will it take off?

[patrick_g]

Spidy and Egon, Some (most) of the microwave builders retained the duty cycle proportioning they had on lower power machines when going to more powerful outputs and at say 1200 watts of cooking power you can overdo stuff before the off portioin of the cycle is reached.

I am not aware of any ovens that turn the power down, unfortunately. They all seem to run full power and duty cycle time average from 10% to 100% in 10% steps. The nicest thing under this scheme is a unit that uses finer steps, i.e. shorter "chunks" of time. Still you get 10-100% in 100% increments but each "on" cycle is smaller so the averaging is smoother and the overcooking is way less. Still less than perfect but better.

Can't guarantee you wont pop a bean though if you aren't using a rotating platform and even then sopmetimes...

Luckilly I like beans that have been popped like puffed rice.

Pat

 

[daTeacha]

Well phooey, to coin a phrase. I thought I had posted a somewhat abbreviated reply to the freezing water experiment, but it somehow got lost prior to actually showing up here. In the interim between that posting and now, you guys have pretty well covered all the things I said and moved on to microwaves, so we just need to wait for the followup experiments.

On microwaves, we have an odd thing going with ours. It seems that often when my wife puts things in there and starts it she gets humming, buzzing, and sparks. I've never had it happen. I think it may relate to the size of the item she puts in the oven, and asked her to note not only portion size but also height. She says it seems to happen when the item is physically short, not sticking up above the plate much. Any ideas about what's going on?

 

[rback33]

Well phooey, to coin a phrase. I thought I had posted a somewhat abbreviated reply to the freezing water experiment, but it somehow got lost prior to actually showing up here. In the interim between that posting and now, you guys have pretty well covered all the things I said and moved on to microwaves, so we just need to wait for the followup experiments.

On microwaves, we have an odd thing going with ours. It seems that often when my wife puts things in there and starts it she gets humming, buzzing, and sparks. I've never had it happen. I think it may relate to the size of the item she puts in the oven, and asked her to note not only portion size but also height. She says it seems to happen when the item is physically short, not sticking up above the plate much. Any ideas about what's going on?

Sounds exactly like what happens if you microwave metal.... don't ask how I know Does it stink like crazy afterwards? Maybe she using a new plate that has some special metal inlay she doesn't know about? I actually put a metal bowl in once... not just a fork or something...

 

[BTDT]

I know if I use cheap styrofoam plate it seems to crackle like rice crispies, don't have a clue why.

 

[patrick_g]

There was a ceramic cup with a metal ring thing in the little finger hole (not visible) but the metal sure reacted with the microwave energy. Suspected the heating couild have been caused by a metal reinforcement in the porcelain and confirmed with a magnet. Was a surprise to have the finger hole a lot hotter than the reheated tea.

Sparks in the microwave oven are almost always due to metal or a fair conductor. Dishes with metallic glazes or gold or silver stripes (typically around the outside edge or such. The microwave energy is just an electromagnetic field at microwave freqs, a simple radar freq transmitter where the food is placed in the "near field" of the transmitting "antenna" (feed horn.) Any fair conductor in the oven cavity, especially metal acts like an antenna and given the the potential for high VSWR (Voltage Standing Wave Ratio) the voltages can be quite high, enough to cause arcs.

So called "Browning Pans" have a layer of a medium conductive material such as vapor deposited metal "fog" on them which conducts enough to take in plenty of microwave energy and has high enough resistance to convert that energy into heat so the surface of the browning accessory gets really hot.

I had a microwave that had a metal rack in the middle. Very handy. The rack would fit into the oven and could be removed, turned around and fit that way too. Unfortunately the one way placed the rack too close to a "hot spot" in the microwave field and the rack would arc over to the back of the oven cavity, burning the plastic a bit and smelled pretty rank. Solution, turn it back around. 50/50 chance of taking it out of the dishwasher and putting it in the RIGHT way.

A test that may be interesting is to put an empty bowl or plate in the microwave oven and also at the same time a glass filled about 1/2 way with water and a similar empty glass. Run the microwave for a few min, stopping when you see signs that the water is really hot (no need to boil it.) Carefully remove the test subject (empty bowl, plate, or whatever) If the test subject is much warmer than the empty glass then the test subject isn't a very good candidate for using in the microwave since it is absorbing a significant quantiy of the microwaves. I have had some test subjects get too hot to comfortably handle and had to rule them as off limits for the microwave.

Pat

 

[daTeacha]

This particular micowave apparently has the magnetotron located in the side, behind a removable plate of some kind. The arcing seems to emanate from the surface of this plate, which has scorch marks on it that look like spots left by a mini welder.

