Re: Battery backup: problem with my APC?

Rod Speed wrote:
David Brown wrote
Rod Speed wrote
David Brown wrote
Rod Speed wrote
Ian D wrote
Rod Speed <rod.speed.aaa@xxxxxxxxx> wrote
Ian D wrote
kenk <kenk@xxxxxxxxxxx> wrote

I was sitting at my desk yesterday during a storm when there was a split-second power outage. Despite the fact that my battery shows all 5 lights lit, the computer died.

Is there a better brand to use than APC? Can the battery be sub-par even though the test lights say it
is OK? What have others of you chosen?

I would be looking at your PC's power supply. There is
a very brief delay between the loss of power, and the
UPS switchover to battery power.

Not with continuous UPSs, there is no delay at all with those.

Essentially the PC is running off the UPS output all the time and the only thing that changes with the mains failure is that the UPS isnt being charged anymore and runs off the battery instead.

That's correct, and those units are the ones with true sine
wave output,

Nope, the type of output is an entirely separate issue.

Both types of UPS generate roughly sine wave outputs when the inverter is active.

Pity he was clearly talking about TRUE sine wave output, which only a small subset of UPSs produce. And it aint even the continuous/online UPSs that mostly do produce TRUE sine wave output.

I don't know exactly what you mean by "TRUE sine wave"

Should be obvious to even someone as stupid as you.

- all UPS's generate a sine wave of sorts when they are active

Wrong, as always. Plenty generate a square wave instead.


You might know about /buying/ and /using/ UPS's, but you don't know much
about sine waves, AC/DC conversion, harmonics, and related technicalities. A square wave (as produced by very low-end UPS's) is just a sine wave with large harmonics. And at the high end, good UPS's use PWM switching to produce something closer to a sine wave - even after filtering, it is still not a "TRUE" sine wave.

(i.e., all the time for continuous/online UPS's, or during power fail for standby devices). The quality of the sine wave varies from
fairly poor (lots of harmonics) to pretty good (few harmonics),
but is /never/ pure.

That last is just plain wrong.


I'll accept that the first part might be wrong - a square wave is a very poor sine wave, rather than just "fairly poor". As I have said, I haven't been looking at such low end devices.

However, if you think that UPS's generate *true* sine waves with no harmonics, I'd love to see the circuit diagrams. I'd also like to know which brands go to great efforts to get closest to a sine wave - so that I can avoid them, as it would be a total waste of money.

If you are restricting discussion only to those UPS's that produce good quality sine waves,

I was JUST commenting on HIS claim about TRUE sine wave output, fuckwit.

So I can't talk about UPS's that don't produce mythical "TRUE sine waves" because a previous poster talked about "TRUE sine wave" UPS's, but /you/ can talk about any UPS's you like? I'm sure that makes sense to you, somehow.


then I'll have to take your word for how standby and online UPS prices compare. Baring the worst of the cheapo devices, the sine quality of any UPS is going to be good enough for computer hardware, and is typically better than you get straight from the mains. Thus it's not a restriction that I've considered.

Completely and utterly irrelevant to the comment I made about his stupid pig ignorant claim about TRUE sine wave output.

The difference is that with a standby UPS, the inverter is not
active unless the power fails, so the output is just a
filtered version of the input.

Thats an entirely separate matter to TRUE sine wave output.

True - though again, there is no such thing as "TRUE sine wave output", merely more or less harmonics.

Wrong, as always. True sinewave is NO harmonics.


Correct - a "true sine wave" has no harmonics. No UPS could possibly produce one. There is no point in an UPS even trying - it makes sense to limit the first few harmonics as much as practically possible, but you get very little gain from going further than that.

Surely you are aware that a "true" sinewave exists only as a mathematical concept - anything in real life is only going to be an approximation?

<snip the incoherent rodbot responses>

If you are talking about DC supply buses to servers,

Nope, its just as true of desktop PCs.


I've only seen discussions of DC supply buses in the context of server racks, where you have lots of machines together. Since desktop PC's are typically spread out, you can't conveniently have a single AC to DC supply for multiple machines.

rather than having an AC supply to each, then I think it's a very good idea. It is quite simply idiotic to take a high voltage AC supply, convert it to low voltage DC for a battery, turn it back to
high voltage AC to deliver to a server's power supply, which then turns it back to a low voltage DC.

It isnt idiotic, its just not as efficient. Many dont give a damn about the efficiency with a device that isnt taking that much power.


True enough for machines with low power requirements. But the discussion here has moved on to multiple machines - for server racks, the electricity price is often a very big part of the cost.

Converting AC to 24V to 48V DC for battery storage, and passing that straight to a server's power supply

Just as true of a desktop's power supply.


It is indeed true of a desktop's power supply - but unless a significant percentage of users start using UPSs with their desktops, the economics won't allow anything but AC supplies on desktops.

would be significantly more efficient in energy use,

Not very significantly, actually.


For people with big installations, even small percentages are significant. But a rough rule of thumb would be 3-5% energy loss for each high voltage AC to low voltage DC conversion, assuming top of the range converters. By avoiding the extra conversion to AC after the UPS and before the server supplies, you'd save up to 10%.

and much smaller and cheaper in hardware.

Nope, its actually more expensive, essentially because that approach
doesnt sell in the same volume that traditional UPSs do.


Economics of scale are certainly relevant. But server rack UPS and supply systems are not huge volumes anyway, and the energy savings would be appealing. And the hardware itself would be smaller and a lot cheaper once volumes are of similar magnitudes.

.

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