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off-topic question about AC electric motors

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bmeyette

Joined: 14 Mar 2007
Posts: 72
Location: Cornish, NH

Posted: Mon May 12, 2008 8:59 am Post subject: off-topic question about AC electric motors

This has nothing to do with RVs, but I know there are a lot of very

knowledgeable people out there and someone might know.



The short question is - what will happen if you plug a 230v motor into

115vac?  Will it still run, albeit weakly?



If you're interested, this is the long version - I bought an air compressor

that the seller said had a motor problem.  Rather than just replace the

motor, I tested it out, because sometimes you can actually buy things that

are not as bad as expected, and just need a simple fix.  



The compressor came with a standard 15a, 115v 3-prong plug on it.  So, I

disconnected the belt driving the compressor and tested the motor by

plugging it in.  It ran fine.  So, I connected the belt and let it try to

drive the compressor.  It starts and runs ok, but then runs out of steam and

starts to slow down.  Then the start circuit kicks in and it picks up speed

again, then slows down again.



So, I figured the motor was indeed bad & I'd have to replace it.  But, after

looking at the motor data plate to see what to order, it clearly says it is

a 5 HP GE 230 volt only (not 115/230) motor.   The whole thing is well used,

so someone in its past must have been using it successfully.  Perhaps the

previous owner (or one before that) either had a 230v circuit with a 115v

outlet on it (REALLY bad idea) or perhaps the guy I bought it from got it

without a plug on the end, assumed it was 115v and put the 115v plug on it &

then saw it didn't work, so he sold it.



So, I am planning to put a 230v plug on it and try it in a 230v circuit.  I

guess I don’t have anything to lose if somehow it is really 115 and I put

230 to it & burn it up , as I would otherwise have to replace the motor

anyway, because it is too weak at 115v.   I just wondered if it was feasible

that it really is a 230v motor and all it needs is a 230v supply.



What do you guys think - will a 230v motor run, but weakly, on 115v?



Thanks,

brian



Checked by AVG. 

1:08 PM

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_________________
Brian Meyette, Cornish, NH

RV-7A QB tipup, supercharged Subaru STi engine, MT CS prop, all glass day/night/IFR panel, being built with solar and wind power

N432MM

http://brian76.mystarband.net/RV-7Ahome.htm

wdleonard(at)gmail.com
Guest

Posted: Mon May 12, 2008 1:33 pm Post subject: off-topic question about AC electric motors

I would look more into it before plugging it into 220.  My compressor, usually meant to run on 110, will often bog down and not run well if the 110 supply is weak (like in many hangars where the electrical system is cobbled together).  Or if I ever tried to run it through a long extension cord, it would bog down. 

 

In other words, ask the manufacturer about your specific model.  They may have modified the motor, or installed a step down transformer or resistors.



Running a 220 motor on 110 could cause issues just like what you describe, but can also cause a high-current situation when it boggs down.

 

Dave Leonard



2008/5/12 Brian Meyette <bmeyette(at)gmail.com (bmeyette(at)gmail.com)>:

 	  Quote: 	
		   --> RV-List message posted by: "Brian Meyette" <bmeyette(at)gmail.com (bmeyette(at)gmail.com)>

 

  This has nothing to do with RVs, but I know there are a lot of very

 knowledgeable people out there and someone might know.

 

 The short question is - what will happen if you plug a 230v motor into

 115vac?  Will it still run, albeit weakly?

 

 If you're interested, this is the long version - I bought an air compressor

 that the seller said had a motor problem.  Rather than just replace the

 motor, I tested it out, because sometimes you can actually buy things that

 are not as bad as expected, and just need a simple fix.

 

 The compressor came with a standard 15a, 115v 3-prong plug on it.  So, I

 disconnected the belt driving the compressor and tested the motor by

 plugging it in.  It ran fine.  So, I connected the belt and let it try to

 drive the compressor.  It starts and runs ok, but then runs out of steam and

 starts to slow down.  Then the start circuit kicks in and it picks up speed

 again, then slows down again.

 

 So, I figured the motor was indeed bad & I'd have to replace it.  But, after

 looking at the motor data plate to see what to order, it clearly says it is

 a 5 HP GE 230 volt only (not 115/230) motor.   The whole thing is well used,

 so someone in its past must have been using it successfully.  Perhaps the

 previous owner (or one before that) either had a 230v circuit with a 115v

 outlet on it (REALLY bad idea) or perhaps the guy I bought it from got it

 without a plug on the end, assumed it was 115v and put the 115v plug on it &

 then saw it didn't work, so he sold it.

 

 So, I am planning to put a 230v plug on it and try it in a 230v circuit.  I

 guess I don't have anything to lose if somehow it is really 115 and I put

 230 to it & burn it up , as I would otherwise have to replace the motor

 anyway, because it is too weak at 115v.   I just wondered if it was feasible

 that it really is a 230v motor and all it needs is a 230v supply.

 

 What do you guys think - will a 230v motor run, but weakly, on 115v?

 

 Thanks,

 brian

 

 Checked by AVG.

