Venting Battery into vent pipe for holding tank - Fiberglass RV
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Old 08-26-2012, 02:03 PM   #1
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Venting Battery into vent pipe for holding tank

I'm adding a 12v system to my trailer. The battery compartment will be under a front seat above the black water holding tank. I'd prefer the battery outside but there is absolutely no room outside on the tongue for a battery.

The vent for the black water holding tank goes right past where I plan to install the vented battery box.

Can I vent the battery box into the vent pipe for the black water tank? I don't want to cut another hole in the side of the trailer?

Anybody know if there would be a problem. The hydrogen gas the battery might produce is flammable. The gasses the holding tank might produce are also flammable?
Lanny
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Old 08-26-2012, 05:32 PM   #2
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Would I tell you to do it? No. Would I do it in my own trailer. Yes

Seriously, I can't see anything wrong with doing that. I seen countless battery installations in pleasure boats and most, even though they are in similar situations to yours, aren't even vented to the exterior even though they're supposed to be.

I think you'd have to be cooking the battery to produce any serious amount of gas and even then it's lighter than air and would just go up the tube and be gone.

Unless someone with a better memory of their organic chemistry courses than me chimes in and gives a good reason not to do it I'd do it.

Ron
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Old 08-26-2012, 05:40 PM   #3
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I would be concerned with fumes from the black water tank entering the living space. Kind of like plumbing a sink without a trap. Raz
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Old 08-27-2012, 09:43 AM   #4
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I believe AGM type batteries like Optima don't need to be vented, that would be the easiest choice.
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Old 08-27-2012, 02:22 PM   #5
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I believe AGM type batteries like Optima don't need to be vented, that would be the easiest choice.
I was thinking the same thing about AGM batteries.

I don't have a battery mount on the tongue and would have to move propane rack forward to make room for one. Had a conversation with a trailer builder I have done business with and he said he could move tanks forward and add the battery rack for about $50. It's now on my to-do list.

However moving the propane rack forward will leave the crank on the top crank jack hitting the propane tank. Short term I can shorten the handle by an inch or two in order to clear the tank. 13 ft scamp is lite so I can afford the loss of leverage from a shorter handle.

Long term it's less than $100 to have him switch me to a 2 inch hitch with a side crank jack mounted in the center of the new hitch, that handle won't hit the propane tank at all and cranking up and down would probably be easier than around and around.
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Old 08-27-2012, 02:49 PM   #6
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not sure how you can do that unless the battery box is sealed up pretty tight, and then vented from out side to draw air in to the box and i'm still not sure you wouldn't simply be venting your waste tank into your battery box. i'm picturing your venting a space, by some how putting a hole in the vent tube for your waste tank? but what keeps those fumes from comming out of said hole?
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Old 08-27-2012, 03:45 PM   #7
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There is another alternative to shortening the crank handle. When I built my tongue box the handle would've been in the way so I rotated the jack. Two of the three holes lined up perfectly and one had to be filed a small amount. It ended up being an unexpected improvement because I can use the crank more easily from either side of the trailer.

Ron
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Old 08-27-2012, 04:28 PM   #8
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There is another alternative to shortening the crank handle. When I built my tongue box the handle would've been in the way so I rotated the jack. Two of the three holes lined up perfectly and one had to be filed a small amount. It ended up being an unexpected improvement because I can use the crank more easily from either side of the trailer.

Ron
Thanks for the info, yours is the type of jack and mounting I would need to have installed, I have the original 1 7/8 hitch and the jack welded onto the side of the tongue. My crank axis is vertical, handle goes round like a merry go round, looks like yours goes round like a ferris wheel. That is what I would need for a better solution. Looks like having handle toward the front would make that easier from either side.

BTW - nice front tank cover. ooh aah shiny! Not to mention a little better wind profile.
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Old 08-27-2012, 05:12 PM   #9
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Wonder why not vent through the floor, I know the gas is lighter than air but a battery box is a tiny air volumn to replace so it would seem that a decent size vent from a sealed box through the floor would work.

Might check out this sealed box with vent kit is just $38 unless you purchase 100' of extra hose. From MTS Products.

MTS Large Vented Polar White Battery Box - Batteries Boxes & Accessories - Battery Supplies - Electrical

I think if one had two fents both through the floor the battery might as well be considered "outside" there just won't be enough gas build up to matter unless your smoking and open case to check your battery. Even then....
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Old 08-27-2012, 06:09 PM   #10
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Jon Vermilye got a pretty good shot of my battery box in this picture. The handle of the battery box rests on the dual tank shelf and then sits down in the A frame. A piece of angle angle iron was welded in to hold the front end. The trailer is not here right now, but I should be able to get pictures over the weekend.

