I have been working on hacking an old wheelchair(Help needed with interfacing voltages from arduino to a wheelchair - General Electronics - Arduino Forum) and now I'm trying to make a 60Amp 24Volt dual H-bridge. I need help with designing my own dual h-bridge. I've looked at the Sabertooth 2x60 but that is out of my budget. Is it at all possible to make one with such high amperage? I would prefer to have it be able to be controlled by an arduino. I've googled it but I can't seem to find anything that fits my requirements.
All help is greatly appreciated,
L
on page 6 (logic level mosfets) you will find candidates for transistors.
http://www.irf.com/product-info/selection-guide/sg-mosfets.pdf
..so it possible to build this. Thee are maybe other powertransistors out there at lower cost.
Needs big MOSFETs (I've used 100V 200A devices in the past successfully), big heatsink,
proper high-low MOSFET gate drivers, lots of thought about protection / fault handling.
I'd look at the open-source motor controller project (OSMC).
Its doable, but there are pitfalls with such high currents (high voltage plus high currents is
much worse).
[ Ah yes, thought I'd posted my thoughts on this before: 24v H-bridge for wheelchair motors - #9 by MarkT - Motors, Mechanics, Power and CNC - Arduino Forum ]
I'll try and document my "monster" H-bridge sometime soon - need to check what devices
I used, but the MOSFETs were probably these: http://uk.farnell.com/ixys-semiconductor/ixfn200n10p/mosfet-n-sot-227b/dp/1427322
nice reassuring 680W dissipation limit and I bolted them to a big slab of 10mm thick aluminium.
High current wiring was aluminium strip (didn't have copper to hand) and its been
tested at 24V 25A continuous (until my dummy load resistors heated up a bucket
of water to steaming hot! MOSFET heatsink not noticably warm 
Using such bomb-proof devices reduces the need for overcurrent protection since
these MOSFETs really will take 200A continuous and just dump 300W into the
heatsink until the main fuse blows.
I need help with designing my own dual h-bridge.
You might want to shop ebay for large h-bridges like below. If you want to go the DIY route, below is a similar sounding project.
http://forum.arduino.cc/index.php?topic=53425.0
http://www.elechouse.com/elechouse/index.php?main_page=product_info&cPath=100_146&products_id=2179
luketheduke:
I've looked at the Sabertooth 2x60 but that is out of my budget. Is it at all possible to make one with such high amperage?
I'd strongly advise you to reconsider building it yourself; there is a very good chance that you will end up spending a significant chunk of money (if not more than it would have cost you to purchase the Sabertooth) blowing MOSFETs as you build and test your homebrew controller.
Now - if your goal is to learn how to build high-power h-bridges (and you have no problem blowing potentially expensive components) - then go for it! But - if your goal is to power your wheelchair and move on with that project, then attempting to build your own high-power h-bridge may not be the best use of your money.
If you insist on going forward, though - I have a couple of suggestions:
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Work with tried and verified designs if you can find them - especially if you are considering an all n-channel MOSFET h-bridge; follow the design to a "T" - don't substitute other parts into the design unless you are absolutely sure that they can be used.
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Consider building a so-called "hybrid" h-bridge:
Use a couple of SPDT relays (or a single DPDT relay) with a contact current rating of the needed amperage (finding such relays/contactors may be easier said than done once you get beyond about 40 to 60 amps - look into automotive and industrial control applications); the relay(s) will be used (with MOSFET or bipolar transistor drivers) to control the motor direction (just like any other relay h-bridge).
Then put a high-current logic-level n-channel MOSFET on the low side of the bridge for PWM control (remember, you can parallel MOSFETs to increase current handling capability - though at a cost of increased gate capacitance - IIRC - that will affect the maximum PWM). Figure on the current rating for the MOSFET(s) to be 3-4x what your motor requires (so if you need 60A of current, find a MOSFET with 180 - 240A of capability - or parallel the MOSFETs to reach that number).
Just remember to switch PWM off before changing the direction of the motor with the relay(s) - unless you really want to weld the contacts together. Also make sure your wiring and all interconnects/traces can handle the current needed (at these current levels, you may want to investigate mechanical mounting of the relay(s) and MOSFETs, and using wire or bus-bar interconnects).