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CD-ROM Aktief 1995 #3
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BATTERY.009
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1992-05-09
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Charging Batteries Can Be A Gas!
Gerald Ames
In an article in Home Power #4, I discussed a working Wind/PV system.
There have been numerous requests for additional information on the
Hydrogen Gas disposal system that I made to vent my lead acid batteries.
So here's how it works!
Hydrogen Gas Problem
Before explaining how the system is put together, some background
on Hydrogen gas is necessary to understand where it comes from and
why it is dangerous. Hydrogen is the lightest and simplest atom
known. The term comes from the Greek words meaning water former.
Each molecule of water (H2O) contains two atoms of Hydrogen and one
atom Oxygen. Hydrogen and Oxygen gas is formed by electrolysis of
water. In electrolysis, an electrical current (such as battery charging)
breaks down water into its two elements. Hydrogen in the presence
of Oxygen forms an extremely explosive mixture, which needs only
a spark, to cause a violent explosion. A good example of what can
happen was recorded on film with the explosion of the Airship Hindenburg
in Lakehurst, New Jersey on May 6,1937. Had the gases in that burning
airship been confined, as they are in a battery, the loss of life
and property would surely have been much greater.
Hydrogen and oxygen gas are produced within the lead-acid cells during
recharging when the cells are approaching full charge. The amount
of gas produced depends on the size of the battery pack, its state
of charge, and the rate of charge that the cells are undergoing.
The higher the state of charge and the higher the charge rate, the
more the cell gasses. Such are the facts of life on lead-acid batteries╔
Options For Gas Disposal
In a home power system, there are several options for dealing with
the Hydrogen gas produced during lead-acid battery recharging. Here
is each briefly, along with its disadvantages for use in my particular
system.
Ignore The Gas
This may work for a small battery bank provided it is not confined
in a small enclosure. This is not a viable option for a system with
20 or more batteries.
Canopy System
A canopy is constructed over the battery bank as a collector, with
a vent pipe attached to carry away gasses. There is no assurance
that all of the gasses will be vented to the outside, so this was
not secure enough in my mind.
Air Circulation System
This system requires that air within the battery room be exchanged
3 to 4 times per hour. In a closed system, where temperatures are
closely controlled, it would be impossible to circulate fresh air
in and keep it at 70íF without great expense.
Hydrocap System
This system utilizes catalytic battery caps which recombine Hydrogen
and Oxygen gasses into water. Essentially it is a good system in
theory, and may work very well. My main problem was the expense
of purchasing enough caps to replace 66 original cell caps at a cost
of $4.75 each plus shipping and handling. Since this type may be
of interest to many home power users, I am including the address
of Hydrocap Corp. at the end of this article.
An Explanation of my System
With the limitations of the other systems in mind, I set out to design
a closed system that would dispose of the gasses safely and at a
reasonable cost. This closed system was made by using a 3 inch PVC
pipe as the main transmission vent, and then connecting it to each
individual battery cell via a clear vinyl tube. The main vent line
is sloped at 2/3 inch per foot of horizontal length to encourage
the gasses to exit rapidly. Hydrogen gas is much lighter than air
and rises rapidly in our atmosphere. This slope was arbitrary, but
worked with the dimensions that I had. The main vent line features
a threaded cap at the lower end which can be taken off to remove
water that is formed by the recombination of gasses and condensation.
The outside end of the main vent is cut on a bevel to reduce the
chances of rain dripping in, prevents birds from making deposits
in the outlet and lastly, it provides a larger end area, which encourages
gas dispersal.
The space between the main vent line and outside wall was filled
with silicone caulk which remains flexible when dry, and allows for
differential expansion without cracking or creating air leaks.
The main vent line is held solidly in place by the hole in the wall
and U-bolts attached to the angle iron stands on the rear of each
battery rack.
In preparation for drilling the holes in the main vent, the line
was marked off proportionally, according to each battery location,
and the vent holes were located within these marked areas based on
good visual symmetry. The holes were drilled approximately 1/3 radius
from the top center, on each side of the pipe. These holes, as well
as those in the cell caps, were drilled slightly smaller than the
outside diameter of the tubing, to assure a tight, leak free fit.
The cell caps were drilled on dead center and the original vent holes
were glued shut.
The tube was then cut to proper length, both ends were sprayed with
polyurethane clear gloss finish to seal off minor leaks, and then
put in place. The tubing used on the 6 volt batteries is 1/8" ID,
clear vinyl and the 2 volt batteries utilize 3/16" ID, clear vinyl
tubing.
This system has worked flawlessly for 3 years now and other than
possible replacement of the vinyl tubing at some future date, the
maintenance requirements are virtually zero. Electrolyte loss through
this system has not been a problem.
Venting System Cost
3" PVC pipe fittings and glue = $13.90
100 ft. 1/8" ID vinyl tubing = $9.00
6 ft. 3/16" ID vinyl tubing = $0.72
U-bolts, angle iron & misc. = $9.27
Total Cost = $32.89
The vinyl tubing costs from $0.07 to $0.12 per foot, depending on
the quantity purchased. I have not included the cost of $4.99 for
the can of Polyurethane clear gloss spray finish since so little
was used. I normally keep a can on hand to maintain the battery
tops, so no additional expense was incurred. All of the products
listed can be purchased at hardware stores, so the system should
be easy and economical for anyone wishing to build their own.
Windup
I hope this article, along with the drawings and photos will explain
how the system was put together. If you have further questions or
comments, please feel free to contact me at any time.
Gerald L. Ames
POB 749
Okanogan, WA 98840
Hydrocap Corp.
975 NW 95th St
Miami, FL 33150
Phone 305-696-2504