signal coming from te AMC. You see, I bought the wrong motor controller which doesn't support more than 10kHz so I had to cheat by telling it the motor was always at full speed.

I have ordered the correct motor controller and I should then have it all working. For the record, VNH3SP30 is the wrong one. VNH2SP30 is the right one, it can handle up to 20kHz PWM (and also more Amps).
Hope that helps someone else to get the right controller 1st time.

Also I have realised that my feedback pot was too loose and I was getting rocking back and forth from the delay of the belt tightening up. I have put a spring on the pot to keep it tight and its much much better now. I think it really needs gears in order be absolutely direct.

thanks