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GeocamperAS · 05-12-2011, 07:43 PM

I had a box made to house 2 batteries that will sit on the tongue between the shell and lp tanks. The guy that made the box for me said I should vent it somehow. Something about hydrogen gasses from the battery. The original battery was inside a plastic box behind the outside battery door. There was no venting of any kind that I could tell.
Do I need to vent?

Aage · 05-12-2011, 07:50 PM

He made the box and didn't make a vent, and yet he knew you would need one?

I don't agree that you need one, but if he thinks you did, why didn't he put one in?

TG Twinkie · 05-12-2011, 08:21 PM

I think it will depend on the type of batteries you plan to use. How tight is the lid on the box? Does it (the lid) have a gasket? Does the box have a drain hole?

Splitrock · 05-12-2011, 08:22 PM

Battery box venting is sort of an issue with me too. My 1976 31' has one 12 volt battery in a drawer under the floor curbside. I'd like to add another battery inside the kitchen area right above the original battery location. How would I vent that? Down through the floor I hope. Who knows?

Gary

vinstream · 05-12-2011, 08:25 PM

If the box does not totally seal (rubber gasket water proof) you should be ok without a vent. I build custom battery boxes that are 100% sealed and are placed inside (to center the weight over the axle) the trailer and must be vented to the outside in the remote case that they discharge. The discharge tube is 1/2 ID to give you an example how little venting is needed. My guess is you have way more than that with the unsealed edges of your lid? New Airstreams do not put a vent in the battery box build in the tongue area. Hope that helps you decide one way or the other. Todd

Splitrock · 05-12-2011, 08:30 PM

Todd, look at my post above. How would I vent my marine type box installed inside the kitchen cabinet?

Gary

Wsmith · 05-12-2011, 09:10 PM

I can send you a 1/4" stainless steel instrument air outlet screen fitting and you can drill I will see if I can find a bulkhead nut or a reducer you can put on the inside to screw it into.

If the lid is tight fitting or has a deep lip I would vent it. Hydrogen can self ignite at a concentration or around 19% with oxygen. If you ever had a battery with a problem and boiling the electrolyte you could possibly get a concentration of Hydrogen.

TouringDan · 05-12-2011, 09:32 PM

Come on Aage. He is the fabricator, not the designer. Where do you put the vent? How big should it be? A discussion would be in order though.

We talk a lot about venting batteries on this forum, but I have not seen any design guidelines. I am putting four 6v golf cart batteries in the rear storage compartment of my Tradewind. I would like to know how many vents to use and what size. I am putting two batteries on each side. I guess I could put one 1/2" vent on each side. I think that this would work, but It is only a guess.

Dan

vinstream · 05-12-2011, 09:36 PM

Gary, I would not vent through the floor, the less holes through the floor the better, rather it should be vented out the top of what ever sealed box you desire. Since you are in your kitchen area it think a simple solution could be to tap into your sink vent stack that vents to the top of the trailer... Todd

vinstream · 05-12-2011, 09:52 PM

Dan, and Others...
If the battery box is in a sealed storage compartment it only needs to be able release the gas build up to the outside. In my case for two reasons... I placed my batteries inside the trailer rather than outside, one to keep them warm in the winter so that they keep a charge better, the other to center them over the axle for weight and so they are closer to my electrical main panel. I also lowered then into the sub frame 4" to gain greater battery size. I use 6 two 90 lbs 6volt AMG batteries. The top of the battery box is then vented to the out side through a 1/2 ID tube that vents into the wheel well .. In the spring I blow air through it to make sure no critters have made a home... I have thought about putting a one way valve on the end but have not... I researched how much venting you needed and used of all things a golf cart manufactures information on venting batteries...Hope that helps! Todd

Mexray · 05-12-2011, 10:14 PM

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...

TouringDan · 05-12-2011, 10:55 PM

Mexray

So what amount (size) of venting would you recommend for four golf cart batteries?

Dan

Mexray · 05-12-2011, 11:36 PM

Dan...I'm not a designer, but the large roto-molded plastic boxes I've seen for (4) 6 volt GC's have two, 2" holes at one end to route the cables, so there's quite a bit of area left over for ventilation...

I know that if I were to make a sealed box to be mounted inside the trailer, I'd want as much ventilation as possible - I don't think one or two 1/2" holes would be enough, IMHO...

GeocamperAS · 05-13-2011, 06:20 AM

if the box in on the tongue, how would you vent an keep water out?

dznf0g · 05-13-2011, 06:22 AM

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

Aage · 05-13-2011, 09:25 AM

Quote:

Originally Posted by dznf0g

I don't think it's as critical for the tongue boxes, as they are not in a living area

Egg-Zackly.

GeocamperAS · 05-13-2011, 09:37 AM

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?

Globie64 · 05-13-2011, 10:53 AM

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?

Wsmith · 05-13-2011, 12:14 PM

Quote:

Originally Posted by Mexray

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.

worldinchaos · 05-13-2011, 12:56 PM

Quote:

Originally Posted by dznf0g

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.

Now we know, and knowing is half the battle! G I Joooooooooeeeee....