COTS Battery Backup

Folderol wrote on 8/16/2017 3:08 AM:

You post is not very clear. You seem to be mixing use cases and attempting to attribute the difference in results to the battery chemistry. If you keep batteries topped off and seldom actually use them they will last a long, long time. I had a power drill with NiCd which lasted some 15 or 20 years because I didn't use it much and kept it from running down. On the railroad they use lead acid batteries (not SLA) for signal backup power, again seldom drained and always on trickle charge. They last a long time as well. Different chemistries, similar use cases and results.

Yep, all BT exchnages (even the tiny "garden shed" rural ones) are battery powered with generator back up. I note you say "ADSL modem". ADSL probably will work under power fail conditions as it comes from the exchnage. The chances are VDSL (Fibre to the Cabinet) won't or if it does not for very long. The cabinets do have batteries but really only to support the kit for a few minutes of a manual switching outage or auto recloser trip/reset.

Not APC kit then, thier stuff cooks batteries in around 3 to 4 years.

Hum isn't it a legal requirement for emergency lighting to run for >3 hours? A 30 min run won't show up a battery that has lost capacity below that required for a >3 hour run time.

That wouldn't be the 'bulging battery' syndrome would it? One of my colleagues came across that some years ago. Crappy over-complicated charge circuit built on cheap PCB (not fibreglass). Current driven series transistor with no heatsink charred the pcb so there was enough C-B leakage to prevent the transistor switching off properly.

Single story office complex with separate single story workshop, both with plenty of access. We were told 1 hour, and since we can easily evacuate both buildings in less that 10 minutes, I don't think we'll have a problem with a 30 min test :)

I've seen the same where I work. Nowadays we all have laptops instead of desktops etc. but they are really used to run MS Office (spit), PDF viewers and as X/RDP terminals onto the compute farms. Until relatively recent times the laptops that were used a lot in the meeting/conference rooms on battery had better battery life that many machines that were plugged into a docking station all their life.

My latest laptop (Dell e7450 Ultrabook) does have a smarter charger. It doesn't immediately rush to charge the battery to 100% as soon as you dock it. Quite often I've seen it indicating 90% charge and running from the AC supply. Only when it's been discharged to nearer 80% does it then charge it back to 100%. There's some power management dashboard software where you can tweak these settings.

Mine is 3yr 2months old and due for replacement in 4 months. If I run in on battery power doing lightweight tasks (browsing, email, X/RDP to the farms etc.) then it will last for over 8 hours still. All the people with e7450s are still on the original batteries. In past times, I'd have expected 30% of them to have needed a replacement battery after 2 years.

Is it better battery design or smarter charging circuity? Who knows. It's bijou and compact and goes like the clappers when you need it to. The only downside is the 1920x1200 screen is small and whilst I don't need glasses to use a 24in monitor, I can't see a thing on this without them.

That's just not true. I have APC units that have lasted over a decade and still going strong. It might actually be closer to two decades.

Not sure what you are doing different, my experience is very inline with the reply you followed up to.

Dozens of APC SmartUPS units in data centers and in the field. Their batteries last between 3 and 5 years and require replacement in 100% of my units. I wouldn't say just APC is at fault, but this is just how long car and motorcycle/lawn motor lead-acid cells last that the standard UPS vendors use.

Much like my much bigger online UPS units. They all use car batteries, and have a definiate maintenance cycle for how often those batteries need to be replaced, just like in your car for it's lead acid battery.

With orginal batteries and actually able to run off battery for roughly the time expected for the load?

My APC UPS has a manufactured date of 11 Mar 98 and it is fine but is on it's fourth or fith (I think) set of batteries. I found out the hard way, twice, that even though it says the batteries are OK, fully charged and decent voltage, try and draw any power from 'em and they die very quickly. Last time there was a strange smell, eventually tacked down to the UPS with an almost too hot to touch case. The batteries:

After that I looked up the spec for the batteries and recomended float voltage v temperature. The APC charge voltage was nearer to the specified cyclic charge voltage at room temperature let alone the 40 C that the batteries ran at. I "got at" the charge circuit reduced the voltage down to what it should be for float charging at 30 C and fitted a small fan. That was back in 2014, these batteries are still good. Left to APC they'd be cooked or very nearly so by now.

