# Microwave Ovens



## Anonymous (Mar 2, 2008)

These are a good source of copper from the power transformer and the magnetron, silver from the limit switches and the pads from the touch control panel and ribbon cable.

Plus a few pounds of iron to be sold as scrap. some ovens are lined with stainless steel which should be sold separately for more money.

I use a chop saw to slice the copper coil once, on the power transformer before incineration.

I have found a few magnetron's which have been soldered together with gold, most have been assembled using silver solder - possibly with a bit of gold as this type of alloy solder is used in hight temperature applications.

As my experiments progress I will make my information available regarding this solder alloy. I welcome comments on this alloy, if anyone has knowledge of its makeup.

The capacitor tank can hold a deadly charge for days maybe weeks so caution should be heeded when dismantling discarded electronic equipment.

*Capacitor Discharge Technique*

The technique I recommend is to use a high wattage resistor of about 5 to 50 ohms/V of the working voltage of the capacitor. This isn't critical - a bit more or less will be fine but will affect the time it takes to fully discharge the capacitor. The use of a current limiting resistor will prevent the arc-welding associated with screwdriver discharge but will have a short enough time constant so that the capacitor will drop to a low voltage in at most a few seconds (dependent of course on the RC time constant and its original voltage).

Then check with a voltmeter to be double sure. Better yet, monitor while discharging (monitoring is not needed for the CRT - discharge is nearly instantaneous even with multi-M ohm resistor).

Obviously, make sure that you are well insulated!

* For the main capacitors in a switching power supply, TV, or monitor, which might be 400 uF at 350 V, a 2 K ohm 25 W resistor would be suitable. RC=.8 second. 5RC=4 seconds. A lower wattage resistor (compared to that calculated from V^^2 / R) can be used since the total energy stored in the capacitor is not that great.

* For the CRT, use a high wattage (not for power but to hold off the high voltage which could jump across a tiny 1/4 watt job) resistor of a 1 to 10 M ohms discharged to the chassis ground connected to the outside of the CRT - NOT SIGNAL GROUND ON THE MAIN BOARD as you may damage sensitive circuitry. The time constant is very short - a ms or so. However, repeat a few times to be sure. (Using a shorting clip lead may not be a bad idea as well while working on the equipment - there have been too many stories of painful experiences from charge developing for whatever reasons ready to bite when the HV lead is reconnected.) Note that if you are touching the little board on the neck of the CRT, you may want to discharge the HV even if you are not disconnecting the fat red wire - the focus and screen (G2) voltages on that board are derived from the CRT HV.

* For the high voltage capacitor in a microwave oven, use a 100 K ohm 25 W (or larger resistor with a clip lead to the metal chassis. The reason to use a large (high wattage) resistor is again not so much power dissipation as voltage holdoff. You don't want the HV zapping across the terminals of the resistor.

Clip the ground wire to an unpainted spot on the chassis. Use the discharge probe on each side of the capacitor in turn for a second or two. Since the time constant RC is about 0.1 second, this should drain the charge quickly and safely.

Then, confirm with a WELL INSULATED screwdriver across the capacitor terminals. If there is a big spark, you will know that somehow, your original attempt was less than entirely successful. At least there will be no danger.

DO NOT use a DMM for this unless you have a proper high voltage probe. If your discharging did not work, you may blow everything - including yourself. 

The discharge tool and circuit described in the next two sections can be used to provide a visual indication of polarity and charge for TV, monitor, SMPS, power supply filter capacitors and small electronic flash energy storage capacitors, and microwave oven high voltage capacitors.

Reasons to use a resistor and not a screwdriver to discharge capacitors:

1. It will not destroy screwdrivers and capacitor terminals.

2. It will not damage the capacitor (due to the current pulse).

3. It will reduce your spouse's stress level in not having to hear those scary snaps and crackles. 

Capacitor Discharge Tool
A suitable discharge tool for each of these applications can be made as quite easily. The capacitor discharge indicator circuit described below can be built into this tool to provide a visual display of polarity and charge (not really needed for CRTs as the discharge time constant is virtually instantaneous even with a muli-M ohm resistor).

* Solder one end of the appropriate size resistor (for your application) along with the indicator circuit (if desired) to a well insulated clip lead about 2-3 feet long. For safety reasons, these connections must be properly soldered - not just wrapped.

