Boiling Batteries -- Shorted Cell ?

[Dockhead]

I got back to my boat last night after more than a month away -- the only time of year I am away from her for so long (holidays).

I was greeted by the smell of boiling batteries.

I pulled up the sole plates and found one pair of batteries boiling away -- incredibly, the electrolyte was still covering the plates. (I have a 24v house system and my house bank consists of four pairs of 12v "leisure batteries" each wired in series to produce 24v nominally.)

The Victron charger was on float putting out a low voltage as it should have.


What caused this??!! Is this what happens when a cell is shorted out? I guess a modest float voltage because higher per cell when one is shorted -- maybe beyond the gassing or boiling point -- ?

Could my boat have burned down because of this? What happens in such a case when the acid is boiled off and the plates are exposed?

Any way to prevent it?

I isolated the malfunctioning battery pair and the rest of the bank -- and the charger -- seem to be working normally.

Grateful as always for any advice!

[atoll]

prolly losse of electrolyte,and the trickle charge senses the voltage.
the victron chargers have a heat sensor tho cut off the charge if over heating.

and yes very real risk of explosion and fire!

did you install a solar panel and wind gen this may be fooling the charger,or other things that draw/creat current

[Dockhead]

No solar or wind yet.

There are eight batteries, and the thermal sensor is only on one of them!

[atoll]

Originally Posted by Dockhead

No solar or wind yet.

There are eight batteries, and the thermal sensor is only on one of them!

need to check all with a hydrometer to find the dead cell,probably in one of them.
how old are they,this normally can happen 3-5 years depending on quality and usage

[Aussiesuede]

Originally Posted by Dockhead

What caused this??!! Is this what happens when a cell is shorted out? I guess a modest float voltage because higher per cell when one is shorted -- maybe beyond the gassing or boiling point -- ?

Usually something external to the battery bank causes the short. The fact that two batteries were affected supports this probability as well; as each of the individual batteries is basically a "cell" in your system and you in essence lost 2 cells. The Victron should sense the lost cell(s) since there would be a voltage drop, and automatically lower total charging amp output.

Originally Posted by Dockhead

Could my boat have burned down because of this?

Yep, but it would have very likely happened quickly (I know that's of no solace). Within minutes of whatever caused the boil over. If you want to get an idea of what'll actually occur, next time you goto replace a dead car battery - hook up the battery to a charger with the polarity reversed. You'll see just how quickly the boil-over, and potential explosion, occurs (obviously do this experiment outside and with plenty of distance between you and the battery).

Originally Posted by Dockhead

What happens in such a case when the acid is boiled off and the plates are exposed?

Fully exposed plates will sulfate - rendering the battery useless.

[atoll]

it also sounds like the charger has no splitter,so is sensing the voltage in the good batteriy bank,and charging accordingly,or has a splitter but it is not cutting off trickle charge completely to the dud cells,hence the boiling

[FlyingCloud1937]

Originally Posted by Dockhead

I got back to my boat last night after more than a month away -- the only time of year I am away from her for so long (holidays).

I was greeted by the smell of boiling batteries.

I pulled up the sole plates and found one pair of batteries boiling away -- incredibly, the electrolyte was still covering the plates. (I have a 24v house system and my house bank consists of four pairs of 12v "leisure batteries" each wired in series to produce 24v nominally.)

The Victron charger was on float putting out a low voltage as it should have.


What caused this??!! Is this what happens when a cell is shorted out? I guess a modest float voltage because higher per cell when one is shorted -- maybe beyond the gassing or boiling point -- ?

Could my boat have burned down because of this? What happens in such a case when the acid is boiled off and the plates are exposed?

Any way to prevent it?

I isolated the malfunctioning battery pair and the rest of the bank -- and the charger -- seem to be working normally.

Grateful as always for any advice!

What makes a smart charger smart??

Hint, it's not the three stages.

Lloyd

[Dockhead]

Originally Posted by FlyingCloud1937

What makes a smart charger smart??

Hint, it's not the three stages.

Lloyd

Practical advice would be gratefully received! Thanks!

[Fuss]

my thoughts...
Assuming the charger is working ok, which i think it is as you said it was floating on low voltage (around 26.4- 27v for example)
the 2 boiling batteries cannot have been boiling long or they would be dry/er than the other 2.
Strange that 2 batteries at the same time are boiling!! are they connected differently to the other 2??
Are some other devices cabled only to the 2 boilers?
Is there a splitter or relay somewhere in the equation?
I think the 2 batteries are not faulty... its too much of a coincidence that both would fail together.... it must be in the cabling setup


what is the voltage of each of the 4 batteries after say 8 hrs off charge and disconnected from each other?.... this will give us some more info to work with.


Is it possible to get a 12v battery load tester and load test each one?

If by this stage they appear ok and the cabling is the same as the other 2.... Can you swap the 2 boilers places with the other 2 and see what happens...(but im sure the other tests will have revealed something)

Yes they blow up eventually,,,, just look around the boatyard at the disgarded battery piles.... I have no first hand experience of this though

[Dockhead]

Originally Posted by Fuss

my thoughts...
Assuming the charger is working ok, which i think it is as you said it was floating on low voltage (around 26.4- 27v for example)
the 2 boiling batteries cannot have been boiling long or they would be dry/er than the other 2.
Strange that 2 batteries at the same time are boiling!! are they connected differently to the other 2??
Are some other devices cabled only to the 2 boilers?
Is there a splitter or relay somewhere in the equation?
I think the 2 batteries are not faulty... its too much of a coincidence that both would fail together.... it must be in the cabling setup


what is the voltage of each of the 4 batteries after say 8 hrs off charge and disconnected from each other?.... this will give us some more info to work with.


