UPS batteries

Hi!

I rarely have power outages here, and my most recent UPS battery change involved a unit that did nothing more than "buffer" a phone system until a generator would come on. Its battery lasted 10 years (1998-2008). The UPS in question is an APC Back-UPS 600.

I attribute part of that long lifetime to the fact that the battery could have degraded to where it had almost no runtime left--but that would have been fine as the generator started and stabilized within a few seconds.

I can't say that I have firsthand knowledge. (Meaning: I've never designed or built a UPS circuit from scratch...) However, the trouble is likely to come from the float charging. I'm of the impression that at least some UPS units have an awfully "hot" float charge and it probably leads to the battery being overcharged. I've seen some Tripp- Lite UPS units that would slowly drive the water out of their batteries if left float charging all the time.

I also think there are some that don't put enough of a float charge on a battery to truly keep it up. I have an older APC Smart-UPS 1000 that demonstrates this behavior--if the power hasn't been out in a while, the battery will drop more quickly than it does when the unit has had only a short time (a few days) between the completion of a battery charge after use and a subsequent power outage.

You also have to consider that some UPS designs depend upon their battery and inverter to deal with *every* little power line anomaly. This too will shorten the battery's useful life. This seems to be true of the inexpensive APC "plugstrip" UPS units that many people have.

Better designs have methods by which to stabilize, boost or trim the power coming out of them without having to use the battery and inverter.

William

Here is where I visit when I have battery questions:

Float voltage is critical for long storage battery life - +/- 0.01V!

John :-#)#

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I know what you mean. By the time you need the UPS, the batteries won't carry a load. I found out that the chargers 'cook' the batteries. I hooked up 2 motorcycle batteries to replace my dead ones. You need 2 to make 24 volts in series. The Belkin UPS boiled the water out of them in 2 weeks. They are poorly designed.

That's not what kills most UPS batteries.

That, but also an unreasonably high float voltage, is what kills them. We've seen literally dozens of UPS' from assorted manufacturers with failed batteries - baked dry, swollen, cracked cases. On fitting new batteries and checking the charger behaviour, we note that the recovery charge rate is definitely "too aggressive" (motive onvious) and the eventual float charge voltage was definitely destined to kill the cells within a year or so.

The only time we were happy that the cells were within the manufacturer approved envelope was ... on DISCHARGE.

Both my old and my new SOLA UPS use a float voltage of 13.5 volts (near enough), which is at the low end of the battery manufacturer's recommendation (13.5 to 13.8). I get about three years out of batteries in the old UPS. Too soon to say about the new one.

Once a month, the UPS switches to battery power for a minute, to test the batteries. Given the current drawn, I have to wonder whether the self test function itself tends to limit the life of the batteries.

Tests on the rejected batteries suggests that they still have 2/3 of their nominal capacity - but maybe they can't deliver the current required.

Sylvia.

I own two APC 1000va units purchased around 2002. Both function perfect and do self tests regularly. Both have 'replace battery' indication if they fail the self test. Neither are tethered to a computer. Also own a 350va APC unit that provides power for my modem and network storage device. It was purchased around 2004 and last time I tested it in Oct it ran for an hour unplugged.

I've seen plenty of APC units fail prematurely though so I really don't understand the reasons why some do and some don't. And I've owned other brands besides APC but they were not long-lived.

That's a long time for a UPS, and suggest's it's not heavily loaded. The self test would be similarly undemanding.

Sylvia.

The 350va powers a cable modem, two USB hard drives and a Linksys network storage server 24/7/365.

The self test on the two 1000va units simulate a power failure allowing them to run off battery power for 10 seconds or so. Enough time for the unit to evaluate the state of the batteries according to how it was designed. One 1000va unit provides power for a SA Explorer HDTV cable DVR and a Panasonic 51" rear projector TV. The other powers a 3 yr old desktop PC and 22" monitor and a 32" LCD HDTV.

I don't think you understand the principals of demand or load well enough.

Define "most".

A quality UPS (not one of those cheap Chinese POS units) will regularly exercise the batteries, running discharge/charge cycles and measuring the results. Then the UPS will tell you the condition of the batteries.

So you keep a mystery what brand and model UPS you are using...

My APC SmartUPS 700 successfully ran selftests up until one of the batteries failed and everything it supplied went down. :-(

It runs with a maximum load of 30%.

I have been contemplating using two full size 60Ah car batteries externally instead of the small 7Ah internals.

Hi!

Don't expect that it will work. If any of my APC UPS units (about 12) are anything to by, the only way you'll know the battery is dead is when it fails to support the load. Most of these are not cheap units, either--they are SmartUPS units that have a true sinewave inverter. So far, only one has ever illuminated the "battery fault" indicator as a result of a self test.

Even if they fail to support the load entirely, this is not enough to trip the fault indicator.

The ones I've seen the most failures out of are the ones that were made in China. Every one of them failed in the same way--I came in and found they were dead to the world. No fuses or breakers had blown, and the batteries were good. Out of four units, three have failed in this way. The fourth works but does not really charge its batteries properly.

None of my APC units marked as being made in the US or India have failed. Some of them are over ten years old (having had their batteries replaced, of course).

