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.
Which one? The new one or the old dead one?
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.
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.
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.
Are you talking about the old motor or the new one you are trying to get
working?
My first thought is maybe each wye isn't properly oriented to the other
one.
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?
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'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.
I
would think it would make it a 2 1/2 hp motor that would get him by for a
while.
If your power source is the low voltage, I think so.
My third thought is to play with the other 6 wires and make another wye
trying combinations to see if those can run it.
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 ****, 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.
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.
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.
Are my thoughts right? Thanks,
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.
Wes
--
Curt Welch
http://CurtWelch.Com/
http://NewsReader.Com/