[Cialug] electronic/power geek wanted

[Matthew Nuzum]

On Thu, 2007-03-22 at 15:59 -0500, James Shoemaker wrote:
>   I have a electronic/power problem in a personal project involving
> controlling and reversing 20A of 110V DC and am curious if anyone in the
> lug has experience in that line.
>   I can't find relays that can take the voltage and don't know enough
> electronics to design an H-bridge (constructing one based on a schematic
> is no problem, but all the schematics I find are for lower voltages)

Are you sure a relay is the way to go? I'd use a FET.

The IRF540 is rated at 100V 30A and is a simple TO220 case. The nice
thing about this is that it won't consume nearly as much current as a
relay and will have much faster on/off times.

I'll bet with a little looking you can find a similar FET that can go
over 100v.

[quickly glances at jameco...]
IRF640 is rated at 200v 18A(nominal, 72A peak) for $0.69 each
I'm not sure what the p-channel compliment is, maybe the IRF9640

Of course, that depends on how hot you're running, you'll want to do the
math to calculate heat sink requirements. I've never tried constructing
an h-bridge that big, but the nice thing about the FETs is that you can
connect two (for each corner of the h-bridge) to get twice the current
throughput. For inspiration, see the "Higher power..." motor controller
listed near the bottom of
http://www3.telus.net/chemelec/Projects/PWM/PWM.htm

He uses the RFP50N06 FET by Fairchild... Fairchild makes some bigger
FETs that may work for you. When I investigated fairchild parts in the
past I had to go through arrow electronics. The nice thing about the
fairchild parts I investigated was that they didn't include the standard
disclaimer not to use them in medical and life threatening situations.
However, they were too $$$ for me.
-- 
Matthew Nuzum
newz2000 on freenode