Easiest Microwave (MOT) Salvage/Re-use Tutorial

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Introduction: Easiest Microwave (MOT) Salvage/Re-use Tutorial

These videos show you how to take any broken microwave and get the transformer out of it, tear it down, and rebuild it according to whatever project you have that needs one. These form the heart of many other projects, which I cover (or will cover if not out yet) in other tutorials.

Hopefully every question you might wonder is explain in detail in the videos. I give plenty of alternative options for tools and methods.

Part 2:



Part 3:



I'm a big proponent of criticism and feedback. My first video had some audio issues. I made parts 2 and 3 several months later after feedback and I think they're much better. Please leave comments if you have any suggestions for improvement, criticism, things you thought were poorly explained, etc. I read it all and it helps me make better tutorials in the future.

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Hi Matt, great tutorial, just wondering if
you could clarify something for me, going through the videos and
comments I couldn't find the answer. The winding direction for the new
secondary should it be in the same direction as the primary, ie: say if
the primary winds clockwise if viewed from above the secondary goes the
same way?

And also does it matter if the primary is on top of the secondary or vise versa?

Cheers

Geoff

Winding direction does not matter unless you're combining multiple transformers or windings together (in which case, you want the end result to be matched so they add, rather than opposite so they subtract to net zero). Think of a sine wave. The direction you wind determines whether you start at the top, or the bottom. It alternates 120 times per second, so, unless some quirky circuit requires that precise of timing and polarity, it makes no difference. To keep my head straight, I usually try to wrap in the same direction, good habit, less confusing if you want to combine transformers later to make it more powerful.

Order of primary or secondary doesn't matter at all. The transformer doesn't have a "top" or "bottom" and it's operation is unaffected by gravity, which is the only way "top" and "bottom" could be defined. Put it on however is convenient. I usually put the primary on first (trapped at the back of the E) because I'm more likely to change the secondary some day, or have to adjust it to fit. Operation-wise it doesn't matter.

Thanks for that, isn't amazing when something is explained in simple logic and common sense comes into play. The only difference is that in Australia we run on 240V @ 50 Hz.

Just as a PS to the last note. That's a fourth way of determining turns required. Measure the voltage of the secondary as I described. Unwind secondary and count turns, you could probably just use a pedometer mounted offset on the unwinding spindle if you haven't got some better turns counting mechanism.

I'd probably use a cordless drill with a 13mm bit of dowell as a bobbin to unwind onto. Those secondarys look like they've got a lot of turns on them. (By your estimates of average primary turns, there should be 1100 odd turns on the secondary). Then divide secondary original voltage by number of turns on original secondary to give turns ratio.

Then multiply by required voltage to give new required turns. Then work out amperage anticipated and look up a copper wire amp carrying chart to get best wire thickness. You could also do a voltage drop test with length, amperage and gauge to give heat rise if you're really feeling gung ho.

Also means you've got a nice little spool of small gauge wire for when you build that Tesla coil you always wanted to...

Great tutorial, just what I need to make a decent cnc servo linear power supply and get away from switched supplies (and save 2-300 bucks as well). Got a dozen MOTs from local tip shop for AUD$2 each, already out of case, including a monster that looks like it's 1500 watt at least (weighs over 8kgs).

Wanted to test the secondary output which lead to some confusion 'til I discovered that MOTs ground one secondary lead to the core (and then the case to I suppose).

As the MM only went up to 600vac and the secondary is probably around 2000vac I made up a resistor string of 90Mohm to boost the MM impedance from 10Mohm to 100Mohm. Had to series eight resistors in the end out of salvage as I didn't have a 90mOhm resistor to hand.

Worked a treat. Secondary was putting out 1890vac, and the two other little secondaries (tertiaries, quaternaries?) were putting out 3vac and 9vac, probably to rectify to 5v for a logic board and 13v for the fan motor....

I thought that maybe the meter could have handled it without the resistor seriesed with the probe, but sadly not! Fizzle, pop, smoke. One dead multi meter. Oh well...

Hello, I've been having some trouble with my transformer. Instead of two welds, one on one side and another on the opposite side, it looks like its made of two interlocking chunks. It was salvaged from a microwave, and when I look at all these videos online on how to cut the weld apart, it doesn't match any. on the label it says OBJY2 and below that, EBJ60664602. Any and all help is appreciated.

Okay, I looked that up. You are right... The welds on that model are in peculiar places in the pics I found.

Two possibilities:

1 - the welds are in weird places but the transformer us a normal not. Cut where the E and I join and follow the tutorial as-is.

2 - the transformer is "interleaved", which means the E and I pieces plates aren't each in a big 100-piece stack that are the welded after, they're alternating every single layer. This is the better way to make a transformer, but harder, and it's almost impossible to disassemble (and then reassemble) without damaging it. In this case you'll have to cut the secondary off and thread your new secondary as per the tutorial "hard way".

Take some pictures in good light (bathroom), post them on Imgur and link the album here, I'll try to help more.

If it was a book I would say it not only contained information I needed it was also an easy enjoyable read. Thank you!

So how many wraps would i need on both P and S for 120v in and 24v @50+amps and size of wire