Battery freezing?

[MarcJ]

Hi there,

thought I'd share my pics of a battery that I think has frost damage. It's one of two 6V gel batteries left on the boat, which has been on it's trailer since November. They were left switched off with no load connected. It hadn't occurred to me that batteries could freeze - the battery under the car bonnet has acid in it - didn't realise it could be a problem with gel batteries, if it is!
I've got the data sheet for the battery - this is the nearest link I could find for the spec (the ones I have are 165Ah): http://www.enersys-emea.com/reserve/pdf/EN-V-RS-009_0114.pdf

Is this frost damage? If not - what's going on!

I'm lucky as I have easy access to a replacement, thought I'd share this in case there's anyone else who didn't know this could happen - if it is frost damage..

Many thanks!

 

[VicS]

It certainly looks like frost damage

I dont know if gel batteries can freeze ???????? I'd not have thought so.

But

The link in your post is to valve regulated absorbed glass mat batteries, not gel type. I guess they can freeze if in a discharged state just as ordinary flooded cell batteries can.

What you doing on here at 2:30 in the morning?

 

[MarcJ]

It certainly looks like frost damage

What you doing on here at 2:30 in the morning?

Good question! Been catching up with work all evening....but keen on getting back on the water soon! Time to go to bed! I'll have a re-read of the spec sheet tomorrow...

 

[vyv_cox]

The concentration of sulphuric acid in batteries is about 33%. The freezing point of sulphuric acid at this concentration is about -45 deg.C. It must have been colder in Nantwich than it was here!

http://www.giantbatteryco.com/GLOSSARY/Sulfuric.Acid-Industrial.Batteries.html
http://www.sulphuric-acid.com/TechManual/Properties/properties_acid_freezingpt.htm

 

[VicS]

The concentration of sulphuric acid in batteries is about 33%. The freezing point of sulphuric acid at this concentration is about -45 deg.C. It must have been colder in Nantwich than it was here!

Yes that is so if the battery is charged but if discharged freezing is possible although I do not remember any vry cold weather this winter when it might have occurred

If the damage was not caused by frezing what was it?.

Interesting graph. I have come across the odd table or two of freezing points but that's the first time I have seen the graph for the entire concentration range.

 

[sailorman]

Where did the electrolyte go

 

[TSB240]

It must have been colder in Nantwich than it was here!

+1 definitely not this winter and I live 6 miles away!

I just cant believe that is frost damage from this winter.

Could it have been accidentally or deliberately shorted without your knowledge?
It does look as though it has burst under pressure from inside. Even stranger are the two separate fractures of the casing .
This does point to freezing ?

 

[MarcJ]

Yes it's a puzzle...the other 6V battery looks fine, although I haven't checked the voltage on it, I got 10V across both when I turned them on, before I noticed the damage.
There was no leaking, no evidence of any electrolyte coming out.
No one has been on the boat - it has had tarps tied around it and they weren't disturbed...

 

[neale]

That freezing point graph is really strange, if I am reading it right. The way the freezing point changes both up and down as the concentration increases doesn't compute in my head. At 77% it freezes at -10°C, at 91% it freezes at -10°C but at 83% it freezes at +7°C. Is that right?

 

[Nigel-in-Oxford]

I would have thought that this is the usual "dead" cell expansion coupled with the case being made brittle by cold weather.
Causing fracturing rather than the usual bulge.

 

[MarcJ]

Never heard of "dead cell expansion" - that sounds right, they hadn't been charged since September I think. I had good intentions of getting a charge into them, but it never happened cos of the weather. A bit of a bugger cos I think it was alright in Feb when I last went to the boat, but it started raining and I never put the solar panel on them!

 

[david_bagshaw]

Dead cell expansion is caused by sulphation, while flat for a while, where the lead sulphate occupies more room.

no chance it has been borrowed and dropped?, as this has not been a freezing winter here in the midlands.

 

[MarcJ]

Dead cell expansion is caused by sulphation, while flat for a while, where the lead sulphate occupies more room.

no chance it has been borrowed and dropped?, as this has not been a freezing winter here in the midlands.

Nope, if you saw how much hassle it was to get them out (and you'd need both unless you had a particular need for a 6V battery...) you'd know why I'm pretty sure no-one has messed with them. The boat is in a rural location, not far from Bridgnorth. It could be in a bit of a "cold well" where it is, next to a river in a valley, but considering the boat's up on a trailer, you'd not think we'd have had it cold enough to freeze it!

 

[VicS]

That freezing point graph is really strange, if I am reading it right. The way the freezing point changes both up and down as the concentration increases doesn't compute in my head. At 77% it freezes at -10°C, at 91% it freezes at -10°C but at 83% it freezes at +7°C. Is that right?

Perhaps your physical chemistry is a little rusty

No reason why it should not be right although I like to see a bit more detail before I understood all of it.

Ignoring some of the smaller deviations from a smooth graph it looks a though two compounds are formed with compositions corresponding to the two main humps at 57% and 84%. Application of a few elementary chemical calculations should enable you to determine the empirical formulae of these compounds.

The dips correspond to eutectics between water and one compound, between the two compounds and between the second compound and sulphuric acid .

A little more complex perhaps but that would explain the basic shape of the graph.

 

[neale]

Perhaps your physical chemistry is a little rusty

Unfortunately my chemistry is more than a little rusty. Myself and the chemistry teacher never saw eye to eye

It just seemed very odd to me that as concentration increased the freezing point goes up and down. I would have though it would be a pretty smooth line, like adding antifreeze to water. Still, you live and learn.

 

[VicS]

A little more complex perhaps but that would explain the basic shape of the graph.

As you have no doubt worked out by while I was having my tea the humps correspond to the tetra hydrate and mono hydrate. I'd guess the irregular shapes around the second dip are due to the formation of the tri and dihydrates with eutectics between each pair.
Id guess the other spike is an experimental error

 

[VicS]

FWIW a more detailed version of the sulphuric acid water diagram

 

[MarcJ]

Thanks Vic! Though I'm a bit cross eyed looking at it!
I re-read the data sheet I've got and snipped this bit from it - self explanatory really! Once totally discharged, the temperature only needed to be freezing to stuff the battery...

 

[VicS]

Thanks Vic! Though I'm a bit cross eyed looking at it!
I re-read the data sheet I've got and snipped this bit from it - self explanatory really! Once totally discharged, the temperature only needed to be freezing to stuff the battery...

Yes which comes back to what I said in #2 and #5. I just dont remember any spell of cold weather this winter when it might have happened. Perhaps there was briefly early on.

Even if nearly pure water when it froze its now worth checking for any acid remaining in the bilges or wherever it would have gone and give everywhere likely to have been contaminated a rinse with a solution of washing soda. Although with luck its all been retained by the glass mat

 

[vyv_cox]

I cannot compete with VicS' brilliant work in tracking down the sulphuric acid phase diagram but you may be interested in similar low melting points resulting from eutectics in metals. Perhaps the best known is Woods Metal with a melting temperature of 70C, despite being composed of elements that all have melting points well into the hundreds. There is a good page on it, and similar eutectics, at http://en.wikipedia.org/wiki/Wood's_metal