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From: Mike Schooley (no email)
Date: Fri Aug 27 2004 - 09:46:34 EDT
Sorry this response isn't very timely, but I've been trying to trouble
shoot a problem posting to the list.
Edmond wrote, "I'm planning a house bank of 2000AH ... in a box under a
settee in the saloon ... Would a continuous louvered opening at the top
of one side of the box into the saloon be adequate ventilation or do I
need a special blower and overboard discharge?"
In general it is not a good idea to vent into habitable spaces because
there are so many ignition sources. It is better to vent overboard.
You can get away with venting into the saloon provided you can assure
that the mixture ratio of air to vent gas (hydrogen AKA H2) is always
below the lower explosive limit (LEL) or lower flammable limit (LFL)
which for H2 is 4%. You will need a vent at the highest point in the
room which is always open while the batteries are charging.
If you are going to use a passive vent, i.e. powered by the buoyancy of
the H2 gas, then it needs to go continuously up until it reaches the
exterior. If you put a water trap in the line it will collect H2.
If you go with positive ventilation, i.e. a blower that runs when the
charger is on, then there are three options. First, if you mount the
blower inside the box it needs to be an explosion proof blower, which
means it does not produce an ignition source, i.e. sparks, so it can
operate in an explosive atmosphere without causing an explosion. Second,
if you seal the box and mount the blower outside the box so it blows
through the box and out the vent it does not need to be explosion proof.
Third, you could mount the blower motor outside the box and the blower
fan inside the box so there is no ignition source inside the box.
The usual disclaimers apply to all discussions involving explosive
and/or combustible products, the author accepts no liability associated
with the use of this advice, don't try this at home, your mileage may
vary...
Regards;
Mike Schooley
Designing "Portager" a 48' transportable trawler
Ex-Rocket Propulsion Engineer
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