How much real fire hazard

alex trent · June 21, 2012, 06:30:39 PM

As I get geared up for a real battery system in my wood house with not FD anyplace some thoughts.

My system is simple. No solar now.

Well wired system in the house..12 ga wire throughout. Modern breaker box and little on each circuit (max is 20 amps and most 15). Actually with the exception of the fridge no circuit has more than 4 amps. Some could rise as new stuff is added, but I do not think it will ever be much.

So the house is fine after the box.

My system uses generator 50 feet away to provide AC to the box through a knife switch which cuts off the battery system. Genset is fused at the generator at 15 amps. Plus I will be there when generator is running, which will only be to charge batteries. Seems safe enough too.

Batteries are 2-100/12V amp Trojan sealed. Might go to 3 or 4 sometime, but not too soon. They go to a 3,000 watt Wagan inverter through a 200 amp fuse...so the inverter is essentially downrated by the fuse, but that is OK since what I get is a lot more than I need. Batteries are inside the house in a closet with tile floor and plycem wall, but there is wood above and in the doors. I plan to put batteries in a covered plastic box...like a Rubbermaid storage box...or maybe a Colman cooler.

Cables will run through top to inverter..2 feet and 00 wire. On a shelf a couple of inches above the box. Inverter runs into knife switch and to box.

Charger plugs into wall outlet and sits next to inverter on the shelf. I turn on manually when I crank the generator. Cables (2 gauge) run through box top to batteries.

Am I correct that my biggest risk (and maybe the only one) comes when i charge batteries? Rest of the time, what could be a fire hazard?

I am going to put a 2" PVC pipe through the side of the box near the top and out the wall which is 4" away. And another near the bottom. I see lots of active ventilation systems, but am thinking I do not need one here.

MountainDon · June 21, 2012, 07:30:17 PM

AGM batteries? They do not off gas with normal operation. No vents needed.

Flooded lead-acid batteries. Off gassing and acid fumes make for explosion hazards as well as damage from the acid fumes. Because of that I would never have anything electrical above a flooded lead-acid battery.

Is the fuse between the batteries and the inverter a fast blow (like a type T), or a slow blow type? Is that fuse in the battery compartment? is that fuse fully encased so that it does not make an arc that could ignite hydrogen? Type T fuses are fast acting and encased to be explosion proof. Type T are safe to use right alongside a lead acid battery. Again, AGM batteries don't have that risk. Fast blow protect best against dead shorts in DC circuits; possibly more important when there are DC circuit breakers downstream, rather than fuses.

The biggest danger for fire is most likely from the stored gasoline for the generator.

In any event a few good fire extinguishers should be on hand. Without the worry of freezing temperatures the 2.5 gallon water fire extinguisher can be a great one (or two or...) to have on hand. Self service for the refill. Great water play fun too.

If you are not concerned about the container being "out of date" you can find used ones on eBay for pretty cheap. We have several of them. There are even ones available that shoot a mist rather than a stream and are rated for class C fires (electrical).

June 21, 2012, 07:44:29 PM

Thanks.

I do not know what type of fuse but will look. It has a shield but not fully encased.

I was going to put it in the box but can easily put it outside and still very close.

I got kind of fixated on this fire risk...not sure why. when I am there it is not a problem and I have two buckets of water on standby so i do not have to wait to fill, plus 2 dry chems.

But I am gone a lot and have to leave the inverter on to run some security stuff and that set me thinking.

My gas and the genset is 50 feet away in a concrete hut!

flyingvan · June 21, 2012, 09:25:07 PM

When I still staffed the fire engines that rolled, we went on the occasional inverter fire, and quite a few back-up power unit fires---usually the charge controllers. Batteries would melt and make a mess with a Ph of 1 or so but they weren't the ignition source. Also these were big industrial applications not small residences. Improperly stored gasoline can be a source but the flammability range is so narrow you don't see it often. Propane leaks are more insidious---the propane can pool in low spots and eventually find an ignition source. Decaying vegetation piles--particularly hay or straw a week or so after a rainfall---can autoignite from microbial thermogenesis. It's a slow process that starts with steaming and smoking and rotting smells, so if anyone's around they'll notice but when people do last minute yard work and leave for the season it happens.
With the big fires we've had here---the Cedar, Witch Creek, Pines, etc----the houses that were lost were the ones that had lumber leaning against them, trees growing up under eaves, beautiful wooden decks built out over a canyon with no defensible space cleared, junk around the yard, trees in powerlines. It's amazing when we fly over neighborhoods---San Diego is nothing but canyons backing up to houses. There'll be a draw (called a chimney) full of heavy fireload vegetation pointing directly at a landscaped yard with no spaces whatsoever. Palm trees are the worst--they go off like Roman candles. The eucalyptus are bad too---very oily, and burning is part of their life cycle but people plant them all over because they'll grow with little water.
Oops, sorry---let me step down off this soapbox---this wasn't what you were asking about

hpinson · June 22, 2012, 12:51:03 AM

Informative, and I had much the same concern and questions right now.

