Two Phase???!?

RandyWilson

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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?
 
first question i gotta ask is how many wires come out of the motor?
 
first question i gotta ask is how many wires come out of the motor?


3. Three plus ground on the lead-in cable. Three from the primary cut-off to the main board, of which there are two blacks and a larger red. Three to each motor, appear to be equal size.

While traditional 2 phase was done with four wires, they did do it with three. The larger center wire tends to support this.
 
Not doubting your word, but some of those old nameplates are hard to read. Are you sure it's 2 phase, not 2 pole? Can you tell what's the rated RPM?

Tom
 
The name plate on the back of the machine id not fully readable. The stampings are very clear, but the printed part is dulled from being painted over. The spindle motor is absolutely clear, both printing and stamping. Then, there are these two stickers inside the electrics box.




mill-sticker.jpg
 
It is possible that it was built as a 2 phase machine in the 60's. I understand that 2 phase is still in use today in some parts of Philadelphia and Hartford, Ct.
 
I'm guessing that running it from 2 phases of a 3 phase static or rotary is possible but won't give you full power from the motor. True 2 phase requires 90 degree sine waves but 3 phase power is 120 degrees per phase. There's type of transformer called Scott which can convert 3 to 2 phase but it's complicated and expensive.
Theoretically it would be possible to program a VFD to give two phase output at 90 deg, don't know if any units on the market could do this.
Changing to a 3 phase motor is probably the most practical thing to do.
MS
 
It is turning out to be a frustrating subject. It totally stumps das Google, to the point that google doesn't even realize it's giving totally useless 3 phase info. And a search of Scott-T transformers in Ebay gives a page of Travis Scott tee shirts. About the only relevant thing that can be found is various forums where people quote that one wiki paragraph back and forth to each other.

The original plan was to replace the table motor with a single phase that fit better. The current one has been replaced with a large anchor, and got quite warm when ran on the static converter; replacement was factored into the purchase price. That would free me up to run a VFD on the spindle.. Even though it came with a RPC, I consider those to be bad magic. VFD is good magic. But it looks like I will be trying to tune the RPC to the spindle motor, and running the snot out of it until the dilithiums pack it in.

Just thinking out lou. It seemed to run fine on the static converter. If the RPC doesn't go well, could it be converter to a static easily? Isn't a RPC just a static in front of an idler motor?
 
I'm guessing here again but probably the static converter didn't have enough "tuning" or phase shift on one of the outputs which worked just fine in this case. And/or the motor isn't too fussy about the absolute phase angle. Basically a single capacitor is all you would need: static12x.jpeg You would have to experiment to find the right capacitance value- probably in the neighborhood of 100-150 uF at 330 volt AC? Maybe could borrow caps out of motors you own till you zero in...
Mark S.
ps maybe the seller would let you take a peek inside his static converter to read the value?
pps Capacitor run (also called permanent split-cap) motors all work like this; making 2 phase from single.
 
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