Battery box ventilation

[TimC]

My solar battery bank batteries state that I should ventilate the area they are in while being charged. They are all SLA AGM. They are in my galley cabinets, so, not an air tight container, yet they are enclosed.

I have several 80mm case fans (12v) to use. Is there a way to run these fans only while my solar panels are charging the batteries? My controller load terminals are always on and it is a cheapo with no options.

If I upgrade controller do the newer ones have an option to shut off the load when the batteries are in float mode?

Am I worrying about SLA AGM batteries off gassing in a non-airtight enclosure?

Thanks
Tim

[John61CT]

No danger, and they don't care, but their minute offgassing can be corrosive.

[working on it]

* If you're still worried about outgassing, then just install one of your computer case fans to expel any possible outgassing from the trailer, and leave it running 24/7/365. A normal 80mm case fan will last for around 30000 hours (or 3.425 years) while only drawing 1-1.2 amp-hours a day (negligible, especially if set to automatically charge).

* I have done so before, running them fulltime for six months in my garaged trailer, after I first built it, using two hi-static pressure 120mm fans, while the battery maintainer hummed away all winter (to keep the interior from getting stagnant)... with no ill effects to fans nor battery & charger. It was not really needed, because I haven't needed to repeat that, since there's enough airflow from convection in my steel garage (basically open at the top and around the sides) to keep the interior fresh enough (at least 'til I prep for the next trip). But it shows that the case fans can be used for low amperage, constant ventilation, if so desired.

* Another thing.... My HHR Panel has a lead-acid battery under the rear floor cover, and has a tube directed from it thru the spare tire well to the outside, to expel any outgassed products. However, that tube broke off, and I didn't replace it for ten years, most of which time I slept back there during ice-storm events when I couldn't commute back home. I also kept it charging while I was in it at night, with my head just above the battery cover panel. I never could smell any outgassing, nor was there ever any sign of corrosion. After I retired, and never had to sleepover in the Panel again, I finally replaced the first battery, after 10.5 years of service, and put another outgas tube there (finally).

* By the way, I always used a Battery Tender, or Battery Minder when my Panel, or any of my trucks were at home (or parked overnight in the company garage). That's why my batteries last for 10-12 years! My Optima Yellowtop in my TTT is only 7 years old, so it has a way to go, still.

[Aguyfromohio]

The official answer is that AGM batteries are not truly sealed. Under normal conditions they don't vent, but during high rate charging or abnormal conditions it's possible. They all have a little overpressure vent that opens at about 2 psi during some conditions. When they do vent, they vent hydrogen. RVIA and other codes require venting for all lead acid batteries including AGM maintenance free batteries. Those codes specifically mention that sealed maintenance free AGM batteries need venting. Hydrogen is lighter than air and floats upwards, so a hole in the top of any container or cover that leads out of a small battery box out to a larger air volume is what they mean by venting. Fans to push gases around are less important than a vent to let hydrogen float away on its own but they sure wouldn't hurt, especially if they are pushing clean air rather than pulling potentially flammable gas past the fan motor.

The gray area is exactly what constitutes "adequate venting". Hydrogen disperses into air very easily; AGMs don't vent often or vent much; and it may be acceptable to vent a small battery box into a bigger cabin volume. The bigger your battery bank is, the more serious the risk. The setup you describe seems to me like the installations that are common in boats. All your thinking appears spot-on.

[TimC]

Thanks for all the feedback. I think I am good with the little ventilation I have. The batteries live behind my galley drawers and just below the counter top. I could drill holes, but, I'm more confident with your feedback about AGM off-gassing that the gaps in the drawers and around the counter top is sufficient.

After doing some measurements last night and then re-positioning my two 18ah batteries I discovered I have room for eight of those little buggers behind the drawers. Wahoo! 144 AHs here I come...

Tim