My system uses AGM, in a well ventilated buried box, with a blade type fuse inline on the 6GA positive battery wire, but in the battery box. From what you say Don, that is OK?

One thing that has been bugging me is what would happen if the buried battery box flooded, completly shorting the battery. I dont' see how this could happen, but what if it did?

Other than that there is a 20 AMP DC breaker at the panel combiner, the charge controller is in an isolated NEMA4 box on a post, and there is a 20AMP breaker right before the DC load (pump). All in an open sandy ledge area at least 25 feet from any trees or vegitation.

June 22, 2012, 08:42:25 AM

My take on this is looks OK. For me at least.

My box is inside so i have more potential problems. But since I have no solar connection/charge controller and only charge when I am present, i am feeling OK.

How are you venting your box? AGM supposed not to need, but be on safe side is good.

My take is that the danger exists when charging and when batteries are running the inverter, with the fuse on the battery to inverter link there is not much fire hazard except in extra ordinary circumstances. Batteries will not catch fire and if the inverter goes blooey, the fuse between it and batteries (200 amps) should shut things down before much hot stuff gets started. i will still place my inverter on a piece of plycem, not wood and build another plycem shelf above it so exposure to wood is not direct.

Squirl · June 22, 2012, 09:12:19 AM

Sealed AGM batteries are not supposed to off gas much.

QuoteFinally, the NEC Handbook includes the following reference to flooded versus sealed battery types: "Although valve-regulated batteries are often referred to as 'sealed,' they actually emit very small quantities of hydrogen gas under normal operation, and are capable of liberating large quantities of explosive gases if overcharged. These batteries therefore require the same amount of ventilation as their vented counterparts."
(Article 480.9)

http://homepower.com/view/?file=HP119_pg50_Meyer&pdf=1

Their biggest threat of explosive gas is from overcharging.

hpinson · June 22, 2012, 09:45:00 AM

And presumably the charge controller should prevent that?

alex trent · June 22, 2012, 04:20:13 PM

Well presumably, the charge controller should and my Iota charger should not overcharge...but I fuss we can presume right to a fire.

Squirl points out an important thing that is likely a misconception and could be a dangerous one about Sealed batteries. I was going to ask..."and where does the gas go" before i read his post. Thank.

All this automatic stuff make me nervous. My Iota has a single light..fast blink is initial charge, slow blink is bulk and steady is trickle. Kind of crude tuff to have to rely on. New battery, charging for 3 hours today never got off fast blink. I shut it down, waited two hours and had.12.6 volts on the inverter meter (no load on the inverter except the inverter). Which means 755 charge...is not the charger supposed to be in the bulk stage by then. I am less afraid of ruining my batteries than having he explode.

If I could put my batteries outside I would. I have a tough to deal with situation.

Question....given all this, i feel a metal box is a safer bet as if something happens inside less likely to melt the plastic. Acid is not kind to metal, but I am thinking about a mat and cleaning with baking soda regularly. Thoughts?

June 22, 2012, 04:26:35 PM

Quote from: hpinson on June 22, 2012, 12:51:03 AM

1. My system uses AGM, in a well ventilated buried box, with a blade type fuse inline on the 6GA positive battery wire, but in the battery box. From what you say Don, that is OK?

2. One thing that has been bugging me is what would happen if the buried battery box flooded, completely shorting the battery. I dont' see how this could happen, but what if it did?

2. If the box flooded and water covered the terminals most likely the worst that would happen is a slow discharge of the battery. That would depend on the conductivity of the water of course. Somehow I don't think there would be sufficient conductivity to cause a catastrophic failure, melting, of the battery. At least that is my thinking.

1. I don't know? Is the fusible link enclosed enough to prevent any arc from igniting any hydrogen? Will the plastic melt or burn away under a dead short? Type T, like these...

are designed to encase the arc.

hpinson · June 22, 2012, 04:36:33 PM

It's not a type T, but this, from NAPA:

The rubber case is pretty stout, but maybe I should look at replacing with the type T.

MountainDon · June 22, 2012, 04:39:55 PM

Quote from: alextrent on June 22, 2012, 04:20:13 PM
My Iota has a single light..fast blink is initial charge, slow blink is bulk and steady is trickle.

