Heating Up of a Flooded Lead Acid Battery During Charging

Will need the individual cell voltages to make a determination if the excess heat is a cell failure. Also in the process of charging some heat is always given off. With out the temperature of the battery, hot is relative term.

http://batteryuniversity.com/learn/article/charging_at_high_and_low_temperatures

If you are only charging the batteries then 27.8V x 6.3A = 175.14W is going into them, that's about the same amount of heat as 3 60W incandescent light bulbs. Get yourself a cheap infrared thermometer and check for hot spots on the connections and all over the cells, everything should be symmetric, any reading that varies significantly from the rest may point to the problem. Keep good records under various operating conditions and you'll soon see any oddities.

You say that there are two 12v batteries.

Are they connected in series to supply 24v @70Ah or in parallel to supply 12v @140Ah?

If they are connected in parallel to only provide 12v, then I suggest that you revisit the settings on your charger as the output voltage that you mention is way too high for charging 12v batteries and is likely on the 24v setting.

It's normal for charging batteries to produce heat, and a cooling fan is often a requirement, especially for flooded cells as they have a high internal resistance, and therefore exhibit more heating under both charge and discharge conditions.

It's quite possible to have an overvoltage charger go unnoticed when connected to a UPS as the voltage regulator on the UPS will often cover up the problem.

I trust that you have provision for safe H2 removal, and wonder if you ever carry out an equalization charge on the batteries.

The battery manufacturer will usually specify the voltages at 25degrees C. When you operate at temperatures above 25 you must reduce the voltages and below 25 you must increase the voltages. For my particular batteries I use a correction of .003VPC (Volts Per Cell) for every degree above 25C. At 40C you are 15 degrees high so 15x.003=.045VPC reduction. Assuming 2.25VPC at 25C you should lower your voltage to 2.25-.045=2.205VPC and since you have 12 cells in series your final float voltage will be 12x2.205=26.46V These figures may vary slightly between different manufacturers but I think your voltage is a bit too high for operation at 40C

For an environmental idea how about encasing the batteries in a waterproof casing and immersing sides in a water bath- if a clean environment could be maintained this could be routed to your water heater which would provide heat for the water system and cooling for the batteries

Great idea however if the batteries are being overcharged it might be wiser to lower the voltage. Constant overcharging is bad on the batteries over time

GA

I bet you are right!!

Good chargers, set to charge the batteries to 100% of capacity, will always have a temperature sensor, to slow/modify or stop charging as battery temperature varies.

Even better, for the longer life and extra reliability of the batteries, is never to charge lead acid batteries above 70% of capacity. That is the capacity "sweet spot".

Basically, the storage efficiency has also a sweet spot at a max of 70% of capacity. Lead acid are not at best very efficient and driving them above 70% reduces it even more....

I have a feeling that one of the following is possibly true:-

1) The charging system has a problem and needs repairing

2) The batteries are aging rapidly and the capacity is already drastically reduced by over charging

3) The batteries are stratifying, due to never being moved and this is eating the lower plates away...a bit of a long shot....

There is a good white paper on LA Battery efficiency here that everyone ould read if they want to use LA Batteries correctly print it out and keep it handy:-

LA Battery Efficiency

Andy, I read your paper and could not find any statement similar to "...never to charge lead acid batteries above 70% of capacity...", which does seem to contradict your opening statement "..Good chargers, set to charge the batteries to 100% of capacity..."

What is stated in your reference is "...if a battery is partially charged for several consecutive cycles the useable battery capacity decreases each cycle, even though the same amount of energy has been presented to the battery each day... An associated full charge, with its attendant gassing, is needed to destratify the electrolyte and remove the residual sulfate. This sulfate buildup can become a problem if this pattern continues for several months. In the short term it can be reversed by a full "equalizing" type charge..."

You might want to read this paper which also agrees with yours:

"...During the constant-current charge, the battery charges to 70 percent in 5-8 hours; the remaining 30 percent is filled with the slower topping charge that lasts another 7-10 hours. The topping charge is essential for the well-being of the battery and can be compared to a little rest after a good meal. If deprived, the battery will eventually lose the ability to accept a full charge and the performance will decrease due to sulfation. The float charge in the third stage maintains the battery at full charge..."

Even this document for the British built Oberon class submarine, which I assume is similar to the RN manuals that you were trained with, mandates a topping charge after the 70% level has been reached...

Search as I might I could not find any reference that suggests stopping charging when the 70% charge level is reached, instead 70% is listed as the starting point for a change in charge rate to bring the battery to 100% charge without damage. Perhaps you could provide your reference(s).

You haven't looked far on the web. Nothing that I posted is new or unknown.....

There is a reasonable paper here that you might like o read:-

Lead Acid Batteries

We are talking today about normal flooded nominal 12 volt Lead Acid Batteries, not Leisure Batteries, though they are in many ways similar, as are Gel.....

