Battery Box Cooling and Venting - Is This Safe?

MrM1

I have a wooden plywood battery box.  I insulated the box, and cut four 2x13 vents in the top (covered with foundation vents) and one of the same in the bottom to draw.  The battery box is outside in a carport.    I used foam insulation and saved the insulation cutouts so I can close or open any combination of the 5 vents.  There does not "smell" to be any battery gas build up inside the box.

In the winter my 4 L16 batteries were pretty happy.  Never getting much above 26C at any time.  But now summer is here and I have seen a hi of 33C on the batteries while charging on a 95*F day with all 5 box vents open.  I wanted to keep the batteries cooler.

Since the temp under my house is warmer in the winter and cooler than the outside air in the summer,   using a 4" PVC drain/toilet connection and 2 ft of 4" PVC,  I added a 4" x 2ft long vent pipe to the back bottom of the battery box that drew air from under the house.  This worked pretty well, but still not good enough to keep the batteries below 30C when charging during the 3-4 hours a day temps were hi.

So I Added a 5" computer fan ... under the house,  attacked to the 4" vent pipe to blow air IN from under the house.  The fan is 2 ft away from the battery bank and blowing air in from under the house into the bottom of the battery box.  The inlet into the box is at the bottom back of the box blowing at the bottom of the batteries.  I can feel air blowing out all 4 top vents of the box.  I closed the vent other vent (looks the same as the 4) in the back bottom of the battery box.  So the battery gasses are being blown out the top (NOT drawn out past the fan and under the house)

The fan is on a timer and comes on at 6am before charging begins and stays on until 9pm long after charging and gassing has ceased. 

Question:  is this safe given the explosiveness of battery gasses and the potential for a spark from the fan?   The fan is DC 12v and is using .5 amps.  It is controlled by an AC wall wart converter sized for the fan loaded and plugged in to an AC receptacle under the house  controlled thru an AC timer.

Here is the vented battery box

Here is the location of the Vent looking down into the box behind and at the bottom of the battery bank

Here is the vent pipe under the house 2 ft away from the box before the fan was attached.  The fan is attached to the furthest open end of the pipe.

Thanks for the feed back.

Estragon

A couple of thoughts, all IMHO.

Hydrogen is lighter than air, so the fan, being at the bottom level of the box is unlikely to be exposed to potentially explosive gas. In normal operation, there may be enough natural circulation to keep concentrations below danger level. The fan should just help.

AFAIK though, hydrogen has no smell, so I wouldn't count on my nose to detect it.

mike95490

Hydrogen has no smell, and is explosive at levels of 5% !!

But it does rise, and would not be likely to get to your fan.  Most small computer fans are brushless DC, and would be very un-likely to light off gas.

Are your L-16's sealed or flooded ?

How many amps are you charging your batteries with ?

And WHY are you mixing Centigrade and Fahrenheit measurements ??   Just to confuse me with how miles per dram my car gets ?

MrM1

mike95490 said:

Hydrogen has no smell, and is explosive at levels of 5% !!

But it does rise, and would not be likely to get to your fan.  Most small computer fans are brushless DC, and would be very un-likely to light off gas.

Are your L-16's sealed or flooded ?

Thanks all.  Yes they Are flooded.  I believe you about hydrogen ...  but what am I smelling when charging.

How many amps are you charging your batteries with ?

I charge at C/10 - C/8 or 435/10 = 43.5 amps to 435/8 = 54 amps.  And seldom above 60 amps depending on Solar.  I also set the limiter in my Classic 150 to limit charging amps to a max of 56 amps. 

And WHY are you mixing Centigrade and Fahrenheit measurements ??   Just to confuse me with how miles per dram my car gets ?

Hmmmm ... because my CC reads C and my outside air temp gauge reads F and I am too lazy to convert for the purpose of asking my  dumb questions.  And hey ... that is probably the only way I will ever challenge you engineer types 

BB.

You are smelling the sulfur in the electrolyte (sulfuric acid + distilled water).