I think you'll find the manual states that a fast blink = bulk (the initial stage where amps are being crammed into the battery as fast as possible), then the slow blink = absorb stage (where the voltage is held constant and low amps are applied) and finally a constant light = float charge. So, it was in bulk charge all alpng, waiting to bring the voltage high enough before switching to absorb charge. It probably just needed a little extra time. When I used iota's in our RV they proved to be extremely reliable chargers. Give it time to go into absorb and float, even with a new battery that could take longer than you might think. You paid for the electronics designed by the engineers, let them do their thing.

Be sure your AGM's do not require any special charging rates; the Iota are safe for flooded lead acid and most AGM, as I understand it. . Most AGM do not require anything special other than not overcharging, but gel cell batteries are different..

hpinson · June 22, 2012, 04:44:40 PM

Check your charge controller documentation too. The Prostar PVM controllers have a switch for flooded/AGM/Gel that you set prior to use.

MountainDon · June 22, 2012, 05:19:00 PM

hp, I have used a lot of those fuses/holders in vehicle applications. They do have a small pinhole in the plastic of the fuse IIRC. A person would have to be having a real crappy day for that little hole to be able to ignite some hydrogen. But then there have been days I was pretty certain things had long gone to hell....

solarseller.com usually has some fair pricing on things like type T fuses. Give them a look. grainger also sells them.

June 22, 2012, 06:26:21 PM

On the Iota charger and my new battery.

i may have been a bit quick on the draw in turning off the charger, but was concerned about overcharging it as I hear that is one of the cardinal sins of battery life extension.. 100 AH battery and three hours on the charger seemed long. When I read the voltage on the inverter before charging it, said 12.3 V which is supposed to be 50%. This means needs 50 amps to get to 100% and I thought the bulk charge would be about 40 amp/hour??

I bought the Iota because it has a good reputation. And I trust the engineers, but while they may have done their job, some minimum wage assembler may not have. "Oh, Doc, I know you want to Hopkins but it's my left leg that needs to come off, not my right"...got to speak up and act, eh?

I just read the voltage at rest after off charger 3 hours and it is 12.7 which means close to 100%. Maybe i misread the slow blink for the fast and it was just about to go to float.

The cheapest battery v meter I can find is $200...that sound right...i would like not to have to rely on the inverter one alone. Not sure why.

MountainDon · June 22, 2012, 07:40:29 PM

Was the battery warm to the touch? As a battery reaches near full charge more of the energy going into the battery is converted to heat. If the battery gets to feeling warm (120 F

) it's probably time to reduce the charge amp rate. Iota doesn't offer a temp sensor like some charge controllers, chargers and inverter/chargers. However, I have never run into a case of having a hot battery with the RV batteries and out iota charger. I never metered the charge process amps but I had a "sense" that the amps going in were falling as the voltage climbed while in bulk stage.

But then, considering AGM batteries... no hydrometer can be used... a meter like a pentametric, setup and calibrated properly could be a useful tool.

The Midnight Solar battery capacity meter is a simple meter for those who can't or won't be bothered by the techy things one might have to deal with to keep a good coulomb meter operational and accurate.

Dave Sparks · June 23, 2012, 09:49:13 AM

Batteries should not be in conditioned space. I am not saying it is not done but there is a reason the building and fire codes do not allow this. If you do this you need to really understand and research the subject.

If I were you I would build the box along an outside wall which is much safe than a closet. Any battery can outgass in normal use or in a failure mode (AGM/GEL).

Good Luck

alex trent · June 23, 2012, 07:44:23 PM

Yeah, I agree with you. I just cranked my "real" system..Iota charger and Trojan AGM batteries. no solar just run genset to charge. With my use, figured about 3 hours once a week.

So on the first go round with the new battery...after 4 hours on the charger still in the bulk stage and battery voltage at the inverter after a 3 hours off charger and not load except inverter is 12.5 V, which for AGM I read as about 75%. Sounds like something is screwed up...any ideas? Could it be my generator which is not true sine wave? I have read things about how they do not supply the right current for charging at full volume. On the other hand, Iota is one of the charger that is supposed to be able to deal with that.

That will likely get fixed, but reinforces the fact that things can go wrong with even good equipment.

