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