Battery insulation

Theo · February 2013

I live in indiana with temps ranging from 0F in the winter to the 90s in the summer. I am wondering how much insulation to use in my battery box.
I have a small diamond plate aluminum truck box (36" x 24") that is going to house the batteries on one side and the rest of the solar equipment (charge controller, inverter, etc) on the other. I am using 2 ago 110a 12v batteries.
So how thick should the insulation around the batteries be to help retain the heat in the winter (when I need juice the most) and also protect the batteries from overheating in the summer as the outside of the metal box will absoarb alot of heat from the sun.
I feel that it is necessary to use this particular box as I am creating a semi-portable system that will live on the top of my van. I needed something that I could house the delicate pricy electronic stuff as well as the batteries and that doesn't weigh a lot and doesn't leak. I don't feel confident that I could build something like that on my own (plus I have already purchased the box.
Any space not taken up by insulation can be used for much needed storage so I'd like to use enough insulation to do the job but not so much as to be overkill.

I am currently thinking of using rigid foam housing insulation and leaving an airspace between that and the outside of the box so that there isn't alot of heat or cold transfer from the metal box. Plus air is a great insulator.
Any thought would be greatly appreciated.
Thanks.

niel · February 2013

Re: Battery insulation

welcome to the forum,
you may want to have something on the bottom be it wood, dense foam, or whatever strong material you have access to. remember insulation only slows heat loss and does not prevent it so in time those batteries will be at the ambient temperature if left with no load or charging source. loads and charging do raise the temp slightly because of the inefficiencies and those losses show up as heat. that heat will not be sufficient on a very cold day to keep a battery very warm as you will not see the standard temp of 25 degrees c (77 degrees f) batteries are rated for.

as far as how thick or precise the insulation is isn't all that critical imo, but leave air spaces (especially up top) and if using foil faced insulation, then be sure it poses no short potentials by removing it.

if this were me i would take extra precautions with the electronics due to possible gassing if the agms should have a gassing mishap.

icarus · February 2013

Re: Battery insulation

I am not sure I would put any insulation in the box. 0f is not that cold, and while performance may suffer a bit, battery life will be enhanced. Heat is the enemy of batteries, and I am guessing that in summer, they would prefer free air, as insulation will only hold in any heat that they do absorb.

Tony

PS, a well charged battery won't freeze until well below -40.

Theo · February 2013

Re: Battery insulation

The batteries will be charged everyday by the panels (lowest daytime temps at about 20F). At night, again the temp can go down to 0F (but that is the extreme) Based on reading alot on this forum, I am still not sure if that is sufficient to warm them up or if I should put a small heater of some sort in the battery compartment. Something like a 5w light bulb.
As for venting, I am planning on putting a couple holes (covered with a clamshell vent) on the side where the charge controller is (above and below) probably coupled with a fan so that there is some air flow. The batteries will be seperated form that area by the insulation. And I think that if I put a hole on the side of the insulation for air intake from the charge controller area and then a hole on the top of the insulation with a tube running from that to the top venthole above the charge controller that this would be suffiecient for safe venting of an agm. Does this sound good? I could always add another fan but that doesn't seem necessary with an ago.

niel · February 2013

Re: Battery insulation

the batteries are really what you want the insulation on as the electronics should not need it. the electronics will want as much air as possible, especially during warmer ambient air temps. as i said before the insulation is not a critical thing for the batteries except if you have lost a tad of needed capacity due to the cold and with that you won't recover that much of the capacity with the insulation.

a light bulb won't do much either as it would take a great deal of heat to bring the mass of a battery up to even a few extra degrees in temperature.

Theo · February 2013

Re: Battery insulation

In terms of weather to insulate or not:

I really want these batteries to be working at maximum capacity in the winter as that is when I need it most. I am very sensitive to chemicals and so do not want to use propane for heat. Beofre anyone gets on me about how inefficient electric heat is let me tell you that I have already gone through this entire winter in the van with only a 55ah battery and a 50w 12v light bulb for my heat (except when using the generator for charging). So 220ah of battery powered heat would be luxurious. I would rather get more juice out of the batteries than more years.
As for airflow during the hot times of the year- I was thinking I might be able to design the insulation so that the top and one of the side panels could be removed. So there would be insulation in the winter and lots of space in the summer.

Also wondering: Is it best to put batteries right next to each other or allow a little space for airflow?

Theo · February 2013

Re: Battery insulation

I am not explaining myself well. The insulation is only for the battery area.

Cariboocoot · February 2013

Re: Battery insulation

If you are going to warm the batteries electrically, where is the power to warm them coming from? If it's from the batteries the result is a net energy loss, not a gain.

You can insulate to retain battery heat in Winter, but it will also retain heat in Summer not reduce gain from ambient air temperatures. I'd suggest being able to adjust the air flow for Summer to get the heat out of the box.

