EV Stuff Dear Richard Perez: Two things; Does anyone know of a battery-powered electric lawnmower marketed in the US? I'm getting tired of the long cord. Also I have an electric car with 17 6-volt and 1 12-volt lead-acid batteries. I keep seeing ads for reconditioned nicad and nickel-iron batteries. Has anyone tried that sort of conversion, and how did it work? Second, I've written a book about my experience as an EV owner with a PV system to power it. The NY publisher Norton will be publishing it this October. It's a book for the mechanically inept- people like me who couldn't possibly do their own conversion, but must buy a ready- made EV. I'm still assuming it's a book HP might want to review. Unless you beg me not to, I'm planning to have Norton send a review copy along. Sincerely, Noel Perrin, RR 1, Box 8, Thetford Center, VT 05075 Hello, Noel. Sorry no info on battery lawnmowers, how about it readers? Nicads and nickel-iron cells are generally not used in EVs because of their low energy density. You are talking lotsa weight and volume for the number of kWh stored. There are exceptionsÄChrysler and GM are both experimenting with special nickel-iron batteries for their EVs. Send us a copy of your book, we'll give it a read. Richard 48 Volt Conversion Dear Home Power; Please renew my subscription starting with #30. The biggest mistake we made was choosing a system voltage of only 12 volts for our 14 Arco M55's. On a sunny day we exceed the capacity of our Trace C-30 regulator and have had to bypass it. We have just acquired 48 two volt gel cells weighing 250 pounds a piece and having a capacity of 1500 amps each. My guess is that this 6 tons of batteries should give us 3000 amps at 48 volts. Information on how to hook up a 48 volt system is very hard to find. For example exactly where does a bypass diode go when you talk of configuring solar panels for higher voltages? Do I ignore the diodes that are built into my panels. Please explain blocking diodes vs. bypass diode and their placement in a circuit. We would like to see Home Power Articles that address these higher voltage systems. Thank you. Sincerely, Nelson & Debby Henne, RD 1 Box 104, Robsonia, PA 19551 INSERT GRAPHIC The bypass diode, used to protect shaded modules in high voltage arrays, is connected reverse bias and in parallel across the output terminals of each and every module. Each ARCO M55 module already have this diode in place, you need to do nothing extra. A blocking diode prevents the battery discharging through the modules at night. The blocking diode is inserted, forward bias and in series with the positive power lead from the PV module, subarray, or array. Richard Poop Paddles Dear Home Power; I always find something new and interesting in Home Power. My interests have long been in individual or independent production of useable and practical energy and its application for the benefit of the less affluent, including myself. I enjoyed Al Rutan's article on methane generation and hop you enlarge on the subject with different designs and their inherent problems and advantages. The Rutan diagram did not indicate how the hard foam/crust which occurs on the top of the effluent is to be broken up, nor did it detail the clean out and recharging of the system. I hope to see future updates on catalytic conversion of gaseous or liquid fuels to heat and thermal electricity and the advances in fuel cell technology, and better batteries. If you could either explain or debunk the idea of magnetic water softening and wether the ordinary householder could benefit from workbench tinkering with the idea it might save us all some scarce resources. I'm always delighted by elegant, simple, and innovative solutions to the problems that confront the envenerate tinkerer and inventor. Thanks for being there, Boyd Getsinger, POB 67, Iona, ID 83427-0067 Dear Boyd, You ask how the foam/crust on the top of the slurry is broken up and also how the system is recharged and cleaned. You're right that there was an omission of how the mixture is stirred, although mention of it was made in one of the articles. Multiple drawings are needed to include all the features without having the picture so cluttered that it is unintelligible. Much of my feeling about what does and does not work has been the result of visiting various municipal sewage plants. The plant at Laurel Montana is a vertical tank with a large paddle mechanism driven very slowly by a motor mounted on the top of the tank. It was a trouble free operation. The plant at Billings Montana was eventually abandoned after the digester failed and several attempts to start it were futile. The major difference between the two was the fact that gas was recirculated in the Billings system rather than the slurry stirred to provide movement. Everyone involved came to the conclusion that this recirculation was .picking up inorganics - sand and gravel - and was literally "shotgunning" the bacteria. They couldn't stand it. In a horizontal tank such as the one pictured in Home Power, a workable solution is a few small paddles along length of the tank, mounted on a shaft either from the top or the side and motor driven, although they could be turned by hand once a day or so. While there is a gathering of "stuff" on the top of the slurry which needs to be moved around, the more important aspect is that food needs to be transported to the bacteria by