Cold batteries.

Lefty Wright · February 2008

My battery bank is inside my house. I know that is not the recommended location because of the hydrogen release and the smell when equalizing. But it does keep the batteries warm.

This spring I will be building a shed attachment to my house to house the batteries and water heater. (in seperate rooms) This addition will not be heated.

I was recently gone for a few weeks and when I returned the interior of my house was just above freezing. The volt meter showed a full charge on the batteries, 14.6V, before I turned on the inverter and plugged in the radio.

About an hour later I looked at the voltmeter and was surprised to see it reading 12.2V. The batteries had never been that low before and my load was really light.

After I lit the fire and the house heated up the voltage quickly rose to normal and has been acting normally ever since.

Now I am wondering how well my batteries will do in their new location, when I build the new addition. I think I will now build the walls with 2X6 studs so I can increase the insulation but the shed will still be unheated.

What do you cold climate guys do about this?

icarus · February 2008

Re: Cold batteries.

My batteries have been in an unheated shed for ~ ten years. They are in a box that is lined with styrofoam and the building is shielded from the wind. I have not done a scientific study, but I know that the battery bank itself generates a fair bit of heat while charging and discharging. (I keep meaning to put a remote read thermometer in it so I can say how much warmer).

When I leave, often for months at a time, the outside temp can and does get to -40f quite often. The batteries have suffered no ill effects. Remember, battery CAPACITY goes down with temp, but battery LONGEVITY goes up, considerably. As long as the batteries have enough charge and charging capacity so that they won't freeze you should be fine.

I'll bet your shed is 10f warmer than the outside air, and if you put your batteries in a styrofoam box, I'll bet they are ~15-20f warmer, so even at -40f O.A.T. the box temp might be ~-20f.

Good luck

Icarus

System2 · February 2008

Re: Cold batteries.

My L-16's are also outside in an unheated shed, but inside an insulated battery box. I've been very pleased with the battery performance this winter. Like was mentioned, they do produce their own heat. Only one day this winter did the battery temp drop a degree or two below freezing, and that was after several days of 0F and below temps. I do see higher charge voltages when they're cold, as I should, but overnight battery voltages, running chest fridge and lights, haven't gone below about 12.6 I've been pleasantly surprised with the batteries operation.
Cheers
Wayne

crewzer · February 2008

Re: Cold batteries.

…the interior of my house was just above freezing. The volt meter showed a full charge on the batteries, 14.6V, before I turned on the inverter and plugged in the radio. About an hour later I looked at the voltmeter and was surprised to see it reading 12.2V. The batteries had never been that low before and my load was really light. After I lit the fire and the house heated up the voltage quickly rose to normal and has been acting normally ever since.

Lefty,

This sounds normal to me. Battery voltage always drops when a loads is applied. Usually, the voltage recovers a bit as the electrolyte begins to self-mix. This behavior is referred to as a “coup de fouet”, or crack of the whip.

Batteries produce electricity as the result of a chemical reaction, and, like all chemical reactions, battery behavior is affected by temperature. The electrolyte in cold batteries tend to be a bit sluggish, and the self-mixing is slower. As a result, the under-load voltage drop is more pronounced than under nominal conditions (i.e., 77 F, or 25 C).

HTH,
Jim / crewzer

Lefty Wright · February 2008

Re: Cold batteries.

If unheated battery rooms work for you guys it will work for me.

I assumed the rise in voltage was caused by the heat from my wood stove.

I didn't know about the battery itself generating heat. Now that that I think about it the voltage rise happened pretty quickly compared to the time it would take for the room temperature to have much effect on the batteries.

Thanks guys, I feel better now.

icarus · February 2008

Re: Cold batteries.

Lefty,

Also remember that the batteries themselves have considerable mass. As such, they are very slow to warm, and very slow to cool. It might take days for my l 16's to come up a couple of degrees even though the temp. has come up ~25f. That has an effect on charge voltage, apparent full charge, and discharge.

Icarus

H2SO4_guy · February 2008

Re: Cold batteries.

A fully charged battery will almost never freeze, even in VERY cold temps. It is all about the SOC (State of charge). The specs are probably on the site of the battery manufacturer. As long as you don't run them flat and if you keep them even partially sheltered, you are probably going to be alright. It is always better to keep them more charged however.

Skip

crewzer · February 2008

Re: Cold batteries.

Link to info on battery freeze points vs. SOC: http://jgdarden.com/batteryfaq/carfaq4.htm#freeze_points

HTH,
Jim / crewzer

System2 · February 2008

Re: Cold batteries.

I've noticed that a good all day charge will raise the temp of my L-16 battery bank by sometimes 4*C. And that's almost 700 pounds of batteries packed together in the insulated box. Even in very cold weather they don't loose that much over night. A couple of cloudy days however will see their temps begin to drop.
Wayne

System2 · February 2008

Re: Cold batteries.

I maintain a solar PV system in a mountain cabin at 10,500'
in the Colorado Rockies. We run ~6 fluorescent lights. There
are 4 Trojan batteries in a cooler. The cabin is pretty much
just used on weekends.

By mid-December the battery temps are ~18 degrees F. The
other day they were up to 24 F. To make this system work,
we turn up the charge set-point to ~15.6 V in the winter. Otherwise,
the batteries don't get charged.

