MOT question

I finally took the time to think about this, and I believe you're right. The current travels around the laminations in the same way, in the same direction and in-phase, so the voltage differences at the weld point are extremely small.

So why the weld? Maybe just to make assembly easier?

Reply to
Ed Huntress
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Hose clamp.

Dan

Reply to
dcaster

My guess is that it is easier to automate.

Dan

Reply to
dcaster

Good luck with that. Safety glasses...check. Fire insurance...check. Earplugs...check.

911 on speed dial...check "Fire in the hole!" Pluggerin!!!
Reply to
mike

Then you must have Xray vision to be able to see with your head that far up your ass .

Reply to
Terry Coombs

I'm not following you. As a ham radio operator since 1959, I've probably pulled 50 transformers apart, re-varnished them, and re-assembled them. Where is all of this danger?

The hard part is getting the damned laminations apart. After that, it's a matter of how well you can squeeze them back together. They never quite fit into the same space.

Reply to
Ed Huntress

So after rebuilding a few you have enough laminations left over to build yourself another one!!!

Reply to
clare

Yes, and that was an old ham joke.

If you had to fit it into a frame, you usually did lose a couple or three laminations. That didn't cause a problem, because I usually underrated my transformers a bit.

But I usually just tied them together without the frame, and lived with a slightly fatter transformer.

Reply to
Ed Huntress

I wonder how many people have been burned-up taking stuff apart with everyt hing atill plugged-in.

Reply to
mogulah

This is what I remember:

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It's not interleaved E-I . I'm having trouble visualizing how you'd use a hose clamp to hold it together. However you clamp it together has to be stable. And not intersect the stray magnetic field. One might imagine it slipping a little and melting the hose clamp and..... I wouldn't do it.

I got 40Amps at 120VAC in the primary of mine when I shorted the output with a welding head.

Transformer winding experience is good. RELEVANT transformer winding experience...priceless... ;-)

Reply to
mike

I'll let Dan speak for himself, but I thought he was talking about holding the laminations together once the weld bead is removed.

I didn't think he was referring to leaving the hose clamps on once the transformer was re-wound and re-assembled, but let him answer. As I visualize it, it would be a shorted, single-loop secondary that would melt right off of the transformer once you got some serious flux going through there.

For how long? That sounds like a fryer to me.

Reply to
Ed Huntress

With interleaved E-I laminations, you have a lot of latitude. When they're not interleaved, a very small change in the gap can give you major changes in inductance.

Nope, a welder. Typical battery tab weld was six cycles of AC. I'm sure I wasn't doing the 15-amp circuit breaker any favors. I had planned to set it up to work off the Dryer breaker.

A low voltage welder is VERY sensitive to the contact resistance at the weld. Energy dumped can vary from too little to too much with slight changes in pressure. I tried to feed back from the weld, but there was so much energy floating around that the output of the comparator was independent of the weld. ;-(

You really want controlled energy dump. I tripped over a 125 watt-second CD welder with two heads for ~$20 shipped on EBAY. Kinda killed the homebrew MOT crap.

Reply to
mike

On the MOT's that I hava there are other welds that will hold the laminatio ns together. No I was talking about using hose clamps to hold the two chun ks of laminations together. No serious flux going thru the hose clamps. F irst the hoso clamp is around the core. So almost all the flux goes thru t he core. Only a little leakage flux escapes the coro, Second the hose cla mp is stainless, non magnetic. So very little flux goes thru the hose cla mp. Third the hose cramp is high resistance compared to copper.

Have you never seen c-core transformers held together with stainless strapp ing?

Way back in the sixties I did some transformer design for a missile.

Dan

Reply to
dcaster

On the MOT's that I hava there are other welds that will hold the laminations together. No I was talking about using hose clamps to hold the two chunks of laminations together. No serious flux going thru the hose clamps. First the hoso clamp is around the core. So almost all the flux goes thru the core. Only a little leakage flux escapes the coro, Second the hose clamp is stainless, non magnetic. So very little flux goes thru the hose clamp. Third the hose cramp is high resistance compared to copper.

