3k st alternator just stopped mid work

[mike90045]

did you have a load on it, when it spun down ?  Leaving any load on the outputs will de-mag the cores, and you have to flash them again.

[tyssniffen]

I did not have a load on it this last crazy 220 experiment time, but yes, there have been times when I shut it down with a load on it, by accident.

maybe I should just flash it and see? 

I'm worried though, that Dieselman said that flashing should only be for when there's NO voltage output.

(and, I'm still not clear on where best to hook up the 12v battery to this thing)

[dieselgman]

Is your machine using an AVR control? If so, then it must be taken out of the circuit during flashing to avoid damage. If you do have that control, then it may prove to be the actual culprit in causing the wild output voltage values you are getting.

There is no issue regarding re-flashing an already magnetized unit.

dieselgman

[M61hops]

Is there any chance you are mixing up the harmonic winding with the stator winding?  Or changing the polarity/phase of the stator windings?  Are any windings shorted to ground?  Something is not right somewhere and you need to start at one end and work through all the possibilities.  Just curious if you hook the ohm meter to the brushes, without any Harmonic or AVR wires connected so that you are measuring the resistance of the rotor winding and brushes, and then spin the rotor, what happens?  What kind of reading do you get and is it steady as the rotor turns?  It's a puzzel      Leland

[carlb23]

is it possible it has a bad harmonic winding? i just went through that with a 2 pole 8kw head and replaced the factory avr with a st115 avr and bridge  from CCG and a bridge rectifier and the head now works.  The only problem i have is that since it takes its brush voltage from the main winding if i put a real big 220 load on the head (trying to start a 3.5 ton air conditioner)the voltage drops down pretty low and sometimes it cant recover back to normal voltage.  I can load it all the way up with smaller loads one or two at a time and it works great.

[tyssniffen]

"Is there any chance you are mixing up the harmonic winding with the stator winding?"

well, I haven't been playing with any of the windings... nor did I switch the wires coming out of the case (that I assume connect up with the windings, etc)   The only re-wiring I did was adding wire lengths to the AVR and the rectifier thing - and the AC output wires.  AND, this thing was doing fine for the 9 years of small amounts of usage before this event. 

I've put in a new AVR and a new rectifier since this started.

Thus, I don't believe I could be messing with the polarity or phase... but I'm open to ideas.

UPDATE:  so I did the field flashing with a 12 volt (and made sure to not have the AVR in place when doing it).   After my crazy test about setting it for 220 and then back, it was only putting out 15 v AC.    Then I did the field flashing - I could hear the alt humming during the process - and then hooked it back up and started it up.   It jumped up to putting out 55 volts!     so, then I did another field flash, thinking maybe I'd done 2 of the 4 magnet or something, but no, another round didn't change anything.

So, now I'm up to 55 volts when doing 650rpm on the gen. 

[carlb23]

can you measure the AC voltage going into your avr and then check the AC voltage at the rectifier.  Also check the voltage at the brushes but this will be DC

[M61hops]

If I was troubleshooting this at this point, I'd check the field current while the engine is running and also the output voltage, as well as the field voltage.  A look at those 3 things should point to the failure point.  Along with repeated ohm meter readings of all the windings and checking for shorts to ground it should become obvious what is wrong.  Every once in a while I've found bizarre things that I'd never suspect though  !  One time I scraped the lighting coil on a Suzuki 250 using the wrong puller on the flywheel and then the engine had a miss when the headlight was on.  Two of the outer windings were a little flattened but the coil measured perfedt electrically.  Replaced the coil and spark miss was gone so I'm guessing that the shape of the magnetic field was somehow altered or weakened by the shape of the wire being changed.  It didn't seem like the winding was shorted or anything, just flattened from round a little.     Truth is stranger than fiction...                                    Leland

[tyssniffen]

"can you measure the AC voltage going into your avr?"

of course, there's 4 wires going in and out of the AVR (http://1.bp.blogspot.com/-D9hCk75zQ18/VbmpPExWPCI/AAAAAAAAGgI/OkA6c21g_EE/s1600/2015-07-28%2B18.30.42.jpg )

but if, when the thing is putting out 55v, I hooked up the meter to one of the white wires and the appropriate red  (which goes into the alternator, not the one going to the rectifier), one was 47v and one was 24.

" and then check the AC voltage at the rectifier."   - 22.3v AC

"Also check the voltage at the brushes but this will be DC"  - 18.3v DC



"check the field current while the engine is running and also the output voltage, as well as the field voltage."

I don't have an ampmeter that will register on this thing.
the output voltage, I assume, is the AC voltage coming off the main black and red terminals on this thing.  right now, it seems to just put out 55v.
what then, is field voltage?  the DC off the rectifier?


thank you everyone for putting up with this ongoing struggle.  I'm going crazy, and practically ready to just buy a different alternator. which I hate.

[tyssniffen]

just for reference, here's the little chart on the side of my AVR (everybody knows what I'm working with, right? this ST 3K chinese alt?)

http://2.bp.blogspot.com/-8TKo5Bsftqc/VjLWVAngz9I/AAAAAAAAGn8/sei0F77d9A0/s1600/AVR-chart.png 

[Tom]

Try feeding the AVR 48 vdc on Z windings. I think the harmonic windings or rectifier are bad.

[tyssniffen]

Try feeding the AVR 48 vdc on Z windings. I think the harmonic windings or rectifier are bad.

you mean switch the wires going in? 

and, this rectifier is NEW - I switched out the old one as part of this process.  I will put the old one back and try again though.

[Tom]

The harmonic winding should be putting out around 48vdc after the rectifier. Your measurements show about half that. So if the avr is fed 48vdc from an external source it should have enough voltage for the field winding's to bring output voltage up to spec. If this succeeds then we have now confirmed that low output from the Z winding's or rectifier are the issue. The fix would then be either a new AVR that works of the 240 vac output or a step down transformer of a 120v leg to feed the rectifier.

[BruceM]

Tom, the wiring diagram he shows for his AVR is the same as CGG's- it takes one 120V leg for excitation.   If it is in fact hooked up that way, the harmonic winding isn't hooked up.

Tyssniffen, It might be helpful to hook up the harmonic (aka Z winding) to the rectifier inputs, disconnecting the AVR completely. This could confirm that the AVR is at fault.  To hook up the harmonic, look at the stock wiring diagram for the ST-3.  Central Georgia Generator has that on their web site.  Since you have an AVR, I expect it came from them.

We all assumed you had a stock ST-3, but it's apparently been set up with an add on AVR. 

[dieselgman]

There are also plenty of ST heads in the USA with AVR controls that were not imported by CGG. We purchased from several other vendors in the past with the same cheap Chinese AVR devices installed.

dieselgman