Is it possible to get a 12v battery load tester and load test each one?

If by this stage they appear ok and the cabling is the same as the other 2.... Can you swap the 2 boilers places with the other 2 and see what happens...(but im sure the other tests will have revealed something)

Yes they blow up eventually,,,, just look around the boatyard at the disgarded battery piles.... I have no first hand experience of this though

Thanks -- I will do all of those tests.

The two batteries which were boiling were a pair wired in series. I have four pairs -- 8 total 12v batteries -- wired up to produce 24 volts. So the pair of batteries which was boiling was a virtual 24v battery. One shorted cell would increase the cell voltage in the remaining cells by 1/12. Float voltage is 27.6, so 2.3 volts per cell. So with one shorted cell, the cells would see voltage equivalent to 2.5 volts per cell or as if charging at 30.1 volts. Yep, I guess that would boil them all right -- is my analysis correct?

In 12 volt terms -- float voltage like 13.8 volts; but charging like 15.05 volts.

Naturally both batteries in the pair boiled -- they are wired up in series like a virtual 24 volt battery.

[Fuss]

Originally Posted by Dockhead

Thanks -- I will do all of those tests.

The two batteries which were boiling were a pair wired in series. I have four pairs -- 8 total 12v batteries -- wired up to produce 24 volts. So the pair of batteries which was boiling was a virtual 24v battery. One shorted cell would increase the cell voltage in the remaining cells by 1/12. Float voltage is 27.6, so 2.3 volts per cell. So with one shorted cell, the cells would see voltage equivalent to 2.5 volts per cell or as if charging at 30.1 volts. Yep, I guess that would boil them all right -- is my analysis correct?

In 12 volt terms -- float voltage like 13.8 volts; but charging like 15.05 volts.

Naturally both batteries in the pair boiled -- they are wired up in series like a virtual 24 volt battery.

Yes, I agree with you and your analysis.... I also now think it could be a dud cell in one of the 2 boiling batteries making the good cells get 2.5v per cell instead of 2.3.

(I would have thought that 27.6 float would have been more suitable to traction batteries and that a lower float would be better for leisure batteries, but that has nothing to do with this problem)

[djmarchand]

As others have said, one or more of the cells in the battery built up sulfate which dropped into the bottom of the battery. When the layer of sulfate got as high as the plates it shorted. As you surmised that 6 cell battery effectively became 5 or less and the higher voltage per cell caused gassing.

You need to replace the bad battery and equalize the rest. Equalizing will solubilize (some of) the sulfate and keep it from shorting another cell.

Sulfating typically occurs when batteries are left discharged for weeks at a time. This could have happened recently or sometime in their past life.

David

[btrayfors]

Dockhead,

If it were me, I'd:

1. Isolate the bad pair. Just take 'em out of the bank. DO NOT replace them.

2. Use the remaining ones until you are able to replace the whole lot. I'd do that sooner rather than later.

3. When you do replace the lot, DO NOT use "leisure batteries". Use either golf-cart deep-cycle batteries or the even more robust industrial 2V cells to build up a 24V bank.

Both the golf-carts and the 2V cells are much more robust than the "leisure batteries" and are much less likely to suffer a shorted cell in the future.

FWIW,

Bill

[Dockhead]

Originally Posted by btrayfors

Dockhead,

If it were me, I'd:

1. Isolate the bad pair. Just take 'em out of the bank. DO NOT replace them.

2. Use the remaining ones until you are able to replace the whole lot. I'd do that sooner rather than later.

3. When you do replace the lot, DO NOT use "leisure batteries". Use either golf-cart deep-cycle batteries or the even more robust industrial 2V cells to build up a 24V bank.

Both the golf-carts and the 2V cells are much more robust than the "leisure batteries" and are much less likely to suffer a shorted cell in the future.

FWIW,

Bill

Thanks, Bill. I did that. Didn't even need to take them out. To take a battery pair off-line, all I have to do is remove the link between them.

What I'm concerned about is the danger that it could happen again, and sometime not when I just happen to come on board. Could I have a fire?! I am checking all the batteries now to see how bad they are.

[Dockhead]

Well, my batteries are shot, I think. I have equalized them a few times since they were left dead for a month by a runaway bilge pump but it does not seem to have done any good.

Out of 8 batteries, I only have two where the hydrometer even floats in ever cell.

The best two (judging by the SG of the worst cell) have the following readings:

117 125 126 125 126 120

122 125 127 127 128 115

The others all have at least one cell which doesn't even float the float in the hydrometer.

My thinking now is that I have spent enough time with this set of batteries, and that I am risking burning my boat down if I continue to play with them.

Since I have to leave the boat for a few weeks tomorrow, I am thinking about taking all the batteries off-line except for the two which floats the hydrometer in every cell. Leave just this pair connected (so that there is something to run the bilge pumps just in case) until I can get back and replace them all.

Any comments on this scheme?

I will install a wind generator together with the new batteries so that this doesn't happen again. I never knew but now understand that if you don't have shore power, you can't keep your batteries alive just with generator and engine power -- you've got to have some means of trickle charging them. Wish I had known