Some people are more sensitive to the "rotten egg" smell. Also the more gassing (charging over approx 95% state of charge), the more electrolyte mist.

Bill

softdown

Since your fans are at the bottom, makes sense to turn them around so they push air up and out rather simply pull the heaviest air out. 

Hot air rises and the gas from the batteries will be slightly heated. I may suggest very well ventilating the top of the box. And I didn't study this  very hard because I'm pre-occupied right not.

Estragon

The box looks pretty well ventilated at the top to me. I think the fan does push air from under the house into the bottom of the box, and out the top vents (which would be right).

mcgivor

@MrM1 said
In the winter my 4 L16 batteries were pretty happy.  Never getting much above 26C at any time.  But now summer is here and I have seen a hi of 33C on the batteries while charging on a 95*F day with all 5 box vents open.  I wanted to keep the batteries cooler.

Nice battery box, I'm sure the ventilation has a positive effect on cooling, the cooler crawl space air will definitely be better than ambient, but the battery outer case material is not a good heat transfer medium, in addition it's surface area is reletivaly small in comparison to the internal plate area, making the dissapation rather slow. My batteries are constantly in the low to mid mid 30°C's during the hot season, ambient 36°C, short of a water bath with refrigerator cooling I can't think of an effective way to moderate temperatures, there is little to no effect using fans alone, in my case. The thought of changing to Lithium, which tolerate higher temperatures, has crossed my mind on many occasions, but that too has its challenges, apparently, but I keep an open mind.

MrM1

Thanks All.  Good to know I might not blow up the North side of my house (or coarse I hold no one here liable for advice in case I actually do)

@mcgivor ... Yeah it's those mid and lower mid 30's I was concerned about.  I guess being a total newbe to Solar and off grid setups, etc (I knew nothing about nothing last september) ,  but i guess I have probably read too much about killing your first set of batteries early and the effects of heat and temps dropping the life span of batteries in half.  Shoot,  I have 3 different types of hydrometers/refractometers for heavens sake.

That being said,   in the winter I kept the batteries all jammed up tight together for warmth (some days never seeing them get above 21C).  Now in the summer, I have the 4 of them spread apart about 1.5 inches (or 38.1 millimeters as the case may be) for cooling.  Adding the fan ... from the first day dropped the temp of the batteries 3-4*C from the day before without a fan in 90 - 95* F temps (aka 32.222 - 35*C).

MrM1

Oh and BTW ... I realize that by cutting a hole 3"s off the floor of the battery box - that  I just ruined it as an acid containment system in case of an epic battery fail.    Sometimes you can't win for losing.

But it does have an alarm contact sensor in it so no one can steal those beasts ... at least without my phone getting a text

mcgivor

The best I can say is average out the temperatures over the course of a year, don't get hung up on a period of hot weather it will pass, for you at least, being tropical myself,  it's rare to see anything below 25°C, think the lowest battery  temperature  I've seen was 23°C, but I am blessed with constant sun, for what that's worth.

Estragon

FWIW, I think it would have to be a pretty epic battery fail to get >3" of acid in the box. The box looks like there's a good amount of space, and a ruptured cell (1/3 the acid volume of an L16) doesn't look like it would get that high. 4 of mine came "dry" and IIRC ~3 gallons filled them all.

I assume you use WBjr end amps to terminate absorb? I'm guessing the L16s are Trojan, and they recommend pretty high charging voltages, which may be a factor in heating and acid mist. My USBattery L16s terminate at ~1% of C, and normally get temp compensated to higher voltage (normally cool/cold insulated crawlspace), but don't heat or mist much at USB recommended absorb. You might want to sanity check the Classic temp compensation just in case it's keeping the voltage too high in the heat. Are they using much water?

softdown

Holy smoke.....a text to notify owner that batteries are being stolen. I worry about many things yet have failed to worry about solar battery theft.  * Interrupts board meeting in Monaco....."Sorry chaps, my batteries are being stolen at my Hampton estate. Just take a quick hop o'er the pond and fix those bloody fools right up."

