Yes, but will recheck.

 

Thanks. Changed polarity and works now although noisy!

 

Now put the motor back in the chainsaw and tried, works but sparks a lot. Not sure where the problem is i.e. field or rmature. Field was rewound as the turns showed blackening but nothing done to armature. So, wonder how to check the armature? Also, is it possible to get winding data for field and for armature?

 

Hoping for a reply. Dont have a growler to check armature, any other way to check?

 

Certainly the field polarity is vital. And all of the pictures were of an induction motor.
NEVER trust yootoob to be presenting truth.

How many turns of what size wire were in the field windings?
And yes, the polarity of the field halves relative to each other is what matters, not so much relative to the armature.

And make sure that the armature is free to turn.

 

If you did not accurately count the turns in the field then you may not have enough turns and you might be doomed.
If you have an ohm meter you can check the resistance between brushes as you rotate the armature. Every pair of segments should be very close to the same resistance.

 

Thanks. Yes, I think I wound less field turns. This could be the reason for excessive comm sparking? In that case, think I should increase from the existing 72 turns to 100 turns.

 

Thanks. Yes, I think I wound less field turns. This could be the reason for excessive comm sparking? In that case, think I should increase from the existing 72 turns to 100 turns.

Reproducing all parameters, including No. of turns is important.
Excessive comm sparking off load, is symptomatic of armature shorted turn. You cannot reliably test the armature with a resistance meter, it has to be done with a Growler.

 

When the suggestion was made to cut out the field coils with a hammer and chisel that was my clue to disregrd all advice from that source. If the armature has shorted turns then replacing the motor may be the better choice, depending on what part of the world the TS is located in.

 

When the suggestion was made to cut out the field coils with a hammer and chisel that was my clue to disregrd all advice from that source.

What is your experience with motor rewinding.
If in your extensive experience with rewinding motors, what method would you suggest??
You obviously did not understand the method used. A method which is quite common.

 

I did rewind a similar sized fan motor, wound the fields right on the laminations I counted turns unwinding the burned up wire from the core . It was indeed rather tedious, no question about that, and it was more like 250 turns, I think. Each winding. Certainly there are faster methods but they might produce a winding that did not fit correctly.
And I am very much aware that a hammer and cold chisle in the hands of an average person are going to damage parts that should not be damaged.

 

And I am very much aware that a hammer and cold chisle in the hands of an average person are going to damage parts that should not be damaged.

As someone who has received qualifying motor rewinding instruction from a industrial source that used this method , the objection I had is the statement

" my clue to disregard all advice from that source"

'

 

I tried the motor today, it ran but started smoking in secs - surprisingly smoke came from the field winding and I had thought it was the armature that was bad. The field winding has blackened. This was the case also when the motor initially failed, it was the field winding. Is this common that the field fails before the armature?

 

There are a lot more turns in the field winding and so more places where things can go wrong. And with a motor running on AC a single shorted turn will get very hot. And because the turns are not anchored solidly by lots of varnish, turns sometimes can vibrate and wear through insulation. Armatures are made more solidly. And sometimes they develop an open circuit in one section. A field winding is simpler to repair.

 

It is a series field motor, so a short in winding will cause excessive current in all coils.
It would have been better to test it on LV DC, e.g. automotive battery etc first.
.

 

Think I am stuck so best way is to get a similar motor but this is not available. Is it possible tht there is a standard that dictates for a series motor 120V, 6.5A, it will have so many turns/gage in the field winding? Motor is made in China, tried to locate actual manuf, so far no luck.

 

Is the current density i.e. A/sq.mm greater for the armature or the field in a univ motor? From my college days (long back!) I seem to recall that the current density used is higher for the field than the aramture but not sure why?

 

The same current flows through both armature and field (series armature/ field motor).

 

But the gage of wire used for field may be different from armature so different C.D.

 

The first thing is to use an ohm meter and check for continuity to the laminations . Disconnect and see which winding has the problem. I am guessing that there are two field windings on opposite sides of the armature.
If only one of the field windings overheated then unwind it until you find the spot with the short circuit. You may be able to repair it and save the wire. OR, did you wind the coil and then put it in place??