Consider this: Get 3, 220 V "variacs" (variable autotransformers) or a
single 3-phase, ganged, 220 V variac. Connect each of your 3 phases
through each of the variacs to 3, 220 V, 200 Watt lamps, 3 in parallel, to
each variac. At full brilliance, the 9 lamps would be "drawing" nearly 3
HP.

Bob Swinney

"David Billington" wrote in message
...
I have been told that large gensets are tested with a tank of salt water?
and the electrodes connected to the phases are lowered to increase the
surface area and therefore current passing through the fluid and so
increasing the load. Maybe you could do something on these lines with a
large car alternator.

Christopher Tidy wrote:

Hi all,

Soon I should have most of the components necessary to build my phase
convertor. I'd like to do a few trial runs in which I wire the components
together and test the convertor's performance before I go to the time and
expense of building a metal chassis to mount it on.

So today I was wondering how I could create a variable load in the range
0.5 to 2 hp. Has anyone done this before? The only three phase workshop
machine I have is a power hacksaw with a 1 3/4 hp motor. This runs
through a static phase convertor I built and I don't really want to
disturb the wiring if I can avoid it.

Ideas I had are as follows, with some disadvantages listed:

Motor bolted to wooden board. Insert 2" x 4" under pulley and lever
upwards to create load. Load control is a bit crude, as is the whole
setup, but I've used it before and it works after a fashion. Sets fire to
wood, too.

Motor bolted to board with slightly more sophisticated homebrew braking
system, possibly allowing weights to be loaded onto a lever. Still crude,
but a bit more controllable.

Motor driving variable pitch propeller in small tank of liquid. Neat, but
I don't know where to get a variable pitch propeller for little money, or
how to match it to the motor.

Bolt car brake disc/drum to motor pulley. Use hydraulic calipers to apply
load. Could be quite neat, but it would be a faff to build because of
needing a reservoir, flaring pipes etc. I'm also not sure how to regulate
the pressure. Plus car parts dealers in our area charge big $$$ for car
parts.

I rather like my final idea. A while back a friend offered my a hydraulic
pump from a concrete crusher (i.e., a test rig for measuring compressive
strength). I think it has a 2 hp three phase motor and is the kind where
the motor is mounted vertically on top of the pump, with the pump hanging
down into the reservoir. So I thought I could cut a 47 kg propane
cylinder in half, make a plate to cover the opening and mount the
motor/pump unit on top. Then I could have the oil circulating through a
needle valve which regulates the load. Plus I'd need a pressure relief
valve, contactor etc. It sounds like a neat idea but I'm unsure how much
the hydraulic bits would cost.

Any thoughts? Has anyone done this before? I don't want to spend too long
on this, because I want to put my effort into the phase convertor, but it
would be nice to have a controllable load.

Best wishes,

Chris