Lead acid battery mystery.

I have a number of used but still functional car batteries which I use for electric fencers and lighting at a stables with no power.

Some are sealed, but for the ones with removable caps I always remove the cap and check the acid level before putting them on the charger.

I have just one battery which always has low fluid in every cell when I bring it back for recharge. It takes an exceptional amount of demin water each time, at least 50 ml per cell if not more. All the cells are similar. But, when recharged, it reaches a reasonable voltage and certainly holds a useful amount of charge.

The cells can't be leaking significantly, firstly there is no sign of it and secondly this must have done a dozen cycles like this over the past year or two. I havn't actually checked the acid concentration, I probably should, and top it up if necessary.

Does anyone have an explanation?

Reply to
newshound
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internal short maybe on that cell

Reply to
The Natural Philosopher

But it is *every* cell, and it does hold a reasonable amount of charge.

Reply to
newshound

Do you do a similar check after it has been charged?

I would expect any water usage would be in the charge cycle.

Reply to
Fredxxx

ponies with strange taste? Water is normally lost during charging rather than any other time, but 50ml a charge is a huge amount.

NT

Reply to
tabbypurr

Yes, so would I. I stop charging when all the cells are fizzing nicely and don't normally have to top up again at that stage.

Reply to
newshound

Yes I know. That's why I am mystified. I've been looking after lead acid batteries for over fifty years, and have never had one behave like this before.

Reply to
newshound

I seem to remember doing this in the old days. With the caps off and the battery on charge, fluid would spit out all over the battery. Just a thought.

Reply to
Mr Pounder Esquire

The fizzing sounds an issue. You ought not allow the battery voltage to be high enough for cells to 'fizz'. A short equalisation charge is all that is needed. What is the charge end current?

What do you mean by 'normally'? Perhaps gas on the plates is raising the level such that after charge it looks ok. I would check sometime after you've completed the charge process.

Next question! Do these batteries get much movement? I have heard of electrolyte stratification being an issue that promotes gassing.

Have you checked the electrolyte density of this battery?

Reply to
Fredxxx

50g is 2.8 moles of water.

You would need 5.6 moles of electrons, so 540,000C

5 Amps would imply a gassing time of 10 days. So something strange is going on, unless you keep it connected to the charger for 10 days or more?
Reply to
Fredxxx

To reply to the two posts together, I recharge the batteries with a traditional transformer/rectifier type car battery charger, so that the current drops off as it becomes charged (because the cell voltage rises). Once a cell becomes fully charged, the current it is passing causes electrolysis, so it "fizzes". In old batteries, the capacity may vary from cell to cell, so you may find one cell fizzing while another is not, that's a good reason to keep charging until they all fizz, but of course you do not want to concentrate the electrolyte by doing this for too long.

I realise that a charged battery may still have some trapped hydrogen and oxygen on the plates. So once it is charged, I will jiggle it and leave it open for a day or two in the hope that the gas all escapes. After that, I check the level and I don't normally find I need to add any more demin water.

IIRC this was originally an 80 amp-hour battery and it certainly still provides more than 10 AH at 12 volts, based on the lights that I run off it. And it is usually powering a couple of PIR lights that also get triggered through the night by cats, foxes, etc, so I suspect it's doing better than that.

I'm certainly not charging it for ten days. Might leave it connected for two days, and while the charger starts at 8 amps or so it has dropped to an amp or so after a day.

Reply to
newshound

If we are talking about 'gassing' here then isn't it actually

*required* as part of the charge process of a flooded lead acid battery to prevent electrolyte (and so charge) stratification?

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I think the second part of your question may answer the first part. ;-)

The 'equalisation stage' duration would (of course) be a function of the (bulk) charge rate and / or also a function of the charge profile of an automatic charger.

Cheers, T i m

Reply to
T i m

Ok.

'As it becomes near to being fully charged ...' ;-)

I think that happens in all / new cells within the same battery but by varying amounts. We used to minimise this (for racing) buy buying batteries made from 'matched cells'.

And the last one 'to fizz' also needs to fizz for a while to minimise stratification.

I think the risk is more the water loss from the electrolyte in general and exposing the plates than any change in 'concentration (as that will be redressed when you top up with water again).

And the water. ;-( Are you sure the cell caps aren't the recombination type (designed to allow the cell to vent pressure but to reduce the water loss)?

Assuming the electrolyte is above or at least level with the tops of the plates, I think you are supposed to top up (after it's been fully charged)?

Ok (the C20Ah rate would be only tested at that rate etc). So, for your 'calibration' of the battery as being 10Ah I believe you would need 48W of 12V lamp and would need to time it down to 10.5V or (ideally) higher (if not a deep cycle battery). So, for it to be 10Ah you would be able to run your (48W) lamp for 2 hours or a 100W for something less than 1hr?

Ok.

That sounds pretty reasonable for a largish / old LA battery. ;-)

So, I might be tempted to not remove the cell plugs when (or after) charging and see if that makes any difference to your electrolyte loss.

Cheers, T i m

Reply to
T i m

Left out in a sunny sheltered location or indoors behind a window and the water is just getting hot and evaporating?

Reply to
alan_m

Well also, you don't really want parts of the plates to "dry up".

Don't know. I used to work with a battery expert who knew all about this stuff, because there are BIG backup batteries on both nuclear and conventional power stations, but he retired to the wilds of Alberta. Certainly those cells are recombination type, but I don't know about ordinary car/tractor batteries.

What I am saying is that before charging, I top up so that the water is at the level of the marker above the plates, after charging the plates are almost always still covered, so I don't normally feel the need to add water then.

