Battery connectors inside a UPS, F1 for F2 subsituted, consequences?

Question

I have a 10-year old APC UPS. Naturally the 12V SLAs were dead, so I bought 8 new ones of similar specs.

After swapping out the batteries the unit starts and charges fine, but when I try and run a load on it then pull the line input power, the UPS shuts down and lights up the red X "battery failed" light while pip-pip-pipping. The load goes down hard at this point.

On inspection, the original batteries used the F2 connector (pictured on the right), and my replacements use the smaller F1 connector (on the left)

Question Is it likely that using the wrong connector with the original F2 wiring is limiting the current that can be drawn? The battery back reads about 52 volts (its 48v nominal with 12V x4 x2 so a total of eight 5Ah batteries) or is my UPS simply broken ?

• I don't have the resources to buy 8 more batteries on the off-chance this is the root cause.

• Should I recreate the battery pack internal cabling with F1 spade connectors - would that help? Or do something else to improve connectivity?

• UPS is an APC 2RU rackmount job rated at 2.2kVA, and has a network management card, so its not a cheap and nasty home-grade device.

• I've changed batteries in over a dozen different UPSs in the last couple decades, so while not an every day thing I haven't made any significat mistakes. Size range from 275VA up to a 6kVA emerson monster.

• Data sheet for the batteries I used

Answer 1

Those batteries are not really suitable

The datasheet for the batteries does not give a maximum discarge rate or current draw, but does indicate that the capacity is cut in half at 8 amps. At 12A, the voltage drops to 10V after only 8 minutes.

At full load, a 2.2kVA UPS will draw 45A from a 48V battery bank. Since you have two parallel sets of four batteries in series, that is 23A per battery. Drawing that much current will cause the battery voltage to drop a lot. The UPS then detects the voltage drop, and decides the batteries must have failed.

All is not lost though - if you keep the current draw low, then the voltage will probably stay up, and the UPS is more likely to work. What load you can manage will depend on details of the UPS which we don't have, so you'll just have to go by trial and error.

Answer 2

As per our comments i thought i would leave a more comprehensive answer: The connectors themselves should not cause the issue - but if enough current was requested they could overheat. Since the batteries have smaller connectors, it is likely they have lower maximum and continuous discharge ratings, which in your own case it seems indicative that you are exceeding this with your UPS.

Rebuilding the packs with larger connectors is very unlikely to aid any benefit as the discharge rating will be most certainly set by the internal resistance of the cells themselves.

If the UPS works with a light load but dies on application of a heavy load it is likely the voltage of the bank is sagging under load, which you should be able to observe on a multimeter when you activate the UPS.

If this is the case the UPS is not lost, but until you can upgrade the cells, or add another bank in parallel to increase current capacity, you may have to attach the UPS to a more suitable load (i.e. Attach less too it)

I know its not what you wanted to hear but I would say its about all you can do in this scenario.

If you decide to run with a load that doesn't drop the UPS like a stone, i would run it for a while and see if the connectors or batteries are getting hot, just in case. But otherwise you should be fine.

Update : You have added the datasheets, yeah - they are unsuitable. Try a light load or you may need to change / add another bank in parallel later on.

Answer 3

Putting a 0.250" Faston on a 0.187" tab is not automatically a problem. BUT, there also are two different thickness of the tabs. The 0.250" tab almost certainly is 0.031" thick, while the 0.187" tab might be thinner. This could lead to very light contact causing the localized heating already mentioned, or even intermittent contact that confuses the control system.

Answer 4

This answer from AnalogKid explains the real issue here. Your voltage observation is spot on for a APC 2.2KVA system in each sled. You have (4) parallel batteries in series 4 other batteries, hence 48v (~52v). The issue is heat. When you use F1/T1 vs F2/T2 you're asking for trouble. Any one of those 16 total (pos/neg) connections is an opportunity to be loose, i.e., arcing and added heat. Add that single loose connection to one or two other loose connectors and things heat up pretty quickly. I have had engineers mistakenly replace the incorrect connector type batteries and the sleds heat up to over 140deg F. They are rated for 104 deg F. The batteries, crack, and leak within months if not weeks of deployment. You will get a noxious small from the sulfereric acid and know.