next topic »

[on:]

Ok, so I have looked around and across the web for a simple Mosfet H-bridge that I can use to power my MKII Tankbot.
  So far all I know is aren't they expensive and hard to get to match your specs, so i decided on designing and building one myself.
I had a mobility scooter motor controller which had 20 N-channel IRF3205 MOSFETs which have plenty of power handling for my needs, I have come up with a simple design to incorporate them on to a veroboard after testing on breadboard but the power getting through to the motor is significantly reduced.
  I think the problem is that I'm controlling the FETs directly from the arduino.

http://www.flickr.com/photos/58848339@N08/5390785968/

http://www.flickr.com/photos/58848339@N08/5390785040/

http://www.flickr.com/photos/58848339@N08/5390178469/in/photostream/   

I have pulldown resistors on the gates of the FETs you cant see them from the photos

[Reply #1 on:]

Couple of items:

1. Datasheet - http://www.irf.com/product-info/datasheets/data/irf3205.pdf
2. These are n-channel FETs
3. Where's your top-side voltage booster?
4. I don't think these are logic-level FETs...?
5. Heatsinks (not sure if they'll be absolutely necessary)?

[Reply #2 on:]

4. I don't think these are logic-level FETs...?

No, they are not. They require a 10vdc gate to source voltage to fully saturate on, so they won't even make
good low side drivers for direct connection to an Arduino output pin.

Lefty

[Reply #3 on:]

I'm going to try using a 9v battery in series for the gate for now (lack of funds) and use another transistor I've got lying around I'll link the two gate's and see how that goes, unless you have a better way of doing it on the cheap.

[Reply #4 on:]

That doesn't help with the top-side gate drive, which needs to be at the motor supply voltage plus 10V. You can do something clever with a capacitor, a diode, and an opto-isolator along with one of those drive transistors.