Dont believe, the PS will kill you.

"It's not the size of the dog in a fight, it's the size of the fight in a dog."

Motor-start capacitors in equipment like Air Conditioners have a completely different function than Filter caps in power supplies. Physical size is generally not the issue as much as the potential stored across them. Motor-start caps provide a phase shift, whereas Filter caps store voltage in performing their job.

You can take a simple .01 uf 5Kv disk ceramic capacitor, the size of a nickel, put it across a 4Kv DC source, remove it, grab one lead with one hand and the other lead with the other hand and I personally assure you, you will not like the sensation you will feel for a brief moment. Conversely, you can take a 100,000 uf 5V capacitor, the size of a propane torch cylinder, put it across a 5V source, remove it and grab the two studs and you will not feel anything.

In most switching supplies, the primary bulk DC is between 150-200VDC. Luckily, these capacitors have a bleeder resistor on them that drains off the charge in a few seconds, once power is removed. Should that resistor fail, you may find that even several minutes after the power is removed, a lethal voltage potential still exists across that cap. You take 200VDC arm to arm and you will see the light at the end of the tunnel. Those with weak hearts may not return from that tunnel. Certainly, working on a live switching supply requires vigilence and caution. I use the rule of keeping one hand out of the circuit, usually in my pocket. If you take a high voltage shot across part of one arm, hand, finger, etc., the heart is not in the path of current flow. The greatest risk then is from injury as a result of uncontrollable muscle reflex. I've smacked my hand on sharp case edges several times and with great force, as a result of this type of mishap. If you take a high voltage shot from one hand down through your foot, you can find yourself performing an amazing broad jump, hence the allusion to "flying asross the room". Dont work on High Voltage equipment barefooted.
With proper respect and precaution, there is no reason to fear working with High Voltage. You simply need to think about each move before you do it. That applies to both live and unplugged High Voltage equipment. If you don't feel comfortable with your experience base, leave the PSU turned off for an hour before you work inside it. Bleeder resistor or not, the other components in the HV circuit should discharge the cap(s) by then.

73, Hoot

Realistically, when working in an environment like a carpeted room and dry hands it is very very hard to get shocked. We have this thing, reflex system, and on dry hands touching something under voltage would induce a slight tingle at first, and progressively increase the harder the object is grabbed (more contact), so if reflexes are in a working order getting hurt is unlikely.

Now if you are a sensation seeker take a salt water bath then play with a plugged in and powered up flyback transformer in a TV, at least 32" CRT for maxiumum effect

LJ5L said:

Realistically, when working in an environment like a carpeted room and dry hands it is very very hard to get shocked. We have this thing, reflex system, and on dry hands touching something under voltage would induce a slight tingle at first, and progressively increase the harder the object is grabbed (more contact), so if reflexes are in a working order getting hurt is unlikely.

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You would be too late cuz when you get shocked your muscles contract.(when you see that you gotta kick em in the butt that way they'll have some time to let go, but you will get shocked)

Hoot said:

"It's not the size of the dog in a fight, it's the size of the fight in a dog."
...............................................................................

73, Hoot

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Very well said Hoot.

I've studied electronics long enough to know that it doesn't take much to kill a man, yes I've been shocked several times, but I'm sure I can be killed by less voltage and current.

Accidents involving electricity at work are not as unusual as you might suspect. In fact, statistics indicate that every day one person is killed at work by electricity.
Shocking Facts

• Electrocution is one of the top five causes of workplace deaths.
• Workers younger than 25 have the highest rate of death from electrical shock.
• Many workplace electrocutions involve touching a power line with long or tall equipment.

Sudden cardiac death occurs from an electrical problem in the heart. Abnormal electrical impulses signal the heart to beat too rapidly, sending the normal rhythmic pumping of the heart into chaos. The heart muscle begins to quiver like jelly and stops delivering blood and oxygen to the body and brain.

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Some ppl need proof, poke around long enough and there you have it I just cant believe how ignorant ppl can be.

Go ahead be my guest, but when I meet you in heaven (or hell ) don't tell me I didn't warn you.

It doesn't have to be dangerous, as long as you know what you're doing.

Hmmmmm, ppl say there is no harm others say there is harm after you've just unplugged it...

