Heat in Motor

"What may be the reason of heat?"

Usually it's failing to understand the concept of 'Amp turns"

Extra heat in motor after rewinding is caused by poor winding or low quality material. Have you checked motor load current? May it be increased due to poor winding. If motor is winded by quality material then no chance to overheat.

I agree, especially as it pertains to "quality of material".

Have you "re-wound" the motor at one of the motor manufacturer's authorised rewinders? If not, then this could be the most common problem with the "street-corner" rewinders. Normally, they do not use the "exact" guage winding wire as was in the original motor, but take the nearest avaialble size - guaged only by their fingers - thus adding to the resistance of the winding and hence more heat.

If you want to avoid motor over-heating in a post-rewound condition, then do rewinding only at a qualified rewinder - preferably one authorised by the motor manufacturer.

Dear,

Reasons for poor rewinding are...

1. Balancing of rotor may not be as perfect as was earlier, prior to rewinding. Causing pulsations in the torque, leading to heat.

2. The problem may lie there in the installation, prior to failure of motor, such as erroded contactor contacts, burnt terminal wires , carbonised terminals, un balanced voltages, over load in the machine - etc...which, may not have been rectified as yet.

3. If not above, then, poor rewinding quality - Strict requirements are better insulation, better Copper wire quality - certified electrolytic grade, not the commercial grade avaialble in the retail market. - Perfect balancing of the rotor. Check the test supply Volts - must be Balanced. Even 3% un balancing causes 11% more heating of the motor.

did you change the bearings? did you count the number of turns per coil BEFORE you started the rewind? do you have the SAME number of turns per coil? have you replace the fan blade on the rear of the motor? are you over loading the motor? do you have the correct voltage? why did you to rewind the motor in the first place?

If you can answer these questions then maybe we will be able to help you without wild guesses, as to the possible cause of your problem

1. I changed bearing..

2. ya , i counted no of turns, SWG, Winding pattern before removing...

3. Ya same turns per coil...

4. Motor is not yet loaded (No load condition) & fan blade was not connected before also...

5. Voltage is correct

6. initially it was burnt so i rewinded..

and i am not authorized rewinder, it was burnt in college lab... it was purchased around 25 years before...

with regards,

have you phased the windings?

You may have used an inferior kind, improperly sized (AWG) magnet wires in your winding? Although you may have duplicated exactly the # of turns per coils, but if you used sub-standardly sized magnet wires (like those manufactured in China) in effect will result in "loose windings", '"over heating", poor insulation, and overall impedance motor problems that you now experiencing! Verify and double check the cross-sectional copper area of the magnet wires you used in the windings, see to it that you separate the insulation coatings in your measurements!

After rewinding were the bearings replaced,are the no-load current,vibration level and noise levels are same ?.

I only have one thought respecting this problem:

"Never send a boy on a man's errand"

That's how you make men.... Send a boy on the errand.

OK!............... But not until they are ready.

You need to be able to crawl before you can walk!

It is not clear when the motor is running --------------

1) whether the motor is overloaded i.e drawing more current than rated current mentioned in the nameplate of the OEM.

2) whether there is any unbalance in three line currents.

3)whether there is any voltage unbalance between three lines.

Overheating in motor may occurs due to various reasons viz;

1)due to poor quality of copper conductors used

2) due to undersize of copper conductors used

3) due to interlayer shorting of laminations( increase of eddycurrent loss )

4)due to improper use of cooling fans during repairing process ( incase of broken fan repairer some times fits new fan which may not properly match apart from dynamic balance problem )

5) fine crack in rotor bars

6)poor condition of bearings or lubrications and misfit/ misalignment of bearings

So to stop overheating problems all the above factors may please be considered.