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Microwave Oven Diagnostics with Indian Snack Food (evilmadscientist.com)
311 points by gus_massa on Feb 28, 2015 | hide | past | web | favorite | 67 comments

"Did you know that if you take apart microwave ovens, there is a really great ceramic magnet inside of the magnetron?"

There is also beryllium oxide in the ceramic insulators of most magnetrons. If the insulator cracks or is broken, that dust is highly toxic if inhaled.

If you want a nice magnet, there are safer ways to get one. Leave the magnetrons alone.

Anytime I see someone mention hacking on magnetrons, I feel it my duty to remind us that the back of your eyeballs don't have pain receptors. If you were to power up thatagnetron outside of the microwave and point it at your face, it's possible you'd blind yourself before you even realized you were in danger.

Just wanted to add something. Itching is the first sign. If you feel itching in your eyes, turn the damn thing off immediately. I nearly blinded myself when I was an idiot undergrad. Kids, take the idiot adult's advice and don't play with it before you understand the theory and working principles extremely well.

IIRC, the danger is actually to the /fronts/ of your eyeballs, the result being cataracts rather than retinal damage.

And the front (cornea) has more pain receptors per surface area than any other part of your body. Not that this would necessarily help prevent cataracts if you expose your eyes to a magnetron.

I didn't realise this until I had laser surgery to correct a cornea problem. Oh dear, two days in a dark room on morfin, before I could even think straight again, no fun. But now I can see better again.

It's also a problem that there is no blood flow through your lenses. If you heat them via microwave radiation, they're going to stay hot for an alarmingly long time.

No doubt the material is toxic, but it doesn't seem breaking it would create a whole lot of dust, similar to any other ceramic. You'd have to machine or sand it.


Careful. ₄Be compounds are not your friend. Do not breathe or touch ANY beryllium dust - ever - at all.

If you're doing anything with it wear gloves; if you even might snap or machine it, you need to work in a fume chamber.

I read the Beryllium oxide page and found this interesting note:

   Formation of BeO from beryllium and oxygen releases the highest energy per 
   mass of reactants for any chemical reaction, close to 24 MJ/kg [1]
and this comment would be incomplete w/o sharing the findings of my wikipedia browsing which lead to making plasma in microwaves with grapes. https://www.youtube.com/watch?v=RwTjsRt0Fzo

[1] http://en.wikipedia.org/wiki/Beryllium_oxide#Safety

All roads lead to Rome.

I assume this article was posted because it was mentioned in XKCD[0] , which also ends on the grape plasma tangent.

[0]: https://what-if.xkcd.com/131/

When I was 12 I disassembled a microwave, unplugged from the wall, and got electrocuted. Not the visible kind like from static or from an outlet, but... I don't know how to describe it. Inside was a boxed case the size of a Kleenex cube, and my hand, palm side, just got sucked right on it like a magnet and bam I nearly passed out and fell off the chair. That was the end of playing with microwaves for me.

I just tried this with papad(ams) and this is what it looks like at 30 seconds: http://i.imgur.com/oclJIS9.jpg

I'm guessing 30 seconds is too much for these. (Although you can kind of see that my hotspots match #1 in the original article)

Experiment replication: one of the core requirements of scientific exploration.

Hooray science!

All these microwaves just need a more complex 'plate spinner' that actually translates the rotating plate across field lines. Kind of like a spirograph... http://i1216.photobucket.com/albums/dd371/benice_chen/hypo_h...

edit: nevermind, didn't realize they kept the 'plate spinners' on during the experiment. The rings in the appalam are artifacts from rotating an anti-node through the food. would have to do something different to get equal heating using ~two points vs. a line

Like a slow-speed random orbit sander? :) [1] Some of the dead areas looked too big for even that to help, and it would mean the maximum plate size would be smaller. Hmm...

OK, I'm going to say that the right answer is to move the microwave source linearly (or change how it's aimed? Or otherwise change its focus) at a frequency that would maximize even coverage of the heating area based on the rotation speed of the turntable.

Another (more limited) possibility is a way to mount a fixed spoon that could stir soup or other appropriate liquids while the bowl turned.

