Keeping Batteries Cool.

[miata2k]

I could be looking for a problem that doesn't exist, but I'll ask anyway.

I've look over the board, but I'm not seeing anything on how to keep batteries cool.  I know you should keep them in an insulated box so they don't freeze in the winter, but it seems like you would need something else for the summer?  Is it possible for them to be too hot?

I have a 12'x7' building where I'd like to keep my batteries.  It is strong, dry, elevated and seems like a great place for the batteries in the cooler seasons, but I'd be afraid to keep my high dollar batteries in this building when its 100+ degrees outside and I'm charging them in full sun.

Thanks,

Chuck

[SamoaPower]

Yes indeed Chuck, elevated battery temperature should be a real concern. One battery manufacturer stated that for every 15F degrees above 75F, battery lifetime is cut in HALF. Considering this, it's easy to see why vehicle batteries don't last long.

Here in the tropics, it's very much a concern of mine and is why I elect to keep them in the air conditioned house where it's a constant 80F. I certainly couldn't afford to replace them twice as often as I do.

Obviously, I don't have an issue at the other end of the scale, so my problem is relatively simple compared to a more temperate climate where you have to deal with extremes at both ends.

I don't have any pat answers for your situation, but I would suggest that you consider higher temperatures more of a threat to battery longevity than the other end.

[TomW]

Chuck;

I am no expert but I am under the impression that batteries being hot long term lowers the life expectancy and cold batteries simply have lower capacity. Freezing kills them pretty much right now tho. Mostly gleaned from reading here and manufacturers sites.

I keep mine in a battery box inside a semi climate controlled room where it keeps them usually between 60 and 80 F.

Again, I am certainly no expert but use batteries every day.

Cheers.

TomW

[Bushwhacker]

Just a thought so humor me. If you insulate your batteries for winter why not make your battery box air/water tight with exceptions of venting. You should have a drain/air inlet in the battery box and a vent to get rid of the nasty gases that the battery will produce when charging. Why not plug the lower drain/air inlet, make a second drain (near a corner of the battery box) an inch or two below the tops of your battery, and run just a wee trickle of water into the battery box to the corner opposite your drain.

As the water flows around your batteries it takes away some of the heat cooling your batteries, and you can run the "warmed" water over to your favorite tree. The first flush of the season could be rather nasty water so run that over to you most hated weed patch, after that the pollutants should be so dilute it won't harm a tree. In the fall simply open your lower drain and plug the summer drain.

OK shoot holes in the plan now...

Cheers,

BW

[miata2k]

I guess water cooling could work, but the building is no where close to the house or water.  I'd  have better luck adding a small window AC unit and just running it at the highest setting. Then I'd have to insulate the whole building, and it wasn't really meant to be insulated.  I'd also have to design in enough reserve capacity to keep the unit running.

The building was build from donated materials to be a Lean-to for the dogs at our rescue.  The idea was they could have a something play on so they could still be outside, yet out of the sun.  Once it was built we decided that the dogs could just run into the kennel to get out of the sun so the building was converted to lawn mower storage.  The doors on the front slide left and right, so there is a bit of an air gap around them.  It could be insulated, but I'm looking to explore other options now.  The lawn mowers now live in a bigger building.

Has anyone every built an underground battery box?  It would be a pain to maintain, but the batteries would stay at a more controlled temp.  I've also thought about using our storm shelter as battery storage, but I'm not sure I want to start running wires and pipes through its walls.  It is metal, so it is possible.

Thanks,

-Chuck

[TomW]

Chuck;

Well, you might consider a super insulated battery box with a vent and a long buried inlet tube so air drawn in is cooled by underground temps.

An underground battery box would probably work but the hoisting and lowering not to mention maintenance of a fair size bank may be problematic underground unless the area is fairly large.

Do not make the mistake of making it difficult to keep an eye on them or to do proper maintenance like inspecting, cleaning and watering. Security is a concern, too if you have kids or visitors.

Good luck sorting it out.

Cheers.

TomW

[ericwahl]

I would suggest at least leaving plenty of space between them.  Tightly packed in an insulated box will get really hot.  Some sort of voltage controlled fan would probably be worthwhile too.

