Things that Work! Home Power tests an ED-160 Reconditioned Ni-Cad Storage Battery Richard Perez Batteries are really the hearts of our systems. Almost all of the systems that you've been reading about in Home Power use lead-acid cells for power storage. This is not because the lead-acid reaction is the best for our use, but because it is affordable and relatively effective. There are, however, other battery technologies that are more effective and efficient at storing energy. Nickel-Cadmium (nicad) is one of these technologies. Only trouble was the cost of nicad batteries were about 6 to 10 times greater than lead-acid systems. Until now that is. When Pacific West Supply near Portland, Oregon started offering less expensive, reconditioned nicads with a five year warranty, we couldn't wait to test a set. These nicads are not only amazing, but will revolutionize the way we equip and use our systems. What follows here are the results of over three months of testing of the ED-160 nicads in actual home power type service. If you need a primer on the nicad cell and how it works, please see HP#12, page 16. Meet the Edison ED-160 Nickel-Cadmium Cell The ED-160 is a wet pocket plate nickel-cadmium cell with a capacity of 160 Ampere-hours at a seven hour discharge rate (that's C/7 or 160 A-hr/7 hr.Å 22.8 Amperes). Each cell is 6.37 inches wide by 18.25 inches tall by 3.37 inches deep and weighs in at 21 pounds. The cells are encased in heavy, transparent plastic making it easy to see their electrolyte level. Since the voltage of the nicad reaction is about 1.22 VDC per cell, it takes ten nicad cells in series to make a 12 Volt battery. Now, these cells are "reconditioned". This means that the cells have been used for uninterruptible power in railroads, hospitals and airports, etc. nicads in this type of service are routinely replaced whether they are worn out or not. Pacific West Supply reconditions these used cells and resells them at a fraction of their original cost, complete with five year warranty. The fact that these cells are reconditioned means one thing to me. The cells we tested had already been in service and would show any problems likely occur through use and age. The Test System We installed the ten ED-160s right next to our lead-acid pack of 4 Trojan L-16Ws. We recharged the cells and put them in service, all the while measuring & recording the voltage of each individual cell that made up the pack. We transferred ALL the equipment connected to the lead-acid pack to the nicad pack and it became our system's only battery. By all the equipment, I really mean everything electrical: the 2.3kW. Heliotrope PSTT inverter, all of our DC loads, our PV array, and our 12 VDC Mark VI engine/generator. We essentially replaced a lead-acid battery pack of 700 Ampere-hours with a nicad pack of only 160 Ampere-hours. This gave the nicads a real workout! Life on Nicads We then proceeded to carry on as normal, using electricity as we always have done. The first thing I noticed was that the nicads had higher voltage under discharge than the lead-acid pack they replaced. We use several 12 VDC lights every evening. The voltage of the lead-acid battery pack would drop to Å12.5 VDC under the load of these lights. The same lights (about a 5.8 Ampere load) lowered the voltage of the nicad pack to only 13.2 VDC. The lights were the brightest we've ever seen them at night without the engine/generator on line at the time. And this is even more amazing when one considers that the nicad pack has only 1/4th the capacity of the lead-acid pack. The 5.8 Amp load represents only a C/120 discharge rate for the larger lead-acid pack, while the same 5.8 Amp load is a C/28 discharge rate for the nicads. This means that the load is four times greater for the nicads in relation to their capacity,and their voltage was still higher! After several days of using the cells it became apparent that their voltage characteristics were much more suitable for home power service than those of the lead-acid battery. Most of PV systems are sized to have between four and seven days storage capacity in their battery. This means that the battery voltage in these systems will stay over 13.0 VDC under normal service. This higher sustained voltage means great performance out of all 12 VDC appliances, including the inverter. The nicads maintained their voltage while being discharged at high rates (>C/10). The operating voltage curves were very flat as described in the chart below. INSERT DISCHARGE CURVES Recharging the ED-160s The next question in my mind was how will they charge up? Well, the same style of flat voltage curve holds true