Safe to open a PSU - once removed from the PC

  Diemmess 09:36 14 Jun 2006

'Throwing this in for some accurate explanation to replace "hearsay".
Whenever the PSU is suspect, sooner or later some post will say how dangerous it is to open a PSU because of residual high voltage on some components.

I agree with those that say it is FUTILE to hope for enlightenment and easy repair of a component fault, far better to accept it is dud and bin it!

A dirty cooling fan is something quite different and should be straightforward with the PSU removed from the computer, and reasonable care taken to avoid damaging other circuit components.

I do not believe those who say there is danger of electrocution, and this is where I'm prepared to be howled down.

As I understand a PSU, there is live mains input which is made safe by removing the power lead. Thereafter a mass of components. Rectifiers, voltage regulators, current limiting devices and so on. There are some large capacity electrolytics which carry a hefty charge but at low voltage, acting as buffers to keep a smooth supply of DC available from the unit.
When isolated, there is no voltage potential present > 15volts. Or so I believe!

There must be many members who know the facts. Can somone back me, or shoot me down?

  SANTOS7 09:42 14 Jun 2006

click here
wealth of information here....

  SANTOS7 09:45 14 Jun 2006

WARNING: The filter capacitors used in many switchmode power supplies can store an amount of energy that can kill - always discharge and confirm this before touching anything.
click here

text taken from link......

  namtas 09:50 14 Jun 2006

Fully edorse SANTOS7's WARNING, The residaul charge in a capacitor can kill when discharge to a lower potential, ie to earth via your body.

  SANTOS7 09:53 14 Jun 2006

Especially when you are stood on a bar stool in a disco stripping back some speaker cable with your teeth, OOOH!!!! look! he flies........

  Simsy 09:55 14 Jun 2006

from my training, many, many years ago;

"Volts is jolts, but millers is killers"

Meaning that it's not the amount of volts that kills you, but the strength of the flowing current... which might be very small, measured in thousands of an amp, (hence "millers", from milliamp).

A car battery is "only" about 12 Volts, but the current it provides to the starter motor when starting a car can be in the region of 200 amps. have you seen what sort of spark they give if you short circuit the terminals?!

Now I don't know if whats left in an unplugged powersupply can kill you... I'm just pointing out that your reasoning that it's safe because there is no voltage higher than 15 volts isn't, by itself, sound.



  seedie 10:02 14 Jun 2006

A few years ago I had power supply trouble with a BBC Master computer. Although I have been working with electricity all my life and had many shocks of varying intensity, including mains, the jolt I got off that one is memorable and would not open a computer PSU unless it had been unplugged overnight.

Some people are more vulnerable than others to electricity so to be on the safe side leave it to discharge before you fiddle.

Good luck!


  dagbladet 10:11 14 Jun 2006

Once bought a small digital camera on ebay as 'spares or repair' to see if I could salvage the LCD screen which had cracked on my own camera. Package arrived through post, opened it, no batteries in camera, took the back off, started to undo tiny screws inside, ZZZAAAAPPPP!!!! an almighty belt shot through my finger which caused me to jump up out of my seat, camera shot out of my hand, finger had deep black line for weeks. Kids thought it was funny though.

  rmcqua 10:18 14 Jun 2006

Sorry, but his reasoning is sound.
Whilst the old adage "'s mills that kills" is true, the quantity of milliamps (current) that can be pushed through the human body is directly proportional to the voltage applied (Ohms law).
The voltage below which a dangerous current is UNLIKELY to flow through the human body is (in international safety standard terminology) known as SELV and is generally accepted as around 60V. DC.

  Graham ® 10:37 14 Jun 2006

An electric shock is just that. Electrocution is death by electric shock.

  ACOLYTE 10:55 14 Jun 2006

I have taken quite a few PSU's apart mostly after they had blown and never had any mishaps,having said that it doesnt mean they cant harm you,i guess if you really must do it then its pot luck as to what happens when you do.

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