 1:08 PM

 

 

 

 

 

 

 

 	


-- 

David Leonard



Turbo Rotary RV-6 N4VY

http://N4VY.RotaryRoster.net

http://RotaryRoster.net  [quote][b]

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truflite(at)yahoo.com
Guest

Posted: Mon May 12, 2008 2:10 pm Post subject: off-topic question about AC electric motors

Brian,



First, if the name plate says 230 volts, yes, wire up

a 230 volt plug and see what happens. 



Second, if the name plate says 115/230 volts, it is a

dual voltage motor.  There are connections under the

cover where the electrical power comes in that need to

be changed.  The name plate should have the proper

connections to change the voltage.  Make these changes

to the voltage you wish to use.  The wires should be

numbered with ink or tags.



A quick lesson in electric motors.  Dual voltage

motors have two coils either in series or parallel.

Each coil is rated for 115 volts and for simplicity,

let's say each coil draws 5 amps of current. If you

wire for 115 V, then each coil loads to 115 V, but,

since there are two coils, the current drawn is 10

amps. Next is crude diagram.



         5A

       VVVVVVV

  10A /       \    10A

------         --------

      \       /

       VVVVVVV

         5A

VVVVVV= motor coils

XXA= amps through each part of the circuit

For 230V connections, the coils are in series, each

loads to 115V but the current remains 5Amps.



 5A      5A        5A     5A

------VVVVVVV----VVVVVV------



The power or wattage consumed is the same between the

two.



115V x 10A = 1150 Watts

230V x 5A =  1150 Watts



Hope this helps and let me know if I can be of more

help.  



Dave Nellis

Electrician for 30 years



--- Brian Meyette <bmeyette(at)gmail.com> wrote:



 	  Quote: 	
		   

 <bmeyette(at)gmail.com>

 

  This has nothing to do with RVs, but I know there

 are a lot of very

 knowledgeable people out there and someone might

 know.

 

 The short question is - what will happen if you plug

 a 230v motor into

 115vac?  Will it still run, albeit weakly?

 

 If you're interested, this is the long version - I

 bought an air compressor

 that the seller said had a motor problem.  Rather

 than just replace the

 motor, I tested it out, because sometimes you can

 actually buy things that

 are not as bad as expected, and just need a simple

 fix.  

 

 The compressor came with a standard 15a, 115v

 3-prong plug on it.  So, I

 disconnected the belt driving the compressor and

 tested the motor by

 plugging it in.  It ran fine.  So, I connected the

 belt and let it try to

 drive the compressor.  It starts and runs ok, but

 then runs out of steam and

 starts to slow down.  Then the start circuit kicks

 in and it picks up speed

 again, then slows down again.

 

 So, I figured the motor was indeed bad & I'd have to

 replace it.  But, after

 looking at the motor data plate to see what to

 order, it clearly says it is

 a 5 HP GE 230 volt only (not 115/230) motor.   The

 whole thing is well used,

 so someone in its past must have been using it

 successfully.  Perhaps the

 previous owner (or one before that) either had a

 230v circuit with a 115v

 outlet on it (REALLY bad idea) or perhaps the guy I

 bought it from got it

 without a plug on the end, assumed it was 115v and

 put the 115v plug on it &

 then saw it didn't work, so he sold it.

 

 So, I am planning to put a 230v plug on it and try

 it in a 230v circuit.  I

 guess I don’t have anything to lose if somehow it is

 really 115 and I put

 230 to it & burn it up , as I would otherwise have

 to replace the motor

 anyway, because it is too weak at 115v.   I just

 wondered if it was feasible

 that it really is a 230v motor and all it needs is a

 230v supply.

 

 What do you guys think - will a 230v motor run, but

 weakly, on 115v?

 

 Thanks,

 brian

 

 Checked by AVG. 

 1:08 PM

  

 

 

 



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rmkeith(at)gwi.net
Guest

Posted: Mon May 12, 2008 6:54 pm Post subject: off-topic question about AC electric motors

Brian,

Remove the access cover to the wiring and check to see if the motor is wired 

for lo voltage or high voltage. The internal taps may need to be simply 

placed on the correct terminal. Check the motor data plate for the correct 

tap arrangement.



 Russ



---

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sheldonb(at)frontiernet.n
Guest

Posted: Tue May 13, 2008 3:15 am Post subject: off-topic question about AC electric motors

If it's indeed a dual voltage motor, the name plate will indicate it...(115 

v (at) some amperage/230v (at) half that amperage)... If the motors name plate 

only says 230v. then it's probably a single voltage winding and there won't 

be any taps to change..  It will eventually burn up running on low 

voltage....

Sheldon



---

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bmeyette

Joined: 14 Mar 2007
Posts: 72
Location: Cornish, NH

Posted: Tue May 13, 2008 8:35 am Post subject: off-topic question about AC electric motors

Thanks to all for the advice.  I tried hooking it to 230v last night and it

ran great.   It's definitely a 230v-only motor, and there's nothing wrong

with it.  So the motor alone is worth way more than the price I paid for the

whole compressor.   Odd that it came with a 115v plug – that threw me.  the

seller must have bought the compressor somewhere (perhaps an auction),

probably without a plug, installed that 115v plug, thinking it was 115v,

then sold it cuz it didn’t work well.   I lucked out on that transaction, as

I was expecting to have to buy a new motor for it when I bought it.



--

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