venting my battery box to the living room?

[brian s]

Howdy, I'm putting together a small stand alone PV system, actually I've had this system running for a while and I'm bringing it up to code.  The issue at hand is battery enclosures.  So, I'd like to build a thick plywood box with a few layers of polyethylene stapled to the interior, a conduit entrance about 3/4 way up the side and  a bunch of little holes in the lid to vent the hydrogen.  I know the NEC has nothing to say about it but I've found bits and pieces of information on the web that seem to suggest this is not the thing to do.  

This is a SMALL AMOUNT of hydrogen we're talking about right, you could smoke a ciggarete on top of the case and not explode.  Is there some danger here I'm not aware of?  Are the mollecules a health hazard.  Why do I see all these photos of venting to the outdoors?

It seems to me that if we were all brewing serious quantities of explosives then serious venting would be specified?

thanks for any replies

[spinningmagnets]

There is also sulfuric acid vapor along with the H2/O2.

http://www.fieldlines.com/story/2007/9/22/142427/436

I like Snow Crow's vent set-up. Easy, cheap,

negative pressure in box, no corrosive vapor

passing through fan, draws very few watts:

http://www.fieldlines.com/story/2007/10/7/51422/5894

"How many people here have telekenetic powers? Raise my hand."

-Emo Phillips

[Fiddlehead44]

        I'm extreemly happy that I don't live in your house. This web site

is firstly concerned with safety. If you want to kill yourself, go for it!

        Fiddlehead

[Kevin L]

It all depends on what your charging doesn't it.  A single 12 AH battery is probably ok.  12 T-105's charging is a entirely different matter, and no I wouldn't suggest smoking a cigar sitting on this bank being overcharged.  Like others have said Hydrogen is not the only byproduct.

[finnsawyer]

The battery compartment on my bulldozer has a nice large lockable lid.  It should vent quickly when opened.  Actually it's not that air tight.  One time when either connecting or disconnecting the battery there was a loud pop and the battery was history.  So, while the hydrogen gas is supposed to rise to the skies, apparently it's not in that big a hurry to do so.  You need to get the battery out of the house and make sure the venting is good.  It would probably be a good idea to wear safety glasses when working around it.  But how often does anyone do that, including myself?  

[brian s]

Ok, no reason for anyone to get mean.  My question is sincere.  I guess I just don't understand the physics of whats happening here.  I'm just not that worried about hydrogen in my living room.  This is a well ventilated box.  How could an explosion occur?  where can the gas accumulate?  Now if you're saying that I corrosive vapors are being vented that's different.  Why no NEC requirement?

[jonas302]

Brain check out this thread about batts and nec code it will probly help clear things up for you  

What size of bank and system do you have?

Have a great day

[ghurd]

We don't really know "what" you are asking.

Is a toaster safe?  Yes?

In the bath tub?  No?

So is a toaster safe?

It could depend on your charge / discharge, and size of the system.

If you have a small system, say under 100W, I know of dozens (100's?) about like it in the house, and almost none have more than protection against conductive items falling on them.  However almost none are in a small or enclosed area.  I never saw a problem.

I am NOT saying it is a good idea, I'm just saying what I have seen.

With a small system, I would be more concerned with corrosive properties of the gasses.  That I have seen (and had) problems with.  Rotted carpet and corroded metals mostly. (system parts to stereos to clocks)

I still use 7.2AH SLAs charged with regulated VW PV in my living room, on a shelf, behind a photo.

I still use 800AH of 12V wet batteries on the basement floor, out in the open.

But there is no way in Heck I would tell someone that's OK without knowing the entire system, including circulation.

"That's all I have to say about that"- Forrest Gump

[DamonHD]

I have a 40Ah SLA (gel) on a metal rack behind me in my office.  It never gets charged very fast so I hope that there will never be any venting.  Even so, I keep a nearby window slightly open to allow any gases to disperse.

If I get a bigger bank it will be going in an exterior shed.

Rgds

Damon

[ghurd]

I didn't say it was a good idea.

This (in it's current and larger and cleaner configuration)

is about 6 meters from this 23.9/7/365 open flame

(23.9 because sometimes it goes out)

and has been for more than a few years now.

And believe it or not, those are improvements from what it was 10 years ago.

I am just saying I am not as afraid of it as many people.  

As long as the free circulation is enough.

I didn't say it was a good idea.

[TomW]

Brian;

So are you seeking approval or do you want honest advice?

I didn't see any meanness. I saw frank comments on very real dangers.

Firearms are very dangerous. I am within arms reach of a half dozen, cocked, locked and ready to rock. Since I am well trained in their use and fully understand the dangers, I have no concerns with them. Most others would be better off with them unloaded and locked in a gun safe. Especially if curious young fingers are involved no rugrats here, however. So, in general, firearms are dangerous in the wrong, untrained hands. The same applies to batteries which have multiple layers of danger.

Your question betrayed your lack of understanding of very real dangers and you were informed of them. Accept the advice graciously. Or not. Your choice.

Again, do you seek approval or honest advice?

Quite frankly, if you are simply looking for a bunch of "yes men" you stumbled into the wrong forum.

Cheers.

TomW

[brian s]

Hi Tom, thanks for the response, as far as the meanness goes I just bristled at the comment 'if you want to go kill yourself' without any meaningful advice.  Everything else was fine.

I am seeking honest advice.  I absolutely appreciate all the input.  I guess what I'm looking for here is an explanation of what is actually happening or could happen with my setup.  Corrosive vapors sounds terrible, explosions terrible.  Some hydrogen floating around my living room, not so bad.  But of course, maybe that is so bad, which is why I decided to stop here for a sanity check.  