I haven't asked her to check which dish she is using when it happens. The everyday eating plates are cheapo's made in China, so there could be metallic impurities in the clays used. Some of those plates do get pretty hot when heating food in them, but the sparking only seems to happen when the quantities are small or low. I don't think the rotating feature would impact the phenomenon, but this one does rotate the food as it runs.

 

[patrick_g]

Some of those plates do get pretty hot when heating food in them, but the sparking only seems to happen when the quantities are small or low.

That's MAGNETRON vice magnetotron.

If you try the glass of water and empty plate test and the plates get pretty hot by the time the water starts to boil then the plates are definitely not the best for the microwave.

The low food issue seems to be consistent with the plates that absorb too much microwave and are lilely to contain conductive elements that cause VSWR problems for the oven.

The microwave energy would have to penetrate the food in the plate to get to the plate. More food would mean less microwave energy getting to the plate.

Try the empty plate and half a glass of water test and report the results. If the plate gets hot at least in some places then it is a bad choice for using in a microwave and over time could damage the oven (and burn your fingers?)

On the other hand I have seen new microwaves for under $40 so maybe you'd rather use the cheap plates and take your chances with microwave longivity.

Pat

 

[daTeacha]

Those same plates get hotter under some foods than others, even when heated at the same time. Reheating rice gets the plate a lot hotter than the chicken on the same plate.

 

[patrick_g]

Da Teacha, Well of course they do. Different foods have different interactions with the microwave energy. Stated in science terms... the exticition coeficient of foods varies in a complex manner dependent on among other things the water and fat content of the foods. The depth of penetration of the microwave enery is a decreasing exponential in a homogenous medium.

A large ham with the outer fat rind trimmed away will not have microwaves penetrate deep into the center and the center will cook because the ourter layers are hot. With the thick ouiter fat rind left in place the fat will be heated tremendously and the microwaves will not penetrate it very much.

The statement that microwaves cook from the inside out is not always precisely true. It is true in some instances. If you put a marshmallow in a microwave it will be charred to carbon in parts of the center by the time you see any visible evidence of cooking on the outside. I discovered that roasting/toasting marshmallows in the microwave was too delicate of a control problem for the course power settings and duty cycle time intervals or my limited culinary skills.

Rice has little fat and lets microwave energy pass through a fair layer with not so much absorbtion as you'd get with fat meat. Chicken absorbs microwave enery more readily than rice but whether it gets hotter faster than rice is a calorimetry problem relating to several factors. IF the chicken and rice were "MAGICALLY" suspended inthe center of the oven the chicken would get a lot more energy than the rice.. The hot chicken can heat the plate it is sitting on but probably not aas fast as the microwave energy will heat a "BAD" plate under the rice which lets eneergy pass through.

Microwave ovens run at about 2.45 GigaHertz which is selected to interact with the polar water molecules. I don't recommend you try this but if you put a half a glass of gasoline in the microwave it would not heat well at all since its molecules are long carbon chains and are not polar and are not resonant at 2.45 GHz.

If you like microwave experiments you can put a burned out tungsten light bulb in the microwave and it will light up when the oven is turned on. At least it will light up prior to exploding. Please don't do this at home kids without trained adult supervision, ANSI approved safety glasses and face shield and viewed preferably over CCTV!

Pat

 

[daTeacha]

How serious is the explosion, really? I would guess the oven door would contain it. Then again, the internet video clips of the diet Coke bottles becoming bottle rockets after adding some Mentos were pretty impressive.

Around here, "Amish Bombs" are pretty popular with the mailbox destroying set. A little HCl from the grocery store, a little aluminum foil, an empty 2 liter, and you're all set.

 

[patrick_g]

da Teacha, It was an "err on the side of safety" thing, a disclaimer like on MYTH BUSTERS, don't try this at home kids. If you blow yourself up, I'm in the clear.

A glass of super heated water is a danger in a microwave because it might turn to steam at any given moment, say just after you open the door. Even just a few oz of water turning to steam all at once is not good to be close to and if only half turns to steam the other half is sprayed out in 4 pi steradians, a scalding danger.

That little window in your oven is supposed to be transparent to microwaves. The emissions of microwave energy is right behind the window. If the oven cavity provides a poorly matched load to the output cirsuits you get a high VSWR which can result in pretty high voltages at microwave freqs. This is most likely what caused the arcing at the window. The material has been partially carbonized (black burn markis) and is not so transparent to microwaves now. When you put your "not really good to use in microwave" dishes in there with not enough food to take up the energy, you may get additional arcing and degradation of the little window. You could replace the window with a microwage transparent cover. If you operate the oven with the little window removed, then spatter, steam, and debris will likely get in where it shouldn't.

