"jim rozen" wrote in message
...
In article , Robert Swinney says...

Having a bit of experience with rotary phase converters, frankly I cannot
say where the "1.5 X" minimum size of idler came from. Perhaps Fitch
threw
it out several years ago when researching the subject, I just don't know.

I may be guilty here - if not of originating, then at least
propogating the factor. Seems like anyone who ever tried to
build a converter with a motor that's 1X never gets it to work,
over the years of observing. They need to go bigger - the 1.5
factor works well if you do the 'capacitor thing.'

I probably first saw the number from Fitch Williams. Likewise
the old saw that the 3600 rpm motors don't make good converters.

Jim


Jim

I suspect there is alot of good guidance to be obtained from most "old
wives tales". Anything written by Fitch Williams or Don Foreman is
valuable.
I havent been able to determine why the 3600 RPM idler would be
undesireable. I sure dont have data 'either way', 1800 or 3600 being
better for idlers.
The 1 1/2 time tool motor seems like a good starting place for identifying
an idler size. I was actually surprized to learn that idlers as small as
1/10th the tool motor's HP could spin up the 3 phase tool motor. The "size
factor" is very dependent on the amount of load on the tool while
'spinning-up'. I have noticed that a Big idler and Tuning (ala Fitch)
really helps get a heavily loaded 3 phase tool spin-up. The Big idler and
the *proper* tuning* both really help smooth out the 3 phase tool motor's
pulsating when the tool is heavily loaded.

What really surprizes me is that the 3 phase tool motor's performance
doesnt seem to care if it has an idler or not whenever the tool is loaded to
less than about 1/2 its name plate max rating. I may have missed something
in my testing and thinking. But, I do have confidance in the findings
since Don Foreman has been kind and patient enough to guide me thru all the
aspects of this project I couldnt understand without his help. I suspect he
would have picked up on any serious errors I made and corrected my approach
and faulty conclusions.

It sure pleases me to read that Pentigrid and Bob Swinney appreciate the
efforts Don and I have made to get some data on how RPCs perform for RCM
type considerations.

Jerry