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-   -   AGM Battery Venting (http://www.airforums.com/forums/f240/agm-battery-venting-175002.html)

3bcamper 11-13-2017 06:18 PM

AGM Battery Venting
 
I inquired about additional batteries, and my local Airstream dealer said that AGM batteries don't need to be vented to the exterior, as opposed to liquid/sulphuric acid type batteries.

The service manager said additional batteries could be installed directly in the occupied space.

Thoughts, opinions, experience, objective facts to the contrary?

Protagonist 11-13-2017 06:25 PM

Quote:

Originally Posted by 3bcamper (Post 2034244)
I inquired about additional batteries, and my local Airstream dealer said that AGM batteries don't need to be vented to the exterior, as opposed to liquid/sulphuric acid type batteries.

The service manager said additional batteries could be installed directly in the occupied space.

Thoughts, opinions, experience, objective facts to the contrary?

The original Interstates had a single AGM house battery located under the front passenger seat, not vented to the outside at all.

AGM batteries do out-gas when charging, but the amount of hydrogen released is so small, and the volume of the van's interior is so large, that it would be all but impossible for the hydrogen concentration to reach a level that is explosive or unsafe to breathe.

RandyNH 11-13-2017 06:32 PM

But still not in normal circumstances: (outgassing)

VRLA batteries

During rapid recharging, the electrolyte may boil and pressurize the case, or gas build-up may be too rapid for recombination. These effects necessitate the “valve regulation”. This is normally in the form of a one-way pop-off valve that only opens in the case of pressure build-up. Even if the valve pops, the immobilizing agent prevents rapid, or any, acid leakage. Most designs are so stable and contain so little electrolyte that they won’t leak acid even if they are cut open.

J. Morgan 11-13-2017 08:01 PM

AGM Battery Venting
 
Quote:

Originally Posted by RandyNH (Post 2034251)
But still not in normal circumstances: (outgassing)

VRLA batteries

During rapid recharging, the electrolyte may boil and pressurize the case, or gas build-up may be too rapid for recombination. These effects necessitate the “valve regulation”. This is normally in the form of a one-way pop-off valve that only opens in the case of pressure build-up. Even if the valve pops, the immobilizing agent prevents rapid, or any, acid leakage. Most designs are so stable and contain so little electrolyte that they won’t leak acid even if they are cut open.



Reading that, makes me want to seal them out of my house anyway.

My next upgrade will move the batteries inside, now I know I will be building a battery box sealed from the trailer body for sure.

I know they stink pretty bad if you pop a vent because of over a single overcharging episode.

That would suck. :)

Titus 11-14-2017 05:27 AM

Interesting that the older AI has a single in-vented battery under the front seat while my AI lounge EXT has two batteries in the back in a sealed box that is vented to the outside. Hard to imagine that Airstream would have spent the money on a sealed box and cut a hole in the van body without a need to do so.

BTW, I also use the vent hole in the battery box to run the negative battery cable from my battery monitor shunt to the negative battery terminal. This way I am able to capture all current going to/from the batteries. In original design the negative side of the Sprinter charging was missed because it got to the batteries by way of the grounded battery box.

3bcamper 11-14-2017 06:06 AM

Quote:

Originally Posted by Titus (Post 2034382)
Interesting that the older AI has a single in-vented battery under the front seat while my AI lounge EXT has two batteries in the back in a sealed box that is vented to the outside. Hard to imagine that Airstream would have spent the money on a sealed box and cut a hole in the van body without a need to do so.

BTW, I also use the vent hole in the battery box to run the negative battery cable from my battery monitor shunt to the negative battery terminal. This way I am able to capture all current going to/from the batteries. In original design the negative side of the Sprinter charging was missed because it got to the batteries by way of the grounded battery box.



I'm guessing that Airstream had safety in mind when they installed the vented box. They would have no control over what type of battery owners may install later when replacing original batteries.

Titus 11-14-2017 08:39 AM

good point about switching battery types.

J. Morgan 11-14-2017 09:04 AM

AGM Battery Venting
 
If there were to ever be a battery fire, a metal enclosure might give an occupant another 2 to 3 minutes to evacuate.

Whenever I think about shirking the idea of a metal enclosure, that point kind of sticks in my mind.

The odds are slim of there being a battery fire if everything is done right and kept proper, but that doesn’t always happen.

rmkrum 11-14-2017 11:21 AM

AGM Battery Venting
 
At least on my AS there is no safety fuse installed right on the battery positive post. There will be one there shortly.

My box is plastic, but mounted external to the interior.

J. Morgan 11-14-2017 01:08 PM

AGM Battery Venting
 
Quote:

Originally Posted by rmkrum (Post 2034515)
At least on my AS there is no safety fuse installed right on the battery positive post. There will be one there shortly.

My box is plastic, but mounted external to the interior.



My batteries are external not boxed and not fused real close to the batteries right now, (but with a lot of effort expended to insure no short circuits), but since I am moving them inside I am going to install circuit breakers at both the positive and negative posts and making a box to enclose them.

I was thinking about getting lazy, moving to AGM’s, and foregoing the box, but It will only take a little while to build a box, and it will make me sleep better. :)

uncle_bob 11-14-2017 01:51 PM

Hi

The risk with an AGM is a shorted cell. In that (rare) case, you feed way more into the remaining good cells than they are happy with. If you have a pair of batteries in parallel, there is a lot of current available when a cell shorts. Even in a single battery setup, the converter or alternator is going to over voltage / over current the battery. In both cases, you get way more gas than you ever would in a normal charge situation.

Yes, it's a cascade failure. Shorted AGM's are rare. Explosive gas mixtures aren't real easy to come up with. How much the combined risk worries you .... that's up to you.

Bob

PKI 11-14-2017 06:47 PM

Hydrogen is a very small particle. It will pass through any material that is somewhat porous. Example is a normal building roof. A sealed steel or aluminum box will trap the gas and should be vented. The flat lid on an AS battery box likely does not trap Hydrogen as H2 is lighter than air and would escape out the sides of the lid. Pat

Protagonist 11-14-2017 07:03 PM

Quote:

Originally Posted by PKI (Post 2034613)
Hydrogen is a very small particle. It will pass through any material that is somewhat porous. Example is a normal building roof. A sealed steel or aluminum box will trap the gas and should be vented. The flat lid on an AS battery box likely does not trap Hydrogen as H2 is lighter than air and would escape out the sides of the lid. Pat

Hydrogen rises. It does not rise, then fall, then rise again to maneuver around the lip of a box lid. So it is possible for a battery box to have an accidental hydrogen trap if the vent is not at the very highest point of the lid.

J. Morgan 11-14-2017 07:18 PM

Quote:

Originally Posted by Protagonist (Post 2034620)
Hydrogen rises. It does not rise, then fall, then rise again to maneuver around the lip of a box lid. So it is possible for a battery box to have an accidental hydrogen trap if the vent is not at the very highest point of the lid.



To me battery outgassing just stinks, the chances of the mixture being right for explosion and fire are slim. I like a metal box in case of fire. It will buy some time, and maybe even smother a fire before it gets big.


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