Nick's idea of half-wave rectifiying is simple, small, and will work
well if the transformer doesn't saturate. (It probably won't).

Another way that would be very small would be to chop the rectified 24
volts at a high frequency, using a MOSFET driven by a 555 timer.
You'd need a snubbing diode as well. This circuit is simple, could
be made small even with commodity thru-hole parts, would not require
much if any heatsink on the MOSFET and would cost about 5 bucks in
parts from Mouser, Digi-Key, or Jameco. This would not saturate the
transformer and it would not run hot.

Email me if you'd like a schematic. Or, find me a teflon liner for a
Cobramatic MK-3A and I'll build the circuit, check it out and mail it
to you. It could even be made adjustable if you like. I made such a
control for a little heater for Karl Townsend. That one was smaller
than an ice cube but it was only a couple of amps. I'd use a 40-amp
MOSFET on yours.



On Wed, 24 Nov 2004 07:23:46 GMT, Gunner
wrote:

Ok...Im way way out of practice on my basic electronics...blush

I found a 12vt dc diaphragm pump of the same type thats in the tig
coolant unit I was given. (Lincoln Magnum)

The old pump and all the gizmos were fed 24vt ac. I did find a tiny
full wave rectifier inside the pump, which apparently only had bad
brushes. Unfortunately..I didnt get all the parts to the motor, else
Id simply stick in a new set of brushes and voila.......sigh

The new pump is 12vdc at 7 amps. The rectifier is no biggie.

What is the best way to drop the 24vac down to 12v?

Dropping resistor? Ok....blush..what value and wattage do I use?

(sounds of derisive laughter in the backround...sigh)

DC-DC converter? Ok..where and how much?

Thanks...

Gunner





"If I'm going to reach out to the the Democrats then I need a third
hand.There's no way I'm letting go of my wallet or my gun while they're
around."

"Democrat. In the dictionary it's right after demobilize and right
before demode` (out of fashion).
-Buddy Jordan 2001