[TomW]

eric;

Good point, I wish I had included but it seemed obvious to leave room for air movement around things

.

Cheers.

TomW

[wooferhound]

Here are a couple of stories about battery boxes and temperature.

http://www.fieldlines.com/story/2007/6/27/7811/44777

http://www.fieldlines.com/story/2005/6/3/155321/5575

[Volvo farmer]

My batteries are in a shed much like that one, in an insulated box. I put a little temperature sensor with digital readout in there last winter. I did find them to be getting a little warm (~85-90F)here in late June so I just opened the top of the battery box and opened the windows and door on the shed. That seemed to help a little. My readout shows them slightly lower than 75F in the morning, and slightly higher in the afternoon. I've still never seen them over 90F though.

We get a pretty good diurnal swing here. Temps lately have been in the 90s but will be in the mid 50s right before the sun comes up. If I really wanted to use some of my precious electricity to cool down batteries, I might try circulating nighttime air through the box until 7AM or so. As it is, I just leave the lid open and quit worrying about it.

[CreativePower]

Chuck,

In a building like that there are several options that you can explore - I think running an AC unit would defeat the efficiency of free "er" energy, and since the building isn't insulated it will take fair amount to cool it down even if the sun wasn't beating down on the building. I would suggest perhaps trying to manage the heat  instead of cooling the building by putting in venting at the top and a forced air intake at either side of the building - this should help with convection flow. Depending how the batteries are stored (if they are just on the floor or in their own box in the building) you could put some heat sinks between the batteries and have the forced air intakes directed over these heat sinks - if you have a battery box then you should leave the top open to make the sinks useful. As for the heat sinks aluminum is a good option - they don't have to be fancy to do a reasonable job - the only thing you really have to consider is surface area of exposure for both touching battery cases and for airflow to take away the heat.

Another avenue to consider.

DF

[snowcrow]

Hi Chuck, If you were to put on a metal roof, paint the shed white, along with venting and insulating, it would be 15 to 20 degrees cooler inside your shed. You could rig the vent fan to come on when the air outside is cooler than the air in the shed and shut off when it reaches the same temp.. For winter you could use a soda can heat collector do the opposite. Just my two cents worth... for the crow's nest!!!

Blessings, Snow Crow

[pepa]

if your problem is heat from the sun during the daylight hours, the answer is to slow down the heat by shading the building. a wood grid or a tarp with air space over the small building will cool things down. pepa

[miata2k]

So even if I insulate the building, add some forced cooling fans and place the building in the shade, it is still going to be over 100 degrees inside when it's over 100 degrees outside.

I may have to rethink this design.

Thanks for all of your input.

-Chuck

[RP]

No, the battery temperature will bw the averge of the temperature*hours of exposure (essentially the average of nightime and daytime temperature) offset by any heat generated by the charging/discharging process.

Check a NOAA climate chart for your area to get typical daytime and nightime temperatures.  If you had for example 8 hours of 100° and 16 hours of 70°, then your batteries would be at 80°.

All this assumes you have some system to flow cool night air through the bank.

[Ungrounded Lightning Rod]

I'd just put them in a vented, insulated box (the battery shed) with the exhaust ducted (broadly for low friction) up to an exit vent near the ceiling, on the same side as the intake.

In the summer the walls and insulation keeps the daytime sun and air heat from warming the batteries, which will stay cool unless/until their self-heating gets them enough warmer than the surrounding air that convection starts in the six-foot or so "chimney".

In the winter I'd close down the (intake) vents so they're just dealing with charging gasses and avoiding overheating, letting the insulated batteries' self-heating and thermal mass keep them warm enough to avoid voltagre droop.

[thyristor]

This is a good and practical idea! I've been working with the dc systems (including large banks of Lead-Acid batteries) in a power generating plant and the specs stated that the battery temperature should be kept below 50 deg. C (about 120 deg. F), then all will be fine. In other words, don't worry too much about precise temperature control, as long as the actual electrolyte temperature does not exceed 50 deg. C (120 deg F). It may be worth your while to just monitor the individual cell temperatures over a period of time to obtain a reliable trend under different climatic conditions and if you do not exceed the mentioned limit, all's well!

Good luck!