Mounting AGM battery

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Mounting AGM battery

Postby bobwhite215 » Sat Jan 14, 2017 2:09 pm

I want to put my AGM battery under the floor of my camper. Was going to build a plywood box to hold it which would be accessible from inside. My question is, what kind of ventilation does the battery need? If I leave an inch or so if clearance all the way around the battery, and drill some holes in the box, will that be enough? Do I even need that? Thanks.

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Re: Mounting AGM battery

Postby tony.latham » Sat Jan 14, 2017 2:32 pm

bobwhite215 wrote:I want to put my AGM battery under the floor of my camper. Was going to build a plywood box to hold it which would be accessible from inside. My question is, what kind of ventilation does the battery need? If I leave an inch or so if clearance all the way around the battery, and drill some holes in the box, will that be enough? Do I even need that? Thanks.

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One of the advantages with an AGM is that they don't need to be in a ventilated space. I think the space around it depends on how you are going to secure it but a bit of room for your wiring is a good thing.

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Re: Mounting AGM battery

Postby elcam84 » Sun Jan 15, 2017 6:29 pm

What Tony said. The vents on the battery are just for when something goes very wrong.

That said a metal battery box is best but in this application it's not a big deal. Did have an AGM battery blow up in a new boat a friend was looking at buying. Luckily it was a two battery and the charge splitter failed and way way overcharged one battery. They had allot of clean up and repairs on that brand new boat. Essentially it ended up putting about 90 amps into the battery until it blew up in a loud bang and mist.

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Re: Mounting AGM battery

Postby dmdc411 » Sun Jan 15, 2017 10:10 pm

If your going to design as a drop in from inside. Why not just put some ventilation holes in. We have 23 fork lifts at work. Granted the batts are not sealed, a bad cell puts off some nasty fumes just walking by! This way your chance of being poisoned by the fumes are minimal.
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Re: Mounting AGM battery

Postby GuitarPhotog » Fri Jan 20, 2017 7:45 am

dmdc411 wrote:If your going to design as a drop in from inside. Why not just put some ventilation holes in. We have 23 fork lifts at work. Granted the batts are not sealed, a bad cell puts off some nasty fumes just walking by! This way your chance of being poisoned by the fumes are minimal.

since Agm batts are sealed, youneedventilation only in case of catrosphic failure. Mine is in the cabin at the head of the bed. If you're going to provide acess and ventilation, just pit in a cheaper wet cell battery.

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Re: Mounting AGM battery

Postby Andrew Herrick » Fri Jan 20, 2017 8:34 am

AGM is also a better battery because it eliminates risk of battery acid spills. Wet-cell lead-acid batteries are cheaper, certainly, but then you have to vent and plan for potential spills. And since hydrogen sulfide (the gas) is lighter than air, you can't just stick some vents in the floor or sidewall and call it good.
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Re: Mounting AGM battery

Postby H.A. » Fri Jan 20, 2017 6:18 pm

Andrew Herrick wrote:AGM is also a better battery because it eliminates risk of battery acid spills. Wet-cell lead-acid batteries are cheaper, certainly, but then you have to vent and plan for potential spills. And since hydrogen sulfide (the gas) is lighter than air, you can't just stick some vents in the floor or sidewall and call it good.


To split hairs,
These batteries dont emit hydrogen sulfide, Just hydrogen along with some sulfuric acid vapour.
But either gas is dangerous, they are both very flammable. Hydrogen sulfide is strongly poisonous & corrosive.
Hydrogen will merely suffocate if it displaces enough oxygen.
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Re: Mounting AGM battery

Postby Andrew Herrick » Sat Jan 21, 2017 11:45 am

H.A. wrote:
Andrew Herrick wrote:AGM is also a better battery because it eliminates risk of battery acid spills. Wet-cell lead-acid batteries are cheaper, certainly, but then you have to vent and plan for potential spills. And since hydrogen sulfide (the gas) is lighter than air, you can't just stick some vents in the floor or sidewall and call it good.


