The horrible groan

[NoSpark]

I have the same problem with my ST5. Nice and quiet in 120v mode heavily loaded, but the slightest imbalance in 240v mode and it growls real bad. The set screw was loose on mine but it wasn't the problem. I even tore mine down and checked the bearings but they were fine, nice quality sealed bearings. The see-sawing voltage is driving me nuts and the only reason now I haven't powered my house with it. I was thinking about hooking up a computer power supply in 240v mode to try and balance the voltage and give me 12v volts for accessories, if that doesn't work I'll try a transformer.

[Crofter]

I guess I am just trying to get my head around what may be causing this, it seams that most think its either uneven bearing load or loose windings either will in time damage the head  so I think it will be best to use  a step up or down transformer. Thanks for all the replies.
  Potter 

If I knew exactly what physically was creating the  noise, I could better decide how much to let it bother me. My reasoning is that some mass must move to create sound waves. If that happens to be wires moving then I am concerned about fatigue breaking or insulation wearing and shorting or grounding. If it is just laminations maybe not so bad. I have inquired about having my st 5 dipped and baked but the price quoted is $150.00 Can. I have planned to pull it down to install a set of 1st rate quality bearings and have a better look around. The original bearings dont sound bad but there can be a heck of a difference in internal finish and life expectancy in a Timken, SKF, etc. and an offshore "will fit"

That Likely will not happen till spring now but it likely wont see 50 hrs service in the meantime. No ideas on a handy way of quickly switching between fixed 110 and 110/220?

[Crofter]

Has anyone seen a coil arrangement plan of the ST? This is strictly armchair engineering on my part, but I believe I remember Mobile Bob describing the stator windings as being 4 in number with only 4 terminals brought out and the other ends joined between pairs. My though is that perhaps coils side by side are joined to create a 110 leg instead of pairs from opposite sides of the stator frame. One arrangement would be unbalanced the other not. Could connecting of the coils differently conceivably end the growl?

[Capt Fred]

Dunno

Use a clamp amp meter to check the load and then turn stuff on or off to balance the load, not to fancy or scientific - but it works, keeps the growlin' down to a minimum.  Pumps and A/C units work really well for this kinda stuff.

Cheers, Fred

[Crofter]

If you are sitting beside the generator perhaps you can switch the loads around but not possible when access to the loads is 200ft away.

Even if the annoying noise was assured not to be harmful, a reasonable electrical balance would be desirable of course, but we have not nailed down why some brands and constructions seem free of this habit.

We still have no takers on the suggestion that perhaps different choices in internal coil connection might eliminate the hum and achieve mechanical balance side to side of the rotor even if the two 120 legs are not electrically balanced.

I am inviting conjecture on possibilities.

[dubbleUJay]

Crofter, would this help at all if you don't already have it:

Out of the:
ST Series Single-Phase AC Synchronous Generator Manual (PDF)

BTW, should I post the manual to the white papers

[mike90045]

BTW, should I post the manual to the white papers

I know of no reason not to.

[Crofter]

Thanks WJ; that is the schematic but not the physical layout of the actual windings. In all honesty I know just a little more than enough to get myself in trouble here. I have done a bit of going in and severing semi permanent internal connections in motor coils to bring out both ends for direction reversal and voltage change reasons etc., but have not had the ST5 apart enough to see if the stator windings possibly have accessible centre taps in each 120 leg. In the meantime I can listen and wonder what makes it tick (growl in this case, lol )

[dubbleUJay]

Here we go guys, the ST manual:
http://www.microcogen.info/index.php?topic=412.0

Sorry Frank, I don't own a ST so I cant help any further, there are more connection diagrams in the manual that might help, I don't know