Battery Temps-Storage-Boxes

[Dexter]

Hello - I'm a bit of a newbie looking for some advice.  I know enough to be dangerous.  

I have a remote cabin which has no power.  I use a Trace inverter and a bank of 4, 6 volt Trojan 105 batteries.  I use a generator to charge.  My problem is that the cabin is a moutain location which is quite cold in the winter.  The batteries are in the basement.  It doesn't freeze in there, but it is in the 30's.  I can't really get any charge retention at all...

I currently don't have an insulated box, but I'm thinking of building one.  However, I'm not sure that will help.  There isn't really anything to build heat in the box for the insulation to keep in.

As well, I understand it needs to be ventilated, but I'm worried about that just letting more cold in.

I'm thinking about moving the batteries and box up to the main floor inside the structure.  It will be warmer there.  Never below 40 when we're not there and more like mid 60's when we are.  However, I'm worried about gasses in the living space.  I could vent to the outside, but then I'm letting cold air in again.  I also worry a little bit about the potential for an explosion and if it's in the living space, there is more change for injury.

So, a couple of questions I could use your advice on.

Is putting it in the living space a good idea?  It's warmer, but is it more dangerous. Would moving to a sealed gel style battery help with that?

How do I vent sucessfully without just letting more cold air in?

Thanks for any info...

[coldspot]

I"m looking into/for a used/free chest freezer. Insulated a bit to start with and should be able to add extra stuff as I go.

$0.02

[Volvo farmer]

The only problem with cold batteries is that you lose some of your capacity. If you are currently using 50% of your capacity, a couple extra batteries would more than make up for the capacity lost because they are cold.

You seem to understand the tradeoffs. I personally don't like the idea of batteries in my living space but others have done it with no problems for years. Batteries will self-heat to some degree just from charging and discharging them. Mine live out in an unheated shed, in a box with 2" foam all around. They seemed to stabilize in the low 40's (F) last winter They are vented to the outside, but the intakes pull air in from the shed.

We're only into our batteries 20% or so daily, so cold temperatures are not an issue. Additionally, I think they might last longer at cold temperatures because heat (over 80F) seems to be hard on them.

 

[Ungrounded Lightning Rod]

Fumes are a serious problem.  The ones during charging are explosive.  They're all acidic, which will rot metals, textiles, and lungs in the cabin.  If you DO have the batteries indoors you MUST vent them properly.

Batteries and their associated wiring are also an acid spillage, explosion, and fire hazard.

Batteries produce heat when charging and discharging - and a little bit when just sitting there, due to self-discharge.  Put them in an insulated (and lightly vented) outdoor container or shack and they'll tend to keep themselves warm when necessary, even in the dead of winter.  They also have high thermal mass so they won't cool off very fast when your generation and load happen to balance for a while.  And if they aren't allowed to get near full discharge (which they BETTER not if you want them to last) the acid acts as a pretty good antifreeze, protecting them from freezing damage when the wind stops for a while while the cabin is not in use.  (That's why you normally don't have to replace your battery when your car sits out in -40 weather, even if the block blows the freeze plugs or cracks.)

If you're REALLY worried about your batteries getting too cold in their insulated box, you can put a VERY SMALL heating element (like 60 watts) in the insulated box with them (under or beside-near-the-bottom), and turn it on when the temperature in the box gets below 35F or so.  (You'll want to use an extra dump load controller deliberately set at the max discharge voltage to insure they shut down and let the batteries cook, rather than sucking them down to damaging discharge levels, if the wind has stopped.)  But IMHO why bother.  Seems to me you'll burn less power overall by just accepting the lowered efficiency from cold batteries when you first power up the cabin if you arrive at a calm time, and letting them heat up from the power drain.

[luv2weld]

The least expensive insulated battery box will be an ice chest (plastic) not

styrofoam. Use 1/2" plastic water pipe for vent. Vent it to the outside of

the building, as straight up as possible. Avoid 90 degree bends if you can.

The vent should be at the highest point possible inside the box. You want

a chimney effect. Seal the plastic pipe with PVC cement so it can't come

loose or be knocked down.

The inlet should be screened and at a low point in the box. Preferably,

vent on one end, inlet on the other. Large ice chests usually have a drain,

so use it as the inlet. Since the air in the basement is never below

freezing, you should have no worries. If you are concerned, put a small

solar panel on the roof. It will keep the batteries warm and prevent

self-discharge.