You are going to need a battery box anyways, why not buy one now and tinker with where it fits?
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Old 08-27-2012, 06:46 PM   #11
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RogerDat
That's the box I have or close to it. It has a hole in the bottom which I plan to vent through the floor with a PVC drain pipe extension. The box is closed and seals pretty tight so I'm not really concerned with the waste tank gas getting into the cabin.
The waste tank vents out the side not through the roof. Same set up as my 86 Casita had except the holding tank is below the floor. So the hydrogen gas from the battery would flow upward to the vent pipe then out since it's an incline all the way.
I'm not familiar with AGM batteries. I will check them out.
Thanks
Lanny
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Old 08-27-2012, 08:32 PM   #12
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I believe AGM type batteries like Optima don't need to be vented, that would be the easiest choice.
You are right Tom, I have one in my trailer and they are great.
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Old 08-28-2012, 05:23 AM   #13
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Is an AGM just a sealed deep cycle battery? Walmart has some for marine trolling motors. Are those the same thing?
Lanny
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Old 08-28-2012, 06:39 AM   #14
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box or no box

If you are putting a battery under one of the seats is a battery box even necessary? If you have one of the origional benches, the space underneith the bench is essentially a closed fiberglass chamber. Is there any disadantage to simply venting the bench to the outside? I realize you can buy a battery box for $40 or less, but is it really needed?

You would need some sort of anchoring system to keep the battery secure, but that need not be that complicated.

Derek
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Old 08-28-2012, 07:19 AM   #15
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Is an AGM just a sealed deep cycle battery? Walmart has some for marine trolling motors. Are those the same thing?
Lanny
AGM or Absorption Glass Mat is a lead acid battery constructed more like a gel cell than a flooded battery. They have a number of advantages over flooded cells but are quite costly. I have one and so far (year 5) I am very happy with it. Raz
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Old 08-28-2012, 07:26 AM   #16
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Derek, It's not in my Casita, it's in my Wally Byam Holiday. It's just a three sided plywood seat mounted in a corner for the other two sides. It's got gaps of 1/4" in a couple places. I'd just feel safer with a box since other stuff will be stored under the seat as well.
Lanny
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Old 08-28-2012, 07:36 AM   #17
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Lanny;

Short summary, vent the battery box, both from below and above. Venting only works if there is an in and an out to create flow.

I would not connect to your black water vent, becasue of the risk of fumes, and if low enough, even fluid entering the battery box.

I put a new battery box in my trailer this way.

The best amateur photography lives on Webshots

and the next 10 or so photos. The items in the vent holes are trailer sink strainers backed with window screening to prevent bugs from getting in either the floor inlet or the top exit vent. The top exit vents out the side of the trailer. I used a water fill cap and cut angled vent slots in it with a rotary tool to vent and also to prevent water coming in when it rains. The inside of the vent is backed up with a piece of 3/4" plywood.

Vic
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Old 09-18-2012, 10:14 AM   #18
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Hey Folks I'm back.
OK I have vented my battery into the black water vent stack. Although the pict doesn't look like it, it all slopes up.

I have put in a small 12 volt sparkless bilge pump fan which pulls air from both the black water and battery box. The black water is pretty much sealed so most of the time the fan will only pull air through the battery box.

All works great except the fan is too strong and noticeably loud. Works great on 9 volts though and hardly makes a sound.

I'd like to cut the power down to the fan from the 12 volts to 9 volts.
Anybody know how to do that? I need some way to reduce the current to the fan.

I installed a 110 relay switch to one leg of the fan so the fan will only come on when I'm plugged into 110 .

Any ideas?
Lanny
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Old 09-18-2012, 11:06 AM   #19
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..........I'd like to cut the power down to the fan from the 12 volts to 9 volts.
Anybody know how to do that? I need some way to reduce the current to the fan...........Any ideas?Lanny

OK, you have your low tech choice and your high tech choice.

High tech, use a DC-DC converter. You put 12 volts into this thing and adjust the little brass screw until you get the voltage that you want. Maximum current is about 2 AMPs.
LM2596 DC Step-Down Adjustable Converter Power Module | eBay

Low tech, you put a resistor in series with the fan. I'll leave it to the EE's to explain how to calculate the ohms and wattage.
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Old 09-18-2012, 03:57 PM   #20
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Raz: Is your AGM battery inside your trailer and vented to the outside?

The Optima AGM Spiral Cell battery User Guide states:

Trunk/Interior Mounting - If battery is mounted inside passenger compartment or trunk, it must be vented to outside of vehicle.

I was wondering if a sealed AGM battery that is classified as NONSPILLABLE could be safely located inside a trailer without venting, but it seems this is still not a good idea.
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