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Old 05-13-2011, 06:22 AM   #15
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The compartments in the newer trailers have two vents below the door. Each one is about 1/2" X 1"

Edit: Perhaps I should be more clear. I am talking about my Classic, which stores the batteries inside the shell perimeter, with doors on either side of the tongue A frame. I don't think it's as critical for the tongue boxes, as they are not in a living area

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Old 05-13-2011, 09:25 AM   #16
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Originally Posted by dznf0g View Post
I don't think it's as critical for the tongue boxes, as they are not in a living area

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Old 05-13-2011, 09:37 AM   #17
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Let's say I would rather be safe than sorry. Is there some type of check valve setup that would allow none pressured fumes to get out but not let rain in?
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Old 05-13-2011, 10:53 AM   #18
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Thanks for this- I'm curious, in my 1964, the battery is in the rear, in a compartment but originally had two 3x8 or so vents from the compartment into the trailer bath... from right where the battery is located. I want to redo this area, and add another battery, vent to the outside etc. but the original battery location and design is curious to me, given this discussion.

curious about avoiding venting through the belly pan, obviously fewer penetrations are better, but wouldn't that be preferable to venting through the shell and creating potential for more leaks?
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Old 05-13-2011, 12:14 PM   #19
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Originally Posted by Mexray View Post
Any flooded cell lead-acid battery MUST be vented to the outside of your trailer for safety...

Hydrogen gas (explosive if ignited) is emitted from this type of battery during normal discharging/recharging cycles...

Proper ventilation is essential to allow the gas to flow away from the battery compartment and then be diluted in the atmosphere...

Sulfur like fumes can be emitted when one cell of the battery becomes damaged and allows adjoining POS & NEG plates to touch (electrical short) - your 12 volt battery now becomes a 10 volt battery that the charging system tries to bring back up to 12 volts (usually at high charge rate)...this then 'overcharges' the good cells, heating up the battery, evaporating the fluid, exposing the plates and emitting larger amounts of hydrogen and those 'sulfur' fumes...Hence, VENTS are required!

The OE battery compartments in the front of older AS's have gaps in the exterior doors to allow the battery to vent the gasses - the inside of the compartment is completely sealed to keep any gas from entering the interior...

Later AS's place the batteries in a steel compartment or plastic battery boxes on the tongue that allow free flow venting of the gases...

I don't think I would attempt to 'vent' a sealed battery compartment into the pluming system's vertical vent pipe...You really need more than one vent to allow for a 'flow' of the air currents around the battery...The pluming vent may be subject to some unwanted air circulation during water flow through the system trapping some of the gas - I just don't think you'll want any hydrogen gas mixed with your plumbing system...
Hydrogen gas doesn't have to be ignited. It can self ignite with the right mixture of hydrogen and oxygen.
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Old 05-13-2011, 12:56 PM   #20
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Originally Posted by dznf0g View Post
I don't think it's as critical for the tongue boxes, as they are not in a living area
I agree, that's the first thing that must be pointed out. There are two reasons to vent the gases. First for safety of inhalation due to toxic gases, and second for ventilation of the discharge gases in a cell-overpressuring scenario.

Modern batteries have enhanced seals--yes, I know they have a vent, but it is not the same vent as 15 years ago. The purpose of the vent was previously for venting any gases as they were formed during the electrolysis reaction of each charging cycle, and this happened constantly. However, these reactions are facilitated differently now in the days of lead-calcium grids becoming the norm as opposed to lead-antimony grids. The self-discharge rate is significantly reduced as is the venting.

If the battery is being mounted externally, I wouldn't worry at all about the venting as long as the box is not 100% waterproof. If you are really concerned, tap in a piece of 3/8" tubing just to equalize the pressure and allow some diffusion of the gases. If the batter is being mounted internally, I would say that your level of venting depends on your level of use. If you are frequently running the battery system down to minimum charge and then recharging, yes, you should certainly put some giant vents in, and what was mentioned about having 2 for proper flow in and out is also very important to remove all gases away from the battery.

In the event that you have some sort of actual vent line on the battery, you can actually just hook this up directly to a tubing line that exits the trailer. This is how some modern sports cars and european vehicles are built when they have the battery inside the passenger area. For instance, on the Mini Coopers, some models have the battery in the trunk compartment, and you will note that the batteries have a single 1/4" tubing line off of a battery vent connection that leads to a spot high up in the engine compartment.

Why high up you may ask? Because H2 gas is light, lighter than anything else, and if you install a vent down, then you will always retain some amount of H2 in the vent tube. Modern batteries vent when they reach a couple psig of pressure, so they will initially have enough force to push the gas out, but the remaining H2 in the line will stay. For optimum operation, you should have one vent going up and out, and one vent coming in low with the air, to keep the purges separate.

Just for fun, let's look at the extreme effects of liquid-gas differences with a visit to high school chemistry:

Let's say you have to put 1 fl. oz of water in your batteries. This is 30 grams of water, and at 18 g/mol, thats 1.7 gm-moles of water. The simplified electrolysis reaction is 2H2O --> 2H2 + O2. This means that 1.7 gm-moles of H2 gas are produced, and at 22.4 L/mole, this is 38 liters, or 10 gallons. That worked out pretty well.

To recap, for every 1 fl. oz of water that you have to replace (or in sealed batteries, let's assume 1 fl. oz per month), you will have 10 gallons of H2 gas.

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Old 05-13-2011, 03:35 PM   #21
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Keeping out water and mice from the battery box, you think a couple 1/8th inch holes toward the bottom and a couple toward the top to give the chimney affect would be enough venting.

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