condennnsa
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electric motor wiring
Hey, everyone.
so I salvaged a big ass 1.8 KW single phase induction motor from a hammermill for milling corn.
I also got its 30uF capacitor. But they were both disconnected from the mill when I took them, so I don't know how to wire the capacitor.
I took my multimeter, and measured the resistances of the 4 wires coming out of the stator.
1-2 reads 2 ohms
3-4 reads 4.2 ohms
2-3/1-4/1-3 and 2-4 show infinite resistance.
So If I'm correct, there are 2 windings on the motor, not connected to one another, one 2 ohms and one 4.2 ohms right?
Everywhere I've read on the internet about permanent split capacitor motors it says that in these motors, both the run winding and the capacitor
winding should be exactly the same, made with the same gauge wire and same number of turns so same resistance.
Can you guys help me on how to wire the cap?
And I have one more question , since the windings are not the same does this mean that I will not be able to reverse this motor by simply connecting
the capacitor to the other winding?
If I get it to work I'll use it to power my aluminum grinding machine, so yeah, i guess this has a bit to do with chemistry apparatus...  i hope i put it in the right category.
thanks
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Arthur Dent
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Hope this helps:
http://stearns.rexnord.com/pdf/Cat_902/26-27.pdf
Robert
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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franklyn
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What makes you think that we are psychic. Guessing at what you have
without knowledge of what is written on the nameplate it's a single phase
motor with a start winding. The capacitor will be in line with one lead ( 3 or
4 ) of the start winding ( the one with the higher resistance reading ) to
provide a phase shift to turn the motor. The motor's turn direction depends
on how leads 3 & 4 are paired with run winding leads 1 & 2 which directly
connect to the a.c. line. 1 with 3 , & 2 with 4 , or else
1 with 4 , & 2 with 3.
A horsepower is 746
watts , 1800 watts is ~ 2.4 h.p. , 1800 divided by 120 volts is 15 amps.
Read the attached excerpts I provided in the attached pdf
Attachment: Single Phase motors.pdf (609kB)
This file has been downloaded 660 times
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condennnsa
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Thanks a bunch franklyn . meanwhile I took it all apart and cleaned it thoroughly and lubed the ballbearings.
I would've mentioned the info on the nameplate, but whoever used the mill scratched it so bad it's become unreadable.
I was thinking, so if the 4 ohm winding is the start winding, does that mean that after I start the motor I can turn off the current through this
winding and the capacitor, without losing torque?
Silly me , I thought that you have to have two identical windings and swap the cap from one to the other in order to change the direction...
What would happen if I were to connect the lower resistance 2 ohm winding to the capacitor? And use the 4 ohm as the run. Could the capacitor
overheat and fail?
oh yeah, here it's 240v mains
[Edited on 3-1-2012 by condennnsa]
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franklyn
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I only have a passing acquaintance with the design and operation of electric motors ,
why I provided for you an authoritative technical resource. What I said is my G U E S S
only. The capacitor will give you a clue , if it is electrolytic then it must be a start capacitor ,
and can only operate for the 3 to 4 seconds needed to start the motor. A run capacitor
that operates continuously will be an oiled paper type. The value of 30 microfarads seems
a bit small for a start capacitor. You can connect the 2 ohm winding to a.c. briefly as you
pull a cord wrapped around the motor shaft to manually turn the rotor as you would do to
start a small gas engine. It should unwrap in the direction you pull and if it runs well then the
other start winding does not also need to run continuously. 1800 watts divided by 240 volts
is ~ 7.5 amps , the run winding wire needs to be at least 20 gage to carry that current.
Examine the rotor and stator for some relay or switch mechanism that will disconnect the
start winding as the motor is running. If there is none then this must be provided externally.
Note that since the capacitor is not fixed to the motor that there could have been switching
circuitry to reverse the motor. Additionally a normally open press switch to momentarily
operate the start winding and disconnect it and trigger a normally open relay that will remain
closed to connect the main run winding with a.c.
.
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franklyn
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I'm sorry I'm an idiot. It happens at times that what should be
an obvious glaring error is overlooked. Disregard my comment
regarding the current capacity of the wire - that is very wrong.
To carry ~ 7.5 amps the magnet wire needs to be at a minimum
13 AWG ( gage ) and with a margin of safety better to be 12 AWG.
This is what will comprise the windings of the motor.
www.interfacebus.com/Copper_Wire_AWG_SIze.html
.
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