Here's my logic at present,

an enclosed box with convection venting through vent pipe to the outdoor seems like a place for hydrogen to accumulate in much greater concentrations than a battery box with a perforated lid or lots of top of the box perimeter holes.  The box in a large, open room.

I have 500 watts of PV at 24V feeding about 700ah of L16s @ 24V  (8 L16s) through a C40 and then powering an outback FX2524

I've had this setup in a drafty little shed for about six months powering the construction of my house.  

Again, my possibly faulty logic is that there are plenty of possible spark sources in that shed but I feel like the open soffits vent plenty of air so there isn't a gas buildup.

What I'm trying to figure out is how that is different than a well vented box in my living room where the wiring will be better, and conduited.

Again, and please, I swear I'm not trying to be a pain here, what is the danger I don't know about?  I want to understand.  If it's corrosive vapors, thats good enough for me, if there are problems with hydrogen buildup then thats good enough.  

As an avid electrical tinkerer, I'd like to post here more, so I hope I'm not upsetting anyone.  I'm not trying to be dismissive of the dangers, I just want to know what they are.

[Fiddlehead44]

Brian,

       Please accept my appoligies. I certainly meant you no harm. I  was

scared that you may not understand the dangers and wanted to quickly ward

you off. Again sorry. Your knowledge is probably superior to mine. I have

a friend that blinded himself when a battery blew up while boosting a car.

Had he been told to wear safety glasses and the proper way to connect the

booster cables, this may not have happened. I've learned from this site,

that you don't fool around with capicators when taking a microwave apart.

When I think of hydrogen, I think of the Hydrogen bomb. I don't pretend

to understand it, but I will use all safeguards around this element.

Sorry if I upset you.

Fiddlehead.

[Darren73]

Brian,

I have to disagree with your comment on "a little hydrogen" floating around inside your house, having felt the shockwave from a small hydrogen explosion and seen the aftermath of the damage it is not something I would wish on anyone else, the heatwave from it fused the coins together inside the pocket of the guy who was a few feet from the blast and lifted the lid off a vessel roughly 12 feet in diameter shearing the lid bolts in the process.

take care

Darren

[TAH]

How did a hydrogen explosion fuse coins? I shockwave strong enough to fuse metal would easily kill anyone even much further away. I've ignited/burned up to a cubic meter of hydrogen and at the same pressure levels LP is far more impresive. Hydrogen rises in air pretty fast and there isn't a lot that will hold it in even without venting.

[joestue]

well i'm not going to disagree with the danger.

hydrogen is detonatable in the ranges of 4% to 79% H2 concentration in air.

having detonated a 200 gallon bag of H2/O2 i can say the energy is enough to kill you.

but the human body needs at least 45 psi of sustained overpressure to cause death.

The styrometric H2/O2 mix at atmospheric pressure can generate a max of 120-200 psi.

additionally the blast is diminished in effectiveness by the resulting negative pressure due to the water formed takes up 1/1000 the volume.

so yeah. its dangerous. it may blow out all the windows in your house. but calculate the max hydrogen production, divide by the ventilation, keep that number below 10%.

[elvin1949]

I DO

 I had a battery explode for no apparent reason.

Guess what I was looking at it at the time.

 Just glad i knew where i was and where the water was. No one else around,and eye's full of acid.

BE CAREFUL lucky i ain't blind.

later

Elvin

[zeusmorg]

 Just to add to the warnings i've seen posted here. A few things i've learned about the dangers of lead acid batteries in my years of working as a mechanic. Poorly maintained batteries pose the biggest danger, bad connections can spark,igniting any built up hydrogen, remember it's not just the hydrogen that's vented but the hydrogen that is built up inside the battery. Acid dangers are also great, always wear safety glasses when working around them, I know one drop that splashed up from a dropped wrench burned my eye, luckily I washed it out fast. Acid can eat up a lot of materials and turn most wood to mush. Never make your last connection on a battery itself, that way any arc is away from your danger source.

 Personally i wouldn't want a sizable bank of batteries in a living space just from the smell of sulfates in the room. Also there are corrosive gases involved, so i wouldn't want them near anything expensive to replace.

 the higher your charge/discharge depth and rate, the more gases are produced,so cycling your system at a low rate, and keeping them from discharging too low is safest, and also the bank lasts longer. Dirt on a battery will hold moisture, allowing a slight but constant connection between terminals sucking the charge out of it.Also if you wish to coat your terminals, do not use standard grease, it doesn't conduct electricity and will make your connection worse,(connection loose causing resistance, grease melts and fills the void) there are several good specific products to use.  

 So, In a nutshell keep your batteries well maintained, CLEAN, and at a decent temperature,(Batteries lose approximately 25% of their capacity at a temperature of 30°F (compared to a baseline of 77°F). At higher temperatures, they deteriorate faster.) and vented enough to disperse the gas and you reduce your dangers.

[zeusmorg]

 Also read pages 38 to 40 http://www.re.sandia.gov/en/ti/tu/Copy%20of%20NEC2000.pdf

[RedLance]

I may be stubborn or fool hardie, but I don't think I'll let this conversation prevent me from using my 1960 John Deer 730, which has 4 6volt cranking batteries housed in the seat base, with only a piece of plywood between me and them.

Had them spark, pop and smoke once, while I was on it...you could smell something, like ozone...hydrogen maybe?

Anyhow, I'm not going to worry.

[zeusmorg]

 You also use your tractor in an outdoor environment, which will dissipate any hydrogen fumes rapidly. Also i bet the surrounding sheet metal in that box isn't in the world's greatest condition, either, is it? Would you wish sensitive electronics and expensive controllers to look like what's under those batteries?

[RedLance]

Very good points.