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'[EE] Is it safe to open a microwave oven???'
2005\10\20@023034 by Juan Cubillo

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Hello group,

About a year ago some spikes in the main power lines damaged my microwave oven. I bought a new one and stored the damaged old one under some books. Today, I was thinking about opening the oven "just to see what it looks like inside". I know this things have some dangerous high voltage capacitors on them. I was thinking about connecting a 10k/47K resistor to the cap leads to discharge it just in case it had some stored volts that may shock me.
Is there any chance that the cap still has a stored charge?
Are there any other precautions I should look at?

Juan Cubillo

2005\10\20@151753 by Herbert Graf

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On Wed, 2005-10-19 at 14:07 -0500, Juan Cubillo wrote:
> Hello group,
>
> About a year ago some spikes in the main power lines damaged my microwave oven. I bought a new one and stored the damaged old one under some books. Today, I was thinking about opening the oven "just to see what it looks like inside". I know this things have some dangerous high voltage capacitors on them.
> I was thinking about connecting a 10k/47K resistor to the cap leads to discharge it just in case it had some stored volts that may shock me.
> Is there any chance that the cap still has a stored charge?

Any chance? Yes. But the chance it has any charge left is pretty much
zero.

> Are there any other precautions I should look at?

Not really, microwaves are pretty simply devices with only a few
components, none of which is much of a treat if it's been unplugged for
a while. About the only thing I can see is something sharp. TTYL

-----------------------------
Herbert's PIC Stuff:
http://repatch.dyndns.org:8383/pic_stuff/

2005\10\20@212258 by Tony Smith

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{Quote hidden}

The transformer is bloody heavy, don't drop that on your foot.  Try not to
get your fingers between the magnets you pull out of the magnetron.  Don't
stick the magnets on your filing cabinet near to your PC and the next day
spend a few minutes wondering why your screen (CRT) has suddenly gone all
wonky.

Oh, and you could probably fix it by replacing the MOV (metal oxide
varistor).  When they wear out, they usually fail shorted.  This blows the
fuse.  Change both (well, fuse at least) and it'll probably work.

Failing that, one of the door microswitches (up to 6!) might be burnt out.
If you look closely, you see they're often rigged to short the active
line to ground if the door is open and you attempt to defeat the door
switches.  Rather than fry the idiot doing that, it blows the fuse and
maybe the switch.  Opening the door while the microwave is running can
damage the switches as well (arcing on the contacts)

Of all the microwaves I've scrounged parts out of, only one was truly
faulty; rather impressive sparks came out of the transformer.

Tony


2005\10\21@175458 by Juan Cubillo

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I just finished cannibalizing my microwave oven and I was amazed how simple
it was inside. The only PCB is smaller than most PIC programmers :) and
besides that there is only the magnetron and a HUGE transformer inside.
The "dangerous capacitor" was the easiest part to remove so now I have a
1.05uF 2100V cap!!!
I also took 3 switches (from the door), 2 relays, a piezo buzzer and some
components.
The bad news... Somehow, I gave myself some rather deep cuts to three of my
fingers and another cut in my right hand palm. Now I have four band-aids
wraped around my hand. It looks like I was trying to feed a crazy parrot! :)
Thanks everyone for the help!

Juan Cubillo

{Original Message removed}

2005\10\22@083757 by Peter van Hoof

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Perhaps a word of caution about the capacitor
Store it with a shorting wire

High voltage caps have the tendency to build up a
charge after they have been discharged

In my company we use high power strobes to cure uv
resins, the powersupply is 3000v with a 33uf cap in
it. If we leave them shorted for several weeks , then
take the short off they develop several hundred volt
high charges in just a few hours, enough for a very
nasty shock or a huge spark

TTYL

Peter van Hoof

2005\10\22@172956 by Juan Cubillo

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Now I'm scared...

My cap has been unplugged for about 2 days and I'm afraid it may have
selfcharged. How can I discharge it in a safe way? I don't want to grab it
and stick a piece of wire shorting it just to find out that it has several
hundred volts in it!
I think I will connect a relay that shorts the cap, the relay is going to be
remote controlled so that I can be at a safe distance from the cap.
Hehe
Juan Cubillo

{Original Message removed}

2005\10\22@181940 by olin piclist

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Juan Cubillo wrote:
> My cap has been unplugged for about 2 days and I'm afraid it may have
> selfcharged. How can I discharge it in a safe way? I don't want to grab
> it and stick a piece of wire shorting it just to find out that it has
> several hundred volts in it!
>
> I think I will connect a relay that shorts the cap, the relay is going
> to be remote controlled so that I can be at a safe distance from the
> cap.

You're making too big a deal of this.  Use some clip leads and hold a
100Kohm resistor accross the cap for a few seconds.  You can even do this
with your hand if you only touch one end of the cap and the end of the
resistor connected to it.  By holding those two wires together you can make
the other two touch for a few seconds.  Or just hold the cap by the
insulated housing and make both ends touch a piece of metal at the same
time.  That might not be so nice on the cap depending what type it is,
although as long as it's not electrolytic even that shouldn't be a big deal.


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