Nicad Battery Voltage Regulation Richard Perez I've been getting a lot of mail on the subject of where and how to regulate alkaline batteries. Many of us are now using large capacity nicad or nickel-iron batteries. Here's what we've been finding out about flying nicads. This info pertains to using ten, series connected, pocket-plate nickel-cadmium cells to make a 12 Volt battery. Voltage Regulation In almost all cases we have to regulate the system not for the sake of the battery, but to protect the appliances. For example, most 12 Volt inverters will shut off at about 15.3 VDC. At moderate rates of charge (less than C/20), ten series nicads will attain a voltage above 16.5 VDC when fully recharged. In order to keep the inverter from shutting itself off, we have regulated the system at around 15 VDC. This keeps the inverter working and protects voltage-sensitive, 12 Volt gear such as TVs, radios, and fluorescent lights. Eventually we will have equipment that is compatible with the slightly higher voltage profile offered by the alkaline battery. Right now, the best performing inverter for alkaline battery use is the PowerStar UPG models. They will run right up to 16.5 VDC. Regulating the system at 15 VDC doesn't mean that the battery never fully refills. It will continue to recharge, but at a slower rate. Eventually the nicad battery fully recharges, it just takes longer. It is possible to float charge ten series nicads at about 13.3 VDC. They still refill at this low of a voltage, but the process takes days instead of hours. We have been using series type controllers,especially the Heliotrope CC60C, with great success. Get a control that can go into the upper voltage ranges so that you can open the system up at a later date. A Working Voltage Profile Consider the following voltage data for pocket-plate cells: The pocket-plate nicad cell will happily float charge at 1.35 VDC. If you want a fast refill (>C/10), then you must open the system's voltage up to at least 1.65 Volts per series connected nicad cell. This means 16.5 VDC for a 12 Volt system ten series cells), and 33 VDC for a 24 Volt system (twenty series cells). Voltage regulation in the area of 1.48 to 1.50 VDC per series connected cell is just fine with the nicad cell. While it refills less quickly, it refills none the less. A Major Advantage of Regulation We learned this information by actually regulating our nicad packs and keeping data on their performance. We noticed the following side benefits of regulation at 1.50 VDC or less per series connected cell. The cells rarely spent much time gassing. This meant less distilled water replacement. Less gassing also means that the mineral oil layer floating on top of the electrolyte was not disturbed as often. This means that less atmospheric carbon dioxide is being worked into the electrolyte and should greatly extend the periods between electrolyte replacements. In our experiences, these nicads enjoy loafing and may even last longer if we don't ride them too hard. A Lead-Acid Mentality in a Nickel-Cadmium World For years we've been very careful to fully recharge our battery. To do less meant expensive early battery death. For years we've watched the voltmeter, and lately the Amp-hr. meter, and wondered if we should start the generator rather than deep cycle the battery. For years we've been slaves to a cranky, temperature sensitive, short- lived battery technology. It's going to take a while to get adjusted to a battery that does not care how we cycle it. In our experience, alkaline cells love deep cycling. They love shallow cycling. The love being overcharged. They love being undercharged. In short, they love being a battery. And I love having them as part of the Crew. Access Author: Richard Perez, c/o Home Power, POB 130, Hornbrook, CA 96044 ¥ 916-475-3179.