This little gadget to drive a 12-volt 50 amp motor from a 24-volt battery source is a very unremarkable design -- but it still amazes me how small, cheap and simple such a thing can be -- thanks to the wizards in Silicon Valley.
It has now passed initial smoke test at the bench. Haven't tested it at 50 amps yet, but it handles 10 amps like it was nothing. I now have no doubt that it'll run my motor.
As always, another beautiful job. Your "dirt simple" is just plain magic to those of us that are "electrically challenged"
Don, very nice as always. How did you lay those traces on the board?
iHave you seen the small speed controls that RC modelers use? Some of them can handle 50 amps and are hardly a bump on the wiring harness
I use layout software to produce the pattern. Such a program (not the one I use but I hear it's quite good) can be downloaded free from
I place the transparency over a piece of pre-sensitized circuit board material and expose it to a sunlamp for a few minutes, then "develop" it in some stuff sold by the same folks that sell the board material. Then I put the board in ferric chloride and etch the pattern.
There's a store here in town that sells the supplies. There's probably one in your area too. One online source is
The only reason I make circuit boards is because I always make mistakes when I hand-wire stuff on perf board. With the layout software, I first enter a schematic which I do usually get right. It then guides me during layout. When I'm done, it can check the layout against the schematic. If it checks, it'll work.
^^^^^^^^^^^^^^^^^ I suggest a small refinement/extension of this design that would satisfy a need, and maybe make you rich. Add a circuit that allows you to vary the percent on-time from 0 to 100% and you will have a speed control for DC motors that doesn't waste power.
Haven't seen those, but I can see how such a thing could be very small if made with surfacemount parts.
Very easy to do. There must be plenty of those available. See Daniel Peterman's post.
FWIW
If you don't care how 'pretty' your PCB looks you can draw on the bare copper board with a sharpie.. The Sharpie has to be brand new since you want lots of 'Sharpie stuff' to stick to the copper. And no I don't mean draw on a photosensitized board, I mean drawing on the bare copper and then etching... FWIW 30 years ago a friend had a bunch of rubber stamps made that were the pad layouts for DIP packages and such.. he'd use them and a Sharpie to prototype that way.
Also there are several companies out there with web sites that will GIVE you the PCB layout software, (and even schematic capture too).. You use their software to layout your board, and then 'push a button' that asks for a credit card number and a shipping address... in 2 days sitting on your doorstep via FED-EX are PCB's... these can be quite high quality, solder mask, silkscreen, the works...
I've used this one for several projects.
Oh and the REAL magic to Don's project are the MOS-FETS... Those things have next to 0 Ohms when turned on and next to no voltage drop either, that's how you can swicth 150 amps...
--.- Dave
Yup! The guys in Silicon Valley put the magic in there, not me. Well, these devices are from STM so they may have been designed in Europe.
The very inexpensive little IR chip does an excellent job of driving them, too. More magic from Silicon Valley.
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