Computer grounding via a UPS not proper - what could be the problem.

[Vivek.M]

My computer gives me a shock; Some details:
Supply: 250 V/50 Hz.
Neutral to Ground at plug-point: 4-5V.
Power On (UPS), but no equipment drawing power: 9V (Computer-case to
Earth).
With everything powered ON: 20V (Case to Earth).
Everything ON: 5V (Earth to Neutral at powerstrip - before the UPS).


My UPS batteries are very weak and give about 4-5 minutes backup on
power-failure. Could this be causing the problem? How do i check to
see if the battery is dead?

 

[Eeyore]

My computer gives me a shock; Some details:
Supply: 250 V/50 Hz.

Surely you mean 230V ?

Neutral to Ground at plug-point: 4-5V.
Power On (UPS), but no equipment drawing power: 9V (Computer-case to
Earth).
With everything powered ON: 20V (Case to Earth).

There's clearly something wrong there since a case should normally be earthed.
But even so - you shouldn't notice even 20V.

Everything ON: 5V (Earth to Neutral at powerstrip - before the UPS).

The neutral voltage is higher than I'd normally expect to see but nothing out of
order.

My UPS batteries are very weak and give about 4-5 minutes backup on
power-failure. Could this be causing the problem?
No.

How do i check to see if the battery is dead?

Do you have a voltmeter ? Check its voltage during the discharge cycle.

Are you sure you're not simply getting 'static electricity shocks' when touching
the PC ? Do you have carpets with synthetic fibre for example ? Do you tend to
wear clothes with a high synthic fibre content ? These are all things that wil
charge *you* up and the PC wil simply *discharge* you when you touch it.

Graham

 

[Vivek.M]

Surely you mean 230V ?

Yes indeed! Terribly sorry ( my analog-multimeter has a 250V slot and
i .. well auto-suggestion! ) The input voltage is fine 235 V.

Do you have a voltmeter ? Check its voltage during the discharge cycle.

I'll do that. I haven't opened it up as yet.

Are you sure you're not simply getting 'static electricity shocks' when touching
the PC ? Do you have carpets with synthetic fibre for example ? Do you tend to
wear clothes with a high synthic fibre content ? These are all things that wil
charge *you* up and the PC wil simply *discharge* you when you touch it.

It's definetly not static; bare floor and absolutely no carpeting or
synthetic fibre. My parents and sister have been getting jolted as
well so it's definitely not a case of clothing. Plus as you said 20V
is a little high and that's off the case. Plus static jolts feel
different.

Any idea where the problem could lie - surely it's in the UPS? Any
idea what could have blown?

 

[[email protected]]

Yes indeed! Terribly sorry ( my analog-multimeter has a 250V slot and
i .. well auto-suggestion! ) The input voltage is fine 235 V.

I'll do that. I haven't opened it up as yet.

It's definetly not static; bare floor and absolutely no carpeting or
synthetic fibre. My parents and sister have been getting jolted as
well so it's definitely not a case of clothing. Plus as you said 20V
is a little high and that's off the case. Plus static jolts feel
different.

Any idea where the problem could lie - surely it's in the UPS? Any
idea what could have blown?

I am betting nothing is "blown." You more likely have MOV protect
devices that have gone leaky in either the front end of the UPS or the
front end of the computer power supplies. Actually could be in any
device on that circuit or any outlet strip that has surge protection.

The voltage you are reading is basically meaningless, unless it was at
full mains voltage. You need to be measuring the leakage current with
a proper leakage meter.

 

[James Thompson]

I am betting nothing is "blown." You more likely have MOV protect
devices that have gone leaky in either the front end of the UPS or the
front end of the computer power supplies. Actually could be in any
device on that circuit or any outlet strip that has surge protection.

The voltage you are reading is basically meaningless, unless it was at
full mains voltage. You need to be measuring the leakage current with
a proper leakage meter.

If your ups is suspect, take it out of the loop. Plug your pc directly in
the your mains and check for leakage voltage on your case. Divide and
conquer..

 

[Vivek.M]

Many thanks you guys! I have isolated the problem and it is in the
UPS. I also spoke to my Dad and he said that he had this problem
before, and the tech had changed a MOV (apparently Dad had the
good-sense to ask - it's apparently a fairly common problem.) Sorry
for the delay in replying and leaving the thread hanging!