I'll just leave it overnight to be safe, but I have been shocked many a times, that flying across the room is no joke, seriously!!!

Although its funny to look back at stupidity its dangerous, and then you do it again.....

this reminds me of some fun I had with my friends a few weeks ago. They had a broken disposable camera, I always wanted to test the flash capacitor on them. So I charged it (only on a aa battery), and stuck it on my friend. He "f"ing jumped up and his arm had marks on it. It was fun but later he got my in the neck and I fell to the floor. I have it somewhere in my room, I'll post what it was. Playing around with them can be quite fun in a slightly disturbing way. My friends messed up, he did it to his mom when she was watching TV. Trust me, it does hurt A LOT.

says, 330WV, 120uF.

An unplug P/S WILL NOT hurt you or kill you. You may get shocked by stored energy in a cap. You can take a insulated screw driver and place across the cap an discharge it. TV's have what is called flyback transformer that can store 25,000 volts. Remember volts do not kill, but amps do kill.

Ok hoot, that makes sense about the size, but realistically, is there anything inside a psu (w/o being discharged first) that could hurt you?

A little theory

I figure for my first ever post, I might post a little theory... according to the books, a 100ma shock through your heart has the capability of killing you. Under worst case conditions (soaking wet with sweat, humid, etc.), a human body can have a resistance as low as 300 ohms.

Using ohms law, E=I*R, you get a voltage of 30v being potentially fatal.

So, using this simplified logic, if any of those caps have a 30v residual charge in them, and you are unfortunate enough to have just run a marathon in Florida during a thundershower, you could kill yourself.

Ok, I'll get off my soapbox. Just in case you're curious, or doubt my sanity, some general guidelines on electrical safety can be found at http://www.ebme.co.uk/arts/safety2.htm#gen.

Hi RxScram, welcome to the forums.

I don't doubt your sanity....others do

Thanks for the vote of confidence

Damn Flouder talk about dust!

Well to be honest back ago I was very dumb cleaning my PSU and then I plugged everything back in the fan didn't work I reconnected the psu fan and then turned it on not noticing my hand was on the capcitator I got shocked stupid enough it happened again(damn I'm stupid) and it felt like a little shock.

It will harm you in most cases if you do have a power enough PSU opened and have your whole hand wrapped around every capcitator in there...

Happy Holiday

While a 30volt capacitor does not have the power to kill this thread does have the power to give a heart attack to someone even slightly enlightened on the subject and common sense.

...and the moral of the story is...

FER GOD'S SAKE BE CAREFUL!!!

Why take the chance? I've had enough of getting burned, cut, shocked because I was impatient and didn't take all the necessary precautions with stuff.

Emmm K..next time I go swiping fansout of old PS's I think Ill make sure they have been unpluged for like 40mins, (I always test them to make sure they work)

kinda like driveing, in a car your always taking a risk..

hehe, your ghetto, swipping fans out of old useless PSU's, Just like me I find that the older dell machines have the best fans in the PSU's, Panaflo's. I also found that some old compaqs had 92mm Nidec and NMB fans in them. Happy fan hunting.

I took apart a P/S yesterday but it was off for a while so I wasn't worried.


Moral: turn off and unplug P/S b4 working on it or be careful.

Shadow ÒÓ said:

Proof, if you've ever seen a capacitor from an air conditioning unit (a home system....the large box outside your house) they are the size of about 1/2 a coke can. Commercial units have dual capacitors which are the size or 2 or 3 cans. I have on several occasions taken a charged capacitor and discharged it on an employee. (actually stuck it to his leg/arm/back of his neck) Great laughs! (sick I know)

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YOU SICK *******!

J/K

Actually being electricuted (not to the point of serious injury or death) actually feels awesome. It's like a high or something. It's addictive.

put it this way , when i was in school [i was high *** f*** to so] i was in gem witch i never dressd out and the teacher just let me walk around and do whatever i wanted. but i stick some foil from a gum wraper in a socket [ stupid i know] and see im still alive. The light all went dem and the socket blew but hey here i am im just alil smarter now though and dont play with sockets when im stoned

[i said im here , i didnt say it didnt blow me up]