I've had good results with APC and Tripp Lite units. Everything else (Belkin, Cyber Power) seems to have a poor lifetime and...interesting...build quality. I have a big stack of CyberPower units and they all look to have failed in the same way--something inside them simply got too hot and gave up the ghost. And every one has had a bad battery. Never seen any Belkin units, but I've heard bad things about them...

Buying a UPS that is larger than you need will also improve the lifetime of the unit and its batteries. The ratings provided by the manufacturers are VERY optimistic and only result in a few minutes of operation.

William

Don't automatically assume that doubling the batteries will extend the run time. I was very surprised.

I've a 9 year old APC Smart-700 UPS. I tried at one point doubling up on the batteries to extend run time. It performed as expected without the powerchute software running - more than doubling the run time.

With powerchute, it performed as if the extra batteries were not there; the run-time calibration 'couldn't see' the extra batteries, perhaps because the EPROM 'knows' that no external batteries were installed. I'd thought the hw/sw would look at the battery voltage (only) and use that value to decide when to shut down; didn't happen.

You may get different results - different models, mfrs. firmware, etc.

Hi William,

(and "All" -- I'll try to address all of the posts I have seen here > I rarely have power outages here, and my most recent UPS battery

IME, when the batteries are toast, you won't get *any* up-time from the UPS. Power goes... and so does the UPS! :-/

Agreed.

I've seen lots of UPS's discarded because they have killed their battery packs. Bulging battery cases, cracks, etc.

Some UPS's actually power the load continuously and are recharging the battery from the AC line (like telco's operate). I would think this would be more stressful on the switching power supply than the battery (as, essentially, the same current is flowing into the battery as out)

I (currently) have: 1x Back-UPS Pro 500 2x Back-UPS ES 550 2x Back-UPS XS 1000 1x Back-UPS RS 1500 1x MX 3000 (all APCC)

I discarded a Belkin unit that appeared to be a repackaged Pro 500 (actually had the nice feature of using a removable power cord!)

I've also previously discarded a Back UPS 600 (?) as it used a different physical size battery that was hard to come by (since it didn't offer any feature that I didn't have on other UPS's -- and, also had two pigtail power outlets on the rear which always seemed like a kludge).

I discarded a large HP "UPS 1000" which was a decent box (I think Astec internals) but totally unsupported. IIRC, it ran off 48V and had another 48V external battery pack.

I managed to blow up another larger UPS (3KVA... the size of a dishwasher) by forgetting that power was still available from the battery pack even though the AC mains were disconnected... shorting a 120V battery into damn near anything destroys the "anything"! :< )

All of my UPS's are connected to PC's or servers. So, all feed reactive loads. Most are oversized for the loads they power. Occasionally, I will run an extension cord from one of them to power a CF light in another room if we have an outage at night. (a "100 equivalent watt" CF runs for a LONG TIME on a small UPS!)

All of the APCC devices have "replace battery" indicators. All of them do a loaded test on power up (for about 2-3 seconds). I am not sure if they periodically run other tests as it is hard to hear the characteristic "buzz" that accompanies the test when a server is running (fan noise). I think all are tied in to their respective computer/server (typically USB or EIA232) though that should just help the machine shut down before power is pulled.

I think all of the APCC designs use low voltage primaries. E.g.,

12 or 24V. I don't know if the battery abuse is consequential to this (perhaps the charging circuits on the UPS's that I've had that utilized 48V or 120V primaries were better designed of necessity?)

I've taken to powering the UPS's off when their loads are not in use. I.e., they can (over?)charge their batteries only while I am using their loads. Thereafter, they act like power strips and let me shut down all of the loads. This is intended to see if the problem I -- and associates -- have been seeing is related to an aggressive float. (it also has the advantage of silencing the silly alarms that signal in the event of a power outage -- if the UPS is on but its loads are NOT, then I really don't want to be bothered by a chorus of half a dozen little "chirpers"!)

I don't think it prudent to use regular lead acid batteries ("car batteries") in these applications unless the batteries themselves could be located in a ventilated area -- I'd be wary of outgassing. I had thought of replacing the gelled electrolyte batteries in the UPS that I blew up with car batteries (this would have required *10* such batteries) and locating the UPS in the garage with the batteries on the outside of the building for this very reason. Then, starving the electrolyte in those batteries to improve longevity.

In the short term, I see no other remedy for "fixing" the battery mongers... :<

Better off to make your own. All you need is a good car battery, trickle charger, RV inverter and a couple relays.

Where did you get that from?

A normal 1000VA unit would not usually have sufficient storage to provide anything approaching 1000VA for an hour. So unless it's a specially high capacity unit, the fact that it can supply its actual load for an hour suggests that that load is nothing like 1000VA.

Sylvia.

That doesn't sound a very sensible design - the expression "next to useless" comes to mind, since it pretty much guarantees the very failure it's designed to protect against. My SOLA UPS certainly didn't do that on any of the times when it decided that the batteries were no longer up to the task.

Sylvia.

Make sure you keep a couple fire extinguishers handy.

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That takes care of one of the killer parameters - float voltage. But at what rate do they recharge after a serious discharge?

The battery current to provide full UPS output is generally pushing the envelope. But vecause it is typically for ten minutes or less, it is generally not that deleterious IMOE.

Capacity, yes. But internal resistance will be too high to allow any decent discharge current..

I haven't checked that. My AVO meter apparently has a significant voltage drop on its current range which messes up the result :(

Sylvia.