Pocket-plate Nicads in Home Power Service Richard Perez I have just recovered from a pain in the neck that lasted twenty years. It started with our first lead-acid battery's arrival in 1970. I've had this pain for so long it became normal and I hardly noticed it anymore. The energy portion of my life revolved around these lead-acid batteries. All the decisions and compromises in our system were to accommodate the cranky lead-acid cells. The list of Dos and Don'ts was seemingly endless. "Thou shalt not discharge more than 80% of the energy in the lead-acid cells." Thou shalt perform regular equalizing charges." "Thou shalt recharge the cells as soon as possible." "Thou shalt keep all connections clean and bright." A never ending litany of limitations and chores all related to the lead-acid cell's delicate and cranky nature-- a real prima donnaÉ Well, things have changed. NiCad cells offer vastly better power storage for home power systems. We like these nicads so well that we are replacing all our lead-acid systems with nicads as quickly as we can afford it. What better compliment can we at Home Power pay? The NiCad Saga During the last nine months we've been experimenting with over 100 wet, pocket plate, nickel-cadmium cells. These cells are made by a variety of manufacturers. None of them are new and all were supplied by Pacific West Supply in Oregon. Some were reconditioned, others were not. Some cells are high rate cells and others are medium rate cells. These experiments have been carried out in four different test systems. Two of the systems are PV/generator sourced, one is stand-alone PV with no generator at all, and one is grid connected. This article is not a primer on NiCads (already done in HP#12, pg. 16), or a test report on a particular cell type (HP#13, pg. 17). This article discusses the different types of nicads now available to home power users and how to effectively apply these cells in our systems. The info here was learned by actual hands-on testing and experience. These tests were conducted on cells between 57 and 2 years old. All had been retired from service by their original purchasers. What we have here is a wide cross section of used nicad cells. As such, any difficiencies due to aging should be apparent. We are very pleased with the life potential of these cells. For example, we tested a Gould XWR7 nicad cell that is over 57 years old and still delivering its rated capacity! Different Brands of Nicads The different brands we have tested are -- SAB NIFE, Edison, Alcad, and Americad. SAB NIFE is a Swedish company and the oldest maker of nicads. Edison Battery Co. made all types of cells for years starting around 1900 and is now owned by SAB NIFE. Americad is a company also now owned by SAB NIFE. Alcad is a British company that has also been around for years. The point here is that pocket plate nicads are made by a variety of companies. And to confuse matters further, each company makes several types and many sizes of cells. The happy news for us home power types is that all pocket plate nicads are light-years ahead of even the finest lead-acid cells. Different Types of Nicads Regardless of manufacturer, pocket plate nicads come in three basic types-- low rate cells, medium rate cells, and high rate cells. All the different types share the same pocket plate construction described and illustrated in HP#12. The major difference between the types is the number and thickness of the plates that make up the cell. Low Rate Cells The low rate cells use a fewer number of thicker plates. They are designed for very slow discharge rates (C/10), nicads will deliver greater than 90% of their rated capacity at cell temperatures greater than -13¡F. Routine Maintenance Nicads require only simple maintenance. They do, however, demand that the user perform this maintenance. How well the user performs this maintenance primarily determines the nicads lifetime. If the capacity of the pack is sized properly, then the quality of user maintenance is the most important factor affecting how long the cells will last. Cell Water Level Electrolyte level should be checked at least monthly and DISTILLED WATER added if necessary. Use only distilled water. Do not use tap water, rain water, well water, spring water, or soda water. Electrolyte water loss is directly related to overcharging the cells. Moderate overcharging doesn't damage the nicad cells, but it does run up the distilled water bill. In no case should a nicad cell be operated with the electrolyte level below the tops of the plates. This can result in arcing within the cell and possibly explosion. In the cells we tested, the minimum and maximum levels for the electrolyte are marked on the transparent cell cases. It's easy to see at a glance where the level of the electrolyte is, and thus we have no excuse for letting the cells get low on water. Cell Oil Layer Check the thickness of the mineral oil layer floating on top of the electrolyte. This oil layer is there to prevent carbon dioxide in the air from reacting with the potassium hydroxide electrolyte. For technical data about this phenomena, see George Patterson's article in this issue. From a user's maintenance standpoint, there should be a layer of mineral oil between 1/8 and 3/16 of an inch thick floating on the surface of the electrolyte. If you need to add more oil then use Chevron "Utility Oil 22". Don't use motor oil, mineral oil from the drugstore, cooking oil, or anything else. If you fail to maintain the oil layer, then the cell's electrolyte will gradually become polluted with carbonates and will require replacement. If the oil layer foams when a fully charged cell is under charge, then this is a good indicator that the oil layer is too thin. So add more oil to foaming cells. Physical Maintenance This is simple. Keep the cell tops free of moisture, oil, dust and sundry funk. The cells we've been using seal much tighter than lead acid types. This means that's what inside the cell stays inside the cell. Apart form dusting the cell tops with a damp paper towel occasionally, we've done no physical maintenance. Compared to a lead-acid system, corrosion of battery cables is nonexistent in nicads. However, don let this lull you into thinking that the chemical contents of the nicad are benign. Nicads contain a powerful base (caustic) electrolyte (like a solution of lye). The electrolyte will burn the skin, particularly eyes. Flush electrolyte from the body with copious quantities of fresh water. And be careful! Electrolyte Replacement After a period of years (about 5 to 20) all nicad cells require that their electrolyte be replaced due to atmospheric carbonate contamination. How long depends how well the user maintains the oil level of the cells. See George Patterson's article in this issue for the technical details of electrolyte replacement. The procedure can be accomplished by a careful and responsible user. Access From the number of calls and letters we've been getting recently at HP, the interest about nicads is very high. Home Power is read by many folks that have had the lead-acid experience and are looking for something better. We urge you to communicate your nicad data and experiences to the common fund. Do this so we may all share what works. I will chew the rag about nicads via phone: 916-475-3179 or write me C/O Home Power Magazine.