Microwaving a Ferrite Toroid

This is a clip from an english kids TV series, they do all sorts of crazy experiments.

plastic explosive in a toaster, dropping a milk float (light truck with many glass bottles of milk) from a 100m crane, a large flour-based fuel-air explosion

Lots of general blowing stuff up.

Have you ever microwaved a CD?

that one's safe to do at home if you stop before it melts.

RD_zsqVU

Aside from the stupidly exaggerated video, if you wanted to cause a microwave to be overloaded to the point of failure, what would you cook in it?

Does a metal fork cooked for 5 minutes actually destroy most microwave ovens?

Essentially a microwave oven is a radio transmitter channeled into a metal box or RF cage.

Does the load on the magnetron tube actually change based on what is placed inside?

Wouldn't it be more likely to blow the oven's fuse than to actually harm the magnetron?

If an object can overload the transmitter to the point of overload/failure, then how is it the metal chamber itself doesn't?

I got a bread bag twisty tie in there once honestly by accident, and the fine iron wire melted open like a fuse wire with two globes of molten iron on the ends.

The earlier part of that stupid video looked realistic. The explosion was either faked or edited. The same Brit TV show did gasoline and dynamite. Somebody probably edited the explosion from one of those onto the more boring circuit board glow and sizzle with smoke.

I doubt that a toroid in a Microwave for

You know the old saying "No guts, no gory"... Just do it!

A simple thought experement gives a pretty good answer:

How many families, workplaces, etc, do you know that have microwave ovens?

How many of those have curious kids, bored employees, etc., that are willing to try microwaving all sorts of random stuff?

How many times have you heard of a microwave oven that stopped working because someone microwaved some random object in it?

(It is, however, pretty easy to start a small fire, and small fires occassionally turn into big fires...)

... and around a tonne of lead-acid batteries

RD_zsqVU

I've heard of ferrites getting cooked with less.. I remember someone saying he got ferrites red hot on mere rectifier snubber duty. They may crack due to the rapid heat stress and saturation (I've cracked ferrites just from saturation!).

Come to think of it, those aren't ferromagnetic at red heat, not like steel... Curie temp is something like 300C, isn't it? Still plenty lossy above there, I'm sure.

Tim

The power can't possibly be more than the magnetron can generate. And that can't heat any mass faster than the laws of physics allow.

So don't be a wuss, do it. Blast it for 5 seconds and see if it's warm. Increase the time until you understand the curve.

John

Yup..fastest way to make totally irrecoverable data.

The exploding PCB clip is from a show is called Brainiac.

btw...A bar of soap in the microwave is interesting.

But....I wanna see ferrite in the microwave :)

D from BC myrealaddress(at)comic(dot)com British Columbia Canada

Well.. I'm stressfree now on damaging the microwave. :)

I'll try one..

I got a material J (Magnetics Inc) toroid OD ~ 1" H: 0.5" in the junkbox. ur=5000 No windings.

Microwave power: IIRC 800Watts

Time: 5 seconds high

Results: It's a hot potato.. ouch..ouch ..ouch.. :P (One of those infrared thermometers would be handy.)

Hopefully the ferrite hasn't changed...

D from BC myrealaddress(at)comic(dot)com British Columbia Canada

Put a cup of water alongside it, to absorbe the reflections and re-radiation from the ferrite?

Some years ago, when uWOs were new, an instruction manual showed a cup of water and an ice cube wrapped in foil. The water boiled, the ice was intact.

And anyway, uWOs are free, if you know where to dumpster-dive. ;-)

Good Luck! Rich

AFAIK, they're outfitted with load isolators these days, to keep reflections in the chamber from reflecting too much power back into the maggie.

Cheers! Rich

On Thu, 22 Jan 2009 11:46:26 -0800, D from BC wrote: ...

Maybe you should have characterized it before you baked it. ;-)

Cheers! Rich

No gory? ;-) This is a fairly interesting slip of the keys, since "gore" usually refers to blood and guts, unless you're talking about the high muckety-muck of the cult of Warmingism. ;-)

Cheers! Rich

Forgot to mention: The reason why I thought of microwaving ferrite is to try a lazyman way of shrink tubing stacked cores together. :P

D from BC myrealaddress(at)comic(dot)com British Columbia Canada

Not a typing error, said exactly what I meant!

If they are isolated beads (the particles) it would quickly heat up, just like water. If it is raw ferrite, it could be "conductive" enough to catch an arc, would still heat up, and probably would not overload your oven.

Could. Like over-charging a cell (battery).

Could.

Could. Likely so if integrated magnetic media. Likely not if the particles are isolated from each other via a matrix of epoxy or whatever it is they use.

Naaah...

Naaah. I suppose it could though.

Probably not.

Probably nearly as fast as water.

Not likely Immerse it in alcohol. In fact, you could simply heat up alcohol and drop it in. That will get the moisture out of it. You could use an oven that you overshoot, turn off, and then put it in as it is cooling down through the desired set-point.

What was it Einstein said about science?

Probably pretty quickly. Whay is it? About a 1.5 inch toroid?

It wont. Arcing Aluminum foil and things will. So watch it, and if it arc, then quit the oscillation (duh). It takes many moments of arcs to hurt it. As long as you keep your eye on your process, (not literally of course) you can be sure that you are not hurting the oven. Hell, what are they anyway... $80 these days?

You should open the oven and check the temp with an IR wand every ten seconds of oscillation. That way, you can closely control the rise.

You can even increase to 12 or 15 second 'bursts' if you think it is progressing too slowly to suit you. I would start out slow though.

Of course. OR, it was one of those military boards with the built in self-destruction mechanism. :-) ;-)

Sounds just like Obama.

Wow! Only 5 seconds huh?

I just bought an IR wand for $20 at Harbor Freight last night. It works great, even though rough focused through a fresnel.

Unless he has another... too late for that!

Ten turns, take readings.

Right now it is characterized as "unknown" or Abbey Normal.