25 hp Phase converter
 

Ive been using a 25 hp phase converter for several years now and it's worked
perfectly except with no load there is "ghost voltage" on the generated leg.
As soon as a load is applied, the voltage is quite even. The ghost voltage
is twenty or thirty volts higher on the generated leg and is no problem for
motors but cnc equipt is very sensitive. To be safe I would turn on a
bridgeport or band saw before applying power to a cnc. I just bought a new
30 hp cnc safe converter for around $1900. If anyone is interested, I feel
my old one should be worth $800. I'm in W. Mich and to lazy to arrange
shipping, so if anyone is interested and within driving distance, let me
know.
Dixon

25 hp Phase converter
 

"Dixon" wrote: (clip) with no load there is "ghost voltage" on the
generated leg.
As soon as a load is applied, the voltage is quite even.(clip)
^^^^^^^^^^^^^^^^^^^^^
Just a suggestion: might you put a little resistive load on--just enough to
kill the ghost?

25 hp Phase converter
 

On 2008-01-14, Leo Lichtman wrote:

"Dixon" wrote: (clip) with no load there is "ghost voltage" on the
generated leg.
As soon as a load is applied, the voltage is quite even.(clip)
^^^^^^^^^^^^^^^^^^^^^
Just a suggestion: might you put a little resistive load on--just enough to
kill the ghost?

My guess is that the RPC has unequal capacitance between legs 1-3 and
2-3 respectively. That was the cause of this symptom on my old RPC.

i

25 hp Phase converter
 

On Mon, 14 Jan 2008 08:30:03 -0500, "Dixon"
wrote:

Ive been using a 25 hp phase converter for several years now and it's worked
perfectly except with no load there is "ghost voltage" on the generated leg.
As soon as a load is applied, the voltage is quite even. The ghost voltage
is twenty or thirty volts higher on the generated leg and is no problem for
motors but cnc equipt is very sensitive. To be safe I would turn on a
bridgeport or band saw before applying power to a cnc. I just bought a new
30 hp cnc safe converter for around $1900.SNIP
Dixon



Hey Dixon,

Glad you brought that up. I had real 3 phase in my last shop, but
made a converter when I moved. It had really (still has really) flaky
traces, although under load it is only a 20 volt spread. Anyway, it
runs all the "straight" three phase stuff just fine, that is until I
hooked it up to the CNC lathe. The only thing on the CNC lathe that
RUNS 3 phase is the spindle motor which is controlled by a plain old
motor-starter panel that is just switched on and off by the computer.
But when they built the whole thong (OEM), they "balanced" the three
phase across all the goodies in the box. so it ran OK for about a
minute, and poooofffff....something went. It had never occurred to me
to re-lug everything across just the "hot terminal", or simpler yet,
start the mill or another lathe or the grinder!! That might have save
me! Anilam wants $9,000 for an upgrade!!

Take care.

Brian Lawson,
Bothwell, Ontario.

25 hp Phase converter
 

"Robert Swinney" wrote in message
...
There is no such thing as "ghost voltage" from a rotary phase converter.
A RPC is an electrical
network consisting of : 2 three-phase motors or 1 single-phase motor and
1 or more 3-phase motors
running from a common source. That source may be 3-phase or single phase
and 1 of the motors (the
idler) can be single phase. The usual RPC consists of a single-phase
motor and a three-phase motor
(load) connected across a single-phase supply with appropriate "balancing"
and starting capacitors.
See www.metalwebnews.com for some good articles on RPCs.

Bob Swinney

Bob, over time I have read many of your posts and they all were well done
and made a lot of sense---until now. WTF are you talking about! I certainly
appreciate you trying to help me, but are you kidding? I've had close to
thirty years experience with phase converters and diesel, real three phase
power, and I've never heard such a convoluted explaination of a phase
converter. I'm sorry, but your explaination sounds like a story one would
come up with when coming home at 5 A.M. and the wife is unexpectedly awake
when you try to sneak into bed!
Dixon

25 hp Phase converter
 

"Robert Swinney" wrote: There is no such thing as "ghost voltage" from a
rotary phase converter. (clip)
^^^^^^^^^^^^^^^^^^^^
I don't believe in ghosts, either, but are we just quibbling about words
here? The OP described a voltage imbalance which evidently has a high
output impedance, so that as soon as it encounters a load the value becomes
negligible. Why do you object to calling it "ghost voltage?" Your
description of how phase converters are configured doesn't answer the
question for me. If you can clarify, I'd appreciate it. Thanks.

25 hp Phase converter
 

"Robert Swinney" wrote in message
...
There is no such thing as "ghost voltage" from a rotary phase converter.
A RPC is an electrical
network consisting of : 2 three-phase motors or 1 single-phase motor and
1 or more 3-phase motors
running from a common source. That source may be 3-phase or single phase
and 1 of the motors (the
idler) can be single phase. The usual RPC consists of a single-phase
motor and a three-phase motor
(load) connected across a single-phase supply with appropriate "balancing"
and starting capacitors.
See www.metalwebnews.com for some good articles on RPCs.

Bob Swinney



Hi Bob

I especially liked the referenced article titled "Induction Motors and
Phase Converters. I have read it many times and am still learning things
about 3 phase motors from the information included therein.

Jerry