Battery Box Cooling

RoySalisbury

Its that time of year again, and we have some extreme heat in the NorthWest AZ desert. I am getting very concerned about my battery box. Even with good ventilation and circulation, the temperatures are HOT in the batter box (110 outside, 104 in the battery box). They will cool back down to about 85 at night, but its just too hot.

So, any good tips on cooling a battery box? I was trying to find a very small A/C unit (like 1000 btu), but the smallest I can find is 5000 btu, and that just seems over kill (its only a 3x3x8 box).

What are other people using?

Roy

Cariboocoot

Re: Battery Box Cooling

Running an A/C off the batteries would cause them to produce even more heat, and would substantially reduce your run time for other things.

The simplest solution is a shovel. Dig down deep and put the batteries where the temperature around them is fairly cool and stable.

Or dig down and put a chimney in through the battery box, drawing cool air up from below and venting the hot out the top. This trick used to be used in house pantries before refrigeration.

RoySalisbury

Re: Battery Box Cooling

Cariboocoot wrote: »

Running an A/C off the batteries would cause them to produce even more heat, and would substantially reduce your run time for other things.

The simplest solution is a shovel. Dig down deep and put the batteries where the temperature around them is fairly cool and stable.

Or dig down and put a chimney in through the battery box, drawing cool air up from below and venting the hot out the top. This trick used to be used in house pantries before refrigeration.

Oh, I would not run the A/C off the batteries.. I have the generator for that. The system is set to start the generator when it pulls over 1kw. .. That is how my indoor A/C is setup.

Unfortunately I can't dig a hole. The building is actually elevated off the ground about 3 feet.

Roy

icarus

Re: Battery Box Cooling

How about circulating some domestic water through a coil under or over the batteries. for example (just thinking off the too of my head) you could use a small, flat water tank under the battery box, with the cold water in from the street/well, then going to the fixtures, so every time you draw water, you refresh the cool water in the tank, taking some battery heat with it? Wouldn't use any parasitic energy. Just one idea.

Tony

RoySalisbury

Re: Battery Box Cooling

icarus wrote: »

How about circulating some domestic water through a coil under or over the batteries. for example (just thinking off the too of my head) you could use a small, flat water tank under the battery box, with the cold water in from the street/well, then going to the fixtures, so every time you draw water, you refresh the cool water in the tank, taking some battery heat with it? Wouldn't use any parasitic energy. Just one idea.

Tony

Might work .. if I had city utilities to draw water from. But no such luck for me.

I have been wanting to do a thermal air exchange system for awhile now, and my have to put it further up on my list. Basically I dig a long trench (around my whole 2.5 acre lot) about 8 feet down and about 1 foot wide. Then take a 4" PVC pipe and lay it in the bottom all the way around. Then I just need a fan powerful enough to push the column of air in one end and out the other. The ground will keep the air at a constant 75-80 degrees. I have some nice solar powered attic gable fans that move a good deal of air, so they may work. But thats a project for later in the year I think.

I have also though of using some Peltzer cooling units from a few 12v box coolers. But they actually pull a lot of power .. too much for the batteries, but not enough to justify running of a generator.

So am back to trying to find a 1000 btu A/C unit someplace. I guess if I have to go 5000 btu its not the end of the world, but seems overkill for such a small space. And my last option is to cut a small ventalation hole between the already cooled control room and the batter box (its just on the other side of the wall). Then put a small 120mm computer fan in the opening and have it pull the cool air from the room and vent it out the battery box .. which would blow across the batteries. Just not sure it would be enough.

Roy

BB.

Re: Battery Box Cooling

The other way to look at the issue... For every 10^oC (18^oF) above ~25^oC/77^oF, the battery bank will age 2x as fast... Every day at 95^oF, the battery bank will age two days.

If this is for 3 months a year, the batteries will age 12+3 months or 15 months every year. After 6 years, the batteries will have aged 7.5 years.

So, how much is it worth to you for your batteries to last another ~1 to 1.5 years (out of 5-8 years) or so?

-Bill

RoySalisbury

Re: Battery Box Cooling

BB. wrote: »

The other way to look at the issue... For every 10^oC (18^oF) above ~25^oC/77^oF, the battery bank will age 2x as fast... Every day at 95^oF, the battery bank will age two days.

If this is for 3 months a year, the batteries will age 12+3 months or 15 months every year. After 6 years, the batteries will have aged 7.5 years.

