Another Rotary Phase Converter

"anytime you switch the single phase supply legs, you reverse rotation"
is that really true? It isn't for a single phase motor IIRC
Mark
i have tested the rotation thing on RPC's that i have built
when controlling 3 phase motors, if you swap any 2 motor legs the rotation is reversed.
we are still powering with a 3 phase motor whether it is running on single phase supply or 3 phase supply, and the same rules apply
i'm sorry if my posts seem to be untrue
 
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What I meant was with a single phase motor it's the start leg (cap, centrifugal switch) that sets the direction- swapping the ac won't reverse-as in
the case of throwing a drum switch quickly from forward to reverse; motor continues to run in forward direction until stopped and restarted. With a 3 phase motor powered by single phase I wasn't sure what happens when L1 and L2 are flipped- I assumed like Jim that the idler would be happy running in either direction
M
 
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if L1 and L2 are flipped, no big deal as far as the single phase power is concerned the direction will remain the same.

i should have specified that if T1 or T2 are interchanged with T3, the motor direction is reversed
my apologies for mixing terms
 
Jim, Mike: Do you think it's possible that the physical phase angle between the two motor shafts could be "wrong" enough to cause a huge
power surge when the idler motor kicks in? I'm just thinking out loud here
Mark
 
you may be onto something Mark.

what i'm envisioning at this point,
is that he has some bad windings in his 15hp motor or something else is wrong with the wiring

i'm of the mind to recommend starting a/or/the 15hp motor from single phase power outside his system
to verify we have a working motor, and verify rotation, take readings on voltage/amperage
if we can start it outside the system ,
we certainly can start it inside the system once we know which direction it turns for the desired pony output
i'd also recommend leaving the balancing caps out of the motor circuit until we can verify the starting system works.

another concern i have, (it may be unjustified),
is that the pony motor being coupled to the idler has to be generating some kinda electromagnetism.
even though it doesn't have power going to it, i have to think there is gonna be some kind of feedback.
whether it is detrimental to the VFD over long periods of time, is what i question
 
I was thinking that with the huge mass of the idler rotor if it comes on line at the wrong phase angle it may draw excessive current until
it catches up with the incoming line phase- but something tells me that's not too likely because there is no load on the idler yet.
I guess the best test would be to try to start the idler up on caps instead of the pony and see what happens then.
Mark
ps I follow what you said about the back emf from the pony damaging the vfd- certainly a concern
 
Here is a really good tech manual from WEG electric motors, everything you ever wanted to know about 3 phase motors. This should keep you entertained for a few hours http://ecatalog.weg.net/files/wegne...f-electric-motors-50039409-manual-english.pdf

OK, onto the problem. Let's break down what I did:

First the latest drawing
1510533339925.png

I am highly confident that the system is wired as above.
None of the caps have been switched in yet.
The VFD is set to coast to stop
The output relay in the VFD energizes CR2 on reaching operating speed.
The VFD run command is dropped out by CR2 and
C2A and C2B contractors supply the power to the idler motor are energized by CR2

EDIT: I should note that the system was tested with light bulbs prior to connecting the idler motor.

Assuming there is something weird going on between the 0.5 HP pony motor and the 15 HP idler motor. The idler motor should have enough torque to twist the tiny flex coupling into a pretzel even running on single phase. That doesn't seem to be happening. Even if the 0.5 HP pony motor were operating at full torque, in the opposite direction, the idler still should have more than enough power to overcome that and the VFD would trip out due to overcurrent, it's set at 2.2 amps.

Changing wiring combinations and pony motor rotation has no effect on the outcome.

Trying to start the idler outside of the system would be a bit hard, and electrically would really be the same because I would still be connect to the same breaker panel.

Feedback from the pony motor to the VFD? Maybe that's possible. Haven't been able to run it long enough to find out. If that's the case, I can fix that.

The only thing that really makes sense to me it that the idler motor is bad, it came out of a known broken air compressor said to have a fried brain, but that is somewhat indeterminate. It could be that the motor failed and that's what took down the system. Unless there is some revelation in the next few hours, I'm headed to the motor shop in the morning.

I suspect there will be a new idler motor in my future :)

I'm still open to suggestions :)
 
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Yeah I just looked at your ohm readings again 0.4, 0.4, 0.2. too far off to be normal I think
Keep us posted...
Mark
 
Yeah I just looked at your ohm readings again 0.4, 0.4, 0.2. too far off to be normal I think
Keep us posted...
Mark

Worse than that, what you may not have noticed was my winding to winding resistance test on the motor later. 0.1 across the board. But that is way low according to the research I've done in the last couple of hours. I seems the the winding resistance should be > than 1 ohm and more like 1.5 or so. That would indicate that the windings are shorted.
 
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