Ignoramus11916 wrote:
It would be really neat if you could figure out a system for starting
the extra idlers when they were needed. Perhaps you could use a system
of current or voltage relays to sense the load on the convertor and
switch in extra idlers as needed? I haven't thought out the details of
it yet, though.


If I go this route, I will simply use a contactor for every extra
idler and regular light switches to control the contactors. It will be
wired so that extra idlers can be started only if the contactor for
the main idler is closed.

I would be tempted to make an intelligent phase convertor. It would be
neat, but I guess it would also be something to go wrong!

One final point: try to get three identical motors if you can. It is
bound to make your convertor neater.


I do not think that I can find matching used motors, but I suppose
that neatness will be only based on appearance.

I doubt using different motors will make much difference to the
performance of the phase convertor - after all, it is only an
approximation to a balanced three phase supply - but motors of the same
power rating can have noticeably different electrical characteristics.
The old fashioned cast iron motors operate at a much lower flux density
that modern TEFC motors. One effect of this is that they require bigger
start capacitors for the same horsepower rating.

If you can't find matching motors, try to find motors which of a similar
construction and run at the same speed. For example, try to get three
finned TEFC motors, or three big cast iron motors. Having three
identical motors might also make mounting easier.

Best wishes,

Chris