So, how much is it worth to you for your batteries to last ~1 to 1.5 years (out of 5-8 years) or so?

-Bill

Good point. A new A/C unit will cost about $500-$600 .. plus the cost of the propane for the generator.. 8 hours a day @ .85 /gallon per hour @ 2.30/gallon .. about $15.60 a day. So just over one summer your looking at $2000 to keep them cool. And a new bank of batteries will cost about $2400 ... seems like a no brainer to just not worry about them.

But that is hard too do when I know they are suffering in the heat.

Fe-Wood

Re: Battery Box Cooling

I like the computer fan idea. A little cooling will help and the buy in is cheep and easy...

icarus

Re: Battery Box Cooling

Regardless of your water source, the concept is the same. You got to bring domestic water into the house anyway, either from a well or creek etc. (assuming you do hve running water). like I said before, completly passive, uses no extra energy, no extra water, just the normal daily flow. (most well water is ~55-60f, a heck of a lot cooler than 105!)

T

inetdog

Re: Battery Box Cooling

RoySalisbury wrote: »

I have been wanting to do a thermal air exchange system for awhile now, and my have to put it further up on my list. Basically I dig a long trench (around my whole 2.5 acre lot) about 8 feet down and about 1 foot wide. Then take a 4" PVC pipe and lay it in the bottom all the way around. Then I just need a fan powerful enough to push the column of air in one end and out the other. The ground will keep the air at a constant 75-80 degrees. I have some nice solar powered attic gable fans that move a good deal of air, so they may work. But thats a project for later in the year I think.
Roy

I am not familiar with the details of those. I would worry about the air resistance in the long pipe unless a pretty high pressure fan was used. Tell me more....

TheBackRoads

Re: Battery Box Cooling

Inet, google Earth Tubes.

inetdog

Re: Battery Box Cooling

TheBackRoads wrote: »

Inet, google Earth Tubes.

Thanks. Found http://en.wikipedia.org/wiki/Ground-coupled_heat_exchanger to be quite helpful.

If you can make your battery compartment reasonably enclosed, you might find a solar chimney on the exhaust to work even better than a small fan. Although it would not cool your batteries at night, you would not be generating as much heat in them at that time. Or the heat from the batteries themselves could cause sufficient convection air flow up the chimney.

RoySalisbury

Re: Battery Box Cooling

inetdog wrote: »

Thanks. Found http://en.wikipedia.org/wiki/Ground-coupled_heat_exchanger to be quite helpful.

If you can make your battery compartment reasonably enclosed, you might find a solar chimney on the exhaust to work even better than a small fan. Although it would not cool your batteries at night, you would not be generating as much heat in them at that time. Or the heat from the batteries themselves could cause sufficient convection air flow up the chimney.

I'll have toread up on this a bit more and see if it something I can implement. If I have to dig down into the ground then I can't do it. No way to get under the building anymore to dig..

Roy

niel

Re: Battery Box Cooling

look into a swamp cooler.

inetdog

Re: Battery Box Cooling

niel wrote: »

look into a swamp cooler.

That still takes water, just not as much. If you have a good well, then it may be an option.

RoySalisbury

Re: Battery Box Cooling

inetdog wrote: »

That still takes water, just not as much. If you have a good well, then it may be an option.

Nope.. I have*to bring my own water in. I have 8 - 6 gallon jugs on site, but that is it (plus 4 - 5 gallon for drinking water).

Roy

RadioGuy

Re: Battery Box Cooling

I am new here and have been learning much about the system I am trying to put together- 14 Solyndra 150-165w panels, xantrex mppt-60-150, Xantrex sw5548, and 600ah 48v fork lift battery. I hope to have it up and running in the next month or so.

I stumbled on this thread while researching just how much venting I'll need (will be fan driven).

Battery box cooling (as well as the box itself) was an issue I had been contemplating. I looked at garden boxes at the big box stores and the only one large enough was $250 and left little room for insulation (it does get below zero here in the winter). In the summer we are pretty much in the high 90s with 105 to 110 not uncommon all summer long. One year we had over 2 months of over 100s.

So an idea hit me. Yes its crazy but solved some problems. Sears had a labor day sale on appliances and I got a 19 cu/ft freezer for $500. Its going to be my battery box. Yes there will be lots of mods (venting, my own freezer controller, small roof, etc). I have already reinforced the bottom for the extra weight and add clearance off the ground, undercoated the bottom and compressor box for moisture protection, and poured the concrete slab it will sit on.

