That was kind of a fun gig. Someone paid me $350 to make a pahse
converter out of parts that cost me about $50 (10 HP Baldor motor,
fused disconnect switch, oil caps etc). Took me about 1.5 hours to
do. This is a rope start phase converter with both legs balanced with
capacitors (90 uF per leg on a 10 HP idler).
At idle, the voltages were something like 243, 247, and 248 volts.
Here's what I know.
1. This Baldor motor does not start from all six of the balancing
capacitors connected to one leg (180 uF). It just does not.
2. The way I made the converter, it starts with a rope pull, and when
it runs it is well balanced, by three caps on one side and three caps
on the other (L1-L3 and L2-L3). It is quiet (all you hear is the
motor, fan etc, almost no humming).
3. To start this motor electrically, would require a starting circuit,
which is of course doable, but much more expensive for the buyer and I
did not have start caps on hand. This is not a sophisticated guy and
he is okay with rope start.
4. For some mystery reason, my own 10 HP Century motor in my own phase
converter, starts great from almost the same amount of capacitors (188
uF), but the 10 HP Baldor does not. So I was lucky with my phase
converter in that I did not need to have electrolytic caps for
The buyer's application is a 7.5 HP wood shaper and he told me that it
works very well with the RPC (I doubt he really would push it so far,
as to get full output from it).
Years ago, like 1975 or so or, uncle sent me out to a friends place to look at
Honking big 25 hp motor and rope start. Guy made a living grinding broaches
engine main bearings and camshaft bores.
Every morning, rope start, switch on the motor, switch on the grinders. I'm not
even had caps on his system but it earned him a living until he retired years
Sometimes good enough is.
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