Subject: Info: UPS Batteries Internal Resistance From: UPS@ Sender: UPS@ I append http://www.berklix.com/~jhs/std/ups_batteries.txt See Also: http://www.berklix.com/~jhs/txt/batteries/#12v & off line ~/txt/batteries/12v_car_lead_acid/text.txt TO be edited. Q: UPS Battery charge did not go below 70% when the box died after about 5 minutes. No shutdown scripts, no warnings of shutdown, nothing. one might suspect a bug somewhere. A: Start with basics: Suspect the battery. Even the microprocessor inside the UPS that NUT talks to, needs good power, if the battery suddenly drops, the microprocessor may not have time to warn NUT of an approaching or actual failure, & NUT might not have time or power. Old batteries can often appear to have a good charge state (= voltage) even when they've aged & developed a high internal resistance. That happened to me a while back when I wasn't even running any software to control UPS. UPS had been running for years, with charge state good (LEDs). I cut power, & it dropped out after maybe 10 secs ! 2 of the 4 batteries had good voltages but high internal resistance. Battery Internal Resistance You need a good Low internal resistance in All batteries to sustain a substantial UPS load. Example. Assume a load of 480 Watts. Assume a UPS is 100% efficient (it never is). Assume you have 4 x 12V batteries. You'd need to draw 10 amps out of your batteries! They'd wouldnt like that! They'd heat up if they could even sustain the load. Assume a load of 240 Watts, That's 5 Amps. 17Ah batteries could deliver that for a while (a number of minutes at least) You would Not get 17/5 = 3+ hours out of them though, as 17Ah is from memory rated at 1 amp discharge). The less internal resistance the better. 2 new ones I measured 2014-04-10 (afer off line a week min.) had 0.092 & 0.096 ohms. Up to 0.3 or possbly 0.5 is not too bad. 2 of the 4 I pulled out of service, (although Voltage looked OK), were 0.52 & 3.0 ohms. The other 2 of the 4 were worse, low voltage too, maybe 11V, dumped, cant remember their high. resistance 2 other old really bad batteries had 2 & 3 ohms. A pensioned off old one with Voc=10.6 after lieing around (used for a carpet weght & odd electrical things), was 5.3 ohms. Even with a modest 0.3 ohms internal resistance, with 5 amp load, V=IR tells us the battery will be losing (as internal heat) 1.5 V of its nominal 12V, before the voltage gets to the UPS. Test each of your batteries' internal resistances individually, run each battery separately into eg 2 car 12V headlamp(**) light bulbs in parallel, Use Ohms law: V = IR. Measure : Voc = Open Circuit no load Voltage (about 13, less than 14). Vload = While bulb burns bright, I = Current through bulb[s] Notes: - Voltmeter: Use an accurate digital voltmeter, not some crude 15V analogue scale, not good enough to make accurate calculation with. - Ammeter: Use any cheap analogue or digital ammeter, if it doesn't read high enough, guess 1.7 Amps per bulb, if you use same bulbs as I do, see below (**). Else make a shunt for ammeter & calibrate the shunt (I did, but that's beyond remit of this article). - Measure voltage (at the battery not at the bulb, to avoid voltage drops in thin wires to bulbs). - Disconnect & reconnect bulb(s) a few times, noting the difference between Voc & Vload, as it's the difference we want, not the absolute voltage. The initial voltage on first reading will soon drop, & is not of interest for this calculation. The current may gradually drop a bit, not much, the average will do. Calculate Rinternal = (Voc - Vload) / I ** Car Bulbs: (These bulbs are Free ! Just tell car owner friends: when they next blow their dipped or main beam filament within the bulb, as they have to replace it for driving, give the old bulb to you as test gear, it costs them nothing & useful to you.) All my old car headlumps bulbs are marked 12V 45/40W, They seem to take about 1.8 amps from a good battery. (I'm mentioning that in case some people have meters that can't take that much current). At 12V that's 22 Watts, (Maybe the 40W marking is for if both filaments are on ? though maybe that's unlikely ? Obviously a car on dipped beam has just one filament on, whether a car on main beam has both filaments on (or just the non offset dipped filament) I don't know - I'll measure it sometime. Battery