Mark Rogers wrote:

On 07/01/10 09:49, stevey.eu wrote:

...

Having only just got back on after 24hours, I have no end of issues, so am thinking a UPS is in order.

That and my LAN switch no longer works.

Any suggestions for suitable replacements would be handy right now.

I tend to only use APC UPS devices. Mostly because they are well supported in linux with apcupsd, in fact I would go as far as to say they are better supported in linux than windows :)

As to the lan switch you will probably find it is just the PSU brick (assuming it is separate because this is a domestic grade 4/8 port jobby) it's probably something common like 12v with a fairly generic size DC connector so you could just test and replace that.

As to buying new ones the only advice I can offer is avoid the Netgear GS560 as it is very fussy about what machines it will provide 1000baseT to (or at least mine is)

Not particularly helpful but I can say that several customers have had UPS deaths recently (varying brands).

What usually causes a UPS to fail and can they be repaired?

On some makes (even more so with cheaper ones) a completely dead battery will cause the UPS to go into a state were you can't power it up, even some APC's suffer from this, although most modern APC units test the batteries even when on a reliable supply and therefore should have been telling you the batteries were shot for ages.

Otherwise you have to look at repair costs taking into account the state of the batteries anyway. Given that battery replacement is usually in the order of 50-70% of the cost of the new unit. There is no point repairing a unit with tired batteries, only to have to replace them later.

Also APC's have a rear mounted circuit breaker that is easily missed, and an internal fuse. Other makes may have similar.

On 07/01/10 11:10, Steve Fosdick wrote:

In a modern unit I would expect both the converters to be switch mode designs and, from what I remember, one of the difficulties of switch mode PSU design is that one generally wants the control electronics powered from the low voltage DC which isn't available until the unit has started up thus necessitating some extra components for a "startup mode". My guess is that in the case of those cheap UPSs they miss out the extra components and use the battery to power the control electronics until the input SMPS has got going in which case if the battery is dead it won't start.

Interesting...

The implication of this is that if I charge the battery outside the unit then I can recover the unit.

Alternatively, if I can provide the necessary DC supply to the control electronics then the UPS may recover itself.

Any hints as to whether this can be done and/or how? I appreciate, by the way, that the whole point of a UPS is that there are high voltages kicking around, so this is a completely theoretical interest and I won't blame anyone if I subsequently kill myself...

Steve Fosdick wrote:

On Thu, 2010-01-07 at 10:18 +0000, Wayne Stallwood wrote:

...

On some makes (even more so with cheaper ones) a completely dead battery will cause the UPS to go into a state were you can't power it up, even some APC's suffer from this, although most modern APC units test the batteries even when on a reliable supply and therefore should have been telling you the batteries were shot for ages.

Interesting.

A basic design for a UPS has a converter that converts mains voltage AC to the correct DC voltage to keep the batteries charged and an inverter that converts that DC voltage back to mains voltage AC, either all the time or when the mains fails[1].

In a modern unit I would expect both the converters to be switch mode designs and, from what I remember, one of the difficulties of switch mode PSU design is that one generally wants the control electronics powered from the low voltage DC which isn't available until the unit has started up thus necessitating some extra components for a "startup mode". My guess is that in the case of those cheap UPSs they miss out the extra components and use the battery to power the control electronics until the input SMPS has got going in which case if the battery is dead it won't start.

yes exactly that, the soft power on feature requires power itself to start the UPS. Normally this is derived from the trickle charge + battery voltage..However when the batteries are in a heavily discharged state they pull down the trickle voltage to the point the control electronics can't operate. Worse than that some really nasty designs (cough Belkin cough) don't supply the trickle voltage until the UPS has started. So in that case you are in catch22 if the batteries are completely discharged.

Reading some articles I found on Google it seems the batteries are generally regarded as the weakest link and, if the point at which one finds the UPS is broken is when it fails to take over when the mains fails this makes this even more likely.

Steve.

[1] There are also some delta conversion units where the inverter can be used to top-up the mains rather than completely replace it.

Yes these are called "On-Line" UPS's where the inverter stage provides the output power all of the time and is driven from either the batteries or mains in. The advantage is that there is zero transition noise when going from Mains to DC derived power and the output is both isolated and immune to transient fluctuations that may be on the supply. Downsides are that It makes the UPS more expensive and less efficient.

Off-Line UPS's switch between filtered mains and the output of the inverter depending on the state of the supply, this causes a changeover spike as they switch between Mains and DC and means that the purity of the output is only as good as the filter on the mains..Also they cannot "correct" a high or low supply without depleting the batteries by flicking over to DC mode....Most small consumer grade UPS's are of this design.

APC's "Smart UPS" range is actually a hybrid. Usually it is running as an off-line type where the output is just filtered mains until it drops out of spec. Then the UPS moves to a On-Line mode where the output is inverter derived but the power is still sourced from mains. This is when the UPS is in AVR move and is correcting either a high or low mains supply. Finally if the mains supply drops completely then they go into full battery mode.