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
just vent it through the floor. RV manufacturers been doing it that way for years.
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
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.
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
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?
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.
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
This company makes a battery vent fan that seems to be the best solution: http://zephyrvent.com/ (http://zephyrvent.com/) .
I haven't priced it because I assume it's a bit pricey.
$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.
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.
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
Does anybody know of a source for the voltage sensing relay?
Don and Cary
1973 05 Eagle
GM 4107
Neoplan AN340
Quote from: Cary and Don on February 24, 2012, 10:32:48 AM
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 (http://ourodyssey.blogspot.com)
Quote from: Cary and Don on February 24, 2012, 10:32:48 AMDoes 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.
Would the heat switch cut on when the inverter is running? It would seem that the batteries would give off heat during discharge. Not that it's a bad thing; I'm just trying to balance loads and keep track of things like ghost loads on the inverter.
Quote from: bottomacher on February 24, 2012, 01:26:33 PM
Would the heat switch cut on when the inverter is running?
Well, maybe, but that's not a bad thing. Excess heat is bad for batteries, so if you were drawing enough load to heat them up, you'd want to be ventilating them.
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It would seem that the batteries would give off heat during discharge.
Not really. The chemistry of a battery makes heat when the battery is charged and absorbs heat when the battery discharges. This is why warm batteries deliver more energy than cold ones (and good battery meters, chargers, and inverters all compensate for this with a temperature probe right on the battery).
BUT, all metal conducting current has resistance, and heats up according to the amount of current being drawn through it. This is why your 14-gauge extension cord heats up when you run that 20-amp air compressor on it. The metal in the battery itself is no exception, to include the plates, bus bars, and terminals. So if you put a large enough load on the battery, yes, it will get warm during discharge.
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Not that it's a bad thing; I'm just trying to balance loads and keep track of things like ghost loads on the inverter.
Well, this is one reason why I would recommend a fan that is powered only when shore or genny is hot. This way, the fan only runs during charging, not while you are running anything from the batteries. But if you wanted to do a thermal switch instead, I would say don't worry about the tiny current the fan will draw. If it's over 95 at the battery, you'll be extending the life of the battery by running the fan anyway. Muffin fans, even ignition-protected ones, use less than a watt, maybe 75 mA or so for a 12v fan. The idle current of your inverter alone is more than that.
-Sean
http://OurOdyssey.BlogSpot.com (http://ourodyssey.blogspot.com)
We were thinking of using a fan like the ones used for cooling computer boxes. We have a 4" one in the compartment that holds all the tv equipment and it seems to blow like crazy. They appear to be brushless.
Don and Cary
1973 05 Eagle
GM 4107
Neoplan AN340
Quote from: Sean on February 24, 2012, 02:59:52 PM(snip) Well, this is one reason why I would recommend a fan that is powered only when shore or genny is hot. This way, the fan only runs during charging, not while you are running anything from the batteries. (snip)
What about those of us that have a separate, dedicated alternator for the house battery bank and charge whenever the bus engine is running? Seems to me a voltage sensing controller (i.e. if it sees charge voltage coming from anywhere, it puts the fan on) would cover all conditions where you'd need the fan.
Quote from: Oonrahnjay on February 24, 2012, 09:27:50 PM
What about those of us that have a separate, dedicated alternator for the house battery bank and charge whenever the bus engine is running?
Well, unless you invest in an expensive three-stage regulator such as a Balmar or Ample Power, your alternator setting is unlikely to charge the house batteries vigorously enough for gassing or heat buildup to be a major problem. That said, a 50DN can put more current into a battery bank than most inverter/chargers, so it really all depends on your setup. But venting the battery compartment under way can more easily be accomplished by designing it so the natural airflow of the coach will draw heat and gasses out, rather than having to use a fan. Moreover, if you do have a fan, but have not carefully managed the under-way airflow, that airflow can easily overwhelm the flushing fan, creating an even bigger problem.
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Seems to me a voltage sensing controller (i.e. if it sees charge voltage coming from anywhere, it puts the fan on) would cover all conditions where you'd need the fan.
Well, sure, but as I wrote earlier, that's more complex and expensive than just a relay. Commercial devices to do this are in the $100 range, although the circuit can probably be built with $10 worth of parts if you know what you are doing. (The capability is also built in to some high-end inverter/charges such as the Xantrex/Trace SW series, as well as some models of battery monitors.) I was trying to offer a less expensive alternative; after all, if money is no object you could just buy AGM batteries instead of flooded and render the whole issue of venting gas out of the compartment moot.
-Sean
http://OurOdyssey.BlogSpot.com (http://ourodyssey.blogspot.com)
Quote from: Sean on February 25, 2012, 12:41:16 AM(snip) venting the battery compartment under way can more easily be accomplished by designing it so the natural airflow of the coach will draw heat and gasses out, rather than having to use a fan.
Yeah, but since my Mama always told me to be double careful, I'm trying to figure out a natural airflow arrangement that works and also a fan. I figure that most of my charging will be done stationary - generator, shore cable, etc. I do have a great advantage since I'm in the process of reinstalling a Peninsula window and I have the body panel outside my battery box off; that give me perfect access to build a vent "tower" in the body cavity higher than the battery box itself with grille for the outlet. That (with a NACA duct inlet low down) should work fine.
Hydrogen should rise naturally, especially when warm, so the vent should work well even when parked, I believe. I hope so; I'm not using a fan.
I'm not using a fan either. One use of the fan, though, is to circulated air through the battery box only during charging. There is, IIRC, a damper in the fan that prevents natrual air circulation when the fan's not running. It's supposed to keep your batteries warmer, and happier.