Rewinding Microwave Transformer

Evening,

I don't have any 35mm2 cable to hand aside from welder cables that I don't want to touch.

I want to ditch then rewind the secondaries with the big csa cable, just a couple of loops to get low V / high A out. If I'm careful as to the lay is there any reason I can't just use 16mm2 in parallel and put the doubled ends into one crimp? OK, not the same as 35mm2 I know but not aiming for  exact science here!  



Cheers

trying to make one of these?

https://www.youtube.com/watch?v=uXEPy6Za6cI

Andy™ said:

trying to make one of these?

https://www.youtube.com/watch?v=uXEPy6Za6cI

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Erm...not quite...

All will be revealed if I make it out of the garage!

He's making an all electric delorean!  

I have a few hundred metres of 50mm tri rated singles if you want a bit?

the Vet had some for Jump,leads....Prob jump a jumbo jet with it

kerching said:

I have a few hundred metres of 50mm tri rated singles if you want a bit?

the Vet had some for Jump,leads....Prob jump a jumbo jet with it

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Ta. What's that, about 1/2" dia? 

Might be just a tad bigger

its down in my offsite storage facility But I have to go there tomorrow to get some conduit bending bits so I can cut some off if you want it?

kerching said:

Might be just a tad bigger

its down in my offsite storage facility But I have to go there tomorrow to get some conduit bending bits so I can cut some off if you want it?

Click to expand...

If you're there then yes please grab a few metres maybe? Will obviously PayPal you something. PM me. Cheers.

If space is tight then there’s nothing to stop you from using two or more 16mm² in parallel. But don’t forget you can’t exceed the kVA rating of the primary winding.

Many years ago there were some cooker rings which worked from a large transformer, about 24 volts I think. I rewound one of those to make a reasonably successful welder using paralleled secondary windings to utilise wire I had.

There is no problem paralleling as long as the same number of turns. I await the outcome of your project with interest.

Geoff1946 said:

Many years ago there were some cooker rings which worked from a large transformer, about 24 volts I think. I rewound one of those to make a reasonably successful welder using paralleled secondary windings to utilise wire I had.

There is no problem paralleling as long as the same number of turns. I await the outcome of your project with interest.

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REVO I think

we sold them to the water board to unfreeze their pipes 

kerching said:

REVO I think

we sold them to the water board to unfreeze their pipes 

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I tried that too, on a frozen pipe to my garage. The only result was to burn out the earth wire to the garage consumer unit. We live and learn!

Tony S said:

If space is tight then there’s nothing to stop you from using two or more 16mm² in parallel. But don’t forget you can’t exceed the kVA rating of the primary winding.

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I forgot to mention, bind the secondary windings to stop them jumping about due to magnetic repulsion.

Tony S said:

I forgot to mention, bind the secondary windings to stop them jumping about due to magnetic repulsion.

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I did wonder whether I could "fill the gaps" with intumescent mastic to the same dampening effect but open and bound would be better for cooling.

Not too sure about the mastic, as you say you need air flow around it. We used resin impregnated tape or varnished silk. Waxed butchers twine is also good as the others will cost a bloody fortune and are hard to get hold of.

Hacksawed thru the weld to split the first trannie  (vice, timber, bfo hammer) and salvaged the primary.

After I fit the new secondaries I'll need to "stick" the trannie back together. One site advocates Araldite ffs! Hardly going to guarantee  continuity on the earthing! 

Can't decide whether to clamp and stick /MIG weld the join or just tack each corner...

I would try to replicate the original assembly. The laminations are actually insulated from each other to reduce eddy currents, and there is some science (that I don't recall if I ever knew) to where they are connected.

As Geoff said the laminations are insulated from each other and there will a break in the magnetic circuit to stop eddy currents. If you’ve cut the transformer core you may get away with gluing it back together with Araldite but you’ll have introduced a 2nd and 3rd break in the magnetic circuit making it inefficient.

I’ve had experience of damaged transformer cores (low frequency induction furnace in KB), on full power the core would heat up dangerously. What had happened the faces of the core air gap had spread so the “powers that be” had it compacted and remachined. Despite me telling them to have it machined on a horizontal miller it was done on a vertical. It chewed up the laminations causing short circuits between the individual laminations.

Geoff1946 said:

I would try to replicate the original assembly. The laminations are actually insulated from each other to reduce eddy currents, and there is some science (that I don't recall if I ever knew) to where they are connected.

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I think it's more of a case that in a ideal world they are insulated from each other across the whole of the mating faces. The continuous welds shown mean that there's some compromise on that ideal.

The bit I cut through was a continuous fillet of weld joining all the laminations. 

Courtesy of @kerching:

Quite how far this diversion will take me this weekend I don't know...Capri to play with, laptop dc jack to replace...bathroom to finish!