* Solder the other end of the resistor (and discharge circuit) to a well insulated contact point such as a 2 inch length of bare #14 copper wire mounted on the end of a 2 foot piece of PVC or Plexiglas rod which will act as an extension handle.

* Secure everything to the insulating rod with some plastic electrical tape.

This discharge tool will keep you safely clear of the danger area. 

Again, always double check with a reliable voltmeter or by shorting with an insulated screwdriver!

*A word of caution when working with magnetron's *

For those contemplating salvaging copper from microwave magnetron's, please read this snip from wikapedia concerning the ceramic insulator.

Some magnetrons have ceramic insulators with a bit of beryllium oxide (beryllia) added—these ceramics often appear somewhat pink or purple-colored.

Note that beryllium oxide is white (see article beryllium oxide), so relying on the color to identify its presence would be unwise.

The beryllium in this is a serious chemical hazard if crushed and inhaled, or otherwise ingested. Single or chronic exposure can lead to berylliosis, a condition that is not curable.

In addition, beryllia is listed as a confirmed human carcinogen by the IARC; therefore, broken ceramic insulators or magnetrons should not be directly handled.


----------



## Anonymous (Mar 2, 2008)

Besides the magnetron having some copper and silver value there are potential health hazards in dealing with the ceramic insulator.

My previous post states that some insulators contain a bit of beryllium oxide (beryllia) added—these ceramics often appear somewhat pink or purple-colored. As a precautionary measure I think one should treat each ceramic as a danger to ones health.

I use a metal lathe to part off the steel which has the ceramic embedded at the ends. Once this has been accomplished you now have a nice chunk of copper.

I have found a gold sometimes silver colored wire mesh which has been formed into a type of shield, resembling a washer.

I have had some of these shields boiling in hot HCL for a couple of hours the only noticeable thing is there has been a color change from gold to silver. No metal has been oxidized.

The shield is non magnetic, and seem to be impervious to hot HCL, does anyone have any idea what they're made from.

The mesh on the far right hand side has been in hot HCL for a couple of hours. The two on the left untouched, with the exception the center one has been un coiled.


----------



## teabone (Mar 2, 2008)

Looks like brass .


----------



## starzfan0211 (Mar 3, 2008)

Gutavus,

You stated that the capacitors can hold a charge for days or weeks. Is there a rule of thumb that can be used to safely assume that it has discharged over time?


----------



## Gotrek (Mar 3, 2008)

starzfan0211 said:


> Gutavus,
> 
> You stated that the capacitors can hold a charge for days or weeks. Is there a rule of thumb that can be used to safely assume that it has discharged over time?



Years Forever. Some early batteries which were really more capacitors still held charges some 100's of years later.

I do electronic repair I always test/discharge my capacitors before removing. Static electricity from storing in a dry place can charge capacitors.

I posted ways to dischard a fly back from a Television the same steps can be used for large capacitors.


----------



## starzfan0211 (Mar 3, 2008)

Ok. No chances then. I have an old microwave that died and I am going to tear it apart in my "spare time". But I was mainly wondering for anything in a computer power supply because we are taking those apart for the aluminum and copper.


----------



## Anonymous (Mar 3, 2008)

starzfan0211 said:


> Gutavus,
> 
> You stated that the capacitors can hold a charge for days or weeks. Is there a rule of thumb that can be used to safely assume that it has discharged over time?



As a precautionary measure for those new to the trade AKA hobby, I listed the warning with the information on how to discharge a capacitor.

Personally I do not believe a capacitor is capable of holding a charge for 100 years this is a stretch of the imagination, and would like to see more posters backing up their statements with a reliable reference source.

It only takes a moment to google a subject.

Another thing one should be aware of there is still a lot of older equipment with capacitors and large oil filled transformers laying about that could contain pcb's treat each find as suspect.


----------



## Gotrek (Mar 3, 2008)

gustavus said:


> Personally I do not believe a capacitor is capable of holding a charge for 100 years this is a stretch of the imagination, and would like to see more posters backing up their statements with a reliable reference source.
> 
> .




I can vouch a flyback retains a charge approx 8years. Enough juice to make me cry. A regular high voltage Cap probably not but why risk it. Get a multimeter test it and giver. Low voltage stuff no big deal just keep your left hand in your pocket 

Don't forget static electricity can charge a cap.


----------



## Anonymous (Mar 3, 2008)

does the humidity in the air allow capacitors to discharge given enough time?