If you retire the oven while it still has a good power supply you have the makings of a good welder if yo want a fun DIY project.

Pat

 

[SPYDERLK]

The amt of water that turns to steam is miniscule due to the extreme quantity of heat that the overheated water must give up to the portion that changes state in order to finance the change. The amount that can change [in grams] is: (sample mass)/540. Y=sampleT-100C, at sea level. I doubt that even extremely pure unpressurized water will go above 105C without boiling unless pains are taken to keep it absolutely still. That means a pint sample would only be able to elevate less than 1/5 ounce to steam energy. A high expansion ratio tho - enuf to blow around a lot of hot water.
Larry

 

[patrick_g]

SPYDY, How much boiling water blasted into your face does it take before it is an unwelcome event? I don't wish to pull along side and compare dorsal fin heights or quibble over explosive forces but your prognostications may underestimate the effect:

*********************************************
In the popular Discovery Channel show Mythbusters, an experiment was conducted where distilled water was placed in a microwave oven for several minutes long enough to boil, but no convection (boiling bubbles) took place. When a contaminant (a sugar cube) was added to the superheated water, it had an explosive effect. However, this effect also occurs with normal tap water, as macroscopic impurities (especially those which carry air bubbles) are needed for boiling to start. The dissolved impurities in tap water are not enough to inhibit the superheating.
***********************************************

Of course the MB bunch only demonstrated one sceanario of many possible.

For me, the risk is great enough to indicate caution. Your mileage may vary and your burn and trauma unit may be a shorter drive.

Pat

 

[SPYDERLK]

Pat, I have successfuly resisted not answering. In actuality, the objective physics stated in my post covers all that you have brought up. I suppose that there is a danger of remaining objective with some,-Idontthinkyou-, in that it may be missed that it takes very little explosive energy to throw a liquid a small distance. The properties of this liquid promote its intimacy with the skin. Add to this factor its T and its high specific heat and you have a problem. You are not going to be burned any worse by the subjectivity of the surprise. Indeed the tendency of the water to spray in the explosive case, rather than travel en mass as if thrown, will dilute the effect, and result in a more pleasant burn. I dont need to try this at home. I just know it. The need for nucleation sites to catalyze change of state reactions is also a real concept to me. Things just have to start somewhere!
Larry

 

[daTeacha]

I'm wondering at what point a burn becomes "more pleasant"!

I took the kids on field trip to a coal fired power plant once a few years ago. The tour guide made a pretty big impression by explaining to them that a jet of dry steam at about 1500 degrees coming from a pinhole leak in one of their steam lines would make a very nice tool to remove fingers from your hand without leaving any blood behind since it would cauterize the wound as it cut the fingers off.

As for welders, Pat, I'll just stick with my Lincoln TM500-500. It weighs 750 lb, will run on 220, 440, and maybe 880 v. It has a 60% duty cycle at 500 amps, so I could basically burn through 1/4 rod as fast as I could load it all day long and not stress the thing. It works as a crude plasma cutter by simply turning it up a bit from the normal 100 +/- amps I use and running small diameter rod. The best thing about it is that it was free.

 

[patrick_g]

SPYDY, OK.

daTeacha, Terrific welder at an even better price. I envy your good fortune. However, for some of us there is a perceived value in not having to rent a crane to move a welder or risk a hernia or worse trying to move it. My welders are way less powerful. I have a wire feed Lincoln "Lunchbox" that is made to handle shielding gas but I only use flux cored wire. I also have a Lincoln "Tombstone" ac/dc/dc reverse stick welder that is heavy enough that I put it on a hand truck type carrier. I sometimes wish I had a more powerful MIG but my little 120VAC unit does over 90% of what I need and the stick will handle the rest. It is handy since you can always find a 120VAC outlet.

I did splurge a bit on my plasma cutter. I went with a Hypertherm 20-40 amp unit and I really like it. I am nearly useless with an O-A cutting torch but can do pretty credible stuff with the plasma rig.

There are some real neat DIY welders that can be done from microwave power supplies. Maybe one of your "little geniuses" would enjoy a project like that. There are refs on the net.

I too was somewhat puzzled by a consideration for varying degrees of pleasantness of scaldings. I guess it would be a simple LESS IS BETTER thing. If all things are relative then being scalded less is better and by extension more pleasant.

You can turn up the heat for me if you want. We have had an arctic draft blow down here and give us an ice storm. One day it was in the 60's and the next it is an ice storm and in the 20's with everything ice coated. The countryside is beautiful but the roads are nearly 100% ice coated. I don't mind driving on ice when there is very little traffic because the danger isn't what my equipment or I will do but what others may do to me.

