[Milsurplus] multi phase AC power

[Kenneth G. Gordon]

On 13 Mar 2006 at 16:26, Richard Brunner wrote:

> Dr. William J. Schmidt, II wrote:
>    My generator is a 30hp 3-phase motor with cap start and caps used to 
> correct the phase shift
> > for the second and third legs of the (generated) phase.  .... 
> 
> Do you mean you excite one phase single-phase, using a capacitor to the 
> third terminal for capacitive starting?  This is an interesting concept. 
>   Normally when a three-phase motor is single-phased it quickly 
> overheats and burns up.  Of course you have no mechanical load on it, 
> but I have seen three-phase motors overheat and fail with little load on 
> them.  Because the excited winding heats up eight times faster than 
> normal, normal overload protection is ineffective.

I don't know for sure, but I am pretty certain that you and Doc. Schmidt 
are talking about two different things.

 I have several articles here on making three phase power from single 
phase, and the one that provides almost commercial quality three-
phase power from a single-phase uses an "idler" motor to do the 
conversion. 

I think this is what Dr. Schmidt is talking about.

No power is drawn from the motor using this method. It just sits there 
and runs. You have to size the motor to the load, and as I remember it, 
the motor has to be at least twice the size the anticipated load would 
indicate.

I'll try to get some URLs together on it. I was fascinated when I read it. I 
had never heard of this method before about a year ago, but apparently 
it is being used successfully in many small machine shops around the 
U.S.

Ken Gordon W7EKB