UPS sealed lead acid batteries - position? - Page 1
Forum section: electronics / general

author: Kuro
author_rank: Regular Contributor
timestamp: February 24, 2017, 05:29:24 pm
content: I have an Eaton Ellipse UPS protecting some small servers. Due to a re-arranging inside the server case, I'd like to change the position of the UPS from standing up straight to lying down flat. According to the manual, it's ok to run the UPS in both positions. The lead acid batteries are sealed, so they can't leak.Since this UPS is getting on in years and may need a battery change or full exchange anyway, I asked the manufacturer about life expectancy of the batteries, when to exchange them, how long the overcurrent protection circuitry works reliably, and also about the change in position.The replies about the life expectancy are about what I expected, vague and the usual 3-5 years timespan. About the position, I had to re-read the reply a few times. Either they don't know about this model (since Eaton didn't make this themselves but purchased the company that did 6 years ago) or they don't seem to know themselves.Therefor I turn to the EEVblog engineers. Can you change the position of a sealed lead acid battery after using it (charge/discharge/continuous trickle charge) for years, or will this affect performance and lifetime expectancy?

author: SeanB
author_rank: Super Contributor
timestamp: February 24, 2017, 06:19:32 pm
content: Best is to have them vent upwards, especially with batteries on continuous float charge, but the VRLA stands for Valve Regulated Lead Acid, so the electrolyte is a minimal fill, all adsorbed into either a gel or in a fibrous mat, so there is no actual wet acid in them. They can be used in all positions, even upsde down, though there the risk of acid venting with the gas is higher, the condensed liquid will go out with the vapour.However, running vent up of on the side is fine in most cases, and does very little to reduce cell life. Biggest reducers of cell life are overcharging, running at high temperature and maintaining float voltage at too high a level for cell temperature, and leaving the cell discharged below around 70% for long periods, along with cycling too deep per discharge cycle.In a UPS you have all this happening, so cell life is really reduced in any case.If putting on it's side best to put the batteries at the bottom, so they do not get cooked too much. If flat make sure there is adequate airflow through the unit.

author: Kuro
author_rank: Regular Contributor
timestamp: February 24, 2017, 07:27:18 pm
content: Thanks for the explanation!So there's no chemical reaction that influences the structure of the cells over the years, making position changes after long operation undesirable? Like the old ballbearing hard disks - after running them for years flat, turning them on their sides was a bad idea because the bearings had "settled" for the flat position. That of course is no longer an issue with fluid bearings.I'll open the battery compartment up and see what position they're on and follow your advice on the next flat position.

author: mtdoc
author_rank: Super Contributor
timestamp: February 24, 2017, 08:18:26 pm
content: As above - position should make no difference for VRLA batteries. In fact for AGMs there is some thinking that the position should be periodically rotated to prevent stratification - though unlike flooded LA this really should not be much of an issue if at all for AGMs.Whether Gel or AGM, no VRLA should ever need to vent. Venting in the case of VRLA batteries means there has been severe overcharging and that the battery is now toast or close to it. The vent is there only as a safety measure - think of it like a fuse.

author: tkuhmone
author_rank: Regular Contributor
timestamp: February 24, 2017, 08:20:27 pm
content: fyi... At least in Eaton 5PX series UPS (I have 5PX2200 model) four 12V batteries are flat positioned, if the UPS is mounted "flat". If the same UPS is used together plastic support blocks - as standing up position -> the mounting screw holes in UPS metal cover are located in the bottom side. This means that all the four 12V batteries are positioned their terminals facing up...

author: Kuro
author_rank: Regular Contributor
timestamp: February 24, 2017, 10:02:00 pm
content: Quote from: mtdoc on February 24, 2017, 08:18:26 pmThanks for your input!Stratification? Could you explain what this is?

author: PTR_1275
author_rank: Frequent Contributor
timestamp: February 24, 2017, 10:27:41 pm
content: Acid stratification is when the acid part of the electrolyte settles to the bottom of the battery. Acid is heavier than the water so the water which is why it sinks to the bottom.In a lead acid battery, the electrolyte is very fluid and will move around a lot more freely. In gel or agm batteries, the electrolyte is suspended in the absorbent glass matting separators, or in gel form. This type of electrolyte doesn't move around much so isn't constantly mixing.I've heard the theory about needing to periodically change the position of a agm battery to stop the acid separating, but I've never seen conclusive proof (and I worked in a caravan / motor home / RV electrical supply shop for 14 years seeing lots of systems and doing lots of testing on various setups over the years)In terms of the original question. I have some ups that have the batteries upright and I have some that have them on their side. The main thing is check the replacement battery data sheet. Some agm batteries (and vrla) say that they can be discharged in any orientation, but must be charged vertically. This is mostly a precaution to stop electrolyte being pushed out of the vent if there is a reason for the battery to vent (normally overcharging or too high a temperature).

author: mtdoc
author_rank: Super Contributor
timestamp: February 24, 2017, 10:27:51 pm
content: Quote from: Kuro on February 24, 2017, 10:02:00 pmHere's a decent explanationBut that article says it does not occur in AGMs. In theory it shouldn't - but the reality is that stratification has been observed in AGMs - it's just that it is to a much lower degree and arguably has no significant effect on battery capacity or lifespan.

author: Kuro
author_rank: Regular Contributor
timestamp: February 24, 2017, 10:47:51 pm
content: OK, thanks very much to both of you. I now know what to look for and how to proceed. Much obliged!

author: Gregg
author_rank: Super Contributor
timestamp: February 27, 2017, 06:09:41 am
content: I used to work with VRLA lead acid batteries and most of the larger cells are installed on their side as shown in the picture of a 48V telco type battery. Note the crack in the cover of the one above the meter and very little leakage, these were glass mat sealed cells, nominal 2V each. These cells were replaced shortly after the picture was taken. Generally lead acid batteries lose capacity due to sulfation, lack of electrolyte or warped plates. A discharge test is the best way to determine if your battery is any good. An additional test is to measure charging current and temperature at float voltage, it should be milliamps and nearly ambient temperature for your UPS batteries; an elevated temperature probably means a partially shorted cell.