I want to put a low rpm motor on a pump to aid a thermosiphon device. It's
for an outside shower, and I think the thermosiphon would just move too
slowly. I found a pump, but it needs a drive. Would I be better off to
just buy a low RPM motor, even a 12v. DC and run it off a transformer, or
would an AC motor work with a dimmer without damage? The resistance on
shaft drag would be minimal, so a small 12v. DC should handle it.

Hint: I got a couple of 1.3 and 1/4 hp motors laying around.

Steve

only universal (AC/DC) motors are amendable to speed control via a dimmer,
and then only if the dimmer can handle the back emf from the motor.

"SteveB" wrote in message
...
I want to put a low rpm motor on a pump to aid a thermosiphon device. It's
for an outside shower, and I think the thermosiphon would just move too
slowly. I found a pump, but it needs a drive. Would I be better off to
just buy a low RPM motor, even a 12v. DC and run it off a transformer, or
would an AC motor work with a dimmer without damage? The resistance on
shaft drag would be minimal, so a small 12v. DC should handle it.

Hint: I got a couple of 1.3 and 1/4 hp motors laying around.

Steve




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On Sep 10, 6:23 am, "SteveB" wrote:

Hint: I got a couple of 1.3 and 1/4 hp motors laying around.

Steve

Try thrift stores and look for a weed wacker. The ones I have looked
at use a PM motor. They turn fast for your application, but can be
run at lower speed with a dimmer. You might also find a exercise
treadmill and use the motor from it. Single phase induction motors
will not work.

Dan

On Sun, 9 Sep 2007 22:23:13 -0700, "SteveB"
wrote:

I want to put a low rpm motor on a pump to aid a thermosiphon device. It's
for an outside shower, and I think the thermosiphon would just move too
slowly. I found a pump, but it needs a drive. Would I be better off to
just buy a low RPM motor, even a 12v. DC and run it off a transformer, or
would an AC motor work with a dimmer without damage? The resistance on
shaft drag would be minimal, so a small 12v. DC should handle it.

Hint: I got a couple of 1.3 and 1/4 hp motors laying around.

Buy the motor you need for the job you want to do - a Shurflo 12V RV
water pump would fit for this - and be done.

You can't use a standard light dimmer on a standard AC induction
motor - they do make fan speed controls that will handle the EMF from
the motor, but they're usually for smaller fractional HP motors like
exhaust fans and ceiling fans. Even 1/4 HP may be too much.

If you want to use a regular pump, you can always rig a bypass
relief valve to lower the output. Don't just throttle it with a valve
on the suction or output, then it cavitates and chews up the impeller.
Or make it a belt drive, and put a speed reduction in the pulleys.

-- Bruce --