To split hairs,
These batteries dont emit hydrogen sulfide, Just hydrogen along with some sulfuric acid vapour.
But either gas is dangerous, they are both very flammable. Hydrogen sulfide is strongly poisonous & corrosive.
Hydrogen will merely suffocate if it displaces enough oxygen.


I should have clarified. Normal charging/discharging cycles of a battery will emit only hydrogen, yes. But overcharging a lead-acid battery at low electrolyte levels can produce hydrogen sulfide gas, which smells like rotten eggs. Thanks for the clarification!
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Re: Mounting AGM battery

Postby bobwhite215 » Sat Jan 21, 2017 1:34 pm

Thanks for all the replies. But to go back to my original question, can I assume that since the battery gives off some forms of gas during charging/discharging that it needs some kind of venting? Can I build the box with zero clearance around the battery (except for required wiring room) or do I need to leave some room between the battery sides and the enclosure box?

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Re: Mounting AGM battery

Postby dmdc411 » Sat Jan 21, 2017 1:56 pm

To be "safe" I would vent it no matter what. Don't want fumes after the fact. Wouldn't hurt to have a little room inside the box to disipate heat. Shim the box so the battery doesn't move around inside the box. This my opinion after all I over do everything! Have very little problems from over engineering!
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Re: Mounting AGM battery

Postby bdosborn » Sat Jan 21, 2017 8:19 pm

An AGM battery is a Valve Regulated Lead Acid type of battery (VRLA) and under normal usage they don't release gas or require venting. However, under abnormal circumstances, they can build up pressure when charging and vent a large volume of hydrogen after the valve opens. You want to have some sort of venting so the gas escapes if it happens. It's a rare event when they vent but the H2 gas build up and resultant explosion has leveled small buildings that weren't vented. Google "VRLA Thermal Runaway" for more information.

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Re: Mounting AGM battery

Postby bdosborn » Sat Jan 21, 2017 8:31 pm

P.S. From the DEKA FAQ on AGM VRLA batteries:

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Deka Linky to VRLA Batteries

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Re: Mounting AGM battery

Postby working on it » Sat Jan 21, 2017 10:19 pm

I don't worry about the AGM batteries at all. Just don't let them die, freeze, or overheat when charging, Location doesn't worry me either. I put my AGM in my trailer's tongue box, surrounded by miscellaneous spare parts and extra electrical cords (there's a plastic barrier separating battery from them). Though the top of the box is sealed with a foam strip, the rear of the box has an open flap where the cables enter. I have the AGM on a BatteryMinder trickle charger year-round (as are all my vehicle batteries); I have never detected any hydrogen discharge whenever I have opened the box. My HHR Panel has a flooded-flat-plate battery under the rear floor. Whenever I had to sleep in it (on icy nights at work, too far to make a round-trip home), I never detected any hydrogen from the battery inches from my nose, even while charging it all night with the vent-tube missing (never saw the need to replace it). And then there are the three Volkswagens I had, all with standard lead-acid batteries under the rear seat. I did detect hydrogen gas when charging them, but only when they were being charged too quickly. P.S. I never let anyone smoke in my VW's.
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Re: Mounting AGM battery

Postby noseoil » Tue Jan 24, 2017 8:45 am

I would build the box, line it & cover it outside with fiberglass & drill some holes for out-gassing. You could even add some tubes (plastic?) to the holes & pot them in epoxy prior to glassing. Drill a hole or two in the back side, so rain isn't driven in on the road. That should work. Make sure to have a gasket to seal the access panel from the inside of the trailer. The holes for the cables could serve as vents as well.
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Re: Mounting AGM battery

Postby lrrowe » Tue Jan 24, 2017 3:52 pm

noseoil wrote:I would build the box, line it & cover it outside with fiberglass & drill some holes for out-gassing. You could even add some tubes (plastic?) to the holes & pot them in epoxy prior to glassing. Drill a hole or two in the back side, so rain isn't driven in on the road. That should work. Make sure to have a gasket to seal the access panel from the inside of the trailer. The holes for the cables could serve as vents as well.


I was thinking of building a box just as described above. I currently use a vented tub which is just to bulky. A custom box can be built which adpats to the inside of my CT better.
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