Single phase Induction motor rewinding problem

Thread Starter

psoke0

Joined Mar 31, 2017
191
hello. i have a air conditioning that uses avaporation and a fan to cool down the room. my fan motor is died. i opened it and windings are burned out. its 200 watt motor 4 poles. it was having 280 turns in each pole 0.3 mm wire diameter. so i bought the wire and i made the windings. i tryed to insert the windings and i just could not do it the slots are too small for 280 turns to get in. i could not do it. so i reduce the turns to 230 and it barely fit. anyway another problem comes in. the motor draws about 4.23 Amps from 230 volt line. i pluged it in and the windings start to heat up so quickly after couple of secons smoke come out. the thing is 0.3 mm wire is not rated for 4 amps. its rated for 1.4 max. i measured the total resistance of stator it is 48 ohms. which is normal for the 230 turns winding. in each winding 12 ohms. well 230/48 =4.7 Amps.
my question is how was the original motor winding worked out for so many years ?
well yes i reduced the turns to 230 turns but even with 280 turns total resistance is going to be 59 ohms. its still 3.89 Amps that the wire cannot handle. how is this works out any information and ideas are appreciated. and sorry for my bad english.
 

BobTPH

Joined Jun 5, 2013
5,458
The current in an AC motor has little to do with the DC resistance of the wire in the coils, it is limited by inductance and back EMF.

Inductance depends in the square if the number of turns. 230 turns will have 2/3 of the inductance of 280 turns.
 

Thread Starter

psoke0

Joined Mar 31, 2017
191
The current in an AC motor has little to do with the DC resistance of the wire in the coils, it is limited by inductance and back EMF.

Inductance depends in the square if the number of turns. 230 turns will have 2/3 of the inductance of 280 turns.
okay so i did measured inductance of each winding and it was 14 mH . if it is 2/3 of the 280 turns that means its 21 mH * 4 = 84 mH so the reactance is 26 ohms. 220/26 8.8 Amps ?
 

MaxHeadRoom

Joined Jul 18, 2013
25,626
If the original had 280 number of turns then it should be possible to rewind the same number, Normally the slot are lined with Pressphan or fish paper, and an insulated wedge type tool is used to tap the windings down in place.
Ensure the lining is the same width.
There is a bit an art to it.
 

crutschow

Joined Mar 14, 2008
30,420
The inductance and resistance of the winding determine the zero speed starting current.
When running, it's mainly the back EMF, determined by the motor speed and load, that determines the current.
But if there are fewer windings than it is designed for, than the iron likely is saturating, which will cause a high current.
The motor needs the original number of turns.
 

Thread Starter

psoke0

Joined Mar 31, 2017
191
The inductance and resistance of the winding determine the zero speed starting current.
When running, it's mainly the back EMF, determined by the motor speed and load, that determines the current.
But if there are fewer windings than it is designed for, than the iron likely is saturating, which will cause a high current.
The motor needs the original number of turns.
If the original had 280 number of turns then it should be possible to rewind the same number, Normally the slot are lined with Pressphan or fish paper, and an insulated wedge type tool is used to tap the windings down in place.
Ensure the lining is the same width.
There is a bit an art to it.
the wire i bought have better insulation then the original wire. so that maybe the reason it does not fit in it.
 

Thread Starter

psoke0

Joined Mar 31, 2017
191
guys so how can i know if the stator is going to saturate with how many turns or thickness of wire i put in or other variables can you guys give me information about this
 

crutschow

Joined Mar 14, 2008
30,420
guys so how can i know if the stator is going to saturate with how many turns or thickness of wire i put in or other variables can you guys give me information about this
Anything less than the original number of turns is likely to saturate the steel since, to minimize cost, they use the minimum amount of steel they can.
 
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