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Another Rotary Phase Converter

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Keith Foor

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#61
OK, So I am looking at the wiring and design on this. And while I hate to pick apart things, I really hate things getting smoked and giving people issues. So, I see how you are wiring up your run capacitors with independent switches. Might be a good idea, but Im not seeing individual wires running back to a high current buss connection. What wire are you shipping the high current back from? Each cap seems to have 12 gauge wire on it, but do they go to a number 6 or something that runs to the motor lugs or is it run on 12 gauge? The running current in each cap with 12 gauge wire will be fine. But the caps as a whole will have alot of current flow. Something to think about. Might also look at the switches. for the smaller caps, a 5 amp switch would be ok, but bigger caps bigger currents. Switches may be rated in HP and not amps. Once your switches are set, make sure that you are not going to exceed the current rating of the switches. Only reason I bring this up is I have seen home built and factory built RPC's that had all the caps jumpered together with 12 gauge wire, and then a single 12 gauge wire running over to the motor. On a 1 or 2 HP converter, it's fine. On a 10 or bigger HP RPC, 12 gauge ain't gonna cut it and what typically happens is all the current, remember that EVERY amp of current in the created leg WILL flow across the run capacitors, overheats the 1/4 blade connector, and it gets weak, starts arcing, gets hotter and finally burns off the wire. If you have already thought of this, then disregard all this.... if not, it might be something to consider.
 

JimDawson

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#62
OK, So I am looking at the wiring and design on this. And while I hate to pick apart things, I really hate things getting smoked and giving people issues. So, I see how you are wiring up your run capacitors with independent switches. Might be a good idea, but Im not seeing individual wires running back to a high current buss connection. What wire are you shipping the high current back from? Each cap seems to have 12 gauge wire on it, but do they go to a number 6 or something that runs to the motor lugs or is it run on 12 gauge? The running current in each cap with 12 gauge wire will be fine. But the caps as a whole will have alot of current flow. Something to think about. Might also look at the switches. for the smaller caps, a 5 amp switch would be ok, but bigger caps bigger currents. Switches may be rated in HP and not amps. Once your switches are set, make sure that you are not going to exceed the current rating of the switches. Only reason I bring this up is I have seen home built and factory built RPC's that had all the caps jumpered together with 12 gauge wire, and then a single 12 gauge wire running over to the motor. On a 1 or 2 HP converter, it's fine. On a 10 or bigger HP RPC, 12 gauge ain't gonna cut it and what typically happens is all the current, remember that EVERY amp of current in the created leg WILL flow across the run capacitors, overheats the 1/4 blade connector, and it gets weak, starts arcing, gets hotter and finally burns off the wire. If you have already thought of this, then disregard all this.... if not, it might be something to consider.
Keith, I appreciate your comments. Please read the description below and see if there is a flaw in my thinking.

It's a little hard to see in the pictures in the posts above. The switches are fed from 60 amp terminal blocks (red and black) on the door which in turn are fed with dual #10 wires from the power distribution block. My biggest concern is really the jumper strips on the terminal blocks, I've had problems with those in the past and will be re-tightening them down the road a bit. The switches are rated at 20 amps. The manufactured leg bus (yellow) is a row of 60 amp terminal blocks fed with four #12 wires (I couldn't find any #10 yellow THHN). You are correct, the caps are connected together with #12 wire, with the exception of the the 60uF caps which are connected to the buss with dual #12's. From the switches to the caps it is all #12 with the exception of the 60uF caps which are fed with #10. The total value of each row of caps adds up to 30uF or less, with the largest cap in the row nearest the buss on the right. The connectors I used are high quality and have a high spring rate for a good grip, hopefully they will be OK. Like you I have seen many push on connectors fail, and if these give me any problems, I'll do something different. I couldn't figure out how to calculate or even guestimate the expected current in each row of caps so I gave it my best shot and also kind of went by a professionally built 20HP RPC that I installed for a customer a while back.

The main power wiring between the power distribution blocks and the main contactors is all dual #10. The motor will be connected with short run # 8 wire from the 3 terminal power block. The lathe will be connected to the 3 terminal power block with a run of #6 THHN.
 
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JimDawson

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#63
1510611795231.png

I'm learning a lot about 3 phase motors. I just got back from the motor shop with some interesting results. The motor shop had never seen one like it. After some head scratching, they hooked up the motor to a 150V, 60 Hz, 3 phase supply and it ran, but was drawing 22 amps which is way high for that motor unloaded operating at reduced voltage, and is consistent with the results I experienced when I tried to fire it up on 240 volts. The conclusion is that either the windings are internally shorted, or........ possibly the motor is so special and designed to run at a minimum of 84 Hz that there are fewer turns on the windings and using bigger wire to run at the nameplate rating of 84 to 114 Hz and that it just won't run at 60 Hz.

