Bill,
>What you are proposing is two generators, correct?
Yes, I feel 2 are much better for the reasons I spoke of in previous post.
>The lowest cost solution would be to go with a 6/1 and a 5KW head. After reading >the material at utterpower.com I am inclined to believe that I might get by with a >6/1 with a 5KW head. Certainly the only load that would be questionable would be a >welder.
>If at some point that isn't enough I can get a larger generator to run the heavy >loads.
>Now about using an induction motor as a generator. Where do I go to learn about >doing this. And how many HP motor do I need to get the same performance I would >get from a 5 KW ST head?
Search the web for the phrase "Induction motor as generator" or IMAG. there is a misleading paper out there which explains most of the facts correctly which many folks are referring to, but it has a hand drawn schematic that is dangerous. It has you using the 3 phases with individual and separate grounded neutrals which is not only illegal and confusing it is downright dangerous.
A quick run down of the IMAG facts on 2 cases, islanding and utility feedback.
Utility feedback is much easier, just connect the 3 phase generator as for a 3 phase motor (except you don't use the third phase, just ocnnect the 2 phases to the single phase service lines), set the pulley ratio such that at full engine rpm the generator rotates about 5% above its rated nominal rpm ( say, 1850 or so for an 1800 rpm motor) and throw the disconnect once the engine is up to speed. Watch your electric meter spin happily backwards, that's all there is to it.
Islanding is a little more trick though. Same as above for pulley ratio, but you don't have excitation regulated by the utility so you have to control things on your own. Frequency is determined by the speed at which you control the engine. I recommend something other than the Lister governor, it is quite crude. I will be using an auto cruise control when I go off-grid. Voltage on the other hand, is determined by the bank of motor run style caps you apply to the windings, from line to line for each phase. You do this by running the genset up to its proper frequency and speed, then selecting the high end of the voltage (typically about 130v line to neutral) by selecting an optimum capacitor set. They are placed from line to line. You don't get the BEST voltage regulation, but plus or minus 10% is normal acceptable limit fo rthe utility so you can do that too. Another thing you can do is add appropriate capacitors across your large motor loads, connected only when the connected motors operate, this is industry standard practice to correct power factor (reduce inductive currents), but it would have the added effect of helping keep your voltage swings more tolerable when those big loads come on line.
One more caveat you need to know: If you seriously overload an induction generator, you won't burn it out, it will simply stop generating. You still want to avoid this though, as you may lose the residual magnetism needed to make the generator start generating voltage at startup. The fix is easy but a hassle, you "flash" the windings with 12vdc current for just an instant, it slightly magnetizes the windings and gets you back in business should the thing not come up to voltage. Also you want to start it up with no load of course, same as for any generator.
All that said, islanding with induction generators might be way too much hassle for most people. But it sure saves lots of generator head cost and is easily replaced/upgraded if need be and can be made to work just fine with a little extra work. Also a second generator of this type would simply lock into the first when parallelling, much like for utility mode previously described. Not sure how this would work with the more traditional field winding controlled genset.
Are you totally confused now? :-)
BIll Kichman
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