Speed/Governor Issues

[Jim Mc]

OK, well  step 1 is to get the governor holding the speed as constant as possible in going from full to no-load.  The longer, weaker spring will help.

Then recognize that the frequency is dependent on the speed, and on nothing else.

So if you have 5% speed droop,  you'll have 5% frequency droop.  It's that simple.

Voltage is a slightly different story, but with an ST head and no AVR, you're pretty much stuck with whatever it provides.  The voltage depends on the speed to a degree, and also on the load.  Bottom line is you may see some improvement from governor tweaks, but you'll probably be fine with voltage in the 120-130 range and frequency in the 58-62 Hz range...

What's your most sensitive load?

[KellyR]

Hopefully the voltage issue won't really be an issue.  I knew that the frequency depended on the speed of the engine.  Hopefully I can get that fixed tomorrow with the governor tweak.

THe only thing I use a generator for is to charge my batteries.  I live off-grid (no utilities for three miles) and have solar panels.  During the winter I need to use the generator fairly frequently because of the loads on the batteries.  I've got a cheapo gas genny that has been great and a high speed diesel I put together with a Meccalte generator and a 10hp diesel from Carroll Stream.  If anyone is buying an engine from Carroll Stream, I'd think twice.  THe recoil broke after about 35 hours and they say that's "normal wear and tear" so not under warranty.  They want $58+shipping for a new one.  I wanted a listeroid because of their reputation for being simple (once you learn them) and hardy.  Plus, they're just cool.  My high speed diesel engine makes a huge racket when it's running, but the lister just thumps along with a pleasant melody.

[Tijean]

Is there any chance that that gen head was designed for 115 V at 50 cycles? If you are turning it then at the speed to get 60 cycles the increase percentage of rotation speed is somewhat proportional to the excess of voltage (137 V) you are seeing.

There have been articles on placing series resistance in the field circuit to reduce output voltage. I would think you would see even higher peaks for two or three seconds after suddenly dropping a heavy load. Seems high anyways compared to what I am seeing with my ST5.

[ronmar]

Yes, the voltage output from a harmonically excited generator is dependent on RPM.

Kelly, because of the operating characteristics of a mechanical governor, it is impossible to get 60Hz under varying load conditions.  The
spinning flyweights are mechanically connected directly to the fuel rack on the IP.  When spinning the flyweights try and pull the rack closed.  The governor spring opposes the flyweights and tries to pull the rack full open.  When you add a load to the engine, the rpm decreases which allows the flyweights to move and the rack opens.  No governor RPM change, no throttle change.  The key for a mechanical is to set it to droop to an acceptable point at it's typical load.  I set mine 62Hz no load and it reliably settles to 58Hz at 3KW.  You want rock steady 60Hz, you need a throttle control mechanism that is not directly tied/powered by engine RPM. 

It sounds like the voltage/RPM relationship on your ST head is a little off.  It is delivering a little too much field current.  To correct this you can install some high wattage resistance in series with the field circuit between diodes and brushes.  Some older gens used a large coil resistor with an adjustable tap to set the output voltage.  I did some tests on mine to reduce/adjust my voltage using several automotive ballast resistors in parallel to give a small resistance high wattage restriction to the field current.  These resistors are designed to limit auto coil current for long durations, but I am not sure how long they would last in this application.  It would of course depend on how warm/ how much energy they would have to dissipate to get to your desired voltage.  Depending on your needs it might take several put together in series/parallel to get an appropriate resistance/wattage configuration.