----------



## Gotrek (Mar 4, 2008)

I don't know but I would imagine it would. But it only takes 2 seconds to test a capacitor so why risk it right.


----------



## Anonymous (Mar 4, 2008)

Gotrek said:


> I don't know but I would imagine it would. But it only takes 2 seconds to test a capacitor so why risk it right.


Goteck good point.

Its a know fact CAPACITORS can KILL YOU. How long they hold a charge is not the important factor. HOW TO HANDLE THEM IS.


----------



## Gotrek (Mar 4, 2008)

gustavus said:


> Gotrek said:
> 
> 
> > I don't know but I would imagine it would. But it only takes 2 seconds to test a capacitor so why risk it right.
> ...



Exactly. It only takes 60 mA across the heart to throw off it's rythm or stop it.


----------



## starzfan0211 (Mar 4, 2008)

Wow. It seems like I really opened a can of worms here :lol: . Having never really dealt with things like that before, I am going to make sure and take the utmost care and respect while taking things apart. 

I appreciate everyone's advice.


----------



## Anonymous (Mar 4, 2008)

I always discharge them, I just did not know how long they would hold a charge and if the charge would bleed off. 

I agree exspecially with TV and Micro wave capacitors you better play it safe and take no chances.


----------



## Anonymous (Mar 5, 2008)

The picture shows the copper from a disassembled microwave magnetron, an end ring has been soldered onto the cylinder at each end of the segments. You can not see the parting line from the picture.

Each segment in the center plus the two silver rings and each end are also soldered into the cylinder.

Those of you that have taken ovens apart have noted the outside copper has been subject to heat by the oxidization present.

If you're wondering why the inside of the cylinder remains nice and shinny, this is because the magnetron is a vacuum tube, absent of oxygen.

Research tells me silver solder used in high temperature applications could be alloyed with gold. So the possibility exits.

I'm currently working on a parting cell to collect the silver - gold alloy values.


----------



## banjags (Mar 5, 2008)

how big is the piece in the picture. Does it make it worth while to take apart microwaves for copper/silver and scrap metal?


----------



## Platdigger (Mar 5, 2008)

So what is that? Like 2 or 3 pounds of copper maybe?
Then of course there is the transformer right?
Randy


----------



## hoardpm (Apr 11, 2009)

You stated that there is toxic ceramic material around the magnatron. So how would you go about safely cracking open the magnatron to get the copper out?


----------



## Anonymous (Aug 27, 2009)

how about a picture of your distcharge tool a picture is worth a thousand words thanks in advance


----------



## Gotrek (Aug 31, 2009)

gembooney said:


> how about a picture of your distcharge tool a picture is worth a thousand words thanks in advance




You can build one yourself or buy one at any electronics hobby store 

Search for High voltage probe.





http://media.digikey.com/photos/BK%20Precision%20Photos/PR-28A.jpg


----------



## butcher (Sep 4, 2009)

for these type's of capacitors a srewdriver can be used to discharge them short them out, adding a jumper to capacitors for storing is a good idea, it is possible the can be charged latter just sitting around, rare but does happen, a capacitor -- well any two pieces of metal close to each other can be a capacitor, there are many types of capacitors , in the microwave an electrolytic , usually foil and a paste electrolyte, a capacitor when a voltage is applied instantly charges to the peak voltage , now it can hold that voltage, for very very long periods of time (how long depends on capacitors construction and its leakage),
some capacitors can hold charges that when discharged can look like lightning bolts, usually not deadly but would hurt somthin powerful, and like drowning in a teaspoon of water, it is possible to stop your heart if shocked at the right portion of the beat. some older capacitors used silver. a capacitor slowly bleeding through a resistor is the essence behind timmers, timeing can be changed by size's of capacitor or changing resistor size, capacitors are used in DC power supplys to remove the ripple or to flatten out or smooth the voltage,called filtering, they can be used to change the phase of voltage and current with a coil or inductor like in motors, when you tune in your old radio to your favorite station you are turning a dial on the capacitor. we used to charge them up and wire them to a friends chair :lol:


----------



## goldmankc (Jan 26, 2010)

I myself just throw the capaciters in a bucket of water. "Throw"


----------



## Barren Realms 007 (Jan 26, 2010)

goldmankc said:


> I myself just throw the capaciters in a bucket of water. "Throw"



What does this accomplish?


