Letters Home Power DC Fluorescent Life This is to correct data reported in my article "Efficient Lighting for the Independent Powered Home" in HP #9. The comparison chart shows "Lamp Lifetime" data based of fluorescent tubes used on conventional ac power. Long-term tests made at Sandia National Laboratories show that tubes used with DC ballasts have only 40-50% of normal life expectancies. A DC ballast is a sort of miniature inverter that feeds the tube ac power, but at a much higher frequency than the usual 60 cycles per second. This shortens the life of the tube (although it also eliminates perceptible flicker that bothers many people). We wish to be technically correct, not to discourage use of DC fluorescents! The tubes are the least expensive part of a DC fluorescent fixture and still have life expectancies exceeding 4000 hours. Windy Dankoff, Flowlight Solar Power Active Solar Thermal Systems In response to the "Saving Energy Saves Money" article in Home Power #10 I would like to come to the defense of active solar systems. Passive systems are not the only means to consider for domestic hot water heating. The primary concern with any solar thermal DHW or space heating system is that of freezing. Of course geographical location is the determining factor in freezing. While there are many quality passive systems being manufactured there are many instances where a passive system would not be best suited. For example, a combination DHW, space heating, and spa heating. Typically solar contractors have a preferred system, that has proven itself reliable, for their part of the country for a given application. This system may be passive or active. In the 14 years Heliotrope General has been in business manufacturing solar differential temperature thermostats we have produced easily over 100,000 controls. Many original controls are still operating and we continue to see new systems being installed. Our current controls are backed by a 10 year warranty and we have a documented failure rate of only 1 in 1500 controls. There are many design considerations for solar hot water heating and active systems have proven themselves to be very viable and certainly workable method of solar thermal hot water heating. If any Home Power readers have questions regarding solar heating I will gladly be of assistance. You may write me at 3733 Kenora Drive, Spring Valley, CA 92077 or call (800) 552-8838 in CA or (800) 854-2674 outside CA. Sincerely, Mark Albert, Heliotrope General Flowers Seems Great. Advertising appearing in HP would seem to benefit everyone... provides sources not available elsewhere. Nitty-gritty writing gets my vote, hands on experience shared with others are a big plus. Keep up the good work. Joseph Petrarca, Marshfield, VT Thanks, Joseph. The appreciation of our readers keeps us going. We try to provide needed information that can be easily used. Neither Karen nor I have ever published a magazine before. Home Power has developed a life of its own and led us places we never knew existed. Sometimes when we're real tired, or things aren't going well, we read through the incoming mail. It's the love and energy in your letters that make HP happen. RP Students Cook with Solar Dear Home Power, I teach in a private school for students with learning difficulties. I was asked to construct solar cookers in my art classes as part of a science project. The idea of putting together solar cookers seemed like a great way to expand design and construction skills. I wanted my students to have a basic background or history of the solar cooker. It was also important to make a connection with its practical uses. I remembered reading an issue of HP (7) which featured solar cookers. What I found was clear, brief and in a language my class could understand. The photos provided a stepping off point from the basic design we would be using. I felt it was important to let you folks at HP know that not only are your magazine articles great for answering energy questions but have also helped a few students understand there are alternatives for their future. As a person who values the future of our planet. I thank you for helping to raise the collective consciousness. Donna Lanen, Princeton Junction, NJ Butane Powered Iron Works! Just wanted to pass on the good word on a wonderful product for alternative living. I purchased the butane iron that Real Goods had advertised in #8 issue. It is so far and away better than 12VDC travel/retrofit "waste of money" and "1000 watt sucker" which required a noisy generator I had before. This gas iron is quiet and HEATS up quickly. It is also easy to turn off and back on again, and I believe I am using less energy because I tended to let the generator run rather than cycle the energy hog up and down. A great bonus is its cordless-ness. Freedom of movement as well as being light weight too. The only difficulties I had in using it was learning to be "firm" when filling it from the canisters, and when it wouldn't fire-up