3 pha motor tips needed

Uncle's 5hp single phase motor for his A.O. Dobbs table saw (big sucker) croaked on him so he went down to the scrap yard and bought a 5 hp 3 phase motor.
I looked at the partially marked wires and the data plate and did my best to figure out it was low voltage wired. Tip is that 3 wires together. From what I can see, your normal 3 phase motor has once set of windings internally connected to form a wye. From there you either add in series another winding to each leg of the wye for HV or you build another wye out of the three other windings and parallel them.
Ohming the windings did not find any shorts to ground. Uncle meter sucks so I can not tell if a winding is shorted to itself but not to frame.
My first thought is maybe each wye isn't properly oriented to the other one.
My second thought is disconnect all the wires, find the three that are internally connected and attach power to just those to test the motor. I would think it would make it a 2 1/2 hp motor that would get him by for a while.
My third thought is to play with the other 6 wires and make another wye trying combinations to see if those can run it.
The forth thought is if I can get set 1 and set 2 to run the motor, try the 3 arraignments of paralleling them to get the 5 hp.
Are my thoughts right? Thanks,
Wes
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I forgot to mention our first attempt tripped my breaker for my rotophase (tm) in a few seconds. That is why I'm working on a logical sequence to test it out.
Wes
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Ah, so you don't have real 3 phase power. So you are running it off a 220 V single phase which gives you roughly 220 volt 3 phase so you do need the low voltage config of the new motor which I assume is a 220 vs 440 range motor?
My idea of testing relative induced voltages could be messed up (or at least made even more complex) by the fact that you are using the RPC which I think doesn't produce equal voltage and power on each phase. But it seems it should still be possible with enough wire swapping and voltage/current measuring. SOunds like one hell of a complex puzzle however. If you are good at solving these sorts of complex puzzles you should be able to work through it.
As another idea, if you just take 110 single phase power, and apply it to one winding, and then measure the induced voltages on the other windings, it might tell you all you need to know about which windings are in phase and out of phase with the other windings of the two sets. Or to be even safer, use a 6v or 12v AC door bell transformer and apply that power to the windings for phase testing? Just some thoughts you should probably ignore for safety reasons.....
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How many leads still have numbers? What are the numbers that you see?
I had this problem with my Bridgeport. Only some wires had numbers and it was wired for 440v at the printing shop where it came from.
i

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Wes wrote:

The three phase motor I was setting up earlier this week had 9 leads. For Low Voltage three of those leads tied together, and each incoming phase was tied to a pair of the remaining leads. I don't recall the numbers right now, but I can stop by the shop over the weekend and take a quick read of the Data plate if you need it.
Stuart
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Stuart Wheaton wrote:

Appending my last post...
The NEMA standard for connections for 3 phase motors (LOW VOLTAGE) is L1 (1&7) L2 (2&8) L3 (3&9) tie together (4,5,6)
The nema standard numbering for the windings is 7,8,9 internally tied Wye, 1&4, 2&5, 3&6.

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Hi Wes
I guess there are no numbertags on the wires. Thats bad. If there is a set of 3 wires connected together, that is a good indication that the motor was wired for its low voltage (probably 220). It is pretty likely that three of the 6 wires show continuity to the 3 wire junction. That will make a Y arangement of thoes 3 windings. The remaining 3 wires need to be *properly* connected to the other three. It isnt easy. If you feel like getting involved in a motor wiring project, contact me.
Jerry KD6JDJ
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Which one? The new one or the old dead one?

Your questions made me do a little research to try and learn more about 3 phase motors and I find this page that seems to match what you are saying:
http://www.joliettech.com/3ph_motors_single_speed.htm
It implies (as I read it) you can have single voltage single speed motors with only 6 wires. Or single speed, dual voltage motors with 9 wires configured for Delata use, or configured for WYE use. Or multiple types of motors with 12 wires. Or dual speed motors in multiple configurations with 6 leads. So it seems that they are anything but "normal".
However, if you have a 9 wire motor with 3 wires connected together as you found it, your conclusion that it's a two voltage single speed motor seems correct.

Are you talking about the old motor or the new one you are trying to get working?

So, what did you do? Wire up the new motor the way you thought it should work and it's not doing anything? Or are you trying to test the old one? Or what?
Is the power you are using the high voltage or the low voltage of the motor you are trying to make work? Or do you not know what the power is and you are just trying to wire it the same way as the old motor was wired? Does the plate on the new motor tell you how to wire it for the voltage you are using?

I've never heard of this until tonight until I read your post and started to do some research to learn something new.
But what I'm reading implies to me that these motors are designed to work off of two different voltages (like 208/220 or 440). You have to wire them to match what your power is.
Each winding is designed to work at the low voltage. So the internally wired WYE for a 220 440 motor is a 220 volt winding.
If you have 440 power, and wire it to only the 220 winding, I would think it would likely burn out the winding. If your power is the high voltage, I think you have to figure out how to wire it or else you could get into trouble.
However, if your power source is the low voltage (208 or 220), then doing what you suggest I think might fine. Use an ohm meter to find the internal WYE leads, and wire them to the the power source and that should make the motor spin if it's working but at less than full HP as you suggest.

If your power source is the low voltage, I think so.

