Another Rotary Phase Converter

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
 
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.
 
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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UPDATE: IT'S ALIVE !!!!!!!!!

Finally have a working RPC. We found a Baldor 15HP motor on ebay for $300, with FREE shipping. Not a bad deal. Had to put bearings in it but that was cheap.

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Fired right up, was drawing about 24.5 amps on L1-L2 unloaded with no capacitors switched in. So I started switching caps in and got the legs kinda close before I ran out of caps to switch in. Need to do some swapping around on the caps. As I switched in caps, the current draw went down to about 16 amps unloaded. Once I complete the balance I suspect that will drop more, then I'll start switching in power factor correction and get it down more. Ideally, I can get the idle apparent power down to zero, we'll see how that affects the new smart meters, kinda curious about that.

Then we load tested it. This is the 6500 watt, 3 phase, Flux Resistor. :grin: ~8 HP worth. Interestingly enough, when loaded, the current was only about 25 amps, which means the incoming power didn't even see the RPC motor, because the load was about 25 amps. Note the ground clamp on the left o_O

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With the caps switched in the T1 T3 leg is a bit high (255V) unloaded and is low when loaded (223V), but the T2 T3 balanced out to within 1 volt of T1 T2 (239V vs. 238V) I have a bit of voltage drop on the line to my shop, the picture is in the unloaded condition.
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Anyway, it has been a long arduous journey to get to this point. In hindsight we should have just bought a motor to start with, would have saved a week's worth of work. But we didn't expect the motor problems we had.

But the good news is that it works now, and we'll get it wired into the lathe this weekend.

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Final update We finally got the RPC wired into the lathe.

It doesn't seem to matter which way you spin the idler motor up to start. I tried it in both directions, and the only thing I noticed was the minor vibration changed a bit between CW and CCW, but nothing bad happened in either direction. Took some experimenting to get the low leg on the correct set of caps, but swapping leads at the motor end fixed that.

I made a slight tactical error when I chose the enclosure, I grabbed a 6 inch deep box off of the shelf and I should have used an 8 inch deep box, I have 2 of them on the shelf. The door won't shut all the way :mad: The caps hit the wireways on the door, poor planning on my part. I'm going to build a 1 1/4 inch extension for the box, not a huge deal, but irritating.

I'm pleased with the voltage balance. 239 (incoming), 237, 239, 236. Incoming power is running 1.4KW with the lathe powered up and the spindle running unloaded. Max system load seems to be about 9.5KW with the spindle at 150% power on accel. What I find a bit odd is the incoming power is 11.8 amps, but the 3 legs of the 3 phase are right around 20 amps. I guess the PF correction is doing its job, glad I added that. Hopefully the power company will only see the 11.8 amps. :grin: But I suspect the new smart meters read KVA rather than KW like the old ones did, I'm going to see if I can figure that out. The incoming power reads about 25 amps with the PF correction out of the circuit. These numbers verified by my Fluke clamp on. Everything seems to run OK.

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Nice - when redoing your door, remember to leave about at least an inch of clearance between the panel door and any current carrying part. I cannot for certain figure out what is going on with your pf and the meter readings. The pf corrected circuit should normally read substantially less current than uncorrected. From your photos, the L1 L2 meter shows 11.8 A before pf correction and about 21A when corrected -- if I am reading your meters correctly and assuming that L1L2 is your single phase input and T1 T2 T3 is your derived 3 phase output. It would be helpful if you can provide a simple one-line schematic showing the connection of the motors, including the load motors and how everything is wired.
 
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