for the charge cycle also. The cells seem to sit forever at below 1.45 VDC per cell at a C/10 rate of charge (14.5 VDC for the ten series cell pack) as they are refilling. When they are about 80% full, their voltage jumps to about 1.55 VDC per cell (or 15.5 VDC for the entire pack). The chart below shows the voltage to SOC info for the ED-160s. Considering how most PV systems are designed, the C/40 rate on this curve represents PV type service for the nicad cells. Yes, we will still need a regulator to control the system's voltage. The reason we need this regulator is, however, different. In the lead- acid system we need regulation to prevent overcharging the battery. In the nicad system we need regulation to keep from feeding too much voltage to the inverter and other low voltage appliances. The nicad cells are remarkably immune to damage form overcharging, in fact they actually like it! However, most of the low voltage gear we use in our system is designed around the lead-acid reaction. Until inverter, appliance and control manufacturers get hip to nicads, we must still use voltage regulation to accommodate their devices. I predict that the first company that markets a 12 Volt inverter that will function at around 17 VDC will sell many inverters to nicad users. The PV panels (36+ sseries PV cells) we now use are effective at about 16 to 17 VDC and will recharge these nicad cells. INSERT CHARGECHART Other Notes on Nicads vs. Lead-Acid Types As you may have guessed, I'm jazzed by the performance of these nicad cells. When I replace our ancient (over 9 yrs. old) lead-acid pack, it will be with nicads. The performance of the nicad makes it possible for us to use less storage in Ampere-hours and still get greater performance out of the battery. But this is not the entire storyÉ As lead-acid cells age, their rate of self discharge increases. Self- discharge is energy lost within the battery and is NOT available for our use. A new, deep-cycle (high antimony) lead-acid system starts out self-discharging at about 6% of its capacity per week. As this lead-acid battery ages, this rate increases increase to up to 25% of the battery's capacity per WEEK. The nicad cells start out at about 5% of their capacity per week in self-discharge and stay there forever! The nicads perform at lower temperatures much better than the lead-acid types. The nicads not only retain most of their effective capacity at low temperatures (Å30¡F.)., and are even immune to freezing (which happens at well below zero). While they won't work while frozen, they won't be damaged. Nicads allow our battery packs to grow! With lead-acid systems, we had to add batteries to our pack within two years of purchasing it new. Lead-acid cells aged far too rapidly for us to mix new batteries with old ones. Nicads, however, don't age appreciably. This means that we can increase our storage capacity whenever we need to and still use our existing nicad batteries. This bring us to a final question. How long do these nicad cells last? How many times can we cycle them? Well, the limiting factor of the nicad's longevity is how we treat them. We determine how long our battery lasts by how we use it. If the nicads are properly charged and maintained (you still have to add distilled water occasionally), then their life in PV systems is virtually forever. You could wind up willing your battery to your kids! Nicad Costs The price of a set of ten reconditioned ED-160 cells is $500., FOB Portland, Oregon. This makes them about about twice as expensive as new lead-acid cells of the same Ampere-hour capacity and voltage. Considering that you can undersize the capacity of a battery by about 30% to 50% due to the increased performance of the nicads, this is a good deal. If you add the increased longevity, expandability, ability to hold the charge, resistance to overcharging, and cold weather performance, then this is a super deal. So what's really going on here? A revolution, that's what. Not a human revolution, but a technical one. We are replacing the very heart of our system-- the batteries. For years ALL the gear we have used, everything from lightbulbs to inverters, has been based on 6 lead- acid cells in series (12 VDC). Now things are changing from 6 lead-acid cells in series to 10 nicad cells in series. It's going to take a while for the industry to catch upÉ Access I'm willing to chew the rag out our nicad experiences. Give me a call at 916-475-3179 and we'll go at it! You can contact Lon Gillas, the fine fellow who recycles these nicads for our use at: Pacific West Supply Co., 5285 S.W. Meadows Rd., Lake Oswego, OR 97035 or call 503-639-4008.