I suspect that multiple wrong configurations will probably still cause the motor to run. It might be very hard to tell when you have it right and if you run it when it's wrong, you might be generating extra heat which could again burn out windings.
It seems to me that if you run the motor with the internal WYE windings, it will induce a voltage in the other windings even if they are not connected. That might allow you to tell which winding was which by comparing voltages between the disconnected windings and and the connected windings. Though I can't really guess what you should see when you do that. However, it seems to me that if you look at the voltage from L1 (one of the connected wires), and each of the other 6 wires, you should see a symmetrical pattern of voltages that will make it obvious which of the other 6 wires are part of the winding which should be wired in parallel with the L1. This I think should allow you to know which pair goes with L1, which with L2, and which with L3. And I would think it would give you the "polarity" of the pairs - but not an answer as to which polarity to wire together to form the second WYE.
That is, I'm thinking if you measure the voltage from the powered L1 winding lead, to each of the other 6 disconnected windings, you should see the highest induced voltage on the pair which is located in-phase with the L1 winding. The other two pairs will be more out of phase and show a lower voltage relative to L1. Or shit, I don't know, maybe the other two will be higher? But anyway, the pair in-phase with L1 should be one set of voltages, and the two out of phase, should be the same, but a different set of voltages.
If that works out to be true, then the only question is which side of the windings to connect to form a the WYE. I think if you are using just the second windings to power the power, it would make no difference as long as you were consistent based on what the voltage tests showed you was the relative polarity of each pair.
But when you wire the two WYE sets together in parallel, I assume you have to get the polarity correct. But I guess, if you get it backwards, the windings will come close to canceling each other out, and you will get almost no power, and if you get it correct, you will get full power. If you have everything else correct, and just get the wrong side of the 3 separate windings wired together so it cancels out the internal WYE, then that doesn't sound dangerous to me. So if you see almost no power, then wire the other three together to form the common instead and you should get full power.
When I thought I had it correct, I would measure voltage and current on all windings and expect to see a fairly balanced set of numbers - if not, something is wrong.

Set 2 I think will run the motor even if you have the wrong sides of the windings connected together. When you then try to connect that in parallel to set one, but have some windings matched wrong, it might end up with all sorts of partially working configurations and partially overloaded configurations.
It depends I guess on how the motor is internally wound and if these windings are meant to cross activate each other (because they are wound next together in the motor) or if it's more like two side by side motors where the windings don't interact much. I would assume it's the first way so getting the "polarity" of some of the windings wrong or getting the phase matching wrong will steal some of the power giving y9u a wide range of different and odd "partially" working modes.

I have no clue but I'm having fun learning and guessing.
All the above guessing is based on theory alone and ZERO experience with 3 phase motors so don't trust any of it with a motor you can't afford to burn out and be damn sure you have good circuit protection on your power source before you use any of my advice. :) And I would disconnect all other (expensive) 3 phase devices if possible while testing in case an incorrect wiring induced odd voltages in the lines.
I also wouldn't try any of it without a good volt/amp meter so I could collect data and verify balance of the load when I thought it was right.

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Here is another page of motor diagrams http://www.electricmotorwarehouse.com/motor_connection_diagrams.htm
Wes wrote:

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Buy a box of fuses!
Find the wye connected set and isolate the remaining 3 pairs.
Run the motor unloaded on the wye set.
Experimentally connect one remaining pair to a single wye radial.
If there is no significant change in motor current or noise this is an OK connection.
If the motor becomes obviously distressed or blows the fuse reverse the connection.
Repeat trying the second remaining pair sucessively on each of the remaining two wye radials.
Of the 4 possible ways of making this connection, one way will correctly parallel the winding and result in a smooth running motor.
Repeat with the third remaining pair on the remaining wye radial.
Good Luck !
Jim
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snipped-for-privacy@yahoo.com wrote:

I tried running it on the center connected wye. Drew too much current and popped the breaker.
The numbers marked on masking tape for that series of wires didn't match the data plate. Should have been 4,5,6 were marked 7,8,9.
I noticed two wires had red tape on them, two had black tape on them, and two had green tape on them.
Well that had to be the high voltage wiring scheme that some maintenance tech must have tagged the wires with at some point to id them for himself.
So I thought, why not try it. Undervolting an unloaded motor isn't going to kill anything. Motor started fine configured for 480 V using my rpc generated 240 V.
At this point I thought I had it. Those colored wires had to be the normal 4,7 5,8 6,9 connections. And since three of those wires were center connected, I thought I knew which ones were the ones to form the second wye. Well that didn't work. So I inverted the coil polarity which didn't work.
Then I thought, go back to where you were before the invert, then rotate the connections each way. Single phasing motor showed 40a 80a depending on which two legs. On the third try of parrelleling the wyes, we got a nice sweet 9 amps or so and no tripping of my circuit breaker.
This would have so much easier if the motor would have run on the one wye, maybe if we could have spun it up to speed it would have kept going.
Motor looks like it was made during the 1930's from the revision dates on the data plates. Runs nice and smooth. Uncle is very happy with his nephew's persistance today.
Uncle lended a hand to the lathe restoration project today. Another thread for that.
Btw, I did get your book eventually from Amazon, took many, many months. It is a good book.
Wes
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