Re: Variable load for testing phase convertor

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" <djb@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:43340AE3.3010206@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>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
>>
>


.

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