Battery box vent

[bottomacher]

I have to figure out a way to vent my battery box (MC9) which is located in the middle bay. Does anyone have an idea for an airtight vent that passes through the bay door? Thanks

[thomasinnv]

just vent it through the floor. RV manufacturers been doing it that way for years.

[TomC]

It has to be vented through the floor in case the battery starts to leak-you don't want battery acid getting into the rest of your bay.  Good Luck, TomC

[KC Eagle]

I bored a 3" hole in the middle bay door and affixed a stainless steel screen to the inside. I then took a piece of dense foam rubber, rolled it into a tube and glued it over the outside 3" vent hole in my battery box. When the door is closed the foam rubber makes a tight seal against the inside of the door. I didn't want to put a hole in the bottom of my box (like I did with my propane box) because the hydrogen off-gassing from the batteries is lighter than air and would build up in the box. I had initially thought of placing a 12v pusher fan on the opposite side of my box but the static vent seems to be doing the job fine with my 4 x 6v golf cart batteries.

[bevans6]

It should be venting both high and low, but the critical one is high, since the off-gases that you are trying to get rid of are lighter than air.  Floor level vents aren't actually venting those gases.   The screened hole in the door is what I did too.  Actually in the wall of the bay just beside the door.

Brian

[bottomacher]

Thanks to all for the replies. The upper vent is what I wanted, since I want to vent hydrogen. Do either of you have a problem with rain being drawn into the vent hole?

[KC Eagle]

No, I've never had any moisture come in the vent hole. The cross flow ventilation is a good idea but the 2nd vent hole (low one) needs to be in the floor or at least not into the bay space in case there is positive pressure on the outside vent.

[Cary and Don]

We are in the process of installing a sealed battery box.  We have a 4" vent hole in the floor.  We plan to install two small 12 volt fans high on the box to pump in fresh air that will be controlled by a thermostat on the batteries.  Our understanding is that the batteries give off gas only when warm.  Putting a vent in the door or roof isn't an option.  Is there any reason to believe this will not work?

Don and Cary
1973 05 Eagle
GM 4107
Neoplan AN340

[Brassman]

This company makes a battery vent fan that seems to be the best solution: http://zephyrvent.com/ .

I haven't priced it because I assume it's a bit pricey.

[chev49]

$80; isn't too high for that fan.
I haven't installed a drain in my battery compartment... looks like i will be doing that real soon now that someone has brought that up.

[Brassman]

Eighty bucks ain't too bad, but the fan that I was thinking about was turned on automatically by a voltage level sensing relay that turned the fan on when the battery voltage was increased by the charger. It was that voltage level sensing relay that was a bit pricey, and that was four or five years ago, IIRC.

[luvrbus]

I kept mine simple I used a outside aluminum vent for a drier takes very little heat or pressure for one to open 

good luck

[Cary and Don]

Does anybody know of a source for the voltage sensing relay?

Don and Cary
1973 05 Eagle
GM 4107
Neoplan AN340

[Sean]

Does anybody know of a source for the voltage sensing relay?

Sensing voltage like this, or for that matter, DC current, is tricky business.  It's not as simple as using a relay, you need to have an electronic circuit.  That circuit would also be using power all the time, albeit a very small amount.

There are two simpler ways to do it.  One is to get a thermostatic switch; they're less than $10 and can be found at Allied, Newark, Grainger, etc.  I would say you'd want one that closes at perhaps 35°C (95°F) and then glue it right to the top of the uppermost or innermost battery.  The switch uses no power by itself and will turn the fan on whenever it gets that warm at the battery, whether that's from charging or just extra heat in the compartment.

The other way to do it is to just assume that the charger only runs when you have shore or generator power, so use an AC-powered fan and connect it to a circuit that is only energized on shore or generator.  Sure, the fan will be running "needlessly" a good part of the time, but it will be using power that is free or very nearly so, and the batteries will be happier anyway.

In either case, make sure you get a fan that is "intrinsically safe," which is code-speak for explosion-proof.  The gas that builds up in battery compartments is hydrogen, which goes boom if it gets a spark, so you don't want a motor with, say, sparking brushes in the same compartment.  The same goes for any relays or other devices installed in the battery compartment.

HTH,

-Sean
http://OurOdyssey.BlogSpot.com

[Oonrahnjay]

Does anybody know of a source for the voltage sensing relay?

Don and Cary
1973 05 Eagle
GM 4107
Neoplan AN340  

     I asked the question a few months ago - I was looking for a relay or sensor that would open up when it saw battery voltage of 12.8 or less but close (and activate the house battery box fan) when the voltage rose above a nominal (13.4V maybe, indicating that the battery bank was being charged from any source).  You may want to look in the archives - I can't find it now.  There was a suitable relay/sensor from a supplier of solar charging systems.

      If memory serves, it  was pretty expensive and, as Sean says, a plain temp switch at 1/10 the price would work better.