----------



## butcher (Jan 27, 2010)

water and electricity usually not a good mix,

well if your water is hard enough (lots of metal ions), they may eventually discharge, but my guess would be depending on the size of the capacitor and the resistance of the water it could take an extremely long time, more likely the capacitor would possibly leak and break down before it ever discharged,making a dangerous mess, electrolytic capacitors may contain an acid such as boric acid (or other acid) and aluminum foil,this in a bucket of water, with a charged capacitor is a bad idea.

use an insulated screw driver and short out leads (terminals) it may spark if large charged capacitor, this discharge's the capacitor, then you could jumper two terminals together for storing safely.


----------



## cpt_squish (May 21, 2010)

Thought I would give you my experience on the microwave ovens

I pulled so far 2 ovens to get the parts and transformer for a tesla coil (not finished but cool)
Our oven died last week and I pulled it all apart, and got approximately:
7-10kg steel (casing and shell and well as transformer core)
2kg copper (some of this was from a second transformer a had laying around, and 2 magnetrons)
silver mylar pad which I accidentally threw out (before I knew it was silver) - really shiny though
Didn't have any trouble with the capacitor - not sure what to do with it though!
The magnetrons also have 2 quite good donut magnets in them - with a bit of care they come out undamaged

The ceramic of the magnetron wasn't a problem I just hit it with a hammer on the edge of a steel plate, it broke up into quite large pieces and no dust.
The electronics contain several relays and transformers which also yeild more copper

Not sure this is economical but a pretty cool thing to pull apart and see how it looks.
Hope this helps anyone interested!


----------



## solar seeker (Nov 7, 2010)

On a realistic note on how long a capacitor can stay charged. I built a leyden jar capacitor using a large soda bottle and a bucket of water which I charged to 2KV using a lighting balast 
it held a startleing charge after a day and a half. On the other hand most CRT computer monitors discharge within 30 seconds thanks to bleed resistors however 2 to 3 days is not an unheard of ammount of time for a monitor to hold a painfully high voltage. Microwave ovens are also unlikely to hold a charge more than a few secconds unless the safety features are disabled in which case 3 days is a reasonable time alotment for the truely leathal voltages to be discharged. In spite of this it's far better to be safe than sorry which is why it's many times better to make damned sure that the capacitor is discharged and stays that way by shorting it out than it is to be killed or mamed by high voltages.


----------



## Claudie (May 15, 2011)

cpt_squish said:


> Thought I would give you my experience on the microwave ovens
> 
> I pulled so far 2 ovens to get the parts and transformer for a tesla coil (not finished but cool)
> Our oven died last week and I pulled it all apart, and got approximately:
> ...



The purple ceramic band on the Magnetron contains Beryllium oxide which is very toxic. It is NOT a good idea to just smash them.


----------



## alha (Jul 19, 2011)

I work in the appliance repair field, and the good news is that many mfg's are using self bleeding caps in current models. I myself use a large flat blade screwdriver with a big plastic handle to discharge them on units I work on, it's worked well for me, and very few I run into have a stored charge. I have a lot fewer worries about discharging caps than I do about doing voltage tests inside running units, where some of the voltages can be in the 1000's. Yippie! Fortunately, that doesn't happen very often, they are pretty easy to diagnose. I've been pulling the mag's apart for the donut magnets from time to time, but really hadn't thought about the copper in them. Have to watch out for the ceramic, though, as this was something I hadn't known about. You learn something new every day.

Oh, and one quick question about the forum, I can't seem to see the date and time each post was made. It seems to sort them properly, but I can't tell when they were made other than the last one which is stated on the main page of each section listing all the posts in order. Am I missing something? I went to my pref's section, but didn't see any setting regarding this. Thanks!


----------



## Harold_V (Jul 20, 2011)

alha said:


> Oh, and one quick question about the forum, I can't seem to see the date and time each post was made. It seems to sort them properly, but I can't tell when they were made other than the last one which is stated on the main page of each section listing all the posts in order. Am I missing something? I went to my pref's section, but didn't see any setting regarding this. Thanks!


Simple. Take a look at the top right hand side of this message. There's a post date stamped there. That's true of all posts. It says, in bold letters: *Posted:*
Do you see it now?

