Battery box vent

[bottomacher]

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.

[Sean]

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.

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.

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

[Cary and Don]

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

[Oonrahnjay]

(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.

[Sean]

     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.

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

[Oonrahnjay]

(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.

[bottomacher]

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.

[Brassman]

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.