Variable load for testing phase convertor

That's what I would do.

Sounds like too much trouble...

All you need, basically, is to test voltages under no load and under high load. Both should be acceptable. If that is the case, what will be under intermediate loads, should also be acceptable.

I guess that makes sense, but it would be nice to know what happens at intermediate loads. It would give a more complete picture. Maybe I should do this after I build the convertor, but I want to get the convertor right.

Chris

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

Use a water pump, and a valve to adjust the flow. For a proper job, mount the pump on bearings so it can rotate, restrained by a spring balance, which is the basis for a Heenan and Froude water brake engine dyno. Geoff

It's a nice idea, but a three phase variac will cost big money. At least round here it will. I've seen them sell on eBay for £100+.

Chris

Thanks for the suggestion. I don't have a water pump, but I've been offered a 2 hp hydraulic pump/motor unit free. I don't see a problem with using this, do you?

Best wishes,

Chris

how about: buy 3 adjustable room heaters from your local store (or borrow from friends), put one heater on each leg, and vary heat setting to simulate varying loads. Return after use.

I thought about using a heater as Xpelair heaters with three phase wiring are quite common here. But I'm doubtful as they're primarily a resistive load and won't behave in quite the same way as a motor.

I think that's slightly too cheeky even for me. I did it one time I urgently needed a landline telephone (I had ordered one but it was taking ages to arrive) and another time I needed a camera flash extension lead for one evening, but I'd be reluctant to do it with a heater. Mind you, some guys I know did it with a big TV during the 2002 World Cup.

Chris

David sez: "I don't see the variacs are required."

You also must not have seen where Chris wanted a variable load.

Bob Swinney

Used to have a 3 phase log taper version for lighting. But it was needed in a project... Now a 'baby' ballet has a wonderful light control panel. Had to get singles with toggle handles not hand knobs.

Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder

Robert Sw> David sez:

Hydraulic pump should work well. Most hydraulic pumps have some "drag" even with no hydraulic load -- which is OK because most loads you'll have on your converter will also have some minimum drag.

You probably know that the fluid will get hot with extended testing. Your "brake" power is being converted to heat. No problem for short tests or with plenty of fluid.

The hydraulic approach is considerably easier than a prony brake if you want any torque measurement. The primary downside is that hydraulics can be messy.

Car brakes, disc or drum, tend to chatter. You don't notice a little chatter when decelerating the mass of a car, but you sure do in something like this! Torque data has a lot of noise in it. (Been there, done that.)

If you have a pressure gage, you can record output power as pressure * flowrate. Flowrate will be pretty constant (displacement of pump * speed) because induction motors only vary a few percent in speed from noload to full load.

Errrr, could you expound just a bit on how one would go about varying the exposed surfaces in such a way as to calibrate the load? Your answer was typical of a great many of those on RCM, lately. It seems like some responders just like to see their names on the PC rather than offer any thought-out, workable, advice. Someone asks a fairly specific question and then they get a ration of BS from the responder. Sorta like: The man asked how to make a wheel of a certain size and you told him to go chop down a tree!

I can see what David's talking about. It's probably a bit more complicated than I'd want to use for this task, but it's still a worthwhile idea. As I see it you drive a car alternator using a three phase motor and connect the alternator's output wires to a pair of rectangular electrodes which can be lowered into the salt solution. The further you lower them, the greater the current drawn from the alternator. I assume that you measure the load by using the voltage and current at the motor. Is that right?

Best wishes,

Chris

I was thinking of 5 to 10 gallons of oil, which I reckon should be okay for short tests.

This is another interesting idea. It sounds very like the electromagnetic retarders used on buses and trucks. I'd wondered about something like this, but I reckon the parts will be harder for me to acquire than the hydraulic parts. I might do a few simple tests before building a nice convertor, then do more thorough tests afterwards, or I might do it the other way round. I haven't decided yet.

Best wishes,

Chris