I'm not sure what you meant about not getting any charge retention.

How old are the batteries?

How long do they sit unattended at a time??

Is there any drain on them while you are not there??

How often do you clean the tops and terminals??

What is the coldest outside temperature during the winter???

  "mountain location which is quite cold in the winter"

I live in the mountains, and 20 below is not unusual, sometimes

30 below. So the term quite cold is relative. (At least that's how my

relatives act towards me.)

Ralph

[snowcrow]

Last February, where my camp is, it stayed below zero for days and hit -54 F one night that week!!! I hiked in to check on things and found the batteries nearly frozen solid!!!!!!! I did save them, although I don't know how?

This year I'm going to build a better box, with heat built in!!  My idea is to make a box lined with 2" foam and a plastic tote with batteries inside that. A vent will be connected to the sealed tote and come out though the side of the plywood box. Inside between the tote and foam, (sides and bottom), will be load resistors on copper tubing, all buried in sand. The copper tubing is both a heat exchanger for the bed of sand and fresh air return for the tote. The load resistors will be connected to the charge controller as a diversion load. I'm also putting in a select switch to send the power to heat water instead.  I'd like to hear your thought and ideas on this.

[Dexter]

Thanks for the great suggestions, pictures and comments!  I appreciate all of the knowledge out there!

To answer a few of the questions above...

"cold" for me isn't as cold as you guys are talking.  Outside it would normally be in the 20's/30's.  Occasionally into the teens.  Rarely, if ever, below zero.  I don't expect the basement to ever get below freezing but I do expect it to be very near freezing.  Say 34 to 35.

This last winter, I left the batteries out in no box at all.  I would run the generator for 3-4 hours to charge and I would not be able to retain enough charge to run the inverter for longer than a few minutes.  I assumed they were not holding a charge due to the cold.  They generally sit all week and then get used on the weekend.  There is no in-bound charge at all during the week (no solar, wind, etc...).  Tops and terminals are clean.

I plan to build an insulated box for them moving forward.  I like some of the suggestions for using a small solar panel to trickle into them during the week.  That will help them from self-discharge and may even help provide some heat.  It will need to be a small panel however, without much good productivity because the location is not all that solar friendly.

My big issue is the vent.  I don't see how cutting a vent in the top and sending that to the outside is a good idea.  I certainly understand how that gets the gases out, but won't that be a direct line for freezing air to drop right on top of the batteries?

Thanks!

[TomW]

Dexter;



My big issue is the vent.  I don't see how cutting a vent in the top and sending that to the outside is a good idea.  I certainly understand how that gets the gases out, but won't that be a direct line for freezing air to drop right on top of the batteries?

Well, you put a couple 90 degree elbows on the top of the pipe so the outlet is facing down which keeps the rain out, too. I use a positive venting scheme where i pull air out of a tube that runs a computer fan if the solar panels are producing. However, I think that if your box is sloppy enough on seals that hydrogen will not build up readily. But venting is probably best.

Cheers.

TomW

[luv2weld]

Dexter,

Think chimney!! Batteries are just a little warmer than outside air. Warm air

and hydrogen gas are both going to rise. Which will keep the cold air from

dropping down the vent tube.

I have more questions about why you have no charge retention. What kind of

charger are you using??? Have you tested the charger to make sure it is putting

the proper "stuff" into the batteries?? After charging, do you test the batteries

to see "where they are"??? Are the batteries sulfated??? Say "Yes", because you said

they sit for extended periods. Do you equalize the batteries??? Do you check the

water/acid level?? How old are the batteries??

My feeling is that cold is not your problem if the batteries never get below

freezing. I think you should look at desulfating the batteries.

If the batteries are beyond saving, then you are just wasting time and money

trying to get them to hold a charge.

Here are a couple of sites about battery maintenance to get you started--

http://www.trojan-battery.com/Tech-support/BatteryMaintenance.aspx

http://www.batteryfaq.org/

battery desulfators--

http://www.flex.com/~kalepa/desulf.htm

http://p198.ezboard.com/bleadacidbatterydesulfation

If you want to build your own, Nando posted a desulfator circuit on the board in January 2007

http://www.fieldlines.com/story/2007/1/15/194123/993

Also, Google search the board for desulfator.

Ralph

[luv2weld]

Forgot to ask----

You do turn the Trace inverter off when you leave to go back to town??

Is there anything else that could be draining the batteries when you are not

there??

Ralph