You also must learn that a battery is two or more cells connected together. 12 volt nominal Lead Acid Batteries have 6 cells each at usually around 2.2 volts per cell.

I just reread the link I posted previously. It tells anyone with the time and understanding just how efficiency is calculated at various levels of charge, all in a very easy to understand manner (for me at least!), with simple graphs of efficiency against charge level at the end. If you don't understand that, nothing I say will ever change your mind....they answer most if not all your questions I feel.

The only parts they have not mentioned (and I haven't mentioned them up to now either in this particular blog) is that for instance, leaving a LA battery in a discharged state (you know what voltage that is I trust!= 10.5v) for long, will result in sulfation damage. The longer you leave it, the more it gets damaged. Assuming all cells in a good normal condition.

My personal tip, against many others who advise that it is OK to do is:- NEVER FLOAT CHARGE ANY BATTERY TYPE, but just for LA, you could float to a max of say13.2 volts, that should do no harm, but I have never ever done it much or seen the need myself, so you are on your own there.....

I like to exercise my batteries to give them "muscle exercise" so to say. Just holding them at one voltage does not de-stratify the acid for example as well as a proper charge/discharge cycle(s) will....and may promote sulfation according to many good web sites. I do disagree with the idea.....I think that its bad for the battery to hold it "still" so to say....

I also like those special devices that "jolt" a battery with a high voltage pulse every few minutes, this appears not only to keep sulfation at bay, but to even reduce/clear it on batteries already with the problem. Though I cannot supply any better infos than the companies who sell the units, sorry.

Someone will one day do a proper comparison and post the results (I hope!)

Just to say, I am convinced they work, though I have only used them on one battery. So its hardly a recommendation or much of a comparison.......

The paper you mentioned, which is from the Battery University, has some good stuff in it, but it recommends charging to100% and the usage of floating, both of which I disagree with. Its otherwise a good website.

Its always best to recharge as soon as possible. I personally will not even leave a battery in such a state for even one day, but I am a bit particular....many are not.

Leaving the battery for long periods with even a charge level below 12.6v, will also damage it, but far slower of course. How slow? I guess more than a few weeks would be bad, but I don't test for that, I recharge as soon as possible as I said before. I am a normal private person, not a test laboratory.

Charging above 13.2v will cause gassing. 13.2v is usually around 70% of capacity for many types, but you need to read the data from the manufacturer for exact levels for the battery concerned.

Gassing not only drives off water, it thereby changes the mixture of the acid of course which is bad for the battery, but it also heats the battery and charging MUST be then temperature controlled, or damage will result. Good chargers will monitor battery temperature, most don't.

Now one further point that is true of ANY battery chemistry, not just LA batteries is that one of the cells is the strongest, another is the weakest (think of them as individuals). Charging to 100% (or overcharge as many chargers TRY to do!), means that the cell that is full first get overcharged. This weakens it.

Conversely, discharging below the discharged voltage OF ANY SINGLE CELL, causes it to be reverse polarized. This weakens it.

This is true for most types of battery around today, not just LA.

The nominal voltage of a discharged LA 12 v Battery, will be a composite voltage of each of the cells, some with less voltage and some cells with more, this means weak cells are still being damaged. One cell could be at 2 volts and another at 1.5, giving in all a voltage above 10.5.

Which is why I NEVER let my batteries go anywhere near that 10.5v value, as without contacts on each single cell and 6 voltmeters across them, I cannot tell which one is empty and which still have power available....e.g. the "state of EACH of the cells at any one time.

In a perfect world, you would have some sort of voltage monitoring on each cell and if one cell hit the discharged voltage of 1.75v (or better, just before!!), stop using the battery and recharge it.

Conversely, when one cell is full, stop charging and simply use it or set it aside for later use.

Or even better, charge each cell individually....that way each cell can have IT'S OWN FULL CHARGE WITHOUT OVERCHARGING.

The end result of charging to full and using till "empty" (= 1.75v per cell), is that one cell fails in an otherwise good battery. Then, as most modern 12v LA batteries are not designed to have a single cell repaired/replaced/cleaned & refilled (which is what we did in the RN), the whole battery gets junked......

With other chemistries, you may be able to replace a single cell, but unless that new cell is from the same batch, manufacturer, life style etc., you usually make the high charge/low charge problem even worse and 5 minutes later the next cell dies and so on.....

You avoid a lot of this by not discharging or charging fully without adding a lot of complicated monitoring hardware/software to the battery or the charger.....now does that make sense to you?

Some like "Lumpy DC" for charging, as they believe it "exercises" the battery better. Could be true. Many cheap chargers do it just for cheapness anyway....

Now you can do what you want with your batteries, you don't have to believe me, just go your own way.

I am simply someone who learnt many years ago how to look after submarine, telephone exchange, boat batteries, almost all are Lead Acid in the Royal Navy (and some of those big batteries are 50 or more years old!!), there is a right and a wrong way to treat such batteries.

You either do it right, or you don't.

