[QUOTE=bohb;26686458]You clearly don't understand how PSUs work, or even basic electronic components for that matter. The only way you're going to get zapped by a capacitor is if you unscrew the damn board and pull it out of the PSU while it's on (which it would probably short out and explode long before then) and touch the leads on the bottom of the capacitor.[/QUOTE]
Sorry, you must be right. The last 5 years studying physics and taking the electronic courses do not mean anything. /sarcasm
If you do not attach a load to a capacitor or short-circuit the two poles, the charge can remain for days or weeks. Depending on the capacity and the type of the capacitor, the instantaneous discharge by a short-circuit through your body can exceed many mA - 10 mA through your heart are btw considered to cause major harm such as death (if the voltage can penetrate your skin)
[QUOTE=bohb;26686458]The [i]absolute[/i] highest voltage present in a PSU is 220v, for both 110 and 220v mains systems; And that voltage is only present on 1/3 or less of the PSU board. The other 2/3 of the power board where the rectification, regulation and filtering are all +/- 12v AC/DC or less, which are woefully inadequate to cause anything other than minor annoyance akin to those gag handheld battery shockers.[/QUOTE]
That's only the AC input voltage. Once the [url=http://en.wikipedia.org/wiki/Switched-mode_power_supply]SMP[/url] converts it (230 V AC) to DC you get 325. Still this is not the point: It's chopped (hence the name of [url=http://en.wikipedia.org/wiki/Switched-mode_power_supply]SMP[/url]) at high frequencies at put to a small coil (that's why we use [url=http://en.wikipedia.org/wiki/Switched-mode_power_supply]SMP[/url]) When you turn off your PSU, the coil's B-Field falls down rapidly causing a high-voltage which can potentially can potentially stored in a capacitor. Touch that guy, bye bye.
[QUOTE=bohb;26686458]Even [i]if[/i] you managed to touch mains voltage in the PSU, it would be no worse than brushing against a frayed electrical cord, and this all assumes you're dumb enough to open it and prod around in it
with your hands or a screwdriver while it's on.
Turned OFF is a completely different story. Once you remove the PSUs power source, bleeder resistors will quickly drain all capacitors in the PSU rendering them harmless. In the case you have a cheap wofat PSU that doesn't have bleeder resistors, you can leave the motherboard or any device plugged in and press the power button once to drain any latent energy out.[/quote]
There is no guarantee the capacitors still hanging on a load so the capacity bleeds out after turning the PSU off. A PSU is not meant to be opened by amateurs at any time.
Analogy: Just because you never had a car accident doesn't mean it's impossible.
[QUOTE=bohb;26686458]If he wants to fix/replace the fan in his PSU, it's more than fine to do so. I'd advise him to invest in a soldering iron though since most of the time the fan wires are soldered onto the PSU board, instead of a connector[/QUOTE]
I do not recommend this in any way. It is possible, of course but potentially dangerous. You better spend 50 bucks on a new PSU than being sorry in meanings of being dead or at least injured.
[editline]17th December 2010[/editline]
[QUOTE=not_Morph53;26688966]100mA (powered USB lol) could stop your heart, but 50mA at 20v to 25v across the chest area would do the trick too.
On a related note human blood = 550 ohms...[/QUOTE]
USB is 500 mA, but luckily the 5V can't penetrate your skin. Our PSU for our [url=http://en.wikipedia.org/wiki/Magneto-optical_trap]MOT-Coils[/url] in the lab are running at 16 V with 200 A current. Touching the wires won't kill you - 16 V is still too less to penetrate your skin an body to cause any harm. But the capacitors can discharge in a short moment causing several mA at high-voltage.
[editline]17th December 2010[/editline]
[QUOTE=bohb;26692386]Because I build circuits with components all the time?
[img_thumb]http://img822.imageshack.us/img822/3100/img0038cof.jpg[/img_thumb][/QUOTE]
Wow, a low-voltage device with a few capacitors, resistors, diodes, op-amps and a voltage-reference - I build ton's of way more complex devices with similar components.
[QUOTE=aVoN;26740058]
USB is 500 mA, but luckily the 5V can't penetrate your skin. Our PSU for our [url=http://en.wikipedia.org/wiki/Magneto-optical_trap]MOT-Coils[/url] in the lab are running at 16 V with 200 A current. Touching the wires won't kill you - 16 V is still too less to penetrate your skin an body to cause any harm. But the capacitors can discharge in a short moment causing several mA at high-voltage.
Wow, a low-voltage device with a few capacitors, resistors, diodes, op-amps and a voltage-reference - I build ton's of way more complex devices with similar components.[/QUOTE]
My bad, I forgot that 100mA was one unit load for USB2, and USB2 supports 5 unit loads.