Unfortunately the shop didn't have a 15 Hp motor in stock, so I'm on the hunt for one. There was a Baldor on the local Craigslist a few days ago for $200, but the ad is no longer up. I have a couple local guys I'm going to check with before I widen my search area.

Stay tuned for the continuing saga :)
 
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Karl_T

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#64
Man, i must be lucky. there's a place called Borchart Industrial , http://www.borchartsteel.com/index.html about 40 miles from me. They must have a 1000 three phase motors in an old warehouse. Their initial asking price is $100 plus $5 a horse. But they will deal if your money is green, if you want several, you'll take an ungly one, yada yada.

I'm sure a new motor will solve your converter issues.
 

mksj

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#65
Interesting, I am always learning new things by following these posts. Hard to know if it the design of the motor or a fault, as it runs.
May want to go for a new motor, but shipping is going to be killer if you need to go that route and can't find anything local. Dealer's Electric often has reasonable NOS and lists one recommended for use as a phase converter.
http://dealerselectric.com/S2532.asp

eCrap special maybe if you can reasonable shipping and are looking for something new. Like the industrial duty Leeson, Marathon and Baldor motors.
https://www.ebay.com/itm/New-Leeson-AC-electric-motor-15HP-1765-RPM/332231194245

Super build quality, nicely done on the cabinet.
 

Ulma Doctor

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#67
well that's a first for me!
i have not seen a motor with a 84 to 114 Hz ratings :chagrin:

was the motor from a screw compressor??? that would explain some things if it were
 

JimDawson

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#70
A little update, nothing is happening on the RPC :grin: I'll have a new motor here in a week or so.

But..... A small problem. We brought in a 25 KW, 3 phase generator to test the lathe. That didn't go well...Tripped the main breaker in the control panel instantly. Based on some very quick troubleshooting, it looks like there is a short somewhere in the main servo drive power circuit. I need to isolate the individual devices to track down the problem. I guess the 1700 mile trip home didn't agree with it. :(
 

Karl_T

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#71
There's something about moving old CNCs... Seems to just kill them.

I bought a really nice Vectrax mill (Brand sold by MSC) with a Fanuc 0M and it ran fine till I moved it into my shop. Now a gremlin lives in there :( I am about to give up and refit the machine to a control I can maintain. The trouble is probably easy to solve by an experienced Fanuc technician. But that guy just don't live in this rural area.

Hope your issues are easier than what I've experienced.

Karl
 

JimDawson

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#72
There's something about moving old CNCs... Seems to just kill them.

I bought a really nice Vectrax mill (Brand sold by MSC) with a Fanuc 0M and it ran fine till I moved it into my shop. Now a gremlin lives in there :( I am about to give up and refit the machine to a control I can maintain. The trouble is probably easy to solve by an experienced Fanuc technician. But that guy just don't live in this rural area.

Hope your issues are easier than what I've experienced.

Karl
I hope so too. It wouldn't bother me at all to rip out the entire control system and install my own, including my software. I'll bet I can get enough money out of the Fanuc hardware to more than pay for a complete retrofit.

I've had a chance to do a bit more troubleshooting and it looks like the main power transformer may have a shorted winding. Phase to phase resistance is 0.8, 0.4, 0.8 ohms. That is not a good sign. Next I'll check the inductance on the windings to see what that looks like. Then maybe head to the local transformer shop to see what they have to say.
 

Blackjackjacques

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#74
Running an AC motor at frequencies less than designed for should cause a pretty quick and substantive increase in magnetizing current and ultimately saturation. With respect to cooling, speed as well as magnetizing current, typical AC motors are designed for a narrow window of both voltage and frequency (V/Hz). You can run a 50 Hz motor at 60 Hz power line frequency and not have a problem with cooling, mag current, but speed will increase 6/5 and pf will also denigrate. If you go the other way, cooling is denigrated as well as mag current, and rpm will, of course, decrease to 5/6 -- generally meaning you have to derate the motor at the very least. VFD rated motors are specifically designed to consider the wider frequency window, and provide adequate cooling means, increased current, etc for worst-case (e.g., lowest speed, etc) circumstances. It sounds like the subject 84 - 114 Hz motor to be an application specific type motor permitting a 1.4 speed range window -- or maybe perhaps subject to some frequency control, etc. Good luck
 
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