Heavily boiled FLA battery

[santaclaws]

Hello,

I have an off-grid sytem (solar + wind) and my battery bank (24V) is a 2S4P topology (so I have 4 strings of 2 x 12V batteries in parallel).

Recently, while being in a short vacation (abroad), I've noticed that the battery bank capacity was going down. I blame it on the very low outside temperatures (the batteries are located in my garage thus the indoor temperature did not felt bellow 10 deg celsius all this time).

Anyway, when I came home I faced a completely different reality: two of my batteries (from the same string) were boiling like hell.

When I've measured the voltages, one had 10.5V and the other one around 15V.

I've checked the water level and it was OK (I've done the same thing about 2 weeks before) thus there was no part of the internal plates exposed to the air.

I've removed the batteries from the bank and left them to cool off (it takes about one day!). I rechecked the voltages and this time and I've got around 9.5V and 11.5V.

I' ve tried to measure the SOC using a hydrometer and I found two cells with slighty lower indication in the first battery but the second one shown quite similar indication for all the cells. Anyway, both batteries shown a SOC bellow 50% or something.

I was pretty confused, as I was expecting the "good" battery to be in an overcharged state (maximum SOC indication).

Anyway, in the next few days, I've tried to slowly charge this "good"(??) battery using various scenarios (constant low current, high pulse charging and so on) but it seems to stall at 12.8V. I left it disconnected for a day and the indication was around 12V.

That's pretty confusing too, as there's no indication of a bad (shorted) cell or deep sulfation.

So I came here to kindly ask you to enlighten me on this matter: what supposed to be the effect of that heavily boiling (for at least two days, I presume)? Like I've just said, the electrolyte level wasn't bellow minimum and the whole battery case was quite hot to touch (maybe 45-50 deg celsius?).

Do you have any advice on how to recover this battery (as I already have an identical one in very good shape - it has been used alone in a 12V back-up system, powering up my routers, cctv and such). I'd like to put them back in the missing string and, as I'll have to relocate during this year, I don't want to spent any more money on two brand new ones.

Btw, for the same relocation reason, I went with marine (I know..) batteries so they have pretty slim Pb plates inside (for your information). Thanks in advance for your time.

[Logan5]

Batteries require maintenance, when batteries are wired in series this maintenance is hands on regular inspections, adding water and adjusting charge parameters. when you use the incorrect battery type for your application as well as parallel wiring of batteries, this maintenance becomes much more difficult. Imbalance of batteries charging is common and the more parallel connections you have the worse it gets. You should have considered 2volt cells to achieve your Amp Hour capacity. All wired in series, 24v = 12 cells to inspect. Your system sounds like it has 48 cells to inspect. You should have a notebook to do your SG readings. battery capacity and or type Mix and matching, used batteries, mixing new and used. Cyclical Solar makes a poor choice for charging batteries and shorten their expected life span.

[santaclaws]

Like I've just said, I deliberately chose this path (relative cheap marine batteries) as I'm going to relocate during this year and I'm pretty sure that the new owner will not choose to keep the off-grid solution.

Anyway, the batteries were brand new and I bought all of them at once.
I really do care alot about them and I did all the required maintenance works (watering, weekly equalisation, voltage readings and so on).

Anyway, having four parallel strings (without separate current monitoring for each branch) has been the weak link.

Nevermind, my actual problem is how to save the "good" battery and, first of all, I'd like to know what really happened with the battery chemistry during that boiling process.

[Wy_White_Wolf]

One cell shorted out. That dropped the string voltage down to 22 volts nominal. All the other strings were still at 24 nominal. So they discharged into and all charging current passed through the bad string boiling there cells and destroying there plates. Both batteries that were in that string are now bad. There is no saving the one battery and could have damaged all the other strings by being at a state of undercharge for an extended period of time.

WWW

[SunEagle]

One cell shorted out. That dropped the string voltage down to 22 volts nominal. All the other strings were still at 24 nominal. So they discharged into and all charging current passed through the bad string boiling there cells and destroying there plates. Both batteries that were in that string are now bad. There is no saving the one battery and could have damaged all the other strings by being at a state of undercharge for an extended period of time.

WWW

My guess is that the battery that was boiled has "plate damage" and nothing would be available to bring it back to what it should be.

