My old 10 HP phase converter could barely survive my 200 amp welding
machine, and the third leg sagged a lot and it vibrated etc.
So, today my wife and son left me alone for a whole day, and I made a
new phase converter out of the old one.
The new phase converter lives in the enclosure from an old Ferrups UPS
that I demolished a year ago. I put it on 4" casters for ease of
It actually has two idler motors. One is a 10 HP idler, and another is
a 7.5 HP idler. The first motor to start is the 10 HP.
If I decide that I need more power, I press a momentary push button
switch after the first motor spins up, and that makes the second motor
come up. It stays up until the system is switched off.
WITHOUT the second motor, my phase converter is a simple phase
converter with starting capacitors between legs 1-3 (3 being the
When the second motor is switched on, it also switches on extra
capacitors between legs 2 and 3. Thus these capacitors (two between
legs 1-3 and two between 2-3) instantly become balancing capacitors.
Effect of this on noise and vibration is very nice.
So, now basically I have a mercedes of phase converters. Some things
need to be finished, such as properly placing that pushbutton, adding
a distribution system for 3 phase, etc.
I used one Allen Bradley starter for the 10 HP motor, and a simple
contactor for the second one. The A-B starter has W63 heaters.
I sawed off the shaft of the 7.5 HP motor with a Harbor freight
bandsaw, and was impressed with its performance. (it did not fit the
No pictures yet, as my wife took our camera.
The new one takes about as much space as the old one, but it is
taller, it has two levels. On the bottom level, the 10 HP motor lives,
and on the upper level, everything else lives -- the 7.5 HP motor and
electrics. The 7.5 HP and electrical shit are separated by a wall.
There is a fan on the bottom section and I need to add another fan for
the top section.
It looks actually not so bad in the ferrups enclosure, like if it cost
me $2000 or some such amount. The ferrups enclosure has better
appearance than particle board.
Another helpful thing was putting carpet underneath the motors, thanks
to Gunner's earlier suggestion. It helps tremendously. The new RPC
only makes a nice humming sound, helping me know it is running.
16 years ago