As an example, on the night of the big local firework display I got two hours of light out of about 50 watts of CFL, and I'd estimate that I have also had a similar amount of light out of the rest of the last charge.

Because you think they might be recombination type? But I am not really losing water during charging. It is vanishing when the battery is in service, with the caps on.

Reply to
newshound

Good thought, but no. It's inside a shed which never gets particularly warm because it is under trees, and in a valley orientated so that it doesn't get much direct sun at the best of times. And its quite cool at the moment. And it is only this one of about four batteries which behaves like this. And you don't get anything like this evaporation in a car battery even in the summer, with the combination of direct sun and underbonnet heating from the engine.

Reply to
newshound

Quite, but assuming you keep the cell caps on and top the cells up after charging and check for any loss in between that might allow the plates to become exposed, you should be ok?

'Ordinary of what age / spec. I think most recent wet LA batteries (especially those marked as sealed but are still 'wet') I would think they would (have to) be.

Understood. However, I think more electrolyte appears *after* charging and so it could overfill the cell if you do it before.

No, quite and that would be expected. The 'issue' is that you should check the electrolyte levels more regularly so that they are above the plates at all times, not just as you are about to recharge them? ;-(

"If low on electrolyte, immediately fill the battery with distilled or de-ionized water. Tap water may be acceptable in some regions. Do not fill to the correct level before charging as this could cause an overflow during charging. Always top up to the desired level after charging."

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Is that 50W 'equivalent of incandescent' (and so say 10W of electrical load) or 50W of actual load?

Yes but of any type really.

Yes, I understand that and agree it doesn't make much sense. ;-(

If you buy a 'traditional' dry-charged LA wet motorcycle battery with a electrolyte pack, after applying the electrolyte and allowing some time (a few hours) for the plates to absorb it all, you fit the sealed plugs and attach the external vent pipe. From then on the only time you remove the plugs is if you need to top the cell(s) up with distilled water.

If I then leave a bike unattended for a long period of time ('years') I too would expect to see some plates exposed and find the battery ruined (sulphated). The most likely reason therefore is evaporation?

Cheers, T i m

Reply to
T i m

Is this battery in open in bright sun oran enclosure that gets very hot?

Reply to
FMurtz

====snip====

Even assuming a capacity of 20AH, that's still only 25% of its original capacity.

Quite frankly, I think, at a mere 25% of capacity, the battery is well and truly "Shagged". I used to run two banks of 'revived' ex-pabx batteries[1] for about a decade before the cells finally became too thirsty to justify the cost of distilled water and the energy to keep them charged.

Although there was plenty of space beneath the plates, the paste in the plate grid structure had eventually disintegrated enough to form a significant layer of debris in the bottom of the cells where it could no longer provide its original function as plate anode material and, if not actually shorting the plates, it was certainly increasing the self discharge leakage rate (hence their thirstyness). I'd had a good ten years worth of service out of 'My Freeby' by then so finally decided to call it a day and weighed them in for scrap (along with a collection of similarly buggered SLAs and car batteries).

One thing to note with SLI batteries is that they're totally unsuited to use as UPS battery packs. It took 3 expensive lessons before I finally realised this. Mind you the first lesson was over ten years prior to the last two and only involved a single car battery connected to a 4A rated

13.8v CB radio mains PSU rather than the strings of 4 used with an APC SmartUPS2000 just a few years ago.

It seems that the continuous float charging 24/7 at 13.8v per car battery is what does them in after just 6 months or so of UPS service.

When used for their intended purpose (Starting Lighting Ignition), they thrive quite happily on their regimen of 14.2v intermittent charging and brief bursts of 100 plus amps starting loads along with the various accelerations associated with accelerating/braking and sideways G forces generated when negotiating corners and tight bends. It seems the 'rough mechanical handling' keeps the electrolyte nicely stirred up and homogenised preventing a deleterious density gradient in the electrolyte that otherwise builds up when wet cell batteries are used in a fixed location.

I reckon there was still more than 50% capacity in those car batteries by the time they became a maintenance liability and an unnecessary drain of charging power demand on the UPS. I have a theory that by sacrificing some some 5 or 10 percent of usable capacity by reducing the float charging voltage to 13.5v per car battery instead of the "standard 13.8v" normally used by APC UPSes, I might be able to get a better than 5 year service life. However, I haven't had the heart to put this to the test so it remains just a theory.

Getting back to your 'battery mystery', I'd say you're simply dealing with a battery that's long gone past its Best Before Date and is well and truly ready to be weighed in.

[1] When I discovered them in a decommissioned PABX, the battery had been disassembled into individual 125AH Tungstone cells and simply left standing for Ghod knows how many years. I picked the best 12 cells out of the 25 that had been left in a completely discharged state to haul back to my basement radio shack and connected each one to a basic 4A 12v battery charger via a current limiting 21W 12v indicator lamp until the almost pure water finally became reactivated with the electrode bound acid and the lamp started to glow before rigging a string of 6 at a time to let me connect them directly to the battery charger (doing this for two bank's worth).

Having revived them sufficiently to be charged as 12v batteries in the conventional way, I then rigged up a dummy load made up of three 0.3 ohm

100W resistors in series and boiled a few bucket's worth of water discharging them after each charge or reverse charging cycle until I was satisfied I'd restored them to as good a state as I could. It seemed I'd managed to get the capacity of each bank to circa 100AH at the 200 hour discharge rate - just over a week's worth running the 1.05A load from my VHF packet radio station setup.
Reply to
Johnny B Good

Could it simply be situated in a very warm place or maybe it is dealing with a higher load on a smaller battery. If its evaporation those plugged cells do leak much more than completely sealed ones will of course. Brian

Reply to
Brian Gaff

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