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)
Gee, I would expect them to be available used cheap - probably
because every other Motorhome and Travel Trailer out on the road uses
a Shurflo Tri-A-Fram pump for the potable water supply... ;-0
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)
It doesn't have to be *exactly* 12 volts, just somewhere in the
neighborhood. Remember, when installed in RV's those pumps have to
put up with 14 or 14.5 volts when the battery charger is connected,
and 9 volts when the battery is darned near flat.
Let's see, I'd start with a bridge rectifier. The pump may run on
AC, but it'll be much happier with DC. Which is why they stuck one
inside the motor of the purpose-built unit. The 10-amp ones will come
in a big epoxy cube package, and will need a heat sink of some sort to
not blow up early - a big chunk of AL plate can suffice.
Then we go 14 volts X 7 Amps = 98 Watts. Gee, go find 100 watts
worth of 12V automotive light bulbs (two headlights in parallel should
do it), attach in series with the pump, hook up a voltmeter across the
pump motor so you can see what's going on, and go for it. ;-)
Or if that thought scares you, go get a Malibu Lights transformer
good for at least 100 watts at 12 VAC, attach the bridge rectifier,
and you'll have about 14 VDC, right where you need it.
The RV pump will have the pressure switch set up for a demand water
system, where the purpose-built pump was set for continuous run. You
could do the same thing if you have a bladder accumulator tank for the
cooling water - let the pump cycle. Otherwise, bypass that
microswitch on the nose of the pump.
Oh, one more thing... If there isn't a relief valve on the pump
output, be careful, you could blow a hose in the torch lead. The RV
pump may put out more pressure than the torch hoses can handle.
Either install a gauge, a pop-off valve (plumbing supply) or both.
-- Bruce --
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
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