How serious is ventilation design with FLA?


New Member
I have 24 6V FLA Trojans in this new bank. I’m not sure how serious I need to be about ventilation. Can I stick a 4” piece of pvc pipe on the top of the high side and call it good?

I was considering a powered exhaust, but torn between overkill, reliability, and even safety behind an electronic device in path of explosive gas.
From my faulty memory, a cubic foot of hydrogen per hour when charging. Corrosion is the least of the concerns. At the right concentration, a relay/light switch spark or a water heater or any ignition source and you have created an actual dangerous condition. Have a look at the results of natural gas explosions.

Adequate ventalation includes good airflow, top and bottom. I wouldn’t rely on a powered fan.


New Member
The enclosure is 2’ x 2’ x 8’ and has 24 6v Trojan T105’s inside. I charge around 60-80 amps.
Hi. Run something like a 4" drain pipe outside on both ends of the enclosure. Your charging rate is quite low and you're running quality batteries so you won't see much gassing but you STILL need some sort of venting. It does not need to be powered.
I’m not familiar with the idea that quality of the battery is relevant to hydrogen gas production.

A google search will lead you to acceptable concentrations of hydrogen gas, rates of air exchange per hour, methods for mitigating buildup. I’d agree that “well ventilated” would include something like the 4” drain pipe top and bottom.



Solar Addict
I used a computer brushless fan to ventilate my box of 6 GC2s. My problem was battery fume triggers CO alarm.


Solar Enthusiast
I used Water Miser caps, greatly reduces any outside venting and stops battery pissing, or you can use a vent tube with a low speed usb powered fan to pull the air outside.


Solar Addict
I believe the comments of low gassing was more based off the low charging current vs the quality of the battery.

But still if the batteries are designed to take day +150 amps (due to them being higher quality solar specific battery design) and he’s charging at 60-80, his gassing won’t be extreme.

As for concerns of running an exhaust fan to evacuate gasses, you’d have the fan come on well before gas levels are even close to reaching lvls of concern. Only downside is it’s another failure mode, it’d be best to design a completely passive system


Photon Sorcerer
The 'bubbling' you hear during charging is oxygen given off positive plates and hydrogen given off from negative plates. It begins at about 13.5v for a six cell 12v battery. At 14+ volts during absorb charging it gets moderate. During any equalization, 15+ volts, it is very vigorous. It causes water loss in electrolyte.

The amount of gas produced depends on charge voltage level and size of battery array.

There is always the case of a failure, like a shorted or low resistance cell that increases the charge rate on other cells causing a lot of outgassing even though the charger is set to a relatively normal float charge setting

Most carbon monoxide monitor sensors will go off in the presence of hydrogen gas. I have one in the garage with batteries and it has gone off twice (Murphy's law, both times at 2-3 AM) when one of the battery cells was going bad with low resistance.
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Solar Addict
I have a small 2” fan the pvc runs across the top of the battery’s with 1/2 holes
up out of the op of the box and then out .
There are 5 3” pvc pipes in the bottom of the box for vents 4 get closed off in winter .
The fans gets powered thru my out back charge controller , and turn on when the battery’s hit absorb and turn off after
they go into float .
I don’t really get much gas while charging but I need a fan to pass inspection 🧐


Photon Sorcerer
I have four GC2 6 volt batteries enclosed in a plastic box with holes cut for the cables and foam insulation sealing any gaps. Over Each battery, I have a 1.5” hose, and all four join to one 1.5” hose venting to the outside.

So except for equalization, I think a 4” pipe is good, provided you don’t come back to a puddle of rain water in your batteries.

For equalization, I open the doors.

I think running the calculator in #4 would be the best. I wish I’d found something like that. I felt like I was the first guy in the world to ever put four FLA golf cart batteries in an RV and vent them.


Solar Addict
I think this is a good option , my fan is drawing the air thru the box
I think it’s better to push the air thru so the the fan dosent get ruined buy the vapor


Photon Sorcerer
Not sure how we know the box is leaky..... anyway use some caulk and seal it.
Or just flip the fan over.

Negative air pressure ventilation is always better for keeping inside sources of contaminating substances out of the box while positive is for keeping outside sources out (with a filter).

If you don't care about where the inside contaminant goes then pick whichever one you like.

Fans are unlikely to be ruined by the gases from a lead battery anyways as you'd be ventilating the thing so much the concentration will be almost nothing.
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