I have several 1000 watt Triplite sinewave UPS. The batteries had a date code of 2021 and testing with an 800 watt resistive load ,two heat guns,I was getting around 3 minutes run time,specs state 6 minutes at 900 watt. Saw some batteries on web for that unit rated at 7.5 amps for $10.00 a piece one year warranty, sounded like a good deal. Installed them ran same test,lasted around 1 minute,called distributor and they want me to test all of them (20). The configuration in UPS is two in series. Using a Fluke current probe ,it measures around 39 amps with 800 watt load,seems like a lot of current being pulled from these little batteries. I measured internal resistance of fully charged battery and is 35 mohm,which seems high since the old batteries read 24 mohm. To speed up testing I was thinking instead of using UPS for testing I was just use a resistive load, have some huge Dale resistors, load the battery to 39 amps until voltage drops to 10.5 VDC and shut down and measure time. I have around 300 bucks in batteries and freight so I guess I'll have to jump thru these hoops for the for the distributor. What do you think of this test process?
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\$\begingroup\$ understand whether you are testing the batteries against their specification, to see if the battery purchase was a scam, OR, are you testing the battery specification against your UPS use needs to see whether the specification is appropriate. Battery capacity will be waaaay different when tested to flat in a few minutes, compared to testing to flat in 20 hours, which is where the battery capacity is specified. Most lead acid batteries do not specify the 5 minute performance. \$\endgroup\$– Neil_UKCommented Jun 15 at 5:55
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\$\begingroup\$ @Neil_UK Just reading, it seems that the specification wasn't at all exceeded. In fact, the questioner appears to have gone out of their way to make sure that they were close, but under, the spec. If the spec says 6 minutes at 900 W and they only get 3 minutes at 800 W, then it's simply not meeting the spec. As I read it, anyway. As far as the replacement batteries, I've no opinion. Just discussing the Triplite spec. We may be at cross-purposes though, with me discussing the Triplite side and you discussing the replacement batteries. I may be misunderstanding that part. \$\endgroup\$– periblepsisCommented Jun 15 at 7:07
1 Answer
The best test process is the UPS. Reason being, it tests the batteries at the power level you're planning to use them. However, this doesn't tell if the batteries are faulty, it just tells if they're good for your use case.
Sure, you could buy a 800 watt electronic DC load, but given that even 300 watt electronic load costs 500 USD if you buy the cheap Chinese versions, that's an expensive way.
However, batteries vary. Some have higher internal resistance and are less suited for high loads. It may be that your batteries are such batteries. In this case, this doesn't indicate the batteries are faulty. It just indicates they're not the optimal type for your use case.
To test if the batteries are faulty, you want to do a C/20 test. For 7 Ah (not 7 amp but 7 Ah), this means discharge at a constant current of 0.35 amperes, until you hit whatever voltage limit you set (10.5 volts would give practically full capacity but even one discharge to 10.5 volts may reduce battery longevity and please remember to immediately recharge them if you ever discharge to 10.5 volts).
I don't want to give any direct links to sellers, but from eBay or AliExpress you should be able to find plenty of sellers that sell this 60 watt constant current electronic load. It's a bit crude since it's a bare circuit board without a case, but it's cheap. It operates on a 12 volt DC21 (tip positive, shield negative) supply and can load your battery up to 10 amperes, with current and low voltage limit being settable. It then tells the Ah capacity of your batteries, and also Wh capacity. Set the current to 0.35 amperes and voltage limit to 10.5 volts and test a fully charged battery.
If the Ah capacity of this fully charged new battery doesn't match the specifications, you know it's a faulty battery.
Besides, you just found that most consumer UPSes are crap. They have way too small batteries and no way to install extra batteries (no external extra battery connector). The batteries being lead-acid, Mr. Peukert will beat the hell out of you. My UPS has two 12V 18Ah batteries for a 24V 18Ah system if no extra batteries are connected, plus an extra battery connector through which I installed four 12V 18Ah extra batteries for six total (24V 54Ah total system). So 1296 Wh of capacity. It's a 600 watt UPS. For your 1000 watt UPS, 24V 7Ah system gives only 13% of the capacity of my UPS, even though your UPS has 167% of the power rating of my UPS. So normalized for power rating, you have only 8% of the battery capacity for the same power rating.
Also, remember that lead-acid batteries that have been sitting on the shelf may require multiple days for full charge. They are partially sulfated and the sulfation will reverse only with time. So, if you install new batteries on your UPS and test immediately, you will not get the full runtime. You need to install the batteries, wait for several days, then test the runtime.
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\$\begingroup\$ I did a test using a resistor bank to draw a 5.5 amp load. Monitored voltage every 15 minutes. At 45 minutes the voltage started to fall rapidly and I aborted test at around 10.5 volts. . I spoke with the manufacturer of battery and gave him date code and determined they were made in 2020 he said they were readey for the scraper. I guess for 10 bucks a piece,the distributor battery sharks was dumping them and hoping no one would check them. My next challenge is to get my money back, at least it was paid with CC, so shouldn't have to much problem. \$\endgroup\$ Commented Jun 20 at 3:45