Strange ST voltage

[lessersivad]

So after FINALLY getting back to the 1115/ST12 project the past couple of days I got to do a test run.

Everything seemed to go OK for the initial start, run, check pulley/belt, etc.

Ran it for a while with no load, but did hook my digital meter across the 2 terminals on the outside of the doghouse. Yep, 240 volts.

Did a shutdown and checked things over. Decided to put on a very slight load (shop lights). Started the unit up, flipped the breaker, nothing. Rechecked connections and voltage across the doghouse terminals, still 240 volt....hmmmm. Checked again but used the ground terminal on the ST this time. ?!?!?!? 240 on one leg, 0 on the other??

Any ideas or clues as to what to look for. I checked the small schematic under the doghouse cover and the buss bar is across U3 to U4 with the wires leading to the doghouse terminals coming from U2 and U1. So by rights I should have 240 volts, which I do. Only it's on ONE LEG!! Other than that I just don't know.

For this test I was back feeding thru a double breaker AFTER I killed the main to the shop. Not safe I know, but it was simply for testing purposes only.

[vdubnut62]

WHICH ground terminal? Mine has one on the frame and one on the doghouse. I used the ground on the ST frame and promptly smoked every
surge protector in the house . I was very lucky. I like to think I have learned a little since then.  USE THE GROUND TERMINAL ON THE DOGHOUSE!
Go look at the schematic on Tom Osbourne's site.
Here is a link.....http://www.centralgagenerator.com/documents/st_manual.pdf
Good Luck!
Ron

[mbryner]

Couple issues here: 

You are in USA, correct?  Then bus bar/shunt/jumper should be across U5-U6, not U3-U4, or you'll end up w/ wrong voltage (higher) when spinning at 1800 rpm.   Maybe you have a different pulley ratio and need to jumper U3-U4?

Also, then U5 or U6 is neutral (eventually bonded to ground).   Ground is ground (unless you are doing funny things like rectifying AC to DC and the DC ground is your house ground, in which case you need an isolation transformer in between).   It shouldn't matter if you are taking ground from the ST case or from the "doghouse."   The doghouse is anchored to the case, no?

Check that you have ~120V across U1 to U5-U6, and ~120V from U2 to U5-U6.

Please someone correct me if I'm wrong.

Marcus

[lessersivad]

Ron, thanks for the link. It completely goes against the manual that came with the gen head on the U3/U4 vs. U5/U6. Which really don't surprise me considering the head is labeled 15kw but the shaft size indicates it's a 12kw.

Marcus, Yep, I'm in the U.S. and according to the link provided by Ron the buss indeed needs to go U5-U6, not U3-U4.

Thanks guys. I hope to get back at it this evening and will report back any findings.

[Ronmar]

When you spin it for 50HZ, it puts out less voltage, so they made longer windings to the U3-U4 taps to put out the correct voltage at the lower 50HZ RPM.  You should have 4 wires comming out of the generator.  Two hots from the ends of the windings, a Neutral that is connected to the bussbar/jumper between the windings(U5-U6) and a ground that is connected to the chassis.  In US domestic panels, the neutral is tied to ground at the main panel, and like ground entering the panel is never run thru a switch/breaker.  Hot to Hot should be 240.  Either hot to neutral should be 120... 

[vdubnut62]

Marcus, it matters very much on my ST head if the ground terminal on the doghouse is used !
Evidently it has some thing to do with the AVR, as I mentioned I got voltage spikes and blinking lights a bunch of smoke from surge protectors
and a mild panic attack for myself.  I'm just glad the Wife wasn't home, or I would still be "in the doghouse" as it were.
Your ST is quite possibly a different animal.
Ron

[lessersivad]

Well I took a look at the connections in the doghouse then took the doghouse loose from the head.

I don't know how I didn't notice that there are NO terminals for U5/U6. There's holes for terminals, but that's it. I also don't know how I missed the AVR either. I'm gonna blame it on frustration 

Apparently in China, as long as numbers match, that's all that counts. There are 4 larger wires leading from the head to the doghouse and this is the way they are labeled going to the terminals.

LINE         TERMINAL

Z3            U3
Z4            U4
U2            U2
Z1            U1

The wires come out in 2 bundles, along with 2 medium sized loose wires leading to the brushes.

1 bundle has U2, Z4 and 2 medium wires.
The 2nd bundle has Z1, Z3 and 2 smaller wires.

I attached a couple of scans from the manual that came with the gen head.

Thanks, Russ

Sorry the pics are so danged big......

[lessersivad]

As a side note. I just went out to take a look under the doghouse on an ST15 that i bought from Joel Koch a few years back. It has no AVR and I have had no problems with it what so ever. Glad I built the frame of the new 1115 project big enough to fit it up if the need arises.

The gen head I'm trying to figure out is suppose to be an ST15 (according to the tag and book) but is physically smaller like an ST12.When I ordered the parts for the bushed pulley I had to go with one that would fit the ST12 shaft.

I'm beginning to think I have a nice anchor......

[mbryner]

You can always take off the AVR and wire it up in the traditional way, at least at first.

[lessersivad]

This evening I disconnected the AVR and wired it without. (After messing with the decompression lever assembly which apparently vibrated loose from the initial test run )

IT WORKS!!

I know I'm going to have to make some better connections after I eliminate the doghouse, but for the initial test run with a load (shop) I'm pretty pleased.

The lights did dim for a couple seconds when I flipped on the air compressor (couldn't help myself ) but picked right up and settled in.

Geez, now I don't know if I'll be able to sleep being I'm as giddy as a 'lil school girl.

Thanks for all the advice.

Russ

[mbryner]

Cool!

[vdubnut62]

Ah, the sweet sound of success!
Ron