Capacity You could calculate capacity in Watt Hours, by running batteries some hours till they grow dim. (You'll need to log current each half hour, as it varies, as batt voltage drops, as resistance of light bulbs depends on brightness. Dont exceed the long term current rating on battery (from memory 1 Amp on a 12V 17AH ?). You can put 12V bulbs in series to increase resistance & reduce current. Battery manufacturers have copious info in PDF on web. I don't bother to do this for my UPS batteries. I would for eg light load picnic fluorescent lighting in a tent, but not for UPS, a UPS is a hungry heavy load, low resistance is Vital, nominal capacity is secondary. Crap Batteries: A few years back, I saw a cheap deal: In UK, Maplin were selling car jump start kits cheap, 25 pounds at 1.22975 eu = 1 gbp. Marked as containing a 17Ah battery, entire kit much cheaper than a Conrad battery. I bought 10 (6 for a friend), drove back home 1000 km, unpacked them, pulled first out of its case, immediately knew it was too light, 3.5 Kg; A Conrad one is 6 Kg. Other previous batteries from other manufacturers have all felt about the same as Conrad, not Chinese lightweight. I tested 1 battery 29 Jun 2010 to see if really 17 Amp Hour as claimed. just 1 tested as it can take 20+ hours to test) Not near so much capacity. they all died relatively quickly, Chinese markings 12V17AH/20HR SEALED RECHARGEABLE BATTERY In line with 2006/66/EC Pb~3% Caution : Don't short circuit battery terminal. NING BO BEI KANG DIAN ZI YOU XIAN GONG SI All out at 2014-04-11. I'm back to buying from Conrad. Another Ning etc found 2016-04-29, that I'd forgotten I'd moved to another car jump start kit: As well as markings above,it (& maybe thus others too) Start with logo: STR R. Steyre Electric. This one 3.6 Kg. There's similar cheap jump start kits on sale in Germany, my guess is some will also have crap Chinese batteries in. For a non crap jump start kit, Simple rule of thumb: Pick it up! kit should weigh maybe at least 8.2 Kg (excluding transformer) My decent black "Energiestation" JS-405 without a battery in, weighs 2.2 Kg., including air compressor & pipe, chassis + heavy jump leads & croc clips, + pcb with meter / LEDs & more 3 small sockets 3 out & 1 in, & big 12V switch, & 12 V car cigarette socket, & swichable light. External transformer not weighed. Battery Prices: At Thu Apr 10 23:40:21 CEST 2014 http://www.conrad.de/ce/de/product/250214/Bleiakku-12-V-17-Ah-Conrad-energy-CE12V17Ah-250214-Blei-Vlies-AGM-B-x-H-x-T-181-x-167-x-76-mm-M5-Schraubanschluss-W/ 59 Euro (same price 2010-06-29 - 2014-04-11 Bestell-Nr.: 250214 - 62 Teile-Nr.: 250214 EAN: 4016138031294 From battey: CP12170 12V17AH Valve Regulated Rechageable battery From title: Bleiakku 12 V 17 Ah Conrad energy CE12V/17Ah 250214 Blei-Vlies (AGM) (B x H x T) 181 x 167 x 76 mm M5-Schraubanschluss W http://www.conrad.de/ce/de/product/250214/AKKU-BLEI-WARTUNGSFREI-12-V-17-AH Disconnect Before Testing: Power down output before testing. Remove mains 220V input before testing. Disconnect batteries before starting. Look for in line fuses on batteries & remove before testing. Shorting between battery terminal with spanners is all too easy a mistake when spanner or screwdriver slips. (The apc_smart_2000 has fuses between batteries 2 & 3 (of 4) making it very convenient to isolate terminals otherwise close adjacent with up to 48V differential. Beware if you dont manage to disconnect the battery, the UPS can still be live, generating 240V. Lethal. Ive seen a UPS kill itself during dismantling, (a screwdriver slipped, the owner guessed the UPS was cheap modern:, designed to be built & sold, not dismantled & service, seemed a good guess !) Changing Batteries: Some manual, APC I think, said change all batteries at the same time. But didn't explain why. An expensive reccomendation if the UPS is personal, not corporate expense, ( 4 x 59 Euros = 236 Euros ( in case this is archived a long time, to allow for inflation, & to allow for readers with other currencies in other parts of the world, a 0.5 litre glass of beer in a bar costs 3.60 Euro), last 2 restaurant meals for 30 & 40 Euros) So I ignored it, & changed batteries individually when each died. I've thought more about it & realised when these batteries die, typially one (occasionaly 2!) of the 6 cells