[QUOTE=aVoN;26740058]words[/QUOTE]
And I've been repairing electronic equipment for 10 years, with tinkering in the stuff since I was a kid. You don't need 5 years of college courses to know otherwise. And the lot of good it has done you, you still treat power supplies like hocus pocus. It seems like you have the theoretical workings of the stuff down, but you have no proper hands on experience, or your instructors are idiots screaming "ELECTRICITY IS DANGEROUS AND WILL ALWAYS KILL YOU."
You make several incorrect assumptions about electricity and how it works. 120v, 220v and even 325v will in most all cases not be deadly, unless you do something ornately stupid like stand in a grounded tin washtub with brine water and press the solder side of the PSU into your face with it being turned on. You completely blew by all of my safety instructions which will make 99.9% sure the power supply is discharged. Even if there is latent energy stored in a cap somewhere, the only ones you have to worry about are the supercapacitors, and even then they won't have enough stored in them to cause anything more than annoyance and some swearing. I've been bitten by 120-277v and several spark plugs ranging in the thousands of volts and I'm not dead; They were painful but not deadly.
If your logic were true, every poor soul on youtube who has been bitten by mains voltage, flyback transformers, CRTs or supercapacitors should have died on camera, which clearly isn't the case. Electricity will always find the shortest path to ground, which is usually from one finger to another, or even to another point on the same finger. The heart is almost always not in the equation for getting hit.
You also missed my post on the "I've been building electronics stuff for a long time." I only posted my opamp because I didn't feel like dragging out my 40 lb SCSI drive and removing the pain in the ass case to naysay you, and I still don't feel the need to do so.
[QUOTE=bohb;26747683]And I've been repairing electronic equipment for 10 years, with tinkering in the stuff since I was a kid. You don't need 5 years of college courses to know otherwise.[/QUOTE]
Of course you don't need it, but it helps.
[QUOTE=bohb;26747683]And the lot of good it has done you, you still treat power supplies like hocus pocus. It seems like you have the theoretical workings of the stuff down, but you have no proper hands on experience, or your instructors are idiots screaming "ELECTRICITY IS DANGEROUS AND WILL ALWAYS KILL YOU."[/QUOTE]
I do not treat them as "hocus pocus", I know how they work. I just pointed out my thoughts about safety and that a person, who does not have any experience with electronics (the thread author) better don't touch it since it can potentially harmful.
[QUOTE=bohb;26747683]You make several incorrect assumptions about electricity and how it works. 120v, 220v and even 325v will in most all cases not be deadly, unless you do something ornately stupid like stand in a grounded tin washtub with brine water and press the solder side of the PSU into your face with it being turned on.[/quote]
I will send you a capacitor loaded with 100 V and enough capacity to kill you, if you touch both ends. What's your postal address?
[QUOTE=bohb;26747683]You completely blew by all of my safety instructions which will make 99.9% sure the power supply is discharged. Even if there is latent energy stored in a cap somewhere, the only ones you have to worry about are the supercapacitors, and even then they won't have enough stored in them to cause anything more than annoyance and some swearing. I've been bitten by 120-277v and several spark plugs ranging in the thousands of volts and I'm not dead; They were painful but not deadly.[/quote]
Now you even state yourself, that some capacitors can still hold a charge - This was my whole point. Safety is not guaranteed. And I've taken shocks of many thousand volts too - Everytime I take off my cloths, I'm "charged" with static electricity. But the charge is not high enough to cause a deadly current.
[QUOTE=bohb;26747683]If your logic were true, every poor soul on youtube who has been bitten by mains voltage, flyback transformers, CRTs or supercapacitors should have died on camera, which clearly isn't the case. Electricity will always find the shortest path to ground, which is usually from one finger to another, or even to another point on the same finger. The heart is almost always not in the equation for getting hit.[/QUOTE]
Bad example. Not every electric shock is deadly but many people underestimate the danger. Also if someone dies or takes serious harm, there isn't a camera running (the "bad example" I mentioned) and if someone posts it on youtube, youtube deletes it generally.
Anyway, can we stop bashing each other? I made my point clear, you made it and everything has been said.
[QUOTE=bohb;26747683]-blabber-[/QUOTE]
Its not the voltage which kills you. You can have 1200v 'through' (technically it wouldn't be flowing but w/e) your body, and only notice a slight tingle. It's the amps which make it dangerous. If it has enough amps, only then will it flow and possibly kill you. So all that stuff about you 'surviving' 277v is total nonsense. Of course it wont hurt because it has no amps behind it.
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