3 phase question

[graduate_owner]

Hi everyone,
Is there anyone out there who can advise me regarding a 3 phase converter?
I have a 3HP static converter which has switches for 1, 2 or 3 HP settings, and a rotary 'boost' knob. I have connected it to a 3Hp motor to make it into a rotary converter. I don't know the correst term for this motor so I shall call it a balancing motor. My question is, if I want to run a 1Hp machine as a load, what HP setting do I select?

(1) 3 hp since the balancing motor is 3 hp
(2) 1 hp since the load is 1 hp
(3) 3hp to start, then change to 1 hp once the balancing motor has started up
Or (4) any setting - it doesn't matter since it is now a rotary not a static converter?

My second question is regarding the boost knob. Do I set it on min, max, midway, or again no longer matters?

Anyone have any ideas?

K

 

[mikefab]

I have a transwave rotary converter and the reason I went for this over a static was that it wouldn't need reconfiguring for different motors. So it runs my 750W morticer or my 3KW planer or saw.
I'm not an expert but would suspect that setting your static to 3HP for the balancing motor (or whatever it is called) and then leaving it would be the way to go. Someone once told me that they had a static converter and the only way that they could get it to run their bandsaw (smallish motor) was by firing up the P/T and leaving it running. This would be analogous to leaving your 3HP motor running I suppose.

I'm no expert on this matter but hope these thoughts might help.

Mike

 

[Myfordman]

I suspect that your boost control will do very little once the balancing motor has started.
All capacitor bank converters are a compromise and the best way to see what is going on is to measure all the phase to phase voltages and aim for them to be as similar as possible.
If you do this after the balancing motor is running and alter the boost setting I suspect there will be no variation.
So set your boost so that that the balancing motor starts reliably.
Start up each of your other motors, measure the voltages and note the best setting for each machine. Stick a notice on the wall for future reference.
You might also notice that the balancing motor should be at its quietest when running with best balance and that the hum turns into a harsh buzz when running with poor voltage balance.

 

[graduate_owner]

Thanks guys. Life would be so much easier if electricity companies would install a 3 phase supply free on request. Some chance!!

K

 

[Myfordman]

Care for what you wish for. Many if not most power suppliers have a much restricted range of tariffs for 3 phase customers compared to the competitive, easy change arrangements we have for single phase.

By far the best solution for domestic mains consumers to run three phase machinery is to use inverters which give excellent phase balance and superior control over acceleration, speed and deceleration/braking. The reliability is very high indeed and so purchasing second hand presents little risk. Kinder the supply too than a converter.
Over the many years I have been supplying refurbished inverters to hobbyists, I have had one back for a broken track on a PCB (bit of a swine to find! but easily fixed with about an inch of fuse wire) and two with fan problems. Easily replaced. got to be 50-60 units with no issues at all.

 

[graduate_owner]

Do you repair inverters then?

K

 

[Myfordman]

Do you repair inverters then?

K

Afraid not they are rarely an economic repair. I only support the ones I supply under warranty.
Usually the makers will not supply circuit diagrams without which repair is nigh impossible.

 

[Monkey Mark]

If I'm reading this right, you are using the SPC (static phase converter) to run a 3phase motor which you are using as an idler to produce a more natural 3 phase supply?

If so, set the SPC for the idler only. Other loads will be supplied by the idlers 3 phase output , which is now the Rotary Phase Converter and not from the inverter.

 

[Myfordman]

Op is not using an inverter. That is the problem!!

 

[Monkey Mark]

Op is not using an inverter. That is the problem!!

Sorry. That was supposed to say converter, but once again predictive text got the better of me.

I'll correct it now.

 

[graduate_owner]

That makes sense, although I will measure the voltages anyway, just to check the boost setting.
My thanks to everyone who relied.
Edit - everyone who replied.
K