once. The Real Goods people helped me locate the c-clip that had worked free in shipping and got the iron back in working order without my having to return it. They are great to do business with too. I have passed on to Real Goods the source of my 12VDC washing machine and I hope they will be able to offer it in their catalog soon. I have been using mine for over 4 years and it's as good an alternative as the gas iron. It's also a big water saver. Thanks Home Power for the reference to Real Goods and thanks Real Goods for supplying me something REAL GOOD! Katcha Sanderson, Paicines, CA Watermellon Power! Your magazine came to my attention at Arizona State University Solar Library. I am a watermelon geneticist and here in southern Florida there is an abundance of highly fermentable vegetable matter (thousands of acres of culled tomatoes etc.) available for energy production. For several years I have been interested in solar distillation of watermelons, since (in Texas particularly) thousands of acres are plowed up each year due to low price for melons. This is a cheap crop to grow, producing many tons per acre and a crushed melon is 95% juice @ 10-12% sugar. Fuel alcohol would be welcome on melon farms to run irrigation pumps. Also I am building a house intended to be solar cooled and powered. Wind is probably out due to hurricanes and building restrictions. Also water purification as swamp water has lots of Fe and H2S. You will be hearing from people in this area. Thanks for the magazine. Nichols Eigsti, 10290 Greenway Rd., Naples, FL 33961 Hydrogen Detection in Battery Areas Preliminary info on a HYDROGEN GAS DETECTOR for alternate energy battery systems, Chestec, Inc. POB 10362, Santa Ana, CA 92711, 1-714-730-9405, speak to Al. Charging batteries in a home power environment often involves a battery room that is WITHIN THE HOUSE (usually the basement). This tends to minimize radical temperature swings, which are not healthy for battery maintenance. However, there is the danger of hydrogen (and oxygen) gas buildup during the charging procedure. In a well-ventilated outdoor installation this presents minimal hazard; indoors, a random spark (eg, from static electricity) can cause a catastrophic explosion. If on top of that, the home is a vapor-barrier enclosed, super- insulated structure, the danger is compounded. Thus, I've been looking for a way to detect the gases, so that a exhaust fan can be triggered in a timely fashion. It appears, after years of searching, I've found a unit that doesn't cost more than the battery system itself. It's made by Chestec and is their model #CBHRB-12v. It will apparently work for 24 volts also. It goes for about $50 plus shipping. Make sure to ask for the model with a relay output (in addition to the standard sounder output), so that you can remote it or turn on a fan, etc. A problem for alternate energy user is that it requires the use of a small heating element; that brings the current drain up to 130 mils standby (and 150 on alarm). I plan to get around that one by providing it with a PULSED power source, so that it checks things out maybe every 6 hours or so; each time it's turned on it must stay on for about 2 minutes, in order for the heater to reach steady-state and do a valid check. A timer based on a multiple 555/CMOS version should do the trick. And/or the duty cycle of the detector could be tied to the photovoltaic charge controller so that it is turned on only during that part of the charging process that will cause gassing. I'll report on how the unit works out and what timing circuits are needed with it. William Schenker MD, Zillah, WA Efficient 12 VDC Light Dimmer First I want to express my deep appreciation for the noble work represented by Home Power. Not only are you learning to live in harmony with the Earth, you labor long and hard to pass your education on to your fellow men. I am sure I am only one among many who extend to you and your crew our true admiration. Enclosed is the spec sheet on the 12 volt dimmer I designed for reading lamps aboard my 63' ferro-cement ketch, Bandersnatch. The basic lamp is a very nice oak swivel bullet lamp sold by JC Whitney for RV use. They come in solid oak and other woods, in various configurations and appear to be made in California. If I remember right, they sell for about $13, but I don't have the catalog with me. I removed the pushbutton that comes on them and replaced it with the dimmer. The Radio Shack pot is a little too deep to fit into the base of the lamp without using a Forstner bit to deepen the recess. The Philmore pot is much smaller and fits without modifying the lamp. The NE555 timer produces a square wave output turning the FET on and off. The pot varies the "on" time of the FET by varying the "on" pulse width of the square wave. This varies the average current through the bulb and thus the power. Since the FET is either completely off or completely on there is little friction to the electricity to cause heat and