Now, in addition to having a nicely sealed (keep the critters and crud out) and insulated box I now can kick on the freezer when the temps are high and cool my battery down to a comfortable 70. When its that hot we have lots of sun and I'll have plenty of extra power. I measured the compressor at 150 watts running (starts up at about 250 the quickly drops down). In addition (not sure if I'll be needing it) I can heat the box with a couple light bulbs if its really cold and I have the spare power.

Just a nutty idea that I had and now am past the point of no return on.

Cariboocoot

Re: Battery Box Cooling

RadioGuy wrote: »

So an idea hit me. Yes its crazy but solved some problems. Sears had a labor day sale on appliances and I got a 19 cu/ft freezer for $500. Its going to be my battery box. Yes there will be lots of mods (venting, my own freezer controller, small roof, etc). I have already reinforced the bottom for the extra weight and add clearance off the ground, undercoated the bottom and compressor box for moisture protection, and poured the concrete slab it will sit on.

Now, in addition to having a nicely sealed (keep the critters and crud out) and insulated box I now can kick on the freezer when the temps are high and cool my battery down to a comfortable 70. When its that hot we have lots of sun and I'll have plenty of extra power. I measured the compressor at 150 watts running (starts up at about 250 the quickly drops down). In addition (not sure if I'll be needing it) I can heat the box with a couple light bulbs if its really cold and I have the spare power.

Just a nutty idea that I had and now am past the point of no return on.

Welcome to the forum, RadioGuy.

Are you proposing to run the refrigeration off the inverter to keep the batteries cool? I hope not; that would be a kind of perpetual motion loop: the power the compressor draws will cause the batteries to heat up necessitating the refrigeration to run more, et cetera.

For this to work you're going to have to control the refrigeration cycle according to having surplus panel power available: batteries fully recharged, PV's still able to supply additional power, compressor runs to cool down 'battery box' without drawing from batteries, box stays cool afterwards with good insulation.

BB.

Re: Battery Box Cooling

Can you 1/2 bury the batteries+box? Only a foot or two below ground, the temperatures are pretty constant.

And, charged batteries will probably never freeze, and cycled batteries+insulation will keep them > freezing (and keep their capacity up).

One or two people here (if I recall correctly), use battery heaters for their cabin when the return in the dead of winter--Run the battery heaters for 1/2 day to get them into the ~40F (?) range... And they will stay >32 F for the balance of the stay from normal daily use (Icarus/Tony--do I remember this correctly?).

-Bill

icarus

Re: Battery Box Cooling

Not me,,,. I don't worry about my batteries when I leave in the winter for an extend time. The box they sit in is in the house, surrounded by 1" foam. A fully charged battery won't freeze until at least -40, and then if it cycles it will be warmer due to it own heating.
I am not sure the freezer idea is the best option. Like Bill suggested, cold is generally not the problem but heat is. Consider the earth sheltered "root cellar" idea. The thing about batteries is that they have considerable thermal mass, so they heat up, and color down quite slowly relative to ambient. I know when I come home in the middle of winter, after having been gone several weeks or months, the batteries (according to the Rogue sensor) take DAYS to come close to ambient. If you have +100 during the day, but only 70 at night, the batteries might average close to say 85f. Personally, I think you are working on a solution in search of a problem. A couple months a year at 80+f over the course of the year isn't going to shorten thier lives very much IMHO.

Tony

I have been known to use a battery heater in my diesel van, along with a oil pan heater, only because the combination of starting current and cold battery available current can make strting problematic. But I don't use one to keep the truck battery from freezing.

T

Vic

Re: Battery Box Cooling

Hi RadioGuy,

Well, I too have been a bit obsessed about high battery temps, and do run A/C in the power room to keep electronics and batts cooler.

However, Know that you own this now-modified freezer ... but, ... seems to me that your 48 V 650 AH batt will weigh about 2000 to 2200 lbs. Know nothing about the freezer, chest, upright etc, but cannot understand just how the reinforced freezer will take that weight. Guess that the freezer must be outside ? If it is outside, seems to me that the high ambient temps would affect its performance, even if it can take the weight of the batts.

Have used insulated battery boxes herre for some years, and have monitored the temp swings of the bank. Discharging at even high currents seems to have very little effect on the electrolyte temp. There is a lotta mass, and time-constant, but seems to be the case when monitoring over an extended time. The largest contibutors to battery temps, are the charge stages that represent the lowest charge efficency of a battery -- the later portion of Absorption stage, and more so, EQ. I do suppose that discharges at C/4 or something would result in a lot of IR losses, and cause heating, but would be surprised that running an extra 4-ish amp on a 650 AH 48 V bank would do it. IMHO.

