3 pha motor tips needed

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3 pha motor tips needed Wes 07-03-2008
Posted by Wes on July 3, 2008, 9:39 pm
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 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

Posted by Wes on July 3, 2008, 10:18 pm
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>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 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

Posted by Curt Welch on July 4, 2008, 1:52 am
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>
> >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 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

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.....

--
Curt Welch http://CurtWelch.Com/
curt@kcwc.com http://NewsReader.Com/

Posted by Ignoramus9935 on July 3, 2008, 11:03 pm
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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

> 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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Posted by Stuart Wheaton on July 4, 2008, 12:37 am
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Wes wrote:
> 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.

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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