My batteries are to be in a steel box in a closet...in a corner with two outside walls. I plan to vent the box right through the wall with 3" PVC near the top of the box. Will only be about 8" from box to outside. Will drill two 1" holes oppose side near the bottom. Passive ventilation, but I think should work. I know shell will rot with the acid, but i will have to take care of it regularly. I will put two 2 pound box of baking soda on the floor of the box on each end, so it there is a big leak that will help. Box is on tile floor and walls are plasterboard, Box is pretty heavy duty.

considerations · June 24, 2012, 10:54:31 PM

"My batteries are to be in a steel box in a closet"

Mine are in a wooden bench I built into the shed wall. They are vented with 3" PVC that contains a DC fan.

The other thing I did was buy those plastic battery boxes that have strapped lids. The batteries are too tall to fit the lids on, but I set each one of them in a box, then in the bench. If the battery decides to leak, the fluid will be contained in the plastic box. Cheap insurance.

flyingvan · June 25, 2012, 12:01:22 PM

"My batteries are to be in a steel box in a closet...in a corner with two outside walls. I plan to vent the box right through the wall with 3" PVC near the top of the box. Will only be about 8" from box to outside. Will drill two 1" holes oppose side near the bottom. Passive ventilation, but I think should work. I know shell will rot with the acid, but i will have to take care of it regularly. I will put two 2 pound box of baking soda on the floor of the box on each end, so it there is a big leak that will help. Box is on tile floor and walls are plasterboard, Box is pretty heavy duty."

Not sure I'd pre-stage boxes of baking soda next to my batteries.

These are excellent instructions for an owner/builder sulphuric acid volcano. In the unlikely even of a catastrophic leak, your sulphuric acid is going to react impressively. If a flood happens to fill the space, you'll make a good NaHCO3+h2O solution with a Ph about 10---if it can get to your electrolytes in your batteries it'll get messy. The carbonic acid will quickly decay into something like Perrier with sulphur salts added in....
When I was on SDFD HazMat, if we had a big acid spill we'd make a mix of soda ash (Sodium carbonate, but sodium bicarbonate would work too) and water in a plastic bucket. We'd dip a cornbroom in the solution and sweep the spill. You get a little reaction (foams up) but you're metering it slowly. We'd keep dipping the broom in the solution and sweeping the spill until no more bubbles would form---then just sewer the product

June 25, 2012, 01:53:56 PM

Not sure what you re trying to say. Be good if you reviewed the thread and the system.

alex trent · June 25, 2012, 05:19:02 PM

OK..

So you are saying it is better to have it leak...say from a cracked battery case...and then deal with it. This avoids all the bubbling and stuff of the acid base reaction. What does the reaction give off? My thought was that in a leak, it gets neutralized as it comes out and makes a mess, but less of an acid that will eat the box away. any vapors get out the PVC vent pipe. On that note, any idea of how long it would take to destroy the box floor...I do not know the actual gauge, but it is a heavy "work" box.. That (putting baking soda in) sounds logical, but surly may not be the case as logic sometimes does not work in stuff like this.

This is to deal with leks, as the box will not get flooded.

flyingvan · June 25, 2012, 08:15:13 PM

Initially you make a bunch of carbonic acid, but as the Ph rises you're basically (

) left with Co2, new water that didn't exist before, and sodium sulfate.
After it's done reacting it's just soda water with the odd sodium ion, suphate ion, and bisulphate ion. Your basement is now full of CO2. The only danger is when the reaction itself is taking place---it can foam up really big really fast while it's neutralizing itself. The car battery cases are made out of polypropylene, which holds something like 85% sulphuric acid just fine. (12 volt batteries electrolyte is around 65%) I think that's what I'd do, just have a secondary containment that's made of polypropylene.

alex trent · June 26, 2012, 06:50:35 AM

I think the CO2 would vent and the foam mostly contained in the box and likely pushed out the vent...but...based on what you say, I think my best bet and not to have to worry about that and the bicarb interaction is to add a polypropylene box to the list of things to get next time I am in the States. Not to be found here. This gives me what I need in containment and they look reasonably strong.

I hate to have to drill my steel box anyway and steel and acid are not the best combination to star with. I'll just vent this one like I was going to do the steel one. Will be passive ventilation, but with 2-or 3 AGMs and monitoring them on the charge, it will be OK. When I hook up solar and have unmonitored charging might have to change.

MountainDon · June 28, 2012, 05:39:35 PM

Since you do not have freezing temps to deal with there is very little chance, IMO, that you will ever encounter a leaking battery case. Especially with the batteries being AGM's. The only batteries I have ever seen leaking were (a) dropped or (b) involved in an accident where they were crushed. I've seen totally discharged and frozen batteries survive without cracking the case.

I would be an excellent safety idea, to have a jug or two of water with the soda dissolved in the water. I'd keep that right handy to the batteries, but not in a box with the batteries. As flyingvan pointed out the reaction can be quite the spectacle.