FLA Batteries & Freezing Weather

Mountain Don

Where do you locate your FLA batteries when the weather includes months of below freezing weather?

Our situation is a part time use cabin at 8800 feet in the mountains of northern NM. Totally off grid; main heating source is wood. After the roads get snowed over by mid December usually, through to March/April we snowshoe in once or twice a month for a weekend up to a week at a time. In between visits the place sits unoccupied and unheated for weeks.

I did not want the FLA batteries inside. Not that it would do much good as the inside is most often colder than the outside when we arrive for a winters stay. The batteries are outside in a lean to small shed. It keeps the rain and snow off but is not airtight. I made the battery bank about a third larger than if there was no winter use to cover the loss of performance in freezing temperatures.

Is there a better way to handle FLA batteries in a situation such as this? In case anyone wonders, the PV system has kept the batteries fully charged for the past 5 winters with no issues. The system would go through a short bulk charge, into absorb and then to float everyday there was sun, as recorded by the OB FM log. Our winters are mainly sunny except for those days when clouds roll over and leave some snow. About 300 sunny days in an average year. Very few days throughout the year when the system does not make it into float. The generator would be run more to exercise it than because of a need to recharge the batteries.

Thanks

EDIT: The CC does have a remote temperature sensor attached to one battery. We are not having any difficulties; simply wondering if there is a better solution.

Photowhit

Re: FLA Batteries & Freezing Weather

Unless drawn down considerably, they should be fine, a temperature sensor and a good Charge Controller, will adjust the charging a bit. Some would suggest burying the batteries in a berm shelter, allow the natural heat of the earth warm them a bit, I think this would be more helpful in the summer time.

BB.

Re: FLA Batteries & Freezing Weather

Put some sheet insulation around the batteries in winter to keep them "warm" or at least not way below freezing (self heating during charging/discharging will help keep them "warm").

Years ago, somebody here used a battery heater on a generator for a day or so to get the bank above freezing, then cycling kept them warm enough (insulated battery box/under cabin floor or something similar).

The danger comes if the batteries are well discharged--Then they can be frozen easier.

http://www.trojanbattery.com/Tech-Support/FAQ/Maintenance.aspx

Can a battery freeze?
The only way that a battery can freeze is if it is left in a state of partial or complete discharged. As the state of charge in a battery decreases, the electrolyte becomes more like water and the freezing temperature increases. The freezing temperature of the electrolyte in a fully charged battery is -92.0^oF. At a 40% state of charge, electrolyte will freeze if the temperature reaches approximately 16.0^oF.

While AGMs can do OK if frozen (no split cases, less likely to be damaged), you cannot recharge a frozen AGM battery--They need to get warmed up first.

-Bill

Cariboocoot

Re: FLA Batteries & Freezing Weather

You mean cold weather like -40? No problem. Mine sit the same place as always; in their battery box with 2" of foam around (and under) them - with the panels & controller hooked up. Charged batteries don't freeze, and the input from the controller keeps them above ambient. For Winter I just disconnect the inverter and put another layer of foam on top.

ramloui

Re: FLA Batteries & Freezing Weather

I did the (almost) exact same thing as Cariboocoot. My batteries sit in the shed. No insulation. I disconnected every load, tilted 2 of 6 panels to near vertical to shed snow and left the cabin for 7 months through the long canadian winter. When I opened the cabin last spring, 100% SOC!!!!

Plowman

Re: FLA Batteries & Freezing Weather

Good to know. I was a bit worried about my Trojans, which are in an uninsulated cargo trailer. Lowest temp we see in my area is ~10F, but usually lows are in the 20s-30s.

Think that'd be a problem if SOC goes down to say 75%? How about 50%? I'll be using them daily, but SOC will dip down at night and I'm not sure how well my panels will work in our cloudy/rainy winter and how often I'll have to run the generator.

mike95490

Re: FLA Batteries & Freezing Weather

Cariboocoot wrote: »

You mean cold weather like -40? No problem. Mine sit the same place as always; in their battery box with 2" of foam around (and under) them ..

What sort of foam do you use under them ? Most closed cell foam will crush under the steady weight of lead & water.

mike95490

Re: FLA Batteries & Freezing Weather

Plowman wrote: »

.... SOC will dip down at night and I'm not sure how well my panels will work in our cloudy/rainy winter and how often I'll have to run the generator.

