MOT hacking

[crossposted alt.binaries.schematics.electronic,sci.electronics.design,sci.electronics.basics please manage followups intelligently, thanks.]

There have been threads about hacking Microwave Oven Transformers, and there are a lot of websites, and I'm sure you've all seen my MOT:

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(the penny was just to see if there were any eddy current effects. None was perceptible. :-) ) So, today, I scrounged a hank of #18 magnet wire, from some guy back in the shop at
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. All I did was do a google search on "transformer rewinding whittier ca" and this outfit came up. Well, it's just down the street, and it's a pretty respectaby-sized shop, in a nice part of town, and I called them on the phone. "Well, I'm looking for about 25 feet of #18." So, just on my good looks, this guy hands me a remnant (about 2/3 of one layer, on a spool about 4" diameter and about 5" long) of wire, and it's on the house! I asked, "Do you want me to mention you in my blog?" (figuring that "blog" would be easier for a motor rewinder guy to grasp than "USENET group") and he said, "Sure!"

So, I'm going to wind a 15-turn pie on my MOT right up close and personal to the existing primary, but first I have to get those pesky magnetic shunts out of the way.

I'm thinking prop the tranny up on a couple of 1-2-3 blocks on the steel welding bench, and just whack them out. How do you guys get your magnetic shunts out of your MOTs?

Thanks, Rich

Reply to
Rich Grise
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alt.binaries.schematics.electronic,sci.electronics.design,sci.electronics.basics

I just tapped them out with a flat tip screw driver away from the primary winding. Comes out easy. Do keep us posted on your progress, my eye's are perked up!

Reply to
James Thompson

Whaddya think yo better than me?

I use wood and a chisel or screwdriver and hammer... :-)

If you want to get the windings off I recommend (I probably did already) hacksawing or grinding the weld off the "I" section, then lightly bashing (can I use those two words together?) the primary off. Then you can glue up a bobbin from cardboard and slip your secondary on much easier. A clamp from the shop keeps the I firmly on the E until you feel like welding it back on or whatever.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Reply to
Tim Williams

Eek! I'm nowhere near that point yet. It seems that the wire I scrounged is somehow stiffer than I remember #18 hookup wire, but it's motor wire after all. The insulation has the look and feel of "Heavy Formvar" or "Polythermaleze" or something. I've threaded a few turns by just threading the wire through the winding window, and it looks like crap - that is, what I've got for a "winding" is kinda tangle-wound, but it turns out that because of the stiffness of the wire, and the toughness of the insulation, it's not all that bad threading it through the eyes, albeit time-consuming. The tangle-winding I have there now I'm sure would work electrically, but it looks like crap, and would probably buzz. So, I dedided, since I intend to show it off, it should look neat, so I've decided to 5-minute epoxy each winding into place as I go along; this should only take 2.5 hours to do 15 turns. ;-)

Cheers! Rich

Oh, and of course, don't forget the boredom medicine of your choice, ;-)

C! R

Reply to
Rich Grise

Golly, Rich, make your life easy, and grind the welds away, and take the center out of your tranny. Then you can wind the windings very neatly. You don't have to weld the center back, you can toss some of your 5 minute epoxy at it, and all will be well.

-Chuck

Reply to
Chuck Harris

Doesn't the extra air gap cause problems?

Reply to
Clifford Heath

I doubt it, those things saturate on the peaks anyway. L will be lower but Imax will be higher.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Reply to
Tim Williams

No, because you are only removing a small percentage of the lamination iron. If you are truly concerned, you can weld it back up.

-Chuck

Reply to
Chuck Harris

Ok. I'd still avoid epoxy because it falls apart with heat. A resorcinol or urea glue would resist that.

Reply to
Clifford Heath

Uh . . . the air gap is part of the way the/a magnetic shunt works - as the secondary draws more current than you want, the magnetic field is diverted into the shunt (bypasses the rest of the core and secondary). Bigger gap sets the current limit higher. Skewed gap gives a sloppy "knee" in the current limit.

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We weren't talking about the shunts. They are popped out. We were talking about opening the core so you can remove the bobbin and wind it easily.

-Chuck

Reply to
Chuck Harris

Oh. MOT I'm using only had a weld on the shunt.

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This one, the shunts just popped out - tap, tap, tap, toink! But, since I'm having so much fun threading this wire through the EI eyes, epoxying each turn into place, I really don't feel like cutting up the core. I can see where it's welded, and I have access to all manner of grinders and a chop saw, and my office opens onto a weld shop, so it's theoretically doable, but I can thread wire sitting down. ;-) Plus, I don't want to introduce any new gaps - I'd rather change as little as possible per experiment. :-)

Thanks! Rich

Reply to
Rich Grise

I know you're having fun. What is the volts per turn? or turns per volt.

American Science and Surplus had some very inexpensive 1 KVA toroid isolation transformers awhile back They are 0.84 volts per turn - Brand new for ~$12 with flat rate shipping. But you can't beat MOT's for cost effective.

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Yup. Can't get much cheaper than free! ;-)

Cheers! Rich

Reply to
Rich Grise

Its a bit late for the u-wave oven you got the transformer from, but a handy tip for curing the problem of the lights keep blowing when people are a bit heavy handed shutting the door - watch out for CFLs with slim bodies and check if they fit the space available before hunting everywhere for the proper bulbs - CFLs seem to be a little more robust in this application!

Reply to
ian field

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