die, & voltage drops from approx 13 volts to 11 volts (ie 1/6 of the 12V nominal), so then as the 4 x 12V batteries are in series in my UPS (an APC) with no intermediate sensor wires to each battery, there's no way the charge controller can see what's happening, so it can only conclude all batteries are a bit low & need a charge. The bad cell will never recover, so all the good cells will be slowly overcharged long term, forever, That will accelerate death of the other batteries. This test occasion, 2 of my my batteries were really bad, one bad & one marginal, so I'm biting the bullet & replacing the whole lot at the same time. http://www.berklix.com Computer Consultancy http://www.berklix.com/~jhs/cv/ My Resume - English & German http://www.berklix.com/~jhs/contact/ Contact - German for business also OK. http://www.berklix.com/free/ Free Software http://www.berklix.org Free Organisations & Clubs --------------------- PS This neeed to become HTML 2016-04-30 12V 17Ah Looks like they've all gone to connections via 2 vertical inset screws, nstead of a hole through 2 vertical flanges. That's going to be a right Pain on my APC UPC that has a fuse PCB with a crew mount, I'll have to build a flange adaptor. URLs http://uk.rs-online.com/web/c/batteries/rechargeable-batteries/lead-acid-rechargeable-batteries/?searchTerm=12V+17ah https://www.conrad.de/de/Search.html?search=12v+17ah http://uk.farnell.com/webapp/wcs/stores/servlet/Search?catalogId=15001&langId=44&storeId=10151&categoryName=All%20Categories&selectedCategoryId=&gs=true&st=12v%2017ah To Merge In: Some batteris can report 13+ Volt, & LED display or meter might show fully charged, but they can still be useless & worth dumping ! I use half dead car headlamps Ive saved as test loads: people normaly throw such bulbs away, but they're ideal as free strong dummy loads, as 1 of the 2 filaments is still intact. Internal resistance can go far too high, & capacity can drop &/ or internal leakage goes way up. To calculate internal resistance, I use 1 or 2 bulbs in parallel for a few seconds (not too long to overheat the battery). To calculate capacity I use several bulbs in series, to decrease discharge current down to rated level (else battery would capacity would appear lower than at rated current). ============= Q on UPS NUT list 2020-01: How to test batteries ? A: As Impedance of bulbs varies according to brightness. I'd be wanting to measure current drawn with an ammeter. A 100W bulb in 110V USA would be different resistance to in 230V Europe etc. Battery discharge time quoted in specs is at rated discharge current. Theres usualy an industry norm of rated discharge current being a factor of capacity in Ah (maybe 10? so eg a 17 Ah 12 V battery might be 1.7 ? but memory is vague, readers can research that on battery specs or wikipedia). UPS typically can pull a lot more current if a heavy load, so of course bats flatten v. quick, & also not good for bats to flatten that fast (or to charge fast either, think plate buckling & also from memory, soft versus had deposition of elecrolyte on plates , out of my depth again, read wiki on chemistry of lead acid & lead gell plates if you want to know) For years now, when my car, friends, or family cars have a duff headlamp bulb where one of the 2 elements main & dipped have blown, & must be changed, I've saved the bulb as an ideal 12V load, sucking about 4 amps each. Put 2 or 3 in parallel & you'll simulate a very hungry UPS (& damage the battery if you do it for long), put 2 or 3 in series & you can provide a gentle load to safely test a 17Ah battery capacity. You could buy new card headlamp bulbs of course ;-) All of above having disconnected batteries from UPS, & testing one 12V battery at a time. Never forget there will be capacitors in there too, sometime bats are v. hard to get at. One can get mains voltage sparks injurious to UPS & humans ;-) Of course above also depends on size of UPS & batteries. They vary drastically. I have 2 lead gell UPS, but I spos new ons are going Lion. Ive been in a battery room of a large phone exchange where each cell was about 1 metre square, & chest height, full of lead plates & open acid, ~ 25 cells of 2V each making 50V, & 3 rows thereof, it was part of a UPS, rather different ratings there :-) I imagine a lot of the above is in the NUT UPS FAQ.