[Sunking]

If a battery or batteries are boiling, and voltage does not go off the chart means you have shorted cells. You brought this on yourself with parallel strings. Only way to fix it is replace all the batteries and use the right size so you do not have any parallel strings. You are stuck in a 12 volt box. Batteries are not 12 volts, they are 2 volts. If you need 500 AH, then buy 500 AH batteries.

Like WWW told you the one battery with a shorted cell, corrupted all your batteries. Learn an expensive lesson and do not repeat it. Havin ganythin godff ggrid is a full time joppb with no days off. You cannot walk away for a few days. If you must leave, SHUT DOWN.

[santaclaws]

(1) Many of you have stated on this forum that is OK to have parallel strings for maintenance purpose (to allow battery disconnection while keeping your system on-line).

(2) I'm living off-grid for about two years and a half and I've spent many vacations abroad (2-3 weeks each) without shutting down my system.

(3) all the electronics involved (+5kW sine wave inverter, solar/wind/gen battery chargers, system logging & monitoring, remote access and so on) are all made by myself, so I could configure it any way I want.

The only thing that was missing (though it was on my todo list all this time) was a separate current measurement for every string and individual battery voltage monitoring. I actually have on my desk the four hall current transducers but I didn't had the time to put them in circuit.

(3) a single shorted cell couldn't really corupt ALL the battery bank but the other single battery in that string (forcing an overvoltage across it)

I have enough solar/wind available to overload (on purpose) the batteries - that's why the rest of the strings had enough power available to be charged as usual (I've checked the logs and the overall system voltage was normal during various charging stages).

The only problem was the extra load (the affected string) during the time when the sun was off. But, from the healty batteries point of view, the bad ones have represented just a regular (extra) load. Like I've just said, I was noticed that the bank voltage was reached a specific voltage (24.5V, by example) one hour earlier than usual (for the same daily consumption). So no dramatically discharging happened inside the battery bank.

That means:

(4) I don't see any good reason to replace the whole battery bank (even the SG measurements of the rest of the batteries could confirm that).

[SunEagle]

(1) Many of you have stated on this forum that is OK to have parallel strings for maintenance purpose (to allow battery disconnection while keeping your system on-line).

(2) I'm living off-grid for about two years and a half and I've spent many vacations abroad (2-3 weeks each) without shutting down my system.

(3) all the electronics involved (+5kW sine wave inverter, solar/wind/gen battery chargers, system logging & monitoring, remote access and so on) are all made by myself, so I could configure it any way I want.

The only thing that was missing (though it was on my todo list all this time) was a separate current measurement for every string and individual battery voltage monitoring. I actually have on my desk the four hall current transducers but I didn't had the time to put them in circuit.

(3) a single shorted cell couldn't really corupt ALL the battery bank but the other single battery in that string (forcing an overvoltage across it)

I have enough solar/wind available to overload (on purpose) the batteries - that's why the rest of the strings had enough power available to be charged as usual (I've checked the logs and the overall system voltage was normal during various charging stages).

The only problem was the extra load (the affected string) during the time when the sun was off. But, from the healty batteries point of view, the bad ones have represented just a regular (extra) load. Like I've just said, I was noticed that the bank voltage was reached a specific voltage (24.5V, by example) one hour earlier than usual (for the same daily consumption). So no dramatically discharging happened inside the battery bank.

That means:

(4) I don't see any good reason to replace the whole battery bank (even the SG measurements of the rest of the batteries could confirm that).

It is your money and you can do with it as you feel. But just adding one new battery into an existing system will more than likely kill it off much sooner then if all of the batteries were the same age and health.

[Sunking]

Hey I do not care if you destroy your batteries, Fine with me. No one here has told you parallel batteries are OK on a cycled battery. At least not anyone who knows something. That is why you destroyed your batteries in 2 years. Replace the bad ones and they will all be destroyed in a year or less. Have at it. .

You wanted to know what is wrong, we told you. You screwed up the design. If you do not like it, leave it and do it your way. Your battery guy will be tickled pink with you replacing batteries every year or two. Do it right and you get 5 years. Your money, waste it as you see fit.

[Mike90250]

(1) Many of you have stated on this forum that is OK to have parallel strings for maintenance purpose (to allow battery disconnection while keeping your system on-line)..........

