I can't recall off the top of my head what the coating on a bucket of magnet wire is rated it.

Ours were enamel dipped and oven baked, after a re-wind.

 

The traditional method we used to use, was chop one end of the windings off with a cold chisel, then punch the winding out, count the turns and make a bobbin former in order to wind the coils.
Presspahn paper was used to reline the slots.

If you use an air chisel you can do it a lot faster and speed the development of white hands in your workers....
Presspahn paper I never heard of that.
We used stuff called DMD ( its basically Mylar with something done to it to achieve a class F rating )

You could push a cold cut winding out but much better to use an oven in a shop.
Less effort to pull out the copper.
Makes clean up easier too because you can see if you have copper spatter in the slots ( this must be removed )
Also leaves an oxide layer on the steel to increase the resistance of the lamination in relation to each other.
If seen it myself... a bad motor with high iron loses will improve after a proper burn out and subsequent dip in the rewind process.

Only varnish I ever seen used was made by PD George.
Everyone used that brand that I knew.
Same for epoxy we used PD George as well.
Always Type F I think the epoxy exceeded that.

Wire however has a factory coating on it I can;t tell you what it is but I don't think its rated to exceed more than 100 volts .
This is not a problem as long as your wires nest correctly and you use some fish paper between the phases or any place you have coil groups hotter than 100 volts touch anything else

 

If you use an air chisel you can do it a lot faster and speed the development of white hands in your workers....
Presspahn paper I never heard of that.

Presspahn was founded in 1925 in Britain, original purpose was insulation used in the manufacture of power transformers.

For a stator, We used a hand cold chisel to shear off the copper turns right at the laminations, then use a drift to drive the old coil out of the slot.
Also use the removed remnants to get the measure of a winding bobbin, if it was an odd ball.

 

We used a hand cold chisel to shear off the copper turns right at the laminations, then use a drift to drive the old coil out of the slot.

If done that too.
Its slow and ok for small machines.
Big stuff you use a air chisel, bigger shops today have a saw to cut the knuckle off.

After a burn in an oven that copper comes out very easy, and its annealed so your not fighting to pull it out.
Bad side of that is all the lead paint and potential asbestos of what ever they used in old motors.
In the leap from Type o insulation they used all kinds of things that as it turns out are actually bad for you....
who knew?

 

Wonder where can I can get a curve of current vs speed for universal motors? Saw one that shows speed on Y axis vs T on X axis. This shows T asymptotic to X axis when speed is 0, would suggest that at standstill i.e. when starting, the current is very high?

 

One of the reasons series field motors are, or were, used as automotive starters, they possess Very high torque at zero RPM due to the high current also flowing through the field.
With no load applied, they gradually increase in RPM, and if not checked by some residual load, can self destruct.

 

Rewinding the field now, seems that armature is fine. Now, scared of interturn shorts. Looked for varnish in electrical stores - no luck. Anyone has any ideas of what is a substitute for varnish that is available in hardware stores?

 

Now want to test it with lower voltage say 12 vdc. Wonder if this is enough to get an idea of how it will behave under 120vac?

 

Off load and easy to spin, it should normally wind up to a reasonable rpm, a good indication, anyway.

 

Tried with 12 VDC, just made a click sound, no rotation.

 

..And you are sure of the field polarity is correct. ?
You require a N & S pole on each.

 

Reversed the pol of 1 pole, applied 12vdc, same click, checked the rotor, did not move, seems stuck. How to check polarity of each pole?

 

There is only two choices, so if you reversed one, then you have covered it !

 

It is stuck in both cases, so I am stuck now! Want to do an indep check to settle this.

 

Tried motor momentarily today, works at full speed but sparked and smoked a lot. Did not want to risk too much damage so ran only for a second. Lot of confusion:
1. Took it to 2 motor shops for growler, one test passed, other also passed but ohm resistance from 1 comm seg to the next varied a lot.
2. Tried to rewind the field so not sure if the turns are correct but from the fill of the winding looks OK, except that the number of turns may be different by say 5, total turns 75.
Based on the above, could it be the field or armature?
Pls note, I am doing this mainly to determine the root cause as I could just as well buy a new device.

 

If the growler test varied alot from one segment to the other it is cause for concern, that is the whole purpose of the test.

 

Thanks. Actually, when he checked ohm readings from segment to segment with multimeter, he noticed variations, not with the growler. Not familiar with growler but thought it was just a overall test pass or fail and he said it passed

 

Checked the armature on a good motor, little sparking and no smoking. Looks like may be the comm or brushes. Here are pics of comm/brushes

 

Checked the armature on a good motor,

So it could be the fields then?
Did you try the good motor armature on the other fields?

 

Just wonder since I had another failure with the motor smoking - is it better to wind the coils outside and then fit them on motor or wind insitu?