[1] https://en.wikipedia.org/wiki/Random_orbital_sander

Many microwaves do something similar - they have a spinning "fan" that's designed to perturb the standing wave pattern.

This is actually a fun way to measure the speed of light. You can measure the wavelength by looking at the distance between the bubbles. That plus the operating frequency of the microwave will give you the phase velocity.

I got rid of mine several years ago and have never once found myself thinking 'gee, I wish I still had a microwave.' You know what takes up less space, saves money, and provides constant utility, which most American kitchens don't have? An electric kettle. The most appliance-happy country on earth (except maybe Japan) and you still boil water on the stove like it's 1815.

Electric kettle? Having an Asian wife, I have learned there is an even better choice, a countertop hot water boiler. It boils the water and then keeps it hot in a super insulated container so the energy use is really low and you always have hot water ready for tea, so you don't have to wait!

We unplugged it once to take to an ice rink and it was still hot hours later.

Funny, my wife's Asian too and I know the exact thing you mean. We like being able to tote the kettle around rather than having the bring the container to it, though. I agree it's more energy efficient.

You can fill the kettle from the boiler. :)

Since realizing most people only have coffee makers and microwaves and are missing out on tools to simplify making great tea, I've made it a habit of giving out airports (dewar flask pump liquid dispensers) as gifts to everyone I know along with some tea-making utilities, like the IngenuiTEA. Water stays piping hot all day, no power needed beyond the initial boil.

Also, am East Asian, can verify: it's pretty uncommon to find a household without a rice cooker, a portable butane grill, or a Zojirushi.

So, when heating up leftovers, you have to clean up an extra pot. That is what the microwave does for me. (That said, I also love my kettle.)

I have a toaster oven for that, but since I cook 6 days out of the week unless I've very busy it's that big a deal. I got sick of the uneven heating and other well-known microwave problems and realized the only things I ever used it for were soup and popcorn, both of which are just as easy to do in a pot.

I've heard that electric kettles don't work as well in the US as in (say) England because our mains voltage is much lower -- and I guess a transformer would be too bulky.

I think this is probably true - in the UK (and EU) our kettles are 3 kW, maxing out our 230 V / 13 A plug/sockets.

American plugs always seemed relatively anaemic (and scary dangerous - where are the switches? where is the Earth? though the EU are also typically unswitched), though you do get to have less bulky mobile phone chargers as a result!

> (and scary dangerous - where are the switches? where is the Earth? though the EU are also typically unswitched)

well the bottom prong on a cord is the ground and anything that is not a wallwort is polarized nowadays so that the neutral and hot are always on the right wire.

by switched you mean it has a fuse in the plug? if so that's not something that america does. we have 15A circuits going to different parts of the house and if there is a possibility of water immersion there will be a GFCI circuit breaker or outlet installed to protect all downstream outlets. overall it works well enough that there aren't a massive number of deaths caused by it. usually you have do something exceptional to be electrocuted.

edit: the kettle I have is 1500 Watts and at 120 volts it's ~12A of current.

UK wall sockets tend to have physical switches. Here's a pic.


Kitchen and dining room circuits are required to be 20 A and GFCI in the US so you could up the wattage if need be. I doubt such a thing exists, though.

They are NOW required to be that, but a lot of legacy circuits are still 15A, and some even don't have GFCI (GFCI only became a requirement in the late 70s/early 80s in the kitchen, bathroom, and anywhere else that can conceivably be near water.

This has spread to AFCI (arc fault instead of ground fault) being put in every bedroom as a requirement as well.

If your house doesn't have GFCI and AFCI everywhere, they're required, you proobably should start retrofitting your sockets.

All of that said, you can use temporary use 1800W devices on 15A legally without tripping the breaker.

What is "scary dangerous" about a switch in the kettle that isn't about a switch at the socket?

That wall sockets are typically in places that won't get wet and kettles are.

It has absolutely nothing to do with use of transformers. Sockets in US and in UK are fused at approximately 13Amps for safety reasons. And 110V at 13amps is 1430W, while 230V at 13 amps is 2990W. You can make a kettle which uses only 1430W of power, but it would take much longer to boil water than a 3kW kettle would. You could raise the voltage to any number you like,but if the socket is fused at 13A you are not going to draw any more power out.

