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Another Rotary Phase Converter

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firestopper

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#31
Nice Jim,
Defiantly the coolest RPC I'v ever seen. I'v wanted to add meters to my system from the start but lost motivation. You just reignited my interest:).
Your work is always inspiring.
 

markba633csi

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#33
Jim just so you know they DO make little clips you can buy for mounting caps, you don't have to make swiss cheese panels for em. I know, you
needed an excuse to fire up the CNC.
I didn't know you were planning to keep all those switches in the design- some of them you'll probably throw once and never again. Hey as long as it works, right? Looks impressive that's for sure. ;)
Mark S.
 

JimDawson

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#34
Jim just so you know they DO make little clips you can buy for mounting caps, you don't have to make swiss cheese panels for em. I know, you
needed an excuse to fire up the CNC.
I didn't know you were planning to keep all those switches in the design- some of them you'll probably throw once and never again. Hey as long as it works, right? Looks impressive that's for sure. ;)
Mark S.

I looked at those clips. They wanted about $4.00 each and you have to drill & tap two screw holes per each. And as you said I have a CNC. :grin: I decided to just put the switches in, makes the setup easier. Thank you.

I should just have bought a 15HP motor, using this compressor motor has turned into more trouble than it's worth. After removing the screw I had to modify the front bell bearing bore, build motor mounts, and fight with it. Just about done now. Hopefully I'll get back to the wiring tomorrow.
 

markba633csi

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#35
Well if it's any consolation I've spent ridiculous darn fool amounts of time rebuilding my bandsaw. Just finishing the hydraulic feed now, there's light at the end of the tunnel- pics soon.
Mark S.
 

JimDawson

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#40
The first test run did not go well. :( The pony motor spun up the idler and everything switched in as planned. The idler took over and ran just long enough for me to look at the voltages (which seemed about right), about 15 seconds or so.......then the 50 amp breaker tripped. :mad: *^^%^&. So disconnect the idler and do a quick phase to phase check with an ohmmeter: 0.4, 0.4, 0.2. That's not good, I think it has a shorted winding. Maybe that's why the air compressor failed. Headed to the motor shop on Monday, I'll have them put it on the bench. I have no way to properly test a 15 Hp, 3 phase motor in my shop. I really kinda hope it is the motor, at least that would mean I didn't foul something up. It was running unloaded, no caps in circuit. Rated at 15 Hp, 48 amps at full load, there is no way that motor could be drawing >50 amps unloaded if it's healthy, even single phasing. :confused 3:

Here is a couple of pictures of the nearly finish panel. Still have to wire in (gray cable) the current transformers (little black things) for load monitoring.

That's a big ball of wires, wrapped with spiral wrap at the bend.
1510455490560.png

The back of the door
1510454828186.png

And the main panel
1510454919266.png

My son designed and machined a mounting bracket for the current transformers, mounts under the 3 terminal power block.
Here is the design, I'll post more pictures later. Made of UHMW.
1510455192409.png
 

Ulma Doctor

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#41
this may sound a little crazy or irrelevant, but is not meant to be disrespectful-

i think you could reduce the start capacitance and try to run a smaller motor first on the system (without balancing caps either)
to test your system before hooking up a 15hp motor.
 

JimDawson

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#42
this may sound a little crazy or irrelevant, but is not meant to be disrespectful-

i think you could reduce the start capacitance and try to run a smaller motor first on the system (without balancing caps either)
to test your system before hooking up a 15hp motor.
Mike, your comments are always welcome. :)

But...There is no start capacitance. The system is spun up to operating speed by a pony motor to reduce the start load. Upon reaching operating speed, the pony motor switches out and simultaneously the idler contactors pull in. The lights didn't even flicker when I fired it off. It ran on the idler for about 15 seconds before the breaker tripped. It sounded a little growly but I assumed that was because there were no balancing caps switched in. I do have a small 3 phase motor I could lash up and see how it reacts with that.

If you have any other ideas I could use some suggestions. Maybe I'm missing something.
 

Ulma Doctor

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#43
Hi Jim,
that's right, you are using a pony motor to start the idler, my mistake.
if the pony motor is up to speed and then single phase power is applied to the idler- it should run if everything is copacetic with the motor.

3450 rpm RPC's take a second longer to spin up
 

JimDawson

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#44
Hi Jim,
that's right, you are using a pony motor to start the idler, my mistake.
if the pony motor is up to speed and then single phase power is applied to the idler- it should run if everything is copacetic with the motor.

3450 rpm RPC's take a second longer to spin up
That's what I was thinking.

My RPC works is a little different than most I have seen. The pony motor is powered by a small VFD. The accel is set to 10 seconds. Once it reaches operating speed, 3450 RPM, the output relay in the VFD is programmed to energize and that energizes a control relay which kills the run command to the VFD and simultaneously pulls in the idler contactors. The VFD is programmed to coast to stop, so the output section just shuts off and allows the pony motor to freewheel.
 

Ulma Doctor

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#45
got it!
yes sir, the design is a bit different- but i like the thought put into the creation. very nice engineering.

i'm sure it will work, we just gotta pin down the problem.
the low resistance on the 15hp motor winding sounds like the real problem

you should only get a grumble from the system when it runs right before balancing is switched in
the idler motor is already spinning so the inrush should be low and momentary.

something else to consider
make sure that the idler and pony motors are running the same relative rotation.
i'd hate to think of what would happen if the pony spun the motor in one direction when the idler would want to run in the other direction.
 

JimDawson

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#46
something else to consider
make sure that the idler and pony motors are running the same relative rotation.
i'd hate to think of what would happen if the pony spun the motor in one direction when the idler would want to run in the other direction.
That would be a major problem. o_O

But let's see if I understand something correctly. Since the idler is already spinning at speed and direction, shouldn't want to continue spinning in the same direction when the single phase power is applied? Does the phase relationship apply to the single phase input? Now I'm realy confused. :confused 3:
 

Ulma Doctor

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#47
anytime you switch the single phase supply legs, you reverse rotation
the same is true in 3 phase supply

something to consider anyway
 

JimDawson

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#48
anytime you switch the single phase supply legs, you reverse rotation
the same is true in 3 phase supply

something to consider anyway
Well that's interesting. I'll try reversing the pony motor after I check the resistance of the individual windings. I didn't go into it that deep yesterday.
 

markba633csi

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#49
"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
 

JimDawson

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#50
i'd hate to think of what would happen if the pony spun the motor in one direction when the idler would want to run in the other direction.
In this case it seems to make no difference. Same result, about 15 seconds and the 50 amp breaker trips. I tried all possible combinations of rotation and connections with no difference. The load seems to be about 15KW, or about 62 amps. In checking the individual windings, I got 0.1 ohm across the board. I'm thinking a bad motor.

I managed to get a screen capture of the operation, the red line is the shop power, the blue line is total property power. Power in KW is vertical. The first spike was me hitting the E-stop before it was fully energized. The next two spikes are the time before breaker trip. When I had it wired as the original test, and only reversed the rotation of the pony motor it ran a couple of seconds longer than the second test. But in the second test the breaker was already warm so that may have been the time difference.

1510515305326.png
 

Ulma Doctor

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#51
"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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markba633csi

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#52
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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Ulma Doctor

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#53
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
 

markba633csi

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#55
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
 

Ulma Doctor

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#56
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
 

markba633csi

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#57
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
 

JimDawson

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#58
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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markba633csi

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#59
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
 

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#60
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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