Capacity of SLA battery - Page 1
Forum section: electronics / general

author: gigabyte091
author_rank: Contributor
timestamp: August 05, 2019, 07:40:33 pm
content: Hi everyone,I salvaged several SLA batteries, 4 of them are Leoch LP12-45, 2 of them are Fiamm 12FLG42 and the last two are Fiamm 12FLG27. Leoch are from 2017 and Fiamms are from 2015.I checked them with DMM and voltages were between 12.98 volts, and the lowest one was about 12.75 volts and then i tested them for capacity with some chinese battery tester and i set it acording to battery datasheet and 12FGL27 showed 25.2 Ah capacity and 24.8 Ah out of 27 Ah. One of the Leoch measured only 38.9 Ah and one of the 12FGL42 showed 37.1 Ah.I read that its good idea when testing capacity on stored batteries to charge them full (14.4V) then disconnect charger for 24 to 48 hrs and then connect it again and repeat this proces several times and then test capacity. Is this good advice ? should i test it that way ?Also they are used in my backup power system, about once a year. Is it better to fully charge them to 14.4 volts and apply topping charge every month or to charge them to 13.5V and leave them on charger ? (i use CV/CC power supply for charging them and they are in my room, ambient temperature is about 23 to 26C

author: sibeen
author_rank: Frequent Contributor
timestamp: August 07, 2019, 07:42:03 am
content: I used to work in the UPS field with larger systems and left this about 12 years ago so my 'knowledge' may be slightly out of date.The voltage of 14.4V is way too high in my opinion and that is a the gassing voltage of an SLA. Drop this down to 13.8 (2.3 V/cell) as a maximum. You should be float charging your batteries between 2.25 and 2.27 volts per cell. If you've already performed a discharge on the battery then charging it up and leaving it on charge for 48 hours should be sufficient.As to charging them up and then taking away the charge voltage and only applying it monthly or so, not sure that this is a good idea. Many UPS manufacturersimplemented this sort of scheme in their UPS systems as a 'battery saver' feature. I suspect it was started by one manufacturer and the rest quickly pilled on as the marketing departments demanded that their engineers put in the feature. It was quietly dropped, at least in the company I was working for as the rate of battery failure actually seemed to increase under this charging scheme and it was also a pain in the arse for the field people to deal with and explain to end users.I would just charge the batteries a 2.25 V/cell (13.5 volts) and leave it at that, especially if your temperatures are as indicated.

author: gigabyte091
author_rank: Contributor
timestamp: August 10, 2019, 05:22:32 am
content: Thank you for the answer, i will do that.When i test them for capacity i charge them to 14.4V at C10 until current drop to about 0.05 to 0.03C and then discharge them according to datasheet. After the test i charge them to 13.7 V.I have many DC-DC modules from ebay which i can use to charge them and leave them floating at 13.5V all the time.Also i find 10 batteries, with voltages from 11.87V to about 12.94V. Hope atleast 4 of them will have usable capacity. (atleast 80% original capacity)

author: woodchips
author_rank: Frequent Contributor
timestamp: August 21, 2019, 10:30:53 am
content: Whilst the float voltage might be 13.5V I have found it is essential to do an equalising charge up to 15.2V or so every 6 months or so. This overcharges the cells, at low current, only 0.01Ca, to make sure every cell has in fact been fully charged.