Must Flooded Lead Acid Batteries be Vented?

lzhome · October 2017

Okay, so I know the short answer is yes. But I'm looking for a "its depends" answer.

Here is my scenario, or actual situation; batteries inside a metal building, you have all seen the metal carports? well this one (12'x12') has sides a window (2x2, opens to 1x2) a standard door and 6' metal roller type door with a 1-2 inch gap at the bottom. Also with these metal building every corner has the over lapping metal panels which creates gaps (1x1 inch) about every 12 inches. So my point is, with the window open, the gap at the bottom of the roller door and the gaps in the panels do I need to do anything else for ventilation? A window fan or ceiling fan maybe?

The whole question is about saving money buy using flooded verse AGM batteries. With AGM I would not worry about venting so I think you see why I'm considering flooded batteries. I don't like the maintenance associated with flooded batteries but that is a different story.

Sakamochi · October 2017

My experiences with the batteries is that they do not do well in high temperatures, I think my 16 Interstates are rated at a max of 110 degrees F. I have a thermostatically controlled very low flow fan that moves air from the outside through the battery box and vents outside. So, your situation may depend on how hot it gets in there AND how much air space you have to get rid of the fumeric ventation. If you have 4 batteries or 40 is another consideration.... (;)

mcgivor · October 2017

The question of ventilation is dependent on many factors such as the volume of the room, battery size and so forth, a simple yes/no answer is not applicable. Hydrogen being lighter than air tends to accumulate close to the roof, so logically ventilation at a high point would be preferred, the calculation for the air changes per hour are pretty complex, most people probably use a logical approach, some active ventilation is better than passive. Large banks in rooms without natural ventilation would need fans, backup fans, montoring systems and alarms etcetera. For my system in a 12' × 10' × 8' room I use a 12V fan supplied directly buy a separate 40W panel, vented at ceiling hight, with a relief vent at floor level, when the sun hits the panel the fan runs. Being off grid, charging, along with the fan running occur only during sunlight hours, so no need for control circuitry, seems to work well in my situation. The attached pdf provides information that you may find useful.

mike95490 · October 2017

How much do you like the smell of battery acid bubbling away in the corner of the room ? Will the acid mist cause any corrosion problems ? Can you construct a simple plywood box to cover the batteries and isolate the fumes ?

lzhome · October 2017

Yes, I will have a battery box but without dedicated venting provisions. After reading (yeah right, I had to bounce over a lot of the math) the white paper on battery venting provided by mcgivor above I'm more inclined to go with AGM. A few years ago I did have two Trojans in the RV overcharge and it was pretty nasty, set off alarms in the RV and the batteries bulged. They were about 8 years old so don't know if it was my fault or just age.

jonr · October 2017

With an open window or gaps, I can't imagine there being a problem. I went through the math once and in a 12x12, well sealed room, the conclusion was "probably OK". But be safe - do the math yourself.

Would be interesting to see more discussion of low cost hydrogen monitors. Perhaps using this?

https://cdn.sparkfun.com/datasheets/Sensors/Biometric/MQ-8 Ver1.3 - Manual.pdf

lzhome · October 2017

Lets say I do have a sealed battery box vented to the outside; how can I hook up an exhaust fan that will only run during periods or battery recharge. Will be using a Morningstar Tristar 60 CC with 48v battery bank.

Marc Kurth · October 2017

lzhome said:

Yes, I will have a battery box but without dedicated venting provisions. After reading (yeah right, I had to bounce over a lot of the math) the white paper on battery venting provided by mcgivor above I'm more inclined to go with AGM. A few years ago I did have two Trojans in the RV overcharge and it was pretty nasty, set off alarms in the RV and the batteries bulged. They were about 8 years old so don't know if it was my fault or just age.

Your batteries likely did not bulge from overcharging, All types of lead acid batteries have vents to avoid pressure buildup.

Flooded/Gel/AGM battery bulging is caused by undercharging. Generally, overcharging will boil out the water resulting in "cooked" batteries that smell very bad.

Undercharging results in sulfation of the plates. Chronic undercharging can cause massive buildup to a point that the sulfate crystals have no place to grow but outwards - eventually splitting the case open. In the mean time, the plates can be pushed together to create a partial short.

If you apply lots of current to a battery with partially shorted plates, you will likely get lots of nasty gas venting and a serious heat buildup.I have seen some with holes melted through the side. All of which is typically caused by undercharging.

I sell lead-acid batteries for a living and I can assure you that 98%+ of early battery failure is due to undercharging. Seems like everyone worries about overcharging, but actual overcharging is quite rare when compared to undercharging!

Marc

Sakamochi · October 2017

My 4 inch duct fan is 4 watts I think. It is connected to a thermostatically controlled switch @ 110 volts. For the purists, this is taboo. I got both on Ebay for maybe $20. But for me, a solar spendthrift, I have it set at 80 degrees and it will run until the cooler nighttime air shuts it down. I have a clothes dryer vent which works perfect and a coffee can lid to close it off in the deepest winter. It can be set anywhere from 50 degrees up to about 100f I think. It is routinely used for green houses, like the really GREEN kind you might find in someone's basement with high intensity lights and blackout curtains....Anyway, My off grid house is on (120v) all the time, so I feel that I can spend the extra 4 watts per hour. It vents at the bottom of the enclosed battery box to the outside of my 10x10 foot shed (enclosed and insulated) and vents out at the opposite end at the top to the outside. It is very quiet, although there are evenings when I can hear the faint ROAR 130 feet away. Usually the crickets drown out the sound.

Sakamochi · October 2017

I forgot to add that I am completely off grid! Wind and solar with a 12 kw Kohler autogen backup.

Must Flooded Lead Acid Batteries be Vented?

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