H Bridge help

Can anybody find, or help me design an h bridge that can control a 24 volt motor drawing 15 amps. This h bridge would need to accept data from a signal pin (HIGH or LOW) and a pwm output pin. Also this needs to use these fets:

http://www.sparkfun.com/products/10213 (n fet) http://www.sparkfun.com/products/10349 (p fet)

I wouldn't try to build a 24V 15A H-bridge yourself -- that's a 360W "power supply" and not something you take on lightly.

The MOSFET's you pointed out are not appropriate. The N-channel MOSFET, for example, has an on-resistance of 0.047 ohms so at 15A it will dissipate 15*15*0.047=10.5W of power. That's a lot of power, and it's going to get really hot unless you heatsink the heck out of it (or cool it with a fan). And you have 4 of them. With an on-resistance of 0.07 ohms the P-FET will be even worse.

I'd buy a motor driver module, something meant for big robotics like the 24v23 from Pololu:

http://www.pololu.com/catalog/product/1456

That this costs $63 should give you a sense for the ballpark of the level of challenge here. Not something you just casually assemble on a breadboard with $0.95 MOSFET's.

-- The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons

Could I Build 2 and run them in parallel? Also, I was planning on using heatsinks and fans. Would this work. Can you suggest anything cheaper because I will be running two motors and the cost adds up quickly.

I was planning on using 2 of these per h bridge with a fan on each one. http://www.sparkfun.com/products/9576

(These H Bridges will be used on a ridable segway like vehicle)

I think this thread is fairly similar in flavor to what you are doing:

http://arduino.cc/forum/index.php/topic,53425.0.html

I particularly enjoyed Reply #27 :)

Please tell me you are not planning on running 15A through a breadboard?

Yes, in theory you could put MOSFET's in parallel and use heatsinks and fans to keep them cool, etc. etc. But at 24V/15A/360W you're just in a different world and my prediction is you're going to waste more time and money on melted components than you are just buying a motor driver module in the first place. Just my opinion.....

-- The Rugged Motor Driver: two H-bridges, more power than an L298, fully protected

Haha - very good Rugged!

I disagree and I think the best way to learn about electronics is to tackle a project like this. The theory behind the H bridge is fairly simple and the hardest part of the whole thing is the background to the mosfets and how to use them in application. How long do you have for the project? If you have the time to learn then have a go at making one. If not, buy one.

I think I know why the breadboard prototype melted, so I’ve got my PCB boards in at the moment. Starting soldering tomorrow. Let you know how it goes. :wink:

I disagree and I think the best way to learn about electronics is to tackle a project like this. The theory behind the H bridge is fairly simple and the hardest part of the whole thing is the background to the mosfets and how to use them in application. How long do you have for the project? If you have the time to learn then have a go at making one. If not, buy one.

I agree with your disagreement: the best way to learn is to melt some components and release some magic smoke. But it sounded like the poster actually wants to build something rather than just generally learn, hence my advice is leaning towards the more practical than the educational. Or as you said so succinctly:

If you have the time to learn then have a go at making one. If not, buy one.

And good for you for being persistent.

-- The Aussie Shield: breakout all 28 pins to quick-connect terminals

the best way to learn about electronics is to tackle a project like this.

So the best way to learn how to climb mountains is to tackle Everest! No the best way is to start with something you have a better chance of completing than being killed by it.

By all means learn how to design H-bridge circuits but start with a 1Amp one. Then progress to a 4Amp one, then a 10Amp one and only then tackle your 15Amp one. Each one is a step up in design and construction and gives you a chance of actually learning something.

Can anybody find, or help me design an h bridge that can control a 24 volt motor drawing 15 amps.

You have been shown how rolling your own H-bridge may not be as simple as expected. You may want to look at the below kit as I doubt you can make something reliable for much less.

http://secure.oatleyelectronics.com//product_info.php?cPath=94&products_id=206&osCsid=30093449b694ae247d94c2bcce5d0560

Maybe this can help http://www3.telus.net/public/a5a26316/WelderPDFs_Pics/OUTPUT200A.pdf you can use mosfet in place of IGBT's

Might be worth a look at the Open Source Motor Controller project to see if they have a suitable design - its definitely in the high-power category and very easy to make something that melts or goes bang without attention to detail and could take the controller with it if not protected.

I retract my previous statement.

Buy one. Buy it now.