I'd also suggest not using a metal box; it's too easy to create a short with batteries surrounded by metal.

Depending on how many batteries you have you may want them close on so that the remote temperature sensor for the charge controller (a must under the circumstances) reads close to what all batteries are at. Mine is tucked between the two rows of two so that it reads the 'middle' temp.

niel · February 2013

Re: Battery insulation

ok on just the batteries as i may have misunderstood. it's good to be sure though.

coot is correct that the energy the bulb would use would exceed any recovery of capacity no matter what you have in mind with the batteries. now if the truck box is inside the van then any heat generated by the batteries would add to the heat inside the van before it would eventually escape to the outside.

if this is good enough for you then great, but if not then your only option would be to increase the size of the battery bank again and increase the amount of pv keeping it charged if you can too, otherwise the genny will be needed to run a bit more.

did you try putting insulation on the walls and ceiling of the van to try to keep that heat in the van longer?

PorkChopsMmm · February 2013

Re: Battery insulation

I needed to build an insulate a quick "good enough" battery box for this winter. I lined a box that had ~3 extra inches all around the batteries with rigid foam insulation and then put fiberglass batt insulation around the batteries. On top are a few pieces of rigid foam plus the plywood lid of the box. I vented the box and this winter, even with -10 degrees, my batteries have been hovering around ~50 degrees. Last winter my batteries got very VERY cold, so I consider this a big win. No other heat source other than charging of the batteries.

icarus · February 2013

Re: Battery insulation

Which sort of begs the question, what is the "harm" in cold batteries. Aside from temporary diminished capacity there is no problems associated with colder battleships unless it gets VERY cold(like -40) temps that most of us don't encounter.

Simply put, unless you need a significant portion of your battery capacity, this is a solution in search of a problem. In my case, if I leave for a matter of weeks in the dead of winter, the inside temp of the house is ~10f, and the batteries are a few degrees warmer due to charge cycles. The batteries remain cold for several days due to thier thermal mass, and they perform just fine. I have 450 ah of batteries, and never have a draw more than about 15 amps (25 if the pump is running) and they can deliver this just fine. It might be different if I needed huge current draw, like starting a very cold engine, but if the batteries are properly sized for the likely loads that are going to supply, then it really isn't a problem in my experience.

A fully charged battery won't freeze until -40 or colder. Even a 1/2 discharged battery won't freeze until well below 0f.

If you read the oft linked battery FAQs you wil realize that a fully charged battery won't freeze until ~-77f. A 50% SoC battery won't freeze until ~-17f. A battery will lose about 50% of capacity at -20f. At 0f, the battery still has ~75% of capacity.

Tony

http://www.windsun.com/Batteries/Battery_FAQ.htm

http://www.batteryfaq.org/

waynefromnscanada · February 2013

Re: Battery insulation

icarus wrote: »

I am not sure I would put any insulation in the box. 0f is not that cold, and while performance may suffer a bit, battery life will be enhanced. Heat is the enemy of batteries, and I am guessing that in summer, they would prefer free air, as insulation will only hold in any heat that they do absorb.

Tony

PS, a well charged battery won't freeze until well below -40.

I used to insulate my batteries, and their temp rarely dropped to the freezing point (zero C). Of course I had to remove all insulation come spring so batteries wouldn't overheat in Summer. Last two winters + this winter, I didn't bother and battery temp dropped at least minus 7 C. For my situation everything was fine, but i don't work my batteries hard either. I figure if I can get away with lower batt temps, then why not, they should last longer. Now well into their 11'th year. Never dreamed they'd last this long and so far, I don't NOTICE any drop off in power except perhaps, maybe, a bit more internal resistance that makes itself known under heavy load. On the other hand, that may just be a function of cold batteries. Wondering if I'll ever have another set of L-16's last this long. Somehow doubt it. I'm spoiled now.

Theo · February 2013

Re: Battery insulation

Lots of good info everybody.

Porkchopsmmm
How did you vent the box?

In general about venting an agm- I wonder what is the temp that they vent at. Would it be safe to not vent in the wintertime to keep in the heat and then open it up in the winter to venting. Or is that just playing with fire?

The box will be on the roof of the van as I don't want any of the stuff (batteries or emf producing electronics in my living space, so the only extra warmth will have to come from insulation.

YehoshuaAgapao · February 2013

Re: Battery insulation

I over-engineered the ventilation in my battery boxes. Used two Delta AFB1212M server fans in 5" boiler vent pipe in each box. It gets as hot as 118 degrees in July here in Phoenix. I'm hoping the fans help keep the batteries cool.

icarus · February 2013

Re: Battery insulation

Heat is my. H more an enemy of battery longevity than cold!

Tony

Battery insulation

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