Frozen flooded batteries

[Mike90250]

For some reason steel wool works to stop mice and rats. I did that to my daughters travel trailer and it worked. Trust me those critter will find a hole or make one if they get that hungry.

Steel wool will rust through in a couple years, and turn to rust dust. Brass Wool from a boat yard (works like steel wool, but does not leave rusty marks on boats) will last many years. Costs a bit more, and if you have a dry area, maybe steel wool will work fine.
Or even the curly sink scrubber pads would do it too.

[gardner]

Temps have been above -10C for a few days and it looks like my batteries have thawed out. It will take some time for the OCV to settle out but at the mo it looks to be ~11.6V @ +2C -- pretty low. It will be 6-8 weeks or more till I can travel to check them out in person.

[SunEagle]

Oooh! I like that idea -- thanks.

For some reason steel wool works to stop mice and rats. I did that to my daughters travel trailer and it worked. Trust me those critter will find a hole or make one if they get that hungry.

[gardner]

Plug holes with steel wool.

Oooh! I like that idea -- thanks.

[Sunking]

I also have to figure out how to stifle the mouse infestations in my generator.

Plug holes with steel wool.

[gardner]

Add one panel wired to a seperate charge controller that is mounted vertally on a south facing wall or on a post mount.

Thanks, Wolf. That will be the plan, I think.

I also have to figure out how to stifle the mouse infestations in my generator. If the spark plug cable hadn't been eaten I might have had a chance to charge things off the generator to avoid this problem in the first place.

[gardner]

I am typing slowly for you to understand.

Thanks, you're a sport.

[Sunking]

I am typing slowly for you to understand.

If your batteries are less than 100%, they are undercharged. FLA Batteries cannot be left under 100% SOC for any period of time for more than a day or two. In cold weather you had better recharge them every day or they can freeze on you. In extreme cold, they should not be used if left in the elements. or else bad things happen to them. If you had keep them charge up, this thread and debate would not have ever occurred. You left them 50% or less in extreme cold and you got exactly what you asked for. Don't blame us or try to divert attention from the fact you abused your batteries and let them freeze.

[gardner]

If the battery Specific Gravity got low enough for the batteries to freeze means they have been in a discharged state for a very long time and have sulfated.

This contains two assertions:

(1) batteries could only have frozen if there were left completely discharged for a long time
(2) they would have inevitably have been destroyed prior to freezing through being left discharged and consequent sulphation

While I agree that my batteries were not fully charged, I can show that they had a SOC of at least 40% and possibly 50% based on OCV. The fact that they froze at ~ -27C implies the SOC was somewhere in the 55% to 65% range. They were definitely not discharged completely, much less left that way for an extended period. FLAs can in fact freeze with an acceptable, if non-optimal, SOC and be destroyed by freezing before they are in danger from sulphation.

It would have been better if my batteries were fully charged, of course. But non-ideal circumstances does not imply total neglect or complete design failure. There are interesting things to learn about low temperature performance of FLA batteries that simple assertions of "abuse" doesn't cover.

[Sunking]

When I first read this I knew that it was wrong as general guidance.

Please do tell what is wrong with the statement. Your charts backs the statement up. You have to let your batteries discharge pretty deep and ignore them before they freeze. Keep them charged properly and daily and it is almost impossible for them to freeze. Secondly if you are in an extreme climate, use AGM batteries.

Your batteries froze because you abused them. Pretty simple. If your system was designed correctly, they would have likely never frozen unless the temps drop below -50 and if that is the case you should be using AGM batteries. What is so hard to understand? .

[inetdog]

A FLA does not have to be totally discharged nor sulphated, and may in fact be in quite reasonable condition, and still can be vulnerable to freezing in winter conditions.

If you follow the general rule of thumb for design of off-grid systems, the batteries will rarely get below 80%, so the 50% freezing point is very conservative.
The other major factor is to take into account is that whenever the batteries are being actively charged or discharged there will be significant internal heating.
That means that as long as you are charging each day, going down to 50% occasionally may not be that big a risk, particularly if you insulate the battery bank in the winter to retain the internally generated heat.

[gardner]

If the battery Specific Gravity got low enough for the batteries to freeze means they have been in a discharged state for a very long time

When I first read this I knew that it was wrong as general guidance. I didn't want to just start a pissing match, but I've done a bit of digging and wanted to put forward some more specific information about the subject of the freezing point of sulphuric acid electrolyte. There are a few useful sources, but this is about the best primary information:

http://www.unionbattery.com/images/2.6.pdf

It includes a useful table of freezing point by specific gravity covering a wide range of acid concentrations from 0% to well above the concentrations found in FLA batteries. Interestingly the freezing point varies in a complex curve. The data covers the conventional ranges of concentration found in SLA batteries pretty well. Combining this with the conventional specific-gravity vs SOC ranges yields this relationship:

SOC	Specific Gravity	Freezing Celsius
100%	1.255 - 1.275	-56.7 - -70.9
75%	1.215 - 1.235	-35.1 - -44.8
50%	1.180 - 1.200	-22.4 - -29.0
25%	1.155 - 1.165	-16.2 - -18.5
0%	1.110 - 1.130	-9.3 - -11.8

In a chart this looks like:

FloodedLeadAcidFreezing.png

I cheated a little in this data since the conventional specific-gravity vs SOC data uses S-G at 25C whereas the freezing temperature references S-G at 15.5C. If I go back and calculate in the S-G temperature corrections I'll follow up.

The net however is the fact that a fully charged FLA is unlikely to freeze outside of Antarctica. Critical in my case though, is that a partially discharged -- even a 50% discharged -- battery can freeze in the weather we put up with here. It can easily drop to -30C in many locations in North America, and a battery charged up to about 60% SOC could be vulnerable.

A FLA does not have to be totally discharged nor sulphated, and may in fact be in quite reasonable condition, and still can be vulnerable to freezing in winter conditions.

[Wy_White_Wolf]

Add one panel wired to a seperate charge controller that is mounted vertally on a south facing wall or on a post mount. That way you don't have to get on the roof and mess with the array.

WWW

[gardner]

That will turn that panel into a 5 watt panel.

Maybe not 5, but I do understand that it will definitely not deliver 50W. However the goal is only to provide a float charge to counter the self discharge. I'm not sure I need more than a few watts. I have some experimenting to do, I guess.

[gardner]

You are below 50%.

Yes, I agree. My estimate was ~40% SOC.

Either way, the batteries are either badly degraded or totally destroyed and I won't know until temps climb above -12C, which will be in effing June at the rate we're going here.