Building voltage regulator for 3ph generator

I want to chime in here with a SPAM like self interested message.

I have a 3 phase Clary OnGuard UPS. It can be used with 3 phase generators to provide single phase output. I am giving it away for FREE, bring a rotisserie chicken in exchange for it and I will be happy. It is about 5 kVa.

If you have a 3 phase genset and want to use it for 1 phase power, and live in Chicagoland, drop me a line or post a followup with your address.

i

i 3 phase gen sets can be reconnected to provide single phase output. I can do it, but you have to go to Don Foreman or Bob Swinney to get the theory and the percentage power out degradition. I think most 3 phase generators will provide about 80 percent of their rated output when reconnected to deliver single phase.

Jerry

Well, a 3 phase UPS can in theory provide single phase output with next to no power degradation, with different UPS outlets being on different legs of 3 phase. Think about it. All it needs to do is step down voltage from 208V to 125V, separately on each leg, and make sure that different legs go to different outlets.

i

Except that you're offering some really good gear, for free.

I looked at this unit that he's offering. Cleary still exists, that isn't the current model but it sold for close to 10 grand when new. The tech specs are available from Cleary, as are repair parts. The tech support person who answered the phone was quite helpful and knew the product line well, so it's something that's definately supportable.

Thank you. It is a weird feeling, to throw away hundreds of thousands worth of perfectly working but unneeded stuff. I have a junk pile that I need to throw away, with at least $100,000 in it. Formerly secret military hard drive formatters sealed in new packaging, for example. All are lying outside, rusting amidst the melting snow. Unbelievable.

i

I never thought of controlling the exciter's field, but that might the easiest approach. If the exciter has a 12-volt field, you could probably just adapt an automotive regulator to do the job. Transform the genny output down to 12 volts for the "sense" voltage to the regulator.

i

Theres alot more to this "single phase from 3 phase generators" than just connecting single phase loads to the three seperate sets of output terminals. I dont sense that you are inclined to deal with that right now. But, if you want to change a generator from a three terminal 3 phase output to a two terminal single phase output, and want to do that without including a UPS, reconnecting the stator windings might be an interesting solution.

Jerry

Hi Don

I went out and measured the field winding of the exciter, it measures 30 ohms, the field winding of the alternater itself measured through the sliprings is 15 ohms. There are two other wires coming out of the exciter, I think that they go to the brushes of the exciter, there is almost no resistance across those two wires. Does this all make sense?

stan

And what's even more so, is that the packaging for those formatters is probably the only thing you'll be able to sell. Yes, I just don't get it either.

Dave

Yes. Does the exciter have a voltage regulator that controls it to 60 volts or ???

If it does, it might be best to let the exciter run at 60 volts and control the field current to the alternator with a separate regulator. That gets rid of one time constant, making it easier to get a stable system.

I'll think about PWM circuits a little.

SBAER wrote:

Hmmm. Probably the "other two" wires are the exciter output. No resistance, as in very low ohms? That is pretty likely. If it needs to put out 6 A to excite the generator, then it shouldn't have more than an ohm or two.

I think the way this would normally be set up is for the exciter output to connect directly to the alternator field. Then, a regulator would regulate the EXCITER field to control the alternator output. Since the exciter field is 30 Ohms, the worst it could take is 2 A. But, most likely, it will normally have much less than 60 V on it, so the current might normally run about 1 amp. It probably had a carbon pile regulator, with a coil powered by the 120 VAC output that pulled a spring away from the carbon pile. What you need to provide is a circuit in series between the exciter output and the exciter field. As output AC voltage increases, it increases the resistance in the exciter field circuit. If you just want to test the whole exciter/alternator before going further, I'd get a roughly 50 Ohm heavy-duty rheostat and wire it between one leg of the exciter output and one of the field terminals. Wire the other field terminal to the other exciter output wire. Wire the exciter output terminals to the alternator field. Set the rheostat to maximum resistance. Fire it up to the proper synchronous speed (probably 1800 or 3600 RPM) and then gradually lower the rheostat resistance while monitoring the AC output voltage. When you apply a load to the generator, you will probably have to turn the rheostat to a lower resistance to maintain voltage regulation. If the alternator has a magnetically "stiff" design, you may find this non-regulated voltage control is perfectly adequate. If not, then you need to come up with a regulator.

Jon

Thanks for your advice, I could read 50 books on generators and not come up with this kind of practical information. I have tested the alternator part of the system by spinning it with a 3/4 hp dc motor while powering the alternator's field with a variable dc power supply. It worked and I was able to st start a small unloaded 3 ph motor. I would be delighted if a simple rheostat would meet my needs, it would probably rule out the use of VFDs though. Maybe the VFDs wouldn't work simply due to the poor speed regulation my homebrew governor is able to provide.

stan

PWM on hold. Can't beat a rheostant for simplicity!

I'm guessing here, but I doubt if VFD's care about frequency. I think they rectify incoming power and synthesize the output waveform.