Don't the PV watts charts tell you sun hours by month ??

long periods (1-2 weeks) of overcast/rain/drizzle keeps me on generator for 2 hrs daily, to keep at 50%, which is why I leaned toward the NiFe bank. 4 years ago, there was no Li-xxxx suitable for prime time that I knew of.

vtmaps

Re: FLA Batteries & Freezing Weather

Plowman wrote: »

Good to know. I was a bit worried about my Trojans, which are in an uninsulated cargo trailer. Lowest temp we see in my area is ~10F, but usually lows are in the 20s-30s.

Think that'd be a problem if SOC goes down to say 75%? How about 50%? I'll be using them daily, but SOC will dip down at night and I'm not sure how well my panels will work in our cloudy/rainy winter and how often I'll have to run the generator.

You ask about letting your SOC get to 50%, but how are you measuring SOC?

If you are using a battery monitor, it may be overestimating your SOC if it doesn't account for the reduced capacity of cold batteries.

--vtMaps

Mountain Don

Re: FLA Batteries & Freezing Weather

mike95490 wrote: »

What sort of foam do you use under them ? Most closed cell foam will crush under the steady weight of lead & water.

I don't quite believe that. Reason being is that XPS foam (blue from Dow and pink from Owens-Corning) as well as polyisocyanurate foam can both be used under poured concrete slabs. Current energy codes requires insulation under most slabs these days. The std big box store XPS are rated for 15 PSI. A typical L-16 is approc 12 x 7 = 84 sq inches. At 15 PSI that should support 1260 pounds; about 10X the weight of a typical L-16.

In case 15 PSI is insufficient for the task there are 25, 40, 60 and 100 PSI rated XPS foam sheets. My house has 25 PSI under the perimeter and 15 PSI under the floor slab. It has not sunk.

~~~~

I have not checked myself so I do not know about the acid reaction with XPS. Does it dissolve or get eaten away by errant drips of the electrolyte?

Plowman

Re: FLA Batteries & Freezing Weather

vtmaps wrote: »

You ask about letting your SOC get to 50%, but how are you measuring SOC?

If you are using a battery monitor, it may be overestimating your SOC if it doesn't account for the reduced capacity of cold batteries.

--vtMaps

I'm using a hydrometer to measure specific gravity, plus monitoring my loads with a Kill-A-Watt and inline DC meter. Don't have a battery meter yet, but I've been looking at the Trimetric 2030, which I don't think has temperature compensation.

Instead of the Trimetric, I could sell my Tristar charge controller and buy a Midnite Kid with Whiz Bang, which does compensate for temperature. It would involve some hassle rewiring my array, plus some additional expense (<$100), but I think it might be worth it for an MPPT controller and an integrated battery meter. Your point about temperature compensation may cinch it, I hadn't considered that before when looking at battery meters.

I just looked up Trojan's FAQ on the subject, they say 10% reduced capacity for every 15 degrees below 77F. I had no idea it was so much. That means at 20F my 225 ah battery bank is reduced to 140 ah, which means my draw of ~45 ah/day @ 12V would be 32% of battery capacity. Dang it, that's not even two days autonomy.

That's why I love this forum, constant reminders of how much I still need to learn

ramloui

Re: FLA Batteries & Freezing Weather

Mountain Don wrote: »

I don't quite believe that. Reason being is that XPS foam (blue from Dow and pink from Owens-Corning) as well as polyisocyanurate foam can both be used under poured concrete slabs. ...
~~~~

I have not checked myself so I do not know about the acid reaction with XPS. Does it dissolve or get eaten away by errant drips of the electrolyte?

Mountain Don,
I work for one of those companies manufacturing this rigid insulation. We make many different grades, each of which has a spec for compressive strength to meet the application. In the case of insulation under a concrete slab, you would want a "high load" material. They can be found with compressive strength as high as 100 psi (oups! just noticed you already stated that...). If your big box store does not carry it, it can surely special order it for you. The big drawback is that the stuff is not cheap for such a small application...

As far as chemical resistance, the resin used will do pretty well when exposed to inorganic acids (HCl, H2SO4...). Not so well to solvents.

Cheers!

vtmaps

Re: FLA Batteries & Freezing Weather

Plowman wrote: »

I'm using a hydrometer to measure specific gravity, plus monitoring my loads with a Kill-A-Watt and inline DC meter. Don't have a battery meter yet, but I've been looking at the Trimetric 2030, which I don't think has temperature compensation.

Monitoring your loads with a kill-a-watt or DC ammeter has the same problem as the battery monitor.... no temp compensation. The load you think you are drawing (based on meters) pulls your cold battery down to a lower SOC than your warm battery.

Don't forget that cold is good for batteries, as long as you plan (design) for the loss of capacity and higher peukert coefficient.

--vtMaps