Harold


----------



## alha (Jul 20, 2011)

No, I didn't. But, the weird thing is, when I hit post a reply, and look at your reply to me below this box I am typing in, I see "by Harold_V on July 20th, 2011, 3:11 am" in the upper right of that box, but still not the word Posted before it. Strange, I know, but in the orig posts, I don't see any of it. I'm using IE right now, I will try using Firefox and see if that makes a difference. Huh. Gotta love computers, glad I got out of that field when I did


----------



## rasanders22 (Jul 20, 2011)

A little information about capacitors. The amount of energy stored that can be stored in cap is .5CV^2. C is the capacitance, the V is the voltage rating of the cap. And .5 is just 1/2. 

So for example the big capacitors they use on automotive stereo systems are 1 farad, 12 v capacitors. Using the formula above those big caps contain only 72 joules. Your typicaly cell phone battery has approx 10,000 joules. A gallon of gasoline has 1.3*10^8 joules. The typical capacitor you are going to find in consumer grade electronics is going to have less than 1 joule. 

Its not a lot of power but it can be delivered very quickly.


----------



## Harold_V (Jul 21, 2011)

alha said:


> No, I didn't. But, the weird thing is, when I hit post a reply, and look at your reply to me below this box I am typing in, I see "by Harold_V on July 20th, 2011, 3:11 am" in the upper right of that box, but still not the word Posted before it. Strange, I know, but in the orig posts, I don't see any of it. I'm using IE right now, I will try using Firefox and see if that makes a difference. Huh. Gotta love computers, glad I got out of that field when I did


I should have made mention. My board choice is subsilver2. If you use a different board display, you may not see the same thing. If you'd like to select a different board style, click the User Control Panel button on your screen, (top right corner of mine) then select Board Preferences. You can pick a board choice from the drop down menu. 

Harold


----------



## jeneje (Jul 21, 2011)

Hey all, just a note about the transformers, the steel caseing around the transformers is silcon steel. Silcon steel is rated as high grade steel and pays more at the scrap yard if have enough to sell, and providing they know the difference.

Kenneth


----------



## resabed01 (Jul 29, 2011)

I've scrapped several over the years. Mainly I go after the copper in the transformer and silver contacts. The other day I scrapped a Danby microwave and was surprised to see the windings of the transformer were aluminum.
First one I've seen with aluminum windings......I guess it's no suprise considering the cost of copper and how they try to produce them as cheaply as possible.


----------



## rusty (Jul 29, 2011)

resabed01 said:


> I've scrapped several over the years. Mainly I go after the copper in the transformer and silver contacts. The other day I scrapped a Danby microwave and was surprised to see the windings of the transformer were aluminum.
> First one I've seen with aluminum windings......I guess it's no suprise considering the cost of copper and how they try to produce them as cheaply as possible.



Transformer has two coils, 1 should be copper although I've seen both to be aluminum. Cheap windings showing up in refrigeration compressors, washing machine and dryer motors.

Something new I noticed the other day, the Chinese are no longer listing the amperage on electric tools which I thought was required by UL and CSA laboratories. 

Regards
Rusty


----------



## qst42know (Aug 15, 2011)

> Something new I noticed the other day, the Chinese are no longer listing the amperage on electric tools which I thought was required by UL and CSA laboratories.



Things keep going as they are and we'll have to adapt to their ways, instead of them complying to ours. What number are they supplying to calculate the required wire guage?


----------



## Photobacterium (Dec 21, 2011)

starzfan0211 said:


> Ok. No chances then. I have an old microwave that died and I am going to tear it apart in my "spare time". But I was mainly wondering for anything in a computer power supply because we are taking those apart for the aluminum and copper.



some scrap places will give you 'steel' prices for a microwave. 7 to 10 cents a pound. about $4 for a 60 pound microwave.

now you're making me want to take mine apart.


----------



## Geo (Dec 22, 2011)

most scrap yards refuse microwaves whole for environmental reasons. namely oil from the capacitor and toxic material in the magnetron. you should be able to sell to these yards if you disassemble the unit first and remove these components. TVR is one (and the largest) of our scrap yards will not buy microwaves under any circumstances.


----------



## meatheadmerlin (Dec 24, 2013)

My yard pays for those large oil-filled capacitors. They call them sealed units. Oil-filled compressors from refrigeration appliances fall under the same category. I don't know what price they give because I never mess with the refrigerated appliances and haven't taken apart enough microwaves since finding out they pay for the capacitors. I was just leaving them in the microwave and getting steel price. I leave the magnetron units in too, I had heard they were dangerous inside, now I know exactly why.


----------

