[DON]

AGM batteries should need no venting. If AGM or Gel Cell batteries vent it is because they have failed, and the tip off is the rotten egg smell. Same with LiFePo4 batteries.

Lead acid batteries need to be in a vented enclosure.

[Tom]

AGM and Gelled electrolyte lead-acid batteries are referred to as Valve Regulated Lead Acid, VRLA. VRLA batteries must be in a vented enclosure. VRLA batteries normally operate in a sealed mode, but they can and do vent hydrogen and oxygen gas to the atmosphere. VRLA batteries will vent some gas when initially placed in service. This is often referred to as the de-wetting process. As they gas off a bit of water the oxygen recombination reaction begins.

All that said, the normal gassing rate is about 5% of a VLA battery. Under the right conditions, a VRLA battery can produce as much hydrogen gas as a comparable VLA battery.

[Jon]

The battery compartment also houses the inverter, the EMS surge protector and most of the other electrical systems. Right now, the batteries are free to vent into the entire compartment. The compartment hatch door has vented panels at the bottom of the door. I am not concerned when driving down the road, as I would assume the air exchange would be pretty good.

My concern is when the bus is parked and connected to shore power, and the batteries are being recharged. There would be significantly less air movement though the compartment. As Hydrogen is light, I would assume it would gather at the top of the compartment, but the vent holes in the compartment hatch are on the bottom of the compartment. I’m wondering, if for some reason the inverter or any of the electrical devices were to create a spark, could there be sufficient hydrogen built up to cause a problem?

[Dick]

I did some rough calculations as I have none of the details.

An air flow rate of 0.5 cfm is sufficient to keep the hydrogen accumulation to 1% or less under worst case condition of 60C at 28.8vdc for 8 total 8-D batteries.

If you provide the number of batteries, model number, and enclosure size I can be a bit more accurate and give you a good idea how fast the system can reach a dangerous condition when the ventilation fails.

Under normal conditions very little ventilation is needed. It’s unlikely, but possible, that your system will actually need 0.5 cfm of air flow.

[Mike]

Mike,

Ok. The battery compartment is 53″ wide 40″ deep and 35″ tall.

I have 2 GPL 8DL lifeline batteries wired in series for a 24 volt system.

https://lifelinebatteries.com/products/marine-batteries/gpl-8dl/

I’m in CA. so no real cold weather, 40’s but have seen over 100 degree summer days.

[Ken]

A pair of 8-D’s isn’t much battery for a Prevost. Most appear to have 6 or 8 4-D’s or 8-D’s.

A pair of 8-D’s need a minimum of 0.35cfm of air flow to keep the hydrogen accumulation to no more than 1% under worst case conditions. I defined worst case as a battery temperature of 60C, (140F), and a charge voltage of 28.8VDC.

With ventilation completely blocked and normal battery charging conditions it will take approximately 700 hours before your battery enclosure would reach a dangerous level of hydrogen. Under worst case conditions it would take approximately 10 hours to reach a dangerous condition, assuming no ventilation.

So, you need very little ventilation even under worst case conditions, (which will likely never occur).

[Mike, 92 Country Coach]

Mike-

Thanks for doing all the math, very scientific! Good to know even under the worst of circumstances, it will be safe. As there will always be some ventilation. And as I’m most concerned about when hooked up to shore power, I could just tilt open the hatch door a few inches, which would then vent out the top of the compartment.

Thanks again!

[George]

You’re welcome!

After crunching the numbers the ventilation requirements are so small that most people would say that Jon was right. However, some ventilation is required. A sealed compartment would eventually become a bomb. I have photos of what can happen when people don’t provide ventilation for battery enclosures. Hydrogen is very powerful.

Disclaimer: The preceding discussion pertains to a specific model and number of VRLA batteries in a specific enclosure. Changing anything completely invalidates all calculations and assumptions.

[Unknown Member]

We have four (4) 8-D Lifeline AGMs in our Liberty XLV Elegant Lady 24volt coach with Allen-Bradley system. Even brand new that was just enough to get us through the night dry camping. Two wouldn’t make it for us.

It just dawned on me that the A-B system probably drawn on the house batteries which dry camping. We never stop learning.