Even tho you do own this modified freezer, the Root Cellar seems to be the hot ticket, as it were. Free coolness, how Kool is that?! Vic

RadioGuy

Re: Battery Box Cooling

Hi Vic,

You are correct about the weight. Actually I'll have about 1800 in the thing. By the way its a chest freezer. The freezer construction goes (from the inside out) sheet metal, solid foam, sheet metal. They had, what I would call dimples, pressed in the metal for its feet. No way they were going to take the weight. For an initial structural test I got in the middle of the thing and jumped up and down on one foot before modification. No movement. I added 5 bars of fence post metal used to replace 4x4s on 6'ft fencing (really tough stuff) from front to back on the bottom. I think it will handle the weight.

I was worried about the ambient temperature as well but according to the manual the ambient temp isn't a problem. It says the only thing to watch out for is that the outside will be very hot in temps above 110. As far as cold goes, which won't be an issue for me since it will never run while cold, the manual says there is no concern.

You are correct that it will have to be outside so I will have to build a roof and some protection for it. I live in a mobile home and have no other provisions for the battery. I like the root cellar idea but had to give up on that. We have ground water not too far below the surface (1ft or so) that is loaded with alkali. It eats through everything! It ate through a piece of galvanized pipe I had in my water line for an outdoor hydrant in less than a year (no more hydrant) and will go right through almost anything so a cellar isn't much of an option.

Thanks!
Blake

Hi Cariboocoot,

You are correct! I am purposing to run the freezer off of solar but only when I have the spare power. The original freezer controller is going bye bye and being replaced by my own (I won't go into the much bigger control/monitor system that I'm working on at this point). Being that I write software using PIC micro-controllers for industrial control of machinery this won't be a problem. Since we can have long hot periods I'm just looking for a way to keep the battery a little happier when I can. During these periods of time I will have plenty of extra power. However, after reading posts about split mini systems today, I may have to reconsider and put the extra power more into keeping myself comfortable.

Thanks!
Blake

inetdog

Re: Battery Box Cooling

RadioGuy wrote: »

Battery box cooling (as well as the box itself) was an issue I had been contemplating. I looked at garden boxes at the big box stores and the only one large enough was $250 and left little room for insulation (it does get below zero here in the winter). In the summer we are pretty much in the high 90s with 105 to 110 not uncommon all summer long. One year we had over 2 months of over 100s.

So an idea hit me. Yes its crazy but solved some problems. Sears had a labor day sale on appliances and I got a 19 cu/ft freezer for $500. Its going to be my battery box. Yes there will be lots of mods (venting, my own freezer controller, small roof, etc). I have already reinforced the bottom for the extra weight and add clearance off the ground, undercoated the bottom and compressor box for moisture protection, and poured the concrete slab it will sit on.


Just a nutty idea that I had and now am past the point of no return on.

One thing you must keep in mind is that the freezer, as originally constructed, is close to airtight. It won't hold pressure, but the air infiltration will be really small.
Sooner or later your batteries will be in a situation where they gas heavily if they are not AGM, or where there is a measurable chance of them venting if they are AGM.
Now you will have a freezer box full of hydrogen and oxygen.
Two suggestions:
1. put some sort of vent tubing at the high point inside to allow the hydrogen to escape. Without the hydrogen, the oxygen will not be a problem. :-)
2. or else make sure the lid can open to release the force of the blast instead of blowing out the sides of the freezer.

Also make sure that the paint on the inside is acid resistant. A gassing battery will produce a weak acid mist which although small in weight will be corrosive.

I know, I tend to go overboard on safety....

RadioGuy

Re: Battery Box Cooling

Hi again all,

Sorry, I only noticed the couple posts that were obviously directed at me (too much speed reading). Thanks all for your thoughts! I am not so concerned about freezing, but it possibly could be an issue. While away for a couple weeks in the winter time I have had my sewer line freeze up a couple times. I won't get into what a mess that turned out to be. So it does get cold. I figure the system will keep itself warm enough though.

