I've recently gotten into scrapping metals from electronics and the such. One problem I've had though is that on lots of the electronics there's a warning stating opening and fooling around inside can result in electrical shock.

I was just wondering what it is exactly in the electronics that can shock me, and how do I disable them?

Also any tips / advice on scrapping is welcome.

capacitors (http://www.columbia.k12.mo.us/jjhs/Technology/S&E0506/schermerp/images/capacitor.jpg) are electronic components that store electrical charge and that can shock you.

Get a high current 1M resistor and two insulated croc clips, and a toggle switch, and wire it up. The current will discharge (careful, the resistor may get hot if the capacitor is a high value...small capacitors aren't a real issue).

Capacitors are mostly found in power supplies in computers and televisions and CRT monitors. Certainly in CRT monitors, voltages of over 600V persist even after the power has been removed.

You may also want to get some insulated tools (at minimum, VDE rated side cutters and a small flatblade screwdriver.

wow, 600v!!! Is that deadly? :eek:

How long do capacitors generally stay dangerous for anyway?

Also, if tooling around in say a cpu power supply, a crt monitor, or any moderately high energy electronic device how easy is it to get shocked by the capacitor?

I would assume the capacitor terminals aren't just going to be hanging out.

Capacitors in switch-mode power supplies can hold 300-600v for about 20 mins or so, but CRT caps quite a bit longer.

And yes, the terminals are just hanging out on the bottom of the board...so watch out! The 1uF smoothing capacitor in microwaves can hold 6kV or so for a while too.

Stuff like VCRs, computers (apart from the power supply) and fine though as there's only a maximum of 30v or so held in the caps.

CRT TVs and microwaves are the most dangerous consumer appliances. In TVs, the tube itself is a giant capacitor, capable of killing you. It needs to be discharged to safely work. Same goes for the big microwave capacitor.

Most everything else isn't terribly dangerous. It might give you a painful shock, but this can be avoided by touching an old plastic handle screwdriver across the terminals. Don't bother with a resistor. If there's any power stored, the screwdriver method will make a nice little snap telling you it discharged.

Most modern AC powered electronics (aside from CRTs and microwaves) have a small board dedicated to supplying low voltage DC to the rest of the device. This board is the only dangerous part. Discharge any big caps on it, and everything else is safe.

Nearly all electronics are designed to self-discharge the caps anyway, but best to play it safe and discharge. It's fun to scare people with the snap sound too.

Nearly all electronics are designed to self-discharge the caps anyway, but best to play it safe and discharge. It's fun to scare people with the snap sound too.
I remember I once shorted out 88,000uF of capacitance in an amplifier with a small screwdriver. It welded itself between the chassis and the terminal...

Huge capacitors take longer to discharge. How long did you wait after unplugging it?

wow, 600v!!! Is that deadly? :eek:

If you stuck it to your heart, yea. Arm to arm, 600V isn't a whole lot and you shouldn't be affected unless you are wet or have a heart condition. I've got hit with a 12KVDC power supply arm to arm, and all it did was hurt.

In TVs, the tube itself is a giant capacitor, capable of killing you.

The tube also has a ground strap around the outside on most modern sets. I also believe the output is too high an impedance to be dangerous. The output is also of high frequency, so the skin effect comes into play, where the skin depth is very small because the permeability of human tissue is small.

Ok, so I opened up this old foot massager thing I have and I found some goodies on the inside. Here's a pic of the outside just so you have an idea of what it is:

http://img228.imageshack.us/my.php?image=img3261js4.jpg

Here's the main circuit board with what I believe to be a 250v cap, the orange thing.

http://img258.imageshack.us/my.php?image=img3263js2.jpg

Here's a pic of the whole inside. Anyone have an idea as to what the ominous looking cream colored thing is on the motor?

http://img295.imageshack.us/my.php?image=img3266ti2.jpg

All in all this was a good scrap. Lots of Cu wire, a motor, and heating elements are present. I'm just a bit scared to fuck with it because I don't want to get shocked. I still have a lot to learn about electronics before I'll feel comfortable messing with this stuff.