I've also seen a couple of rack mount APC UPS's with cooked/swollen batteries. One had to be junked as to remove the batteries would have required the chassis cutting apart.

Any sensible user of these devices should be replacing the batteries @ the recommended intervals which would be long before they ware stating to show signs of failing.

you don't want for find out your UPS batteries are shot when you have that power outage & loose critical data

A car battery is lead acid but they have very different characteristics to those used in UPS's or other applications that require deep cyclic use. A car battery will not take kindly to a single deep discharge and a handful of such cycles will almost guarantee a car battery becoming useless.

Car batteries last much better than they used to. 20/30 years ago, you'd expect to replace the battery after 5 years or so. Last car was

For deep discharge cyclic use you need a battery designed for that use, sometimes known as a "leisure" battery,

I don't think my APC unit has a recommended interval. Instead it has an automatic "test" mode that lights a "replace battery" light. IMHO this test mode is another contributory factor to short battery life in APC UPS's. It doesn't perform a decent cycle.

Routine replacement is OK for a situation that absolutely requires power but not particulary economic for many other cases.

So why cook the batteries thus shortening their useful life? Two things spring to mind: High charge rate to reduce the time required to after the UPS has shutdown due to low battery, restoration of mains power and the UPS restarting. Fair enough but why have a fixed charge rate? It's not exactly difficult to switch from a high rate to a float rate. Or APC just want to increase the sales of their rather expensive "battery packs".

Three years is *NOT* the expected lifetime of lead acid batteries of *any* kind. When I buy a quality battery for my car it lasts five years or more and automotive use is one of the worst applications for lead acid.

I worked for the rail road and we had batteries in service for 20 years before they needed replacing. That was an optimal application for lead acid. They were trickle charged with very intermittent use, nearly the same as UPS (I don't expect they trickle charge once the cells have been used). Phone company use is the same, large batteries that are on trickle charge

Replacing the battery every 3 years is recommended by the UPS companies because they make a lot of money on the replacement batteries.

Can't say. It is hard to get that info from APC and I can't find a model number on the unit other than the info on top. Mostly I'm too lazy to dig it up at the moment. I am using it to power the modem and router and seems to do that for hours, so that's as much test as I need. My laptop will only run for an hour or so on batteries, so no point in worrying about longer times.

So you have a bad UPS, not bad batteries.

Umm. I think that was exactly the point being made.

It's now over 30 years since I did any serious work with batteries so things have no doubt improved, but what I learned then particulalry regarding SLAs might suprise. I was mostly concerend with standby use, so only studied trickle charge situations.

First off, charge voltage is inversely proportional to temperature, and one of the companies I contacted was kind enough to send me a schematic of a simple compensated voltage regulator, with a thermister which had to be *in* *Thermal*

Secondly, not all batteries (even from the same manufacturer) have the same reference charge voltage - so check the specs. As far as I remember, for a 12V

The life expectancies I saw at that time for that battery size were in the range of 5-6 years for 50% retained capacity. That was with no deep discharges. I remember being surprised that the curves suggested the life was slighter shorter if there were virtually no moderate discharges over that time.

s/nobody/hardly anybody/

Here's one that does:

Well that rather proves how out of date I am :)

Looks like a nice range of kit, and I see they do support an optional external temperature sensor, although it's for the ambient temperature in the vicinity of the battery not in contact with it.

On mine the sensor is mounted in a lug that you can attach to one of the battery terminals along with the charging wire.

That's good. You won't get much closer to the internal temperature without making holes :)

Would you care to share that schematic? Please?