Motor problem

dusty · Post by **dusty** » Mon Aug 19, 2013 11:11 am

[quote="JPG40504"]I think it is worth a second look by Dusty!]
I've sorta taken that second look.

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Looking close, you can see signs of heat. Some of the lacing is still missing. I retied the exterior leads back in place.

Now I am wondering.

Can I apply power to the individual windings without assembling the motor? If there are problems within the windings that caused the heat, would it be the same without the armature installed?

JPG · Post by **JPG** » Mon Aug 19, 2013 11:54 am

dusty wrote:I've sorta taken that second look.

. . .

Looking close, you can see signs of heat. Some of the lacing is still missing. I retied the exterior leads back in place.

Now I am wondering.

Can I apply power to the individual windings without assembling the motor? If there are problems within the windings that caused the heat, would it be the same without the armature installed?

IIWM, the next step would be Formvar(insulating varnish). Especially in the 'major concern' area. I would saturate those slots.

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The where to buy 'link' had 10 local locations. I got my can on line per a post by Bill Mayo(Amazon???)

Whoops! Forgot this http://www.sprayon.com/products/clear_insulating_varnish

i.e. do not give up yet.

Future reliability could be an issue.

I would NOT apply 'power' while disassembled.

P.S. 'Fortunately' the charred area is the start winding.

dusty · Post by **dusty** » Mon Aug 19, 2013 12:39 pm

JPG40504 wrote:IIWM, the next step would be Formvar(insulating varnish). Especially in the 'major concern' area. I would saturate those slots.

[ATTACH]22547[/ATTACH]

The where to buy 'link' had 10 local locations. I got my can on line per a post by Bill Mayo(Amazon???)

Whoops! Forgot this http://www.sprayon.com/products/clear_insulating_varnish

i.e. do not give up yet.

Future reliability could be an issue.

I would NOT apply 'power' while disassembled.

P.S. 'Fortunately' the charred area is the start winding.

OKAY, I will not but can you tell me why you feel that way. I do not mean to be challenging you; only wondering why.

I had a debate with myself and decided that that would be no risk. No result either except maybe "no smoke".

Each winding is an inductive load so it would not be a dead short.

billmayo · Post by **billmayo** » Mon Aug 19, 2013 12:56 pm

Since I had to buy a 12 can case of insulating motor varnish, I have extra cans and would be happy to send you a can if you desire one. I was unable to find a single can of insulating varnish when I brought them. Contact me for price. If the start windings ohm reading is between 6 to 9 ohms and not shorted to ground, the motor should be OK. Same for the run winding .5 to 3 ohms and not shorted to ground. With both the start and run winding leads outside the case, it is easy to wire a DPDT switch to operate the motor in both directions. I have been using heat resistent plastic like ties to rewrap the motor windings. I have used common plastic ties but never checked later to see if they became damaged. The motors did not have any new smell after hours of operations with them so believed they were OK.

Only apply power to an assemblied motor as the counter EMF limits the current flow. The run windings will draw 50 to 70 amps on their own and quickly melt and burn. Years ago, I played with using an electrical lock for an instantance lockdown of the motor rotor (sawstop idea) where power could only be applied for 5 to 10 milliseconds at a time without overheating the run windings and tripping the breaker. The loud noise each time prevented me from doing more research into this idea.

JPG · Post by **JPG** » Mon Aug 19, 2013 1:08 pm

That is why!

The lack of 'counter emf' is why motors have such high start current.

Remember the 'start' relay discussion re Mark VII motors that do not have a start switch? The back emf from the start winding 'picked' the relay and held it picked until the motor coasts down.

mountainbreeze · Post by **mountainbreeze** » Mon Aug 19, 2013 2:22 pm

I have a question about the reversing switch...

What would happen you switch the direction of the motor while it is running?

dusty · Post by **dusty** » Mon Aug 19, 2013 3:25 pm

In a couple of the images I posted, you can see what appears to be masking tape in addition to the waxed string. Does that tape have any specific function.

In the areas that JPG highlighted as be of concern there appears to be what looks like straws around the wires - except in a few locations. Is this an insulating material? Is the absence of that material a problem or will the varnish fix that?

JPG · Post by **JPG** » Mon Aug 19, 2013 3:40 pm

mountainbreeze wrote:I have a question about the reversing switch...

What would happen you switch the direction of the motor while it is running?

I assume you meant reversing the position of the forward/reverse switch while motor is running.

If so, the answer is nothing.

Once the start circuit is opened by the start switch, there is nothing going on in the start circuit. Reversing the switch will have no effect until the start switch contacts again close. They will close when the motor slows down enough to let the centrifugal weights close them.

Dusty's earlier concern was attempting to reverse the rotation prior to the motor coming to a complete stop. That time period is only between the start switch reclosing and the motor stopping. The start up then has the additional task of reversing the rotation direction by overcoming the inertia in the opposite direction.

JPG · Post by **JPG** » Mon Aug 19, 2013 3:58 pm

dusty wrote:In a couple of the images I posted, you can see what appears to be masking tape in addition to the waxed string. Does that tape have any specific function.

In the areas that JPG highlighted as be of concern there appears to be what looks like straws around the wires - except in a few locations. Is this an insulating material? Is the absence of that material a problem or will the varnish fix that?

I do not see the tape in yer pix, but 'spagetti' or woven insulating tape is commonly used in the area of splices.

The slot insulators are there primarily to prevent scratching the enamel during winding. They also insulate the winding from the core. The burned away areas appear to be at the opening in the core. Varnish 'may' suffice there.

Your worst 'defect' is if two adjacent winding turns are shorted. Nigh impossible to detect by measuring resistance. Hopefully the varnish will prevent then from touching in the future. If the turns are shorted now, varnish will not 'separate' them and make the motor usable.

What happens is very high current flows in the shorted turn(only). It becomes a low 'resistance' secondary(like a transformer).

Unless you 'see' a short(very unlikely) do not move any winding wires.

dusty · Post by **dusty** » Mon Aug 19, 2013 5:18 pm

Too late. I was trying to cleanup the wax string loops that I had put in and I broke the start winding right where it was spliced onto a piece of wire that goes to the start cap.

Now I have to deal with making a reliable connection on the varnished winding wire.

Somewhere in my stuff, I have crimp connectors but where. It may be Christmas before I locate those.