Thanks for bearing with me while I'm learning, and answering the questions.

If you stuck it to your heart, yea. Arm to arm, 600V isn't a whole lot and you shouldn't be affected unless you are wet or have a heart condition. I've got hit with a 12KVDC power supply arm to arm, and all it did was hurt.

The tube also has a ground strap around the outside on most modern sets. I also believe the output is too high an impedance to be dangerous. The output is also of high frequency, so the skin effect comes into play, where the skin depth is very small because the permeability of human tissue is small.

12KV from a TV power supply is nothing. The current is too low to do any damage. The capacitor releases 12KV in a very high current pulse.

What does a ground strap on the tube have to do with anything? It's simply one terminal of the capacitor.

And how could a capacitor have a frequency? You can charge it with whatever you want, but it still discharges as DC. DC is, of course, immune to the skin effect.

You should know this stuff, Argon. It really surprises me.

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Yes, the cream thing is the coil of the motor. Don't worry; it's harmless. You're perfectly safe playing with it, as long as you keep your hands away while it's plugged in. Once you have a better idea of what you're doing, then you can start doing things with the power on.

12KV from a TV power supply is nothing. The current is too low to do any damage. The capacitor releases 12KV in a very high current pulse.

What does a ground strap on the tube have to do with anything? It's simply one terminal of the capacitor.

And how could a capacitor have a frequency? You can charge it with whatever you want, but it still discharges as DC. DC is, of course, immune to the skin effect.

You should know this stuff, Argon. It really surprises me.

A flyback output is around 30KVDC @ 20-30kHz. The glass is a poor storage device, having lead impurities. The gound strap is just that: it grounds the outside of the tube. Ever touch a modern CRT and wonder why it doesn't have a static charge on it?

Clearly I was thinking of the output of the flyback, as opposed to this dubious charge storage on the surface of the tube.

Lastly: http://home.san.rr.com/nessengr/techdata/rlc/rlc.html#under

Ok, so I opened up this old foot massager thing I have and I found some goodies on the inside. Here's a pic of the outside just so you have an idea of what it is:

http://img228.imageshack.us/my.php?image=img3261js4.jpg

Here's the main circuit board with what I believe to be a 250v cap, the orange thing.

http://img258.imageshack.us/my.php?image=img3263js2.jpg

Here's a pic of the whole inside. Anyone have an idea as to what the ominous looking cream colored thing is on the motor?

http://img295.imageshack.us/my.php?image=img3266ti2.jpg

All in all this was a good scrap. Lots of Cu wire, a motor, and heating elements are present. I'm just a bit scared to fuck with it because I don't want to get shocked. I still have a lot to learn about electronics before I'll feel comfortable messing with this stuff.

Thanks for bearing with me while I'm learning, and answering the questions.
There's nothing at all for you to get shocked in there at all. You could lick the circuit board as long as it's unplugged - that capacitor is only a very small suppression cap. It reduces RF noise given out by the unit. Again, it's leads are quite lickable if you unplug it.

Note that the black thing is a relay, which can be very useful if you like building random things.

That cream coloured thing on the motor is its windings. Under there is a big coil of wire - it's covered in cream tape to protect it from damage. It's a shaded pole induction motor, which has no brushes - I'll go into detail if you want to know how it works.

Don't worry, the coil of wire under the cream tape can't hold any charge. (AP2K and Spatula...yes, I know the collapsing EM field might count as a stored charge...so shut up :D)

A flyback output is around 30KVDC @ 20-30kHz. The glass is a poor storage device, having lead impurities. The gound strap is just that: it grounds the outside of the tube. Ever touch a modern CRT and wonder why it doesn't have a static charge on it?

Clearly I was thinking of the output of the flyback, as opposed to this dubious charge storage on the surface of the tube.

