"Ned Simmons" wrote in message
...
On Mon, 6 Oct 2008 11:28:41 -0400, "DrollTroll"
wrote:


"Ned Simmons" wrote in message
. ..
On Sun, 05 Oct 2008 23:11:20 -0400, GeoLane at PTD dot NET GeoLane at
PTD dot NET wrote:

I'll be picking up my Bridgeport 2 HP 2J in a couple of weeks, so
it's time to start working on a rotary phase converter.

Others have given you good advice on rotary phase converters, but I'll
give you my take. Having run Bridgeports on rotary converters, static
converters and VFDs, a rotary would be my last choice. A VFD is much
more convenient, even with a 2J variable speed head, and a static
converter is more than adequate. RCM dogma says that you can't plug
reverse a BP with a static converter, but I did it for many years, as
does a friend of mine with 3 mills in a commercial shop.

What is "plug reverse"?

Plugging is reversing or decelerating the motor by rapidly switching
two motor leads. E.g., reversing a Bridgeport by switching directly
from forward to reverse without pausing at off.


The reversing issue on a static converter:

On static conversion, the motor can be reversed via the BP switch, as long
as the leads being interchanged are L1 and L2 -- or so I think. AND, of
course, the starting caps placed between L1-L3 or L2-L3.

It's been quite a while since I've had a BP connected to a static
converter, but that sounds right.


The problem with static converters is that they seem to strain the motor
after startup, unless they are switched out, and balanced run capacitors
are
switched in.

But if this is done, then I agree, static conversion, at least for one
motor, may be preferable -- altho, you will have to de-rate that motor.

I'm not aware of any undue strain on the motor without run caps, as
long as, as you say, you don't push the motor too hard. And if you're
driving a Bridgeport's motor to capacity, the machine is probably
dancing across the floor.

I can "tune" an rpc almost by ear -- the combination of caps across the
various legs that results in the quietest motor operation corresponds with
the most uniform voltage across all three legs!!

I assume this noise is some kind of electromechanical imbalance in the
motor -- in the stator winding(s), the rotor, etc.

Needless to say, stock commercial rpc's with those big-assed start caps that
are never switched out make a helluva racket, AND yield a 270 V third leg.

--
DT




--
Ned Simmons