Have you never seen c-core transformers held together with stainless strapping?

Way back in the sixties I did some transformer design for a missile.

Dan

Won't it still try to develop one volt per turn?

Reply to
Jim Wilkins

Most of the ones I've used have been small ones with a stainless or plated-steel frames, but open at the bottom. So there is no closed circuit.

Reply to
Ed Huntress

I was thinking of fried windings.

Reply to
Ed Huntress

laminations together. No I was talking about using hose clamps to hold

the two chunks of laminations together. No serious flux going thru the hose

clamps. First the hoso clamp is around the core. So almost all the flux

goes thru the core. Only a little leakage flux escapes the coro,

Second the hose clamp is stainless, non magnetic.

If being non magnetic is relevant, explain how copper works as a transformer winding???

So very little flux goes thru the hose clamp.

I'd agree as long as the clamp holds position.

Third the hose cramp is

high resistance compared to copper. Not sure that's relevant. We're working with a KW. The point is not that the material is high resistance. The point is that a hose clamp has regions of MUCH lower cross sectional area, the place the tightening screw engages. Higher resistance, more heat, less volume, higher temperature.

I concur that, if you can get the core positioned so that all three surfaces are planar and all the dings due to grinding it apart are aligned so they don't raise up the gap, it'll work fine. If you can't do that, or it shifts due to heating or mechanical abuse, causing current in the clamp, things can go to hell rapidly.

Think about how and where a hose clamp applies force VECTORS on rectangular items. How does that relate to the need to have a perfectly straight I-section with no gaps anywhere in the magnetic path. In the end, only the side that hosts the screw has any force controllability and the force vector ain't in the direction you want.

My point is that without interleaved E-I cores, it's gonna be difficult to create a stable gap, or lack thereof between the E and I blocks with a hose clamp. I have enough trouble clamping a hose without bunching it up and causing a leak. YMMV.

My motivation is not to criticize you. I expect you'll do fine. My motivation is that these posts last forever and people of lesser experience than you reading this in the future might hurt themselves. You can get a crap load of energy out of a MOT. I would not encourage a newbie to cut one apart and just slap it back together with a hose clamp.

How are those hose clamps holding up in the missile during launch? ;-)

Reply to
mike

If the hose clamp was magnetic, more of the leakage flux would go thru the hose clamp.

It is relavant. The power dissipated in the hose clamp is the product of t he voltage and current. Increasing the resistance decreases the current. So if there was one volt on genorated on the hose clamp and the resistance of the hose clamp was one ohm, then the current would be one amp and the po wer in the hose clamp would be one watt. If the resistance of the hose cla mp were two ohms, then the curront would be 1/2 an amp and the power would be 1/2 a watt.

However the voltage in the hose clamp is more like 50 millivolts and the re sistance of hose clamp is less than an ohn. But more resistance still mean s less power in the hose clamp.

I see no problem, but then I have separated MOT's and replaced secondary wi ndings. It is very easy to clamp the two sections of the transformer core together. The weld in very shallow and there is a nice wide flat section o n one piece to clamp to a nice wide flat section on the other piece.

You laugh but a lot of the heat shielding is held on by hose clamps. And t he Trident II missile has a good record.

SUNNYVALE, Calif., June 4, 2014 - The U.S. Navy's Trident II D5 Fleet Balli stic Missile, built by Lockheed Martin [NYSE: LMT], has achieved 150 succes sful test flights, setting a new reliability record for large ballistic mis siles. The Navy launched two unarmed missiles June 2 in the Atlantic Ocean from a submerged Ohio-class submarine, marking the 149th and 150th successf ul test flights of the missile since design completion in 1989.

Reply to
dcaster

Nope.Very little if any flux transitions in the conductor encircling the shole core.

Reply to
clare

I couldn't remember how I put my isolation transformer back together (about 10 years ago) so I went and dug it out to check. I arc welded it back together!! About 110 turns of #14 wire on each winding.

Reply to
clare

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