None of the moderators or vetted regulars EVER said that, that I know of. Our common response to parallel batteries is either the Smartgauge site where they explain all the math as to why it is bad, or Sunking trots out the 12V : 2V statement.

[littleharbor]

Keep in mind this is the same guy who wants to hook up a 5000 watt 12 volt inverter to a cigarette lighter plug to power his "regular evening activities" But don't worry he has a degree in electronics.

"I have a degree in electronics but you can show me some pictures to get it right.

So let me repeat once again: you can even use a 5kW inverter with a 2-300W load and no damage would be done to any cigar socket."

[SunEagle]

Keep in mind this is the same guy who wants to hook up a 5000 watt 12 volt inverter to a cigarette lighter plug to power his "regular evening activities" But don't worry he has a degree in electronics.

"I have a degree in electronics but you can show me some pictures to get it right.

So let me repeat once again: you can even use a 5kW inverter with a 2-300W load and no damage would be done to any cigar socket."

The problem is how do you guarantee not to use more than that 300watts. The inverter doesn't care as long as you stay below it's maximum but you still have the problem of overheating and burning up the wiring between the battery and inverter. The best way to prevent that would be to install over current protection which blows a fuse when you go to 400 watts.

The NEC sets down the rules for safety. It states that you have to protect the wire so you don't over amp it which can cause a fire. They don't just allow a person to determine how much will be used but how much the physical properties of the circuit components can handle. That is why there are breakers and fuses installed to prevent fires.

[inetdog]

Most DC power sockets (used to be called cigarette lighter sockets) are protected by a 10A fuse. That will limit you to at absolute most a 150W continuous load.
Even 300W portable inverters recommend using direct wiring rather than power plug if you are going to be using more that about 100W from them.

[SunEagle]

Most DC power sockets (used to be called cigarette lighter sockets) are protected by a 10A fuse. That will limit you to at absolute most a 150W continuous load.
Even 300W portable inverters recommend using direct wiring rather than power plug if you are going to be using more that about 100W from them.

I guess the hard part would be to "tap" the EV battery system which would not be close to 12 volts. That voltage would be somewhere down the line in the circuitry.

[santaclaws]

Keep in mind this is the same guy who wants to hook up a 5000 watt 12 volt inverter to a cigarette lighter plug to power his "regular evening activities" But don't worry he has a degree in electronics.

"I have a degree in electronics but you can show me some pictures to get it right.

So let me repeat once again: you can even use a 5kW inverter with a 2-300W load and no damage would be done to any cigar socket."

It's funny how fustration actually works.

You "managed" to hi-jack this thread by moving here the entire discussion from the other thread, which had a completely different subject!

Fortunately, the moderators didn't agree with you. Guess why?! Well, that's because of the first low of electronics: "a fuse is meant to blow".

FYI, even the cheapest car in the world has a fused cigar socket (due to regulations). So you CAN'T surge more than 10-30 amps (depending on fuse ratings, which depends on internal wirings) even if you're using a 50kW inverter! Keep calm, no one is being hurt.

But if you want to check my knowledges, please open a separate thread and ask me anything about my DIY off-grid electronics (high power inverters and chargers, control and monitoring circuits - you name it). FWIW, they're all MCU based thus you can ask questions about coding/programming, too.

Now if we can go back to the original subject of this thread, I have few more comments to add.

Okay, you're perfectly right: series battery topology is the more preferable by far. But, if the parallel strings "does't work", how come they actually.. work?!

Well, there is a self regulating mechanism due to variable internal resistance of the battery, which is mainly related to its SOC.

That's it, when the batteries are used in a S+P configuration, there will be a self-ballancing mechanism (ohm low) as to get equal internal resistance for each string (which roughly means equal SOC).

These physics laws could only be "canceled" by the chemistry; if a battery has been abused (sulfation, overcharging) it will act erratically, due to inconsistent current path. In this situation, you can no more count on "internal resistance <=> SOC" relationship.

Anyway, by using an equalisation charge more frequently, the actual SOC of every battery of the bank will be set to 100℅ hence any cycling unballance will be removed.

The key factor when using series/parallel configurations is to keep all the batteries in a healthy condition (by avoiding sulfation or deep under/overcharge) as to allow identical chemistry behaviour.