therefore the FET runs cool and wastes very little of our precious electricity. The life of electronic equipment is also directly related to its operating temperature, as I am sure you are aware of. The dimmer works nicely but I have not had it long enough to give it a real "life test", nor have I used it for anything but the little bullet lamps. I think it would work well for motors too (fans, etc.), but have not tried it out on them yet. I know you use Macs but can you support editorial submissions on IBM 5" format too? Sure would make life easier for SOMEONE at Home Power. I have a Sanyo MBC-775 transportable I bought on sale from C.O.M.B. for $900 that I like very much. It has a standard footprint but a low profile, 2 360K drives, an 8" color CRT and only uses 80 watts according to specs. Unfortunately it requires voltages above 12VDC so I will have to run it with an inverter. I have a Panasonic KX-1080i printer I am very satisfied with. My personal correspondents have all applauded my switch from handwriting to word processing (PC-Write). Using different colored ribbons, varying the fonts as I write and always using NLQ or better (ImagePrint) softens the harshness of plain vanilla output. However, I still use pen and ink for my most intimate communications even though I compose it first on the word processor. I am working toward self-sufficiency aboard Bandersnatch and will keep you posted on any significant developments that others may be able to take advantage of. A fellow traveler, Norman, S/V Bandersnatch, Green Cove Springs, FL P.S. I was in a waterfront dive one night a few weeks ago and received a lesson in assumptions. While watching the lizards stalk various unidentified prey along the overhead I was astonished by a light fixture. There were several incandescent fixtures and one fluorescent fixture, the whole group controlled by one dimmer. Lo and behold the fluorescent bulbs were dimmed right along with the incandescents, and quite effectively too. So much for my "conventional wisdom". (Doesn't it say on every 120vac dimmer package "For incandescent lamps only!"?) I just ASSUMED they knew what they were talking about. Maybe you could find out more about this development. Get the Power Co. to go PV? I would be interested to hear from Home Power readers about the idea of getting state utility regulation boards to force utilities to subsidize and finance auxiliary PV systems by allowing purchasers to pay them off through their electric bills. The Philadelphia Electric Company is owner of one of the last nuclear power plants in the nation under construction. They say they need it because of peak summer power demand. But I suspect that a few thousand PV systems all over the city would take the edge off that demand quite nicely. We must remind the power companies that they are state-sanctioned monopolies serving at OUR pleasure -- even if they seldom act like it. Does this concept sound familiar to HP readers in other states? Are similar notions making progress anywhere? Please print my address: Noel Weyrich, Box 42044, Philadelphia, PA 19101. Thanks! A recently developed electronic gadget to appear on the market is a motion sensor light control. Called a passive infrared detector by burglar alarm people, Taiwanese manufacturing has now brought the price down to around $20 for homeowner installation. Basically it detects movement of heat-emitting bodies by means of a special lens and infrared electronics. They come with floodlight sockets for security lighting, but can be used to turn on other devices. Some models can be connected to operate on 12VDC such as the Heath-Zenith SL 5410A. The similar 5310 does NOT - it seems to need both 9V and 24VDC. I would guess similar units WITH internal transformer (such as 5410A) are likely to be 12V. The transformerless models are very lightweight, you can tell by heft. If you'd rather not try converting, Real Goods sells a 12V model for $68. You could also wire one up for an indoor light - enter a room, the lights come on, leave and they go off automatically. One thing, large dogs will trip the lights the same as a human, cats are detected but only at close range. Here's one way to convert the Heath-Zenith SL 5410A to 12V operation: Open the cabinet by removing 4 long sheet metal Phillips-head screws in the corners. They are tight, keep a firm steady pressure to avoid stripping the heads. Carefully separate the halves. Note there is a molded rubber gasket - make sure this stays in its groove. The detector half plugs into the power supply half via a 3-pin plug. Set the detector half aside where the pins won't get bent. Lift off the rectangular cover and remove the power supply board via 2 Phillips screw. With a soldering iron and solder-sucker, desolder the 2 primary and 2 secondary pins on the transformer, also the mounting tabs. If you don't have experience soldering the new thin copper Taiwan circuit boards, have an experienced technician do it. They are VERY easy to