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 Post subject: Microwave oven transformer... reversed.
PostPosted: Sat Sep 30, 2017 5:29 pm 
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Joined: Fri Feb 01, 2002 1:01 am
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Location: Mideast USA
Hi.
As is, with no modifications, connecting mains to the high voltage winding; would the low voltage winding be capable of some spot welding to sheet metal ? Never tried playing with those...



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 Post subject: Re: Microwave oven transformer... reversed.
PostPosted: Sun Oct 01, 2017 7:11 pm 
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Joined: Thu Oct 26, 2006 7:11 pm
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Location: Maryland
No, the winding gauge and ratios are wrong. But if you leave the primary winding and remove the secondary windings then rewind the core with a high current secondary that will work.
Here's how https://mad-science.wonderhowto.com/how-to/turn-microwave-oven-transformer-into-high-amperage-metal-melter-0140772/

Additionally this idea has been covered by many YouTube 'stars' !



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 Post subject: Re: Microwave oven transformer... reversed.
PostPosted: Fri Oct 27, 2017 8:17 pm 
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Location: USA,World
I dont think he should remove the welds holding the core together just to put in 2 turns. I'd cut out the secondary winding with Plato wire cutters or a knife. Then feed through the new secondary.

I once made a twelve Volt power supply that was resistant to damage from shorting out the 12V. It had a lot of voltage drop on the loaded secondary. It used a microwave oven transformer that was turned around like was asked about above here.


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 Post subject: Re: Microwave oven transformer... reversed.
PostPosted: Mon Oct 30, 2017 3:23 am 
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Joined: Fri Feb 08, 2002 1:01 am
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Location: USA / North Carolina / Fayetteville
you can also carefully cut the secondary out with a hacksaw, and then tap out the secondary..


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 Post subject: Re: Microwave oven transformer... reversed.
PostPosted: Wed Nov 08, 2017 7:02 am 

Joined: Mon Dec 06, 2004 1:01 am
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Location: Tennessee
One of my students made one of these, he cut the secondary off with a hacksaw being careful not to cut the primary. He wound the secondary with 2 turns of #6 thhn and it worked perfectly for his needs. He had to tie the secondary in place with wire ties to keep it tight with the core.I think the open circuit voltage was about 2 volts.

edit: As with all spot welding, you must keep pressure on the tips whre the weld is going or it'll just blow out holes..


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 Post subject: Re: Microwave oven transformer... reversed.
PostPosted: Wed Nov 08, 2017 2:02 pm 
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Joined: Fri Feb 01, 2002 1:01 am
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Location: Mideast USA
Thank you gentlemen. Good to learn from your experiences.
So about a Volt per turn to expect... With a few fatty AWG turns, a substantial battery charger/eliminator could also be implemented.

I wonder if with the primary energized and not loading the secondary there is some things needed to consider.



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 Post subject: Re: Microwave oven transformer... reversed.
PostPosted: Wed Nov 08, 2017 3:31 pm 
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Amazingly versatile transformer, that is. Wind it for whatever you like!
Only concern about an unloaded secondary with the primary powered, is contact between the secondary wires! Lotta amps!


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 Post subject: Re: Microwave oven transformer... reversed.
PostPosted: Wed Nov 08, 2017 4:44 pm 
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Location: Maryland
I once rewound a 24 volt, not so smart fork lift battery charger, for 12 volt service, one heck of a boost charger that one was!
The formula you need is Lotta Amps=Lotta Fun! :shock:



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 Post subject: Re: Microwave oven transformer... reversed.
PostPosted: Sun Nov 12, 2017 11:22 am 
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Location: NewJersey
Joseph wrote:
I dont think he should remove the welds holding the core together just to put in 2 turns. I'd cut out the secondary winding with Plato wire cutters or a knife. Then feed through the new secondary.

I once made a twelve Volt power supply that was resistant to damage from shorting out the 12V. It had a lot of voltage drop on the loaded secondary. It used a microwave oven transformer that was turned around like was asked about above here.


Hi there,

That's how many of the older wall warts were made too. The leakage inductance acts as a current limit for the output and thus for the input.

I have one sitting here waiting for some sort of mod.



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 Post subject: Re: Microwave oven transformer... reversed.
PostPosted: Tue Nov 14, 2017 12:00 am 
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Location: USA,World
Howdy, I had an old Texas Instruments calculator that appears to have predated the TI 30 that had a wall wart using a transformer like that. I seem to recall that it even regulated the output with just a zener diode.

Presently I have a choke that I made with a roll of wire as the magnetic core. I would like to replace that with a transformer-type core, possibly one from microwave oven.


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 Post subject: Re: Microwave oven transformer... reversed.
PostPosted: Wed Nov 29, 2017 12:37 pm 

Joined: Mon Dec 06, 2004 1:01 am
Posts: 294
Location: Tennessee
Have you seen this? While I don't agree with everything he's done, it still works.
https://www.youtube.com/watch?v=vrlvqib94xQ


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