My caravan battery is over 11 years old, it demonstrates a capacity that is as good as it was when new. The chargers I build very occasionally for myself and sometimes for others, follow the rules I mentioned above, with a few tiny refinements that I keep to myself, and up to now, no sign of ever going wrong or getting a damaged cell.

Only topped up once with distilled water in all that time, by the way.....It will live longer than I, I feel.

In case you still do not understand why 70% as a top charge, then succinctly put, that gives the maximum battery life for that particular battery. If you are happy with replacing them more often, that is your choice not mine. I recommend a battery 30% "larger" than required and to only charge to 70% for maximum life. The gives the same capacity available, and a far longer living battery.

I am sure you can tell me why, but I already know why :- REMEMBER, SUB BATTERIES ARE ALWAYS CHARGED TO 100% FULL!

If you don't know, ask me and I will tell you, its not a secret anymore.......anyone can know!!

Do you own/use a submarine? If not, then forget that point completely, it is for everyday use irrelevant!!!...unless you are a Submariner......

Actually, if you REALLY looked around on the web, you will find just about EVERYTHING that I have posted already there, including good explanations. There is of course some rubbish and neophytes have problems sorting the good and the bad of course..

Remember, there is really almost nothing new under the Sun with regards to LA Batteries!!

Furthermore, I have better things to do than to teach people further for no pay, or find them websites to corroborate for them the information that I have in my head and have put down here already, so take it or leave it, your personal choice.

PS.I have posted all of the above infos, sometimes with further/better links, several times on CR4 over the last 4-5 years. Have a look around, maybe some of the links will be still active....You obviously didn't look on CR4 either by the way.....

Do have a great day......

Hi Andy: You definitely have had a lot of experience with LA batteries. My experiences were first with a job with GTE working in telephone equipment rooms on huge 2V cells each the size of a refrigerator. Then I moved on to Solar Systems which I am doing now. We are having a lot of problems with the heat in this country.

In my comment I was suggesting the application of a temperature correction formula which I used recently on some sealed VRLA batteries from (LIBERTY LS 12-100) and based on thier manual I float my batteries at 13.67V in my air conditioned room at 25°C (We get 4 or 5 power failures a week here so they get exercised often and I never take them below 11.5V each)

I believe that watered batteries should indeed be held down around 13.2V as you suggest. Do you disagree with the bulk/absorption stages in modern charging systems. I phoned C&D Technologies one day and asked them why we keep the sealed batteries at 13.67 and watered type at 13.2 Thier explanation was that since watered batteries can be charged up to 14.8 or 15V during the bulk absorption stage they are then allowed to drop down to 13.2V afterwards. However, since sealed batteries are not allowed to reach this high a voltage during bulk/absorption we keep them a bit higher in thier normal state.

Do you agree with this? Would you suggest to our inquirer that he keep his voltage a bit lower due to his 40°C ambient temperature?

By the way, what sort of temperature would be found in a submarine battery room?

Regards

John

You bring some interesting comments, close to my own ideas, many thanks.

I personally try never to gas a battery, I am convinced that this is the single biggest area causing damage to batteries. Other than letting them sit around discharged of course!

Due to the fact that I restrict charging voltages to within tight restrictions, I do not need to worry so much about temperatures, except that above 26°C, I stop the charging completely. I don't think that it has ever happened.....

The batteries only get warmed slightly by the ambient, not by my charging rate as it is only a max of 8 amps on a 100 amp battery....less than C/10. I cycle the battery between 12.6 and 13.2 volts.

Keeping to around 13.2v as a max, cannot harm anything....other than slightly reducing capacity.

With regard to the sub batteries, the temperatures below vary depending upon the season and location. They are always located at the lowest point and are therefore cooled mostly by the outside water effects.

I do not remember them getting too hot (its a long time ago!), they are so big and heavy, temperature variation in the battery itself was very, very slow, but in Arctic conditions, they were sometimes cold, which reduces capacity and has to be taken into account.....We did not charge too quickly in peace time, to keep them cooler...

I worked on refurbishing and testing such batteries mostly in maintenance sheds, making sure the "Dockies" were doing their job.

Onboard when underway, I looked after SONAR, listening gear, torpedoes, anything electrical and the tubes (not forgetting small arms and diving gear!!). I had a wide ranging and interesting jobs...

Thanks Andy: I hope our exchange of ideas has helped the original submitter resolve his issue

I agree with your comments, hopefully he has a good idea of what to do.

Sadly, most companies selling Solar storage, in my very limited experience, sell the right number of batteries for 100% of the storage at 100% of Battery capacity.

No "free space" plus the batteries get pulled about quite roughly....

And because a battery charged (or even over charged/over heated and over gassed) starts to lose capacity within a couple of years at best, the required amount of energy storage capacity drops below 100%. You see this with many, even modern, cars......

That is why I like the 70% rule, batteries are not overworked and if the need arose, you can always charge up to 100% occasionally......spare capacity is there!!