ruin. By removing the transformer, you separate the relay contacts from the power supply (so you could switch a different voltage or circuit). The Red and Black wires are now a Normally Open switch circuit which is already internally fused for 4 amps. Connect 2 wires to the holes where the 12V secondary went (The side with most of the electronic parts. They lead to a small black circular device with 4 pins.) The White wire is not used and can be cut off. The 2 wires you added are now your 12VDC supply to the detector. They are on the ac side of a bridge rectifier (the black thing) so EITHER polarity will work without damage. Be aware the electrolytics are 16VDC rated, so this unit should be on a circuit that is disconnected when you are equalizing your battery. I've run it from 11.8V to 15V with no problem or change in sensitivity. The idle current is a miniscule 5 milliamp. This increases to 65 ma (plus whatever you have it turn on) when the relay energizes. Follow the set-up instructions with your unit. The 5410A can see a person walking 50 to 70 feet away in a pie- shaped arc of 100¡. It seems to be impossible to sneak up on it. S. Marshall, Dover-Foxcraft, ME Keep PVs Decentralized! Wouldn't you know it? I've read every issue of Home Power, one through ten -- cover to cover, including ads -- but what motivates me to write, finally is a gripe. In "Photovoltaics - The Alternative to Life in a Greenhouse", Gary Starr wrote that "a piece of desert land about 2 miles square could host a solar generating plant with the power production capacities of a large nuclear or coal plant." The greatest beauty of solar power is its availability at (or very close to) the point of use. The sun shines almost everywhere that power is needed; why pay a utility to ship you some sunshine from hundreds of mile away over unsightly and environmentally damaging powerlines? Four square miles of PV's is obviously better than a large coal or (especially) nuclear plant, but it is an absurdity compared to dispersed PV's at points of use. Let's not do anything to encourage centralized power generation of any sort. It is true that PV's can beat fossil fuel and nuclear plants at their own game, but so what? It's a game we shouldn't be playing. I designed my retirement home (which I'm still working on) to be passive solar and it works even better than I imagined. The county required me to get a propane wall furnace, not accepting a woodstove as an adequate back- up to solar, but I haven't installed the furnace yet and used the stove more for cheer than warmth. An aspect of passive solar that I haven't seen much reference to is heat gain from the earth under the slab. Without any auxiliary heat, it kept the air temperature at 45¡ when it was minus 10 outside in February. Since the house shell was finished and insulated, it has never gotten below 50¡ inside except when it was sub-zero outside. If I had put insulation between the earth and slab, presumably the slab would have warmed faster and cooled faster, with greater daily temperature swings. But I think it makes better sense to recruit the entire earth to "try to keep my house no colder than 50-something in winter and no better than 50-something in summer. Photovoltaics are fascinating, but let's not overlook the benefits of direct solar heat gain. So much for opinionated opinion. Now for a question. When I can save enough from Social Security payments and part time work, I plan to have a modest electrical system with batteries, inverter and PV panels. (I wired the house conventionally before I was aware of the 12 volt option.) My "need" for electricity is urgent only because of music. I have a fine hi-fi system, but have had to rely on a portable radio powered by three AA nicads, which I recharge with solar chargers. The best that can be said is that the sound is reminiscent of music. My question is, can I enjoy my hi-fi equipment before my utlimate solar electric system is in place? Would it be practical, for example, to get batteries and inverter ahead of the rest and recharge the batteries with the 4 KW generator I already have? This would depend, I suppose, on how often the battery(ies?) would need to be recharged with only the hi-fi system as a load. I probably average six or more hours a day listening to KSOR (the local PBS station). Frequent recharging would pose problems. My "portable" generator isn't very and I use it mostly at the wellhead nearly 300 feet from the house. But if batteries would only need recharging every week or so, I wouldn't mind the inconvenience. I would also need to consider how long the generator would have to run to recharge the batteries. It is used almost entirely, up to now, to pump water from a 400 foot well. To repair or replace the generator is an expense I can ill afford, so I must minimize its use. Thanks for the enlightenment and encouragement you freely provide. It's a service you're entitled to take great pride in. Hugh Nash, 7021 Quarry Rd., Weed, CA 96094