Not sure about the UK, but most Europeans circuits are rated and protected for 16 amps, not 13. That's ~3.5kW at 220V.

I've got an electric kettle (glass) that will boil 1.7L in about 4 minutes. It even shuts off it self off when the water boils. Works very well, not bulky at all. It is this one: http://www.amazon.com/Hamilton-Beach-40865-Electric-1-7-Lite...

They make 1800W kettles in the US. My 1500W kettle boils 8 cups of fridge-cold water in about 4 minutes.

They still work much better than a stovetop kettle or heating water in the microwave

What are you doing with all this boiled water?

Letting it cool down so I can have the thrill of boiling it again.

Seriously, tea, coffee (15-20 cups in a typical day, between two of us), plus cooking. It's often faster to boil water in the kettle and then pour it into a pot and switch on the gas than to boil it from cold in the pot.

tea and/or coffee

A kettle plus a toaster oven strictly dominates microwaves and toasters, particularly for things like reheating pizza or cooking chicken breasts. Toaster ovens also get hot much quicker than an oven, making them far more convenient to use.

Recently moved into a house without a microwave, but we do have a toaster oven, so it evens out. I often wish I had a teeny tiny microwave to melt a stick of butter quickly though.

Really? Is that true?

Or boil in our Keurig machines.

My microwave has a feature that when you press the "Start" button without entering a time, it just runs for 30 seconds on high.

One time I hit the start button and it started running based on the value of the clock (e.g. it was 4:23pm and the oven kicked on and counted down from 4 minutes and 23 seconds).

I suppose it could have been a weird coincidence, but my partner is very strict about leaving "unused time" on the microwave and obsessively hits the Clear button. Plus it seems unlikely that there would be that much unused time left (it's usually a few seconds), or that I happened to use the microwave exactly when the unused time synced up with the clock.

> but my partner is very strict about leaving "unused time" on the microwave and obsessively hits the Clear button.

The same here. She gets really mad about that. I can't really blame her, since I am am just the same about a bunch of other stuff.

I'm the one that hates it.

My microwave is my most visible clock in my apt (small sf sub). Whens its paused it doesnt show the time and just constantly blinks.

I make appalams in microwave too and have the same uneven cooking problem - putting them vertically seems to help. Here is a commercial product that says so too. https://www.papadumexpress.com

Most things your microwave aren't so flat though. Usually they have a bit of height which reduces the uneven heating somewhat.

But even for heating flat items (such as Naan) I haven't noticed any uneven heating with my giant Panasonic microwave.

xkcd had a nice what-if on this recently (http://what-if.xkcd.com/131/). He points to the way ice and water react to microwave radiation as one of the main culprits for uneven heating (of frozen stuff).

Previously I've seen similar tests done with oatmeal and sugar. Put oatmeal on plate and then sprinkle sugar on top. The purpose of the oatmeal is to insulate. The sugar should get brown on those places where the microwaves hit.

You can do the same with sliced cheese, I've heard.

If you microwave slices of smoked cheese (on baking paper), they become crispy crackers (lowcarb, even).

Or chocolate bars.

cheese is expensive, papadams are cheap

That seems like a useful thing for a small crowdsourcing site to. It's useful information to know before buying a microwave.

Cooking them in a pan of hot oil is so much more satisfying anyway. They double in size in about a second.

And taste much better.

Can't you just coat them lightly with oil? That ensures that they get heated up more evenly.

True, and fried appalams are tastier anyway.

What would happen if they raised the plate a few inches from the bottom? With this experiment they're only looking at a cross-section of the wave.

Receipt paper could serve the same heat-sensitive purpose and might be easier to find.

dry heat-sensitive paper won't work; microwaves work by resonating with water molecules to vibrate them and cause them to heat up.

Uhh... you think water is the only molecule with a dipole moment?

of course not. you're right, i should be more general an say any electric dipole, but what i was trying to point out was that microwaves don't directly radiate heat and instead vibrate/rotate certain molecules. so, heat sensitive paper isn't going to work, unless there's some that have dye that will interact with a microwave.

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