PMG wiring help please

[bschwartz]

OK, I'm trying to hook up a PMG I got from Tom Osborn, and things just don't make sense to me.

This should be the easiest thing on the planet, but I'm missing something.

There are 4 wires U1, U2, V1, V2

I checked the voltages between the connections before bridging for 120v/240v

These are the bizarre readings.

U1-U2                121V
U1-V1                123V
U1-V2                198V
U1-ground           96V
U2-V1                162V
U2-V2                119V
U2-ground           76V
V1-V2                121V
V1-ground           78V
V2-ground           95V

I also checked for continuity, and I have the following

U1-V2     .3 ohms
U2-V1     .3 ohms

All other combinations yield infinite resistance.
All measurements made with a fluke meter.


Any thoughts?

[rcavictim]

My first thought is to contact Tom and ask him.

My second thought is to NOT use a high impedance AC voltmeter to measure what you get on the various wires because looking at the ends of two separated windings with no physical connection will often give you a totally bogus and confusing voltage readings through capacitive coupling between the windings.  If you like put a series connected pair of 10 watt (not critical just use low wattage lamps) 120 volt lamps (so you can safely look at 240 volts) in parallel with your Fluke meter leads and do those voltage readings again.

[bschwartz]

First, I only mentioned that it was a generator from Tom for identification purposes.

Tom has helped me out over the years, and he owes me nothing.  He has in fact probably lost money having me as a customer.  He has been fantastic, and I will definitely make additional purchases from him in the future.

As such, this generator is what it is, and I don't personally feel comfortable asking him for more than he has already done for me.

As per your suggestion, I hooked up a small 40w load and retested.......

You were absolutely right about the capacitive coupling. 
The only combination that yielded any real voltage were U1-V2, and U2-V1.

Sadly, the readings were not good.
At 60Hz, the U1-V2 winding was 196v, and the U2-V1 winding was 164v.

Any combination of paralleling the windings made the engine impossible to turn over by hand cranking indicating a short or internal load of some kind........

On the bright side, my 40w bulb put out the light of a 60w bulb.
I can also produce over 300v in series.

I guess now I just need to find a use for a high voltage single phase AC generator 

Thanks for the input.

[Tom Reed]

Didn't do the math, but perhaps it is a 50 hz 240 volt gen head?

[bschwartz]

I had the same thought, but it is clearly labeled 1800 RPM 60Hz, 120/240.

Assuming it was a mislabeled unit, 115v 50Hz spun at 60Hz I think would produce 138v still not near the voltages I'm reading.

Also, the two legs being 30v apart still wouldn't be right.

Thanks for the suggestions............... anyone else have anything to chime in before I take this thing apart and go back to the poor voltage swing ST head?

[Geno]

Is yours the 6.5 KW unit? If so I have the same one. Haven't used it yet. Mine supposedly came strapped for 240. The pic shows how it came. That would mean V1 and V2 equate to U5 and U6 in the ST diagram. If mine is hooked up for 240 you should be able to figure out how to hook it up for straight 120 if desired with a meter. Good luck and let me know how you make out. I didn't get a diagram either.

<addition> How have you had it strapped while testing?

Thanks, Geno

[Apogee]

You guys really need to contact Tom.

He's a great guy and will help you as I'm certain he's been through this before and can give you insight.

I wouldn't be guessing...

Just my $.02,

Steve

[bschwartz]

Steve, I'm sure you are right that Tom would help if asked.
What I'm trying to say is that he has already helped me SO MUCH already, that I don't feel like I can impose upon him any longer. 

There really doesn't seem like much left to the situation.
This thing is putting out too much voltage at the rated speed.
There are only 4 wires to play with, and I've tried every combination.

I'll chalk this up to a learning experience, and shelve the PMG for now.

Thanks for the input.

[billswan]

B schwartz

Well could some sort of transformer be used to get you from the 300+ volts back down to 120 and or 240?

Someone must have made a big boo boo winding that critter.

Why not put a big load on each winding to see how the volts might run at a higher amp output.

Maybe someone could use it to drive a stick welder, then the welder would just be run at a lower amp setting to account for the higher input voltage? Might work if the welder is light intermittent duty.

Billswan