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 batteriesÉ 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 70ˇF 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