Perhaps I'm going too far on the other end as well but heck, $500 for a nicely pre-made, insulated, sealed box that gives me an added capability isn't so bad either. It saves me the time of construction of a box and with the price of things I probably would have that much, or at least close to it, building something. I will add, however, that you cannot just punch holes through the side of a freezer. There are pipes both inside and out. I have an app for that! A thermal imager but its display needs repair before I can use it again. With it I'll be able to see where I can run things through the side. Pretty much anything below 9 inches from the bottom is ok (from feeling) but not ideal.

Also, I do have the tendency to over engineer things but its better to have more than enough than not enough.

Thanks All! This forum is great and I'll be using it often as I go through this process.

Blake

Vic

Re: Battery Box Cooling

Hi Blake,

Thanks for the added info. Good Luck with the weight. Another thought is recharging batteries dumps some heat into them. The freezer can probably keep up with the heat contribution. Would guess that if you took the battery to about 85% SOC, recharging would probably contribute a total of approximately 1500 watts of heat into the battery box during the recharge time, altho there will be some delay in all of the heat to migrate into the batt box.

I had considered a cool plate that the batteries might sit on, inside my batt box, and circulate chilled water through metal tubing attached to the cool plate. But there are even more demanding projects needing attention, here.

Please keep us updated on your too cool progress. Thanks, Vic

RadioGuy

Re: Battery Box Cooling

Hi Inetdog,

That is the issue that really got me digging through the forum.

I figure on putting in pipe that feeds in fresh air in on a tube that puts it in to the box at a lower level and then pulling the air out of the top with a fan to keep the hydrogen vented. I am giving considerable thought to how best to handle the issue. The inside top has lots of shaping that can trap hydrogen and I'll be taking all that out. I want to make this thing right.

You are right though, I won't be locking the box so an explosion will pop the top but I really don't want that happening. The thing I'm trying to figure out is how big of a fan and piping do I need (2", 3", 4"?) for this application.

Blake

inetdog

Re: Battery Box Cooling

RadioGuy wrote: »

Hi Inetdog,

That is the issue that really got me digging through the forum.

I figure on putting in pipe that feeds in fresh air in on a tube that puts it in to the box at a lower level and then pulling the air out of the top with a fan to keep the hydrogen vented. I am giving considerable thought to how best to handle the issue. The inside top has lots of shaping that can trap hydrogen and I'll be taking all that out. I want to make this thing right.

Blake

Hydrogen is lighter than air by a large fraction and also diffuses like crazy. As long as you allow an exit near the top of the box and an incoming air anywhere else, I doubt very much that you will need either a fan or specifically a bottom vent.

Volvo Farmer

Re: Battery Box Cooling

You should be able to build a battery box out of plywood and foam for less than $150. I think the only way you're going to properly vent a freezer is through the lid with a fan and a couple large holes, which tend to let all the cold out as fast as you make it. Also, I think those fans should be running throughout the whole charge cycle. I had an insulated plywood box for my first set of batteries. Mine live in an unheated outbuilding in a climate similar to Delta. They stayed above freezing all winter long and I could store distilled water in the box for re-watering. My new batteries didn't fit in the box so I'm going to go without one this year and see what happens. I got my batteries plenty hot on a number of occasions trying to equalize them in that box.

Hehe, if you want to drive down to Durango, I'll sell you my old battery box for $100. It fits eight L-16s and four or five gallons of distilled. 2" of foam and a pond liner over the foam to keep acid spills off of it, vented top and bottom, and a slanted roof to encourage hydrogen to vent out the top.

RadioGuy

Re: Battery Box Cooling

Hi Volvo Farmer,

I lived in Durango for several years. I may have seen your system while there.

You are correct in that I intend to do exactly what you are saying. Pulling in cold air and pulling gas out of the very top (flat roof with a fan on the outside top). Yes, it is a compromise, but I hope to be able to find a balance that will work. I'm too far down this road to give up now (well it wouldn't be first time at having to change course and give up on what my bright idea was). I guess I should have thought of bringing up my box needs earlier to see what folks have available earlier (can yours hold a 38 1/4 by 20 1/2 battery?). What I want to find out is just how much do I need to pull in and take out to be safe.

I think I would like to make a trip down there and meet up with you to see what you have and learn more. I'm mostly full of theory (uhmm crap) and reality would help me much more.

But, I do have to stress that heat is the real problem here. When I moved here I could not believe how hot and how long it remains hot for only being 100 miles north of Durango). That is the key issue I'm trying to deal with to give my investment (Babs- a friend named my battery that- big ass battery system) as long of a life as I can. Since heat is the big killer that is the issue I am trying to address.

Blake