ST-15 low voltage

[cujet]

Back in 2005-6, I built a Listeroid 20/2 genset with a Chinese ST-15 generator head. It was supposed to be one of the "good ones", with metal fan, heavier castings, bearings that actually last, an AVR and so on. I paid a premium for it.

Well, it produced about 100V per leg. So I tried turning up the AVR and I turned the screw so hard, the potentiometer simply exploded into a mass of tiny parts. AVR was removed and voltage peaked at 109 per leg, with no load. To make matters worse, the power is not accepted by my microwave, TV, computer, UPS', security system and a few other things.

So I spoke with Tom from Georgia Generator, I've ordered a new AVR that is powered from one of the 120V legs. This should allow me to adjust  the voltage up to the proper 120V. But, just as important, it eliminates the Z winding and the resulting sine wave distortion.

I have a small capacitor bank I may try and a number of new bridge rectifiers. I'm holding out hope that the ST head will finally produce proper power.

To be continued...

[bschwartz]

I think the AVR can only adjust the voltage down, and still uses the Z winding.

[cujet]

bschwartz,

In this case, the wiring is changed. Rather than use the Z winding, we use one 120V leg to provide the power for the field. Because this is more than enough field voltage, the genset could achieve very high output. So, a regulator is required.

According to Tom, he has been able to "save" a number of ST heads this way. From what I read, this method is also used on Generac gensets when the excitation winding fails. It's not uncommon to fix a generator head this way.

I fully expect this will take care of my low voltage situation.

This leads me to look into another "fix". Mike Montieth made my ST pulley. He also has a weighted generator flywheel available, so I could possibly reduce flicker. I would be very satisfied if I could:

1) Achieve proper voltage
2) Reduce flicker from the combustion event RPM fluctuations
3) Achieve a quality sine wave, free from excessive distortion

So, I am on a mission. We shall see.

[Horsepoor]

Chris,

What about the likely camshaft timing issue you noted on earlier threads? I noticed the camshaft concern didnt make the above list - is it no longer a concern or id you develop a work around solution?

Bruce

[cujet]

The cam issue still exists. A while back I started to measure the injector cam lobe timing. It's way off. The only "work around" I can think of is to remove the pin, properly index the lobe and re-drill for the pin at 90 degrees to the previous hole, and possibly off to the side a bit. However, it may be possible to install a new lobe and drill accordingly.

The issue is not that the inj timing is off, but that the engine won't reach full power on that cylinder, due to lack of lift.