Em Quinta 07 Janeiro 2010 08:27,
[email protected] escreveu:
You are confusing a UPS with a emergency electric generator; those are the
ones that start working after the power goes off.
A UPS needs to keep the power up without letting it go down even for a split
second.
Let's be more scientific: at 50 Hz, there are zero-crossings every 10 ms.
The only switch a ups does when the power goes off is that it stops charging
the batteries. The output of a UPS is allways given by the same circuits
regardless if the power is on or off
with power on:
main power -> AC-DC converter -> DC-AC converter -> output
-> charge batteries.
with power off:
batteries -> DC-AC converter -> output
this is the only way that an ups can keep the output on without any breaks.
So the computer is fed from the UPS *always*,
and the "switch over is only from (accum to ) or (mains to D2A) ?
M-A2D-D2A->C
----B-D2A->C
so resuming: if the ups's output is given the wrong voltage, frequency,
sinosoidal wave, etc... you have two choices:
1- repair the ups
2- replace the ups.
What did I write to suggest that "the ups's output is given the wrong" output ?
How would that cause the earth-leakage to activate ?
============
philo said:
So the conclusion is reversed from what has happened
It was a ground fault which *caused* the power interruption.
The UPS simply was on because the "mains" breaker had tripped
No it's a chain of events over a few milliseconds.
The UPS detects that the mains is 'abnormal' and switches;
which causes an earth-leakage abnormality.
My problem is that since the earth-leakage AFAIK is mechanical,
it should not react to the spike caused by the UPS.
What are typical earth leakage response times?
=============
if you have electrical questions, it's better to put them in
sci.electronics.basics
yes, the boys here are just guessing.
i can tell you that if you desconnect the earth, ther will be no more a
neutral in the output, you will have two live lines with a voltage
between them, and that could cause other issues.
Yes disabling the earth-leakage-detector is not good.
==========
david wrote:-
This is only true with a double-conversion type UPS, which most cheap PC-
type UPS's are not. Most cheap UPSs have a transfer switch in them, so
the power is actually interrupted for a few milliseconds when the mains
fail.
Yes, I'd expect the computer PSU to 'hold over' for 2 cycles: 20 ms.
It seems that none of you are considering the interaction back to the
earth-leakage ?
== Thanks for any reasoned answers [not guesses].