some kind of movement throughout. They don't have the mobility of fish. In our guts, the action is accomplished by peristalsis. Any kind of mechanical movement simulates this. The recharging is done on a continuous basis, either daily or frequently, as opposed to a batch system where everything is enclosed and sealed. Notice the fill pipe at one end of the drawing and the overflow at the other end. The advantage of the limited and frequent introduction of new material is that the chemical balance of a plus pH is easier to maintain as well as a steady gas output. Cleanout is needed rarely if the manure is relatively free of sand and gravel. The digested material merely spills over past the baffles which provide a seal to prevent gas escaping or air entering the tank. If livestock are picking up a fair amount of inorganic material on their hooves, this can be a problem. Provision has been made by a bottom drain with a gate valve at the floor of the tank. The reason for the uneven floor of the fill basin shown on page 45 of #27 is to hold back most of the sand and gravel before it enters the tank. Hope this will help. - Al Rutan, The Methane Man Antenna Adventure Dear Home Power; About a year ago I began to build my own solar electric system with the intention of providing power for my amateur radio station and a few back up lights. The events of the last several years ( the Loma Prieta earthquake and Oakland fire ) here in the East Bay near Oakland and an interest in the technology of solar power definitely encouraged me. I began to acquire the needed components at some of our local bay area hamfests and to talk with people who were doing similar things This is how I found out about your wonderful magazine. One person whom I work with has an amateur repeater at 8,000 ft in the Sierra Nevada mountains that is solar powered and he suggested very strongly that I use a temperature compensated charge regulator to protect my gelled lead- acid batteries. I choose a SCI model 1 with the temperature compensation option, this regulator has worked well until just recently when an odd problem cropped up. One morning while working 10m SSB, running 90 watts into a 4 element yagi that is 35 ft high and located 25 ft away from the radio, I heard the charge relay drop out on the regulator and at 10:00 in the morning my batteries are definitely not charged. I reset the regulator by disconnecting the panels and keyed a carrier causing the relay to drop out. Further investigation showed that this would only occur if the beam was pointed towards the house, my station is in the garage, and that this would also occur using a dipole antenna but not with a trapped vertical I also have in the backyard. The match on the yagi is fair, 1.7:1 and on the dipole terrible, 3:1 and flat with the trapped vertical. All the radio equipment is grounded to a ground rod that is under the radio bench using 1 inch copper braid and the batteries are tied to the same ground point. I then tried various methods first of which was to relocate the coax to the yagi but to no avail. I then called SCI in Canoga Park and the factory suggested ferrites on all the power leadsÄbattery, panels and grounds, and capacitors between the positive and negative leads. After several hours of work I did the above, plus ran larger gauge wire for the battery and braid to the charger case. Then I noticed the temperature compensation sensor that is attached to a battery with a 10 ft long wire, close to a quarter wave length at 10 meters. I took a ferrite donut from an old switching power supply and then wrapped the sensor wire through it 6 times as near to the charge controller as possible, end of problem. Previous testing had shown that the ferrites on the regulators ground and hot leads hadn't been effective. After thinking about this for awhile I realized that the temperature sensor is a thermistor and that it must operate in the millivolt range making it very RFI sensitive. This SCI is a good regulator, I have only had one other problem that turned out not to be a problem but just a quirk not mentioned by the manual. Had there been a schematic provided, I may have figured the cure out sooner but SCI considers that to be proprietary. I'm a communications technician by trade and have been interested in electronics since I was a child and am definitely a tinkerer. Your magazine is something that I look forward to every 2 months. many environmentalists seem anti technology, while condemning they offer no viable options other than freeze in the dark. The people who write this magazine are not that way at all. They have an alternative and, rather than use empty rhetoric, demonstrate that it works and is worthy of consideration by the best of all methodsÄshowing it functions in practice. Tom Murphy ( ARS N6IHU), 15929 Via Alamitos, San Lorenzo, CA. 94580 RFI is sneaky. Good detective work, Tom. Many controls use voltage sensing, current sensing, and temperature sensing. In most cases there is a very sensitive OpAmp connected to a long set of wiresÄ perfect invitation to radio frequency interference. If you have wires longer than two feet, then make a twisted pair of the wires. Still use ferrite beads and capacitors (÷ 0.01æF). Bottom line is most designers of RE gear don't give enough consideration to either their units sensitivity to RFI, or worse yet, the amount of RFI their unit generates. Richard