Estragon

If you already have an alarm system, adding a contact would be pretty cheap, so why not?

MrM1

Estragon said:

FWIW, I think it would have to be a pretty epic battery fail to get >3" of acid in the box. The box looks like there's a good amount of space, and a ruptured cell (1/3 the acid volume of an L16) doesn't look like it would get that high. 4 of mine came "dry" and IIRC ~3 gallons filled them all.

I assume you use WBjr end amps to terminate absorb? I'm guessing the L16s are Trojan, and they recommend pretty high charging voltages, which may be a factor in heating and acid mist. My USBattery L16s terminate at ~1% of C, and normally get temp compensated to higher voltage (normally cool/cold insulated crawlspace), but don't heat or mist much at USB recommended absorb. You might want to sanity check the Classic temp compensation just in case it's keeping the voltage too high in the heat. Are they using much water?

1. WBJ yes ... but I end on time bc using end amps to 1% and the batteries were not getting full to 100% SG and not using any water

2. Trojan Yes

3. Absorb charge voltage for 24v bank ... 31.5 ... Yes Yikes ... but that is what I have to set it at to reach 100% charged to SG.  And Trojan Tech support said it would not be a problem.  "oh you're fine ... (hee hee ... this fool will be buying new batteries in a year)"

4. Before I upped the voltage - which I did in small increments until I get to 100% SG -  I was NEVER using water, none at 29.6v up to 30.5v.  Now at 31.5v  I use about 1 quart every month.  maybe less.  But not much. But all cells reach 1.277-1.290 nearly every day

5. Will check my Temp comp

6. I have my Classic 150 set with a charge limit of current to 56 amps (this is NOT the same as the output limit you find in the control panel or local app - see attachment).  I can still get full current from the array/CC for loads,  but it limits charge amps to 56 or less.  8/C for my bank is 54 amps.

MrM1

softdown said:

Holy smoke.....a text to notify owner that batteries are being stolen. I worry about many things yet have failed to worry about solar battery theft.  * Interrupts board meeting in Monaco....."Sorry chaps, my batteries are being stolen at my Hampton estate. Just take a quick hop o'er the pond and fix those bloody fools right up."

Blah ha ha ha ha ... Right?!?   That's what I'm talking about.   Aint no body gonna walk off and run off with my dayum batteries.  LoL   But it also keeps would be "No Gooders" from going into the battery box.  The house alarm goes off,  the central monitoring station gets called (or maybe I turned that off for the one contactor), and my phone gets a text that the battery box has been opened. 

If you already have an alarm system, adding a contact would be pretty cheap, so why not?

You are correct.  The contacts are part of a larger alarm system and only cost $20 a piece.  I had an extra one so I thought,  "why not?"

Estragon

I don't worry about getting up to full SG every day, just ~monthly when I check water, EQ, clean, etc. My 4 year old L16s use ~ 2-3 gallons (for 12 batteries) over a ~6 month summer season. Target absorb voltage (48v bank at 9.5°C) is 60.5 today. At 25°C target would be 58.8.

I'm not sure if the higher Trojan recommended voltages as something to do with their contruction, alloys or whatever, or just a different opinion on how best to charge.

softdown

Estragon said:

I don't worry about getting up to full SG every day, just ~monthly when I check water, EQ, clean, etc. My 4 year old L16s use ~ 2-3 gallons (for 12 batteries) over a ~6 month summer season. Target absorb voltage (48v bank at 9.5°C) is 60.5 today. At 25°C target would be 58.8.

I'm not sure if the higher Trojan recommended voltages as something to do with their contruction, alloys or whatever, or just a different opinion on how best to charge.

My guess is that pure lead batteries may have different charging characteristics. Pure lead offers:
Higher efficiency
Higher self discharge rate
Higher water usage rate
I suspect they tend to last  significantly longer
Costs more

Forklift batteries are pure lead I believe. Why would calcium be a high performance battery element? Calcium is cheap.