UPS Battery Charging - Are My Batteries Boiling?

[Lojix]

I have just put 2x 7.2Ah 12v sealed lead acid batteries into one of my UPS's after servicing them (they were recovered from old equipment and were badly drained). I refilled the cells, charged them up and they test okay. The UPS is an 'Opti-UPS 1000C', 24v (2x12v) after connecting it up, I can hear the batteries bubbling as they take the charge current and measure at 28.5v on my DMM.

Question is... Does this seem okay? When charging the batteries, it's always said leave the cells uncapped to let the gas escape and avoid pressurising the cells and causing the battery to explode. However this is not possible in a UPS and I have never noticed the batteries bubbling in any of my UPS's prior to this.

I'm having visualisations of a battery exploding and covering me in sulphuric acid!

[eccerr0r]

Re: UPS Battery Charging - Are My Batteries Boiling?

Recovering those SLAs seems very unlikely, of the ones that I have, even after watering them, they just don't have the capacity like they used to. There's no need to uncap as they are design to release pressure automatically. At 28.5V if your 2 batteries are gassing, if they don't stop gassing relatively quickly, they are likely tired and won't run the UPS for long (or at all).

[Lojix]

Re: UPS Battery Charging - Are My Batteries Boiling?

Thanks for clarifying. Based on that information I might move the one sitting under my desk connected to my PC. Breathing even trace amounts of sulphur couldn't be great... and yes, I agree about the capacity loss after recovering SLA batteries. Their initial charge can take 3 or even 4 days at low current and the voltage doesn't seem to climb much at all for a long time. But I seem to have a surprising ratio of recoverables. Although I've noticed the more sulphated the plates are, the more it affects their holding capacity, but most are still definitely at a usable level.

[japlytic]

Re: UPS Battery Charging - Are My Batteries Boiling?

In a book of electronic circuits, I saw a circuit for a temperature compensated SLA battery charger, and the description of the circuit highlighted that the charging characteristics of SLA batteries are strongly linked to ambient temperature, with temperature compensation being desirable to prevent overcharging and undercharging.

I think temperature compensation for SLA battery charging is highly desirable in UPS units to help maximize battery life - would you agree?

[Lojix]

Re: UPS Battery Charging - Are My Batteries Boiling?

I agree completely and via use of a thermistor, doesn't seem to be that difficult to incorporate into the system. I'm not sure to what degree temperature compensation is built into the charge cycle of UPS's (if at all). I'm putting it down to cost over effectiveness on the manufacturers' part... One thing for sure is that 'effectively' charging SLA batteries is a whole lot more involved than one might first think and considering its a fundamental function of a UPS, they don't seem to do a great job at it!

[eccerr0r]

Re: UPS Battery Charging - Are My Batteries Boiling?

Actually though sulfuric acid is dangerous and will eat through organic materials, I'd much rather be around it than say, ricin or plutonium or something...
The only risk for these batteries is the explosion risk if you don't vent any hydrogen produced by the gassing.

Most of the dead SLAs I get end up with internal shorts or high self discharge and thus useless... and I still should get a new set of batteries for my 1000VA UPS that's just sitting there empty after the last set of batteries died.

I wouldn't say charging the batteries is a fundamental function of a UPS - it's to keep the connected devices running. Charging is only a recovery function after it has done its job...

[Lojix]

Re: UPS Battery Charging - Are My Batteries Boiling?

Actually though sulfuric acid is dangerous and will eat through organic materials, I'd much rather be around it than say, ricin or plutonium or something...

Good point. Based on that comparison I'd have to agree.. Although in my experience the average home office is generally not as likely to contain Ricin or Plutonium.

The only risk for these batteries is the explosion risk if you don't vent any hydrogen produced by the gassing.

Storing a box underneath you at your desk that carries a risk of explosion, albeit slim to unlikely, is still a risk that deserves a little caution and respect in my opinion.

I wouldn't say charging the batteries is a fundamental function of a UPS - it's to keep the connected devices running. Charging is only a recovery function after it has done its job...

It goes without saying that the primary function of an Uninterruptible Power Supply, is to keep the supply of power uninterrupted. However I would find little use for a UPS which did not incorporate some type of recovery function in the system. Inefficiency and the sheer cost of replacing batteries would be just the first of many points not worth mentioning.

[kc8adu]

Re: UPS Battery Charging - Are My Batteries Boiling?

if the charger is a 3 stage type it may hold around 14.4 for several hours.it waits for the current to drop to a preset value and switches to float.those batteries may just be junk and will never drop thus boiling them.one only needs to slightly moisten the separators.no free liquid needed or desired.most of that type are not worth doing anything to unless fairly new.they are usually goners.

[Lojix]

Re: UPS Battery Charging - Are My Batteries Boiling?

no free liquid needed or desired.

Really?! This is the first I have received this advice. Is this due to contained pressure/equilibrium or other another reason? ...I'm guessing it's ideal for the chemical reaction?

Probably like many others, I've been following the misconception that they should be filled to just cover the plates.

[eccerr0r]

Re: UPS Battery Charging - Are My Batteries Boiling?

Charging batteries at (cells)*2.4 volts per cell CC to CV, is the "quick cyclic" charge voltage. This has the problem of possibly slowly splitting water but charges the fastest safely. Ideally float voltage is more like 2.3 volts per cell (and both these numbers are dependent on temperature). I would think most UPS are two stage charging, which may not be the best for battery longevity but has the fastest recovery time and cheap design cost.

The AGM cells should not have free liquid in them at all - it's also called "starved electrolyte" for a reason - it's not totally saturated. The age old idea to cover the plates is for flooded (i.e. no glass mat) cells only. The chemistry between the two is the same, just that you don't need as much electrolyte as the mat holds the electrolyte by the plates.

[joshnz]

Re: UPS Battery Charging - Are My Batteries Boiling?

Really?! This is the first I have received this advice. Is this due to contained pressure/equilibrium or other another reason? ...I'm guessing it's ideal for the chemical reaction?

Probably like many others, I've been following the misconception that they should be filled to just cover the plates.

sealed lead acid battery use absorbed glass mat or gel they have no spill-able liquids.

You are thinking of automotive battery's that use flooded construction.

[Lojix]

Re: UPS Battery Charging - Are My Batteries Boiling?

Thanks guys. Somehow that little piece of pretty important information slipped by me.. So would over filling the batteries have an adverse affect and if so, should they be drained to the appropriate level?

I read somewhere that when the rubber cell caps are pulled inwardly at the cell opening, it means they need water.

[rhomanski]

Re: UPS Battery Charging - Are My Batteries Boiling?

Is this you? Or a relative?

[kc8adu]

Re: UPS Battery Charging - Are My Batteries Boiling?

dilutes the electrolyte.and now cant remove excess without weakening it more.and if the cells vented with the battery hot when it cools you get a vacuum.says nothing about water loss.

Thanks guys. Somehow that little piece of pretty important information slipped by me.. So would over filling the batteries have an adverse affect and if so, should they be drained to the appropriate level?

I read somewhere that when the rubber cell caps are pulled inwardly at the cell opening, it means they need water.

[Lojix]

Re: UPS Battery Charging - Are My Batteries Boiling?

dilutes the electrolyte.and now cant remove excess without weakening it more.and if the cells vented with the battery hot when it cools you get a vacuum.says nothing about water loss.

Summed up perfectly

[Lojix]

Re: UPS Battery Charging - Are My Batteries Boiling?

Is this you? Or a relative?

Me on a 'bad hair' day