Remember that battery capacity goes down with temp, but
battery voltage (resting) goes up. Counter-intuitive. But
charge set-point has to go up to fully charge the cold batteries.

Richard Jones
Boulder, Colorado

niel · February 2008

Re: Cold batteries.

i'd be curious as to what charge controller you're using as many today have the option of a battery temperature sensor to automatically raise or lower the charge voltage due to temperature fluctuations in the batteries.

System2 · February 2008

Re: Cold batteries.

Niel:

We have a Mark 22 from Specialty Concepts. When I took over the
care of the cabin PV, I saw that they had a battery temp option.
I got excited! The first call to them told me if I sent the controller
to them, they could fit the temp sensor. When I was ready, the
second call told me there was no option to retro-fit....

I've looked at other controllers and from what I've seen, they all
will adjust for battery temps down to around 50 degrees F. That
does us no good. In the cool, high-mountain summer, the
batteries barely get UP to 50 degrees.

I like to joke that the whole solar industry is in Arizona where
everything is 77 degrees. (Or the batteries are in an occupied,
heated house, and so kept warm.

Anyway, since we learned to up the charge set-point in the
winter months, we have not had a low-voltage shutoff, which
we used to have regularly. So PV works at these temps--you
just have to learn how to manage cold (COLD) batteries.

[The controller is vintage, maybe ~5-6 years old. Before that
we had a home-made controller from about 1988, or so.]

Richard Jones
Boulder

icarus · February 2008

Re: Cold batteries.

Richard,

I know that the bluesky series of controllers temp probe works to ~ -40:
http://www.blueskyenergyinc.com/pdf/BSE%20Batt%20Temp%20Sens%20DataSheet.pdf

I would guess that Xantrex and Outback controllers would work as well.

The Xantrex Truecharge 20/40 (ac charger) states : "At low temperatures the TC will not begin charging until above -5F/-20C, although the warranted minimum operating temperature is 32F/0C"

As I stated earlier, my batteries live in a very extreme environment and seem to suffer little from the cold.

Icarus

Solar Guppy · February 2008

Re: Cold batteries.

Xantrex, Outback, Morningstar, Blue Sky all have temperature compensation and all work well below 0C ...

None of these company's are in the Southwest either :roll:

You need to get yourself a controller that handles temperature compensation or your batteries will die a quick death capacity wise.

Its the most basic feature of any charge controller, even the oldest pwm types have it like the Xantrex C40/60's which are over 10 years old now.

niel · February 2008

Re: Cold batteries.

rjones,
maybe you should consider another cc as you could've had this for about the same money you had thrown into the mark22.
http://store.solar-electric.com/tracc35solch.html
even used c40s are commonplace as they had been around just about forever.
the bts is still an option, but you were going to spend extra on that anyway and you'd have up to 35amps and not 22amps. i also dislike the shunt types of controllers like yours as they have to dissipate the excess power in the form of heat. either sell the mark 22 or keep it as a spare for backup, but i recommend you're getting a new controller.

crewzer · February 2008

Re: Cold batteries.

Richard,

As indicated, there are many charge controlelrs available with temp comp features that work down to very low temperatures.

Considering your location and environment, you might also want to consider an MPPT controller. Your Mark-22 controller is a PWM type, and it sets the PV array at the battery voltage during bulk charge mode. However, the available PV voltage in your location in the winter is quite high, and an MPPT controller will turn this "extra" voltage into additional charge current.

Considering that the winter season means short days and long, cold nights, this addiitonal energy might come in useful at your cabin.

HTH,
Jim / crewzer

System2 · March 2008

Re: Cold batteries.

Thanks for all the good information on controllers that
have temperature compensation that will work for us.

I had looked at the specs of the Blue Sky 2000E but
didn't get that its compensation would go as low
as we need.

Time to plan an upgrade next summer!

Thanks to all again. This is late since I haven't been
on the site for several days....

Richard

westbranch · March 2008

Re: Cold batteries.

Richard, what do you have for panels, etc?

Eric

System2 · March 2008

Re: Cold batteries.

Eric:

We have two bp solar panels. BP 3125S, I think. They were
new two years ago, replacing some 18 year old panels.

Our controller is a Specialty Concepts Mark/22 from about
6 years ago.

A logical diagram of our setup is
http://jones.colorado.edu/jones/CMC/BrainardWiringDiagram.pdf

Richard

westbranch · March 2008

Re: Cold batteries.

Richard, the reason I ask is that as you can see I have a 2000e and have been happy with it, we are up in the mountains too and get a great winter boost from the MPPT feature...

BUT, now I am looking at more panels and have run up against the 20 amp (max 25) limit for more than 2 of my panels @ 6.99A Imp, 7.75A Isc.:roll:
So if you think you might want to expand to more than 20 amps in the future you might want to look at a higher rated model...

cheers,
Eric

System2 · March 2008

Re: Cold batteries.

Eric:

Thanks for your comments. We have panels rated at ~16 amps
but in the cold, high altitude, I have seen 18.2 on our controller
display.

I intend to put in a 2000E this summer. Blue Sky confirmed to
me that their temperature compensation would handle our
range of 15-55 degrees F.

With fully charged batteries we have plenty of juice for ~3
days. We currently only have ~100 watts of lights. Since
we used to use kerosene lamps, that seems plenty bright
for a backcountry cabin. So I don't envision any expansion
of our system.

Richard

Cold batteries.

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