Two Phase???!?

Do you have an ohmmeter with a low ohms range (x1)?
Mark S.
ps try to post some more pictures of motor
 
No, all I have is automotive meters with a 200 scale. They are inconsistent with sub-1 ohm tests. Pictures tonight.
 
Pictures will be coming, if needed. I spent the evening re-wiring the borrowed trailer. It seems I always end up re-wiring any trailer I use. As much as people like to attribute it to old Joey Lucas, Dim-Flicker-Off was invented by 3-M with their damn scotch-lock connectors and developed to a fine art by the trailer wiring industry. A new harness from HF, a dozen FAA approved but splice connectors, and a foot of heat-shrink later.


This has been an interesting adventure. I learned more today about the 1890 politics of Philly, the city topology, and the battles of Edison, Telsa, and Westinghouse, than I really planned on. I *AM* going to have to dig out that old biography of Tesla I picked up off the bargain table a few decades ago but never got around to reading.


While Peco offers both five wire and three wire 2 phase, the little bit I found suggests they are mutually exclusive. Since the machine was built to handle four incoming lines, and the motor diagram shows L1-L4, I have to assume it was designed for five wire 2 phase (fifth wire being common neutral).

The 2 phase diagram on the motor, as others around the web, show 8 connections and four leads coming in. This one has 9 and 3. A few of the wires have the original T-* markings. A few are blank, or too faint for my eyes, anyway. And a few have clear markings of type and manufacturer, obviously not matching the OE wires. Conclusion, the motor itself and been reworked.

The drum switch has a few wires with non-OE crimp eyelets.

Ringing out the switch, The connections of two leads to L1 and two leads to L3, which the switch reverses. Bundled wires (with non-OE tape) are two to L2, and the final three ganged together. This does not come close to matching the two phase diagrams, but matches the diagrams I find for low voltage Wye 3ph perfectly.

Conclusion. The machine has been rewired 3 phase, without correcting the labeling.

If you want pictures, Mark, I'll dig them off the camera. But at this point I'm 95% positive it's wired 3phase.


Now my next quandry. Is it permissible to run a VFD off of the quasi-three phase of a RPC? That would save me considerable wiring If I could repurpose the lathe's VFD 220V circuit to the RPC and feed the VFD and mill from the RPC.
 
Hi Randy, yes you should be able to run a variable frequency drive from the output of a rotary phase converter. VFDs rectify and filter the incoming AC to make DC then chop it at high frequency to make the 3 phase output. There may be some distortion of the RPC output because of the loading effect of the VFD however. I can't say how that might affect any other motors that may be connected to the RPC. Or, conversely, if switching other motor loads in parallel with the VFD input might endanger the VFDs input protection circuitry. It might be better to play it safe and buy a dedicated VFD for the mill that takes single phase power in.
Mark S.
 
So I got the new mill home and was cleaning it up some. I found the serial number. And the production date of 1960. And 220V as expected. and Ph = 2. Two. Definitely a 2. So I look at the spindle motor. 220V 2P. We ran this at the sellers place off of a static converter, and it came with a 3 hp RPC.

I'm about to start tracing wires. I know that in 1890 Ph=2 means I screwed today. But two phase was dead LONG before this machine was built. I'm doing the research, but hopefully someone has a clue what this is about. Did Cincinnati really build 2 ph machines in 1960?

You're not crazy! Two phase was used (and may still be used) in some parts of PA. Feed from Niagara Falls, I believe. I bought a Sheldon Horizontal Mill (ca. 1950's) which also had a 2 Phase motor. By using a capacitor (trial and error to find correct value) and got it to work fine. If you want to pursue this further, drop me an email and I'll see if I can dig up the information for my hookup. I sold my Sheldon about 2 yrs ago but should still have the paperwork around. Good luck, Mike
 
Thanks Mark, I'll figure something out. When I wired this barn not that many months ago, I went all overkill via a 60A sub panel with four 220 and four 110 bays. It's full already, and I haven't even ordered the lift, yet.


Whether I go VFD or keep the RPC depends on mood, weather, lunar positioning, and what I end up doing with the table motor. It is currently a 3 ph... well some sort of poly-phase motor. I will have to replace it with a single phase to go VFD; which may happen since it's health is suspect.


I wonder if anyone makes a 240V power strip....
 
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VFDs can be used with RPCs, but ones needs to factor in the quality of the wave and voltage stability. Most VFDs have some form of input protection relative to voltage and some have phase loss/distortion, the latter may need to be deactivated if there is a significant phase imbalance. The main limitation of running 3 phase VFD off of single phase is the ripple is the buss greater and thus the input circuity is more vulnerable. Many 3 phase input VFDs can be run on single phase, but they need to be derated as such. The derating factor can be modified to some degree through the use of an input reactor or DC bus choke. One also needs to consider the load on the VFD and if it is going to be pushed to its maximum continuous rating in some applications where the load is continuous. In a mill or lathe, the load is much lighter and usually not continuous so you can get by using a VFD that might be smaller than in other applications. Many VFD manufactures like Yaskawa give two VFD power ratings for a particular model, one for normal duty and one for severe duty. I think you would be fine to run a 3 phase VFD off of your RPC (this is also supported by the RPC manufactures information), you might consider going to the next size up VFD if the price difference is nominal. I have done this in a number of installs with VFDs running off of RPCs and have not had any problems, but the quality of the RPC and the phase/voltage balance may have an affect. My meager understanding of RPCs is that the more motors running off of the RPC tend to stabilize the generated leg power.

I have not seen any VFDs that are designed for true 2 phase output, and even if it could be configured it would probably be costly. My other concern is the age of the motor, often the insulation becomes a bit more sketchy over time, so you would probably want to operate the VFD pretty conservatively (say 30-60Hz with an overload of 120%) and keep the carrier frequency at the lower end. A motor upgrade may also be a reasonable alternative if there is a suitable modern replacement, but yours seems to be a bit unusual. Interesting discussion, but I have read a few other posts through the years of others having the same experience as you.

Instead of a 240VAC power strip, just get yourself a 2 gang electrical box and put in two duplex 240 sockets. I did this on my last mill for the axis drives in addition to a 120VAC power strip.
 
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Apostl10 -- did your Sheldon have a three wire or a five wire? I'm having trouble visualizing how you would bridge a cap in a five wire (four hot) that is effectively two separate single phase systems chained together.
 
Randy: you would tie the two windings together in the correct phase- see my schematic above- to give 3 wires from the 4, then use a cap for the phase shift.
Mark S.
ps but this is just academic cuz your motor is 3 phase for sure
 
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