Lastly: http://home.san.rr.com/nessengr/techdata/rlc/rlc.html#under

I'm talking about the charge within the glass itself, not the static charge on the outside. The aquadag coating on the inside and outside of the tube form the two plates of a capacitor. Glass might not be the best dielectric, but it certainly holds enough of a charge to be deadly.

Well of course capacitors can create a frequency when part of an RC circuit, but not when it's directly discharged across the terminals.

I'm talking about the charge within the glass itself, not the static charge on the outside. The aquadag coating on the inside and outside of the tube form the two plates of a capacitor. Glass might not be the best dielectric, but it certainly holds enough of a charge to be deadly.

Well of course capacitors can create a frequency when part of an RC circuit, but not when it's directly discharged across the terminals.
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Yeah, found that out the other day.
Found a 14 inch TV behind a charity store, it was broken.
So I took it home , plugged it in & found it wasn't worth fixing, (there was a break somewhere on the board, it went with the board out, but turned off when the board was placed where it should be)

AFTER breaking the little glass thing inside the TV tubes main end plug, letting the gas fill the tube.
IF you don't do that the whole screen may EXPLODE if you crack the screen!

So I stuck the screwdriver under the big flat red rubber bit thats got a thickish wire running to the main circutboard, & levered it up & ZAP!
Shit that hurt!
I didn't relise the screen holds a charge too!

So I kept earthing it out, but the charge mounted up again so I decided to undo the screws on the screen & not play with the wires for a while.

Once I'd done that I smashed the board & pulled the wires off & smashed the transformers out & unscrewed the Ali heatsinks & threw all the wiring into a plastic bag for scrapping later.
Thats about it.
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You will get about 50gms of copper from that motors winding.

Sometimes if you put that in a vice you can bash the winding & its core off the rest of the motor.
Then just slide the iron core outta the winding & pull the rest of the wire off where its soldered on.
Or balance the motor on a bench vise etc & use a large knife & hammer to cut thru the wire core & pull the wire out.
I got a large Kitchen knife & cut 1/2 the blade, lengthwise, off with a grinder.
I have used a sharp axe before too..
Cut down into the metal strips so the blade slides between them, or the winding will revolve & you won't cut thru it all.

If you undo the 2 screws you can pull the rotor out.
Sometimes the end metal strips are Ali & theres little bronze bearings inside it.

Theres two little copper wires welded around the motor core, if you get enough (I'll wait till I have 20 or more) you can cut thru them in the right place & then pull them out with plyers.

Theres a long Ali strip holding the motor on, unscrew that (or use safety glasses & bash it off with a hammer) & break the rivet holding the other metal strap to it.

I'd just rip the other plastic coated wire out & cut the plugs off with side cutters, save the plugs, if you get enough you can burn what plastics on it & get NZ$4 Kg for it.
Put the wire in with the other stuff untill theres enough to burn off.
I have a drum & chuck all the screws/magnetic metal into that & chuck the plastic into the rubbish bin.
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I was taking off a hose clamp off a rubber tube on a copper tube today.
Got the clamp off & decided to force the screwdriver under the rubber tube to take it off.
The screwdriver slipped & went directly into my heft hand where all the meat is at the base of my thumb.
Real Dark Blood started pouring out of it, covered it with a papertowel untill it stopped bleeding & then ripped the loose skin off.
It still hurts now, swollen up a bit too. Damn!

Watch out for cameras. One time when I was around 13 or so I was taking apart an old, 80's style disc camera, it probably hadnt been used in several years(dont know for sure). I I touched one of the leads to the flash and obvoisly shorted something out, giving my thumb and got a mean shock. My right hand was numb for about a min or more, i dont really remember

That big red suction cap thing is the HV lead from the flyback transformer. I'd say rip it out and save it for future projects.

As for small capacitors(400v, 25-100uF) just use a screwdriver.

wow, 600v!!! Is that deadly? :eek:

Volts jolt, mills kill.