# transformer coil wire question



## SE18 (Dec 29, 2013)

Hoping someone can answer this. I'm in process of building a spot welder like this fellow did:

http://www.youtube.com/watch?v=d5pGN6pqkyY

I discharged the caps, got everything removed now and am tearing down the transformer to rewrap it. 

I'm going to reuse the primary winding, along with a length of 2ga I purchased (discarding the secondary that was in the transformer)

In the process of removing the primary (to get to the secondary to remove that), I very slightly nicked some of the primary copper wires that were exposed. The nicks are superficial and everything is intact.

So the question is, is the primary still useable?

Thanks


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## SE18 (Dec 29, 2013)

well, i found some liquid electrical tape so I'm going to cover them up and proceed


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## Rbeckett (Dec 29, 2013)

Nail polish or varnish will work also.  The primary and seconday coils must be insulated along their entire length and not allowed to touch themselves or each other to get the maximum effect of the field.  Commercial transformers use epoxy impregnated paper and heat to seal the wraps.  Once the coil is wound sufficiently it is baked in an oven  t o set the epoxy and encase the wires in insulation.  There was a How it's made TV show that shows the entire process and you might look around and see if you could locate that episode and give it a watch.  It was very informative and would help you proceed safely and efficiently.  Worth a look anyway.

Bob


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## SE18 (Dec 29, 2013)

thanks. I did find one vid:

http://www.youtube.com/watch?v=sqMGgVZXseA

it'll be a while b/c I'm doing other projects too but once it's done I'll post in the welding section and do some trial experiments


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## miro (Jan 18, 2014)

Yup - just make sure that you've got the primary isolated and you'll fine.
At worst, you'll get a big flash and trip a breaker.

I've used a MOT several projects ( low voltage outputs) including a spot welder. I get about 950 A on the secondary at just under 1 volt.
At 950 A secondary current, the primary current is just over 8 A, well below the limits of a 15A circuit.

But I DO use a momentary contact switch with  a NORMALLY OPEN position. And I have physically set it up so that activating the switch takes a deliberate physical act. That way  I cannot accidentally close the switch.

miro


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