On Thu, 01 Dec 2005 14:46:57 -0800, Grant Erwin
wrote:

jim rozen wrote:
In article , Grant Erwin says...

I have a phase converter with a 7.5hp idler. I never envisioned having to run a
7.5hp load, but now I want to try it. This is a question for either someone
who's done it or for one of the pointyheads who abound on this NG. If I were to
first start my phase converter, THEN start e.g. a 3hp motor with no load, can I
then run a 7.5hp load motor fully? My thinking is that the 3hp motor would act
as an "idler booster". In this way my phase converter (I'm hoping) can be made
to act as though it had a 10hp idler.


Short answer, yes.

If properly tuned it might start it without the extra three in there.
This sort of depends on what kind of load you have.

I'm pretty sure I can *start* the thing (big abrasive cutoff saw) but what I
want to do is to source enough current so I can run the saw fully. I always
thought you could run one size down e.g. if you have a 7.5hp idler you can run a
5hp motor fully.

I am considering adding some run caps to the idler booster unit, so when I
switch the unit off they will be out of the circuit. Only when the idler booster
is running would the extra run caps be apparent.

GWE
Grant,
I have a phase converter which uses a 15 hp idler motor. I can run 60
hp with it. The largest load I have run on it at one time was 32 hp.
Two of the lathes connected have 10 hp DC spindles and so contribute
nothing to the system like they would if they were induction motors.
The manufacturer said that I can start 15 hp with it. I also have a
7.5 idler motor hp unit made by Eyelander up in Everett. I could start
the 10 hp CNC lathe by using the soft start in the DC spindle drive.
After the spindle was up to speed I could run the lathe flat out and
take just as heavy a cut as when the lathe was connected to real 3
phase.
Eric