Pat

 

[rback33]

Hey Pat.... I would made you a deal... I woulda kept the cold air up here is you keot the moisture down there.... we got sleet not ice where I am at so the roads are really just snowpacked.

 

[daTeacha]

I just couldn't pass up the welder at the price, especially since I didn't have one at the time. The portability issue just hasn't come up -- I do my welding in the shop or just outside the door. Field repairs are a non-issue so far. It's an old fashioned stick welder, no wire feed, no gas, etc. It was originally used in a Terex plant near where my BIL lives, with about 6 guys using one machine to assemble earth movers, running a common ground strap and each guy with his own stinger. Yeah, it's a bit much for what I do, but again, at the price I can't complain too much.

 

[patrick_g]

Hey Pat.... we got sleet not ice where I am at so the roads are really just snowpacked.

I took the Prius into OKC for our free oil change/tire rotation (Free changes as long as we own it.) For variety I went up to Shawnee and took I-40 which was essentially completely clear. In one area west bound traffic got congested and at one point slowed to 15 for a couple hundred yards. There was an 18 wheeler on the shoulder facing the wrong way, and a HP on scene. A little later there was a 10 wheel dump truck (looked to be full of sand) upside down in the median. except fot that, traffic was 70+ but most businesses had ice rinks for parking. Ice rinks with gently rolling hills and grades. I went to one of the Scottish places for lunch (Mc D for a chicken sandwich) and when I was leaving there were a few cars parked "nose in" to the curb on a slight slope who couldn't back out. One guy in a pickup was especially fun to watch, must have hit 80-90 MPH on his speedo following the concept that if you press the accelerator and it doesn't go good enough to suit you then press it more. The Prius backed out just fine from immediately uphill of the truck and I got out of there before BAD things happened.

Coming home the other day froma trip to pick up iron materials for a project the secondary highways near Konawa were all ice. I was a tad late getting hoime and my wife was worried. I was late because I stopped to pull folks oiut of the ditch. One of the scenes was particularly entertaining.

A couple in a SUV were being pushed by hand by 4 guys who stopped to help. They were straining to push the SUV INTO THE DITCH! Their thought was they woiuld build up speed on the downhill and then the driver would make it back up to the road. Afterall they colidn't push it back up on the road so it was supposedly better than no plan at all. I just sat and watched for a few seconds and then rolled my window down and asked if they wanted the SUV in the ditch or on the road. They explained the plan (I kept from laughing and shot a 180 in prep for using my 12,000 winch on the front of the 1 ton Dodge-Cummins. Winch was totally ice encrusted and woild have been a hassle to use, possible but a hassle. I grabbed a couple HD racheting cargo straps and they hooked me up and I backed slowly and put the SUV back on the road. I didn't ask why with 4X4 they couldn't just ease it out.

Although driving on ice is more dangerous I have the requisite skills and I know my equipment. What I can't control is the other folks out there who go 30MPH right up to a stop and then slide through the intersection at 30MPH, maybe dong a 180 or 360 on the way if one of the tires caught a bit of traction hitting a dry patch. I have banked turns in my driveway. If you break traction while going too slow you could slide off the drive and go down the hill. If you go too fast and break traction you could go off the drive and go right into the adjacent pond. Within the band of allowable speeds there is no problem.

So far my closest call was coming to the garage too fast. You have to make a 135 degree turn while starting down a mild slope to the bottom of the apron and then up hill slightly on the apron into the garage. IT was glaze ice with a film of water on top (very slippery) and I was in a nice 4 wheel drift with slight braking. If I used more brakes it opened up my turn and made me head for the location where I really didn't want an impromptu door. I had to ease in a little throttle so I could steer the front wheels better (4X4 Dakota) and got the front headed throgh the garage door but at a 10-15 degree angle. I delayed turning the wheel as long as I could considering the JUNK in the garage and then straightened it out and stopped. Luckily the floor was dry. I credit 50% skill and 50% pure dumb luck that I didn't mess anything up.

I have a new icy garage apron approach policy:
DEAD SLOW on the 135 degree turn until lined up on the entry.

Pat

 

[patrick_g]

I just couldn't pass up the welder at the price...Yeah, it's a bit much for what I do, but again, at the price I can't complain too much.

I do about 1/4 of my welding in the field using the MIG and flux cored wire. My genset handles it just fine. I had thought of getting a combo welder/genset but I don't do that much HD welding afield. What I am considering now is if I would use my plasma cutter enough in the field to warrant getting a gas powered compressor or a more powerful generator that can run the plasma and an electric compressor at the same time. A fringe benefit of the larger generator is it could be a better backup generator for the house. So far we have dodged the bullets of this ice storm and only had one brief power outage of about a second and a half.

Pat