Charge Ahead Since I am a new subscriber, I'm not sure if you've already talked about this or not... But here goes, I'm living in a trailer that is powered by two Solarex MSX 64 watt modules, a Bobier 8 Amp controller (with a bypass toggle switch), Equus digital volt meter and two 135 Amp/hr group 27 12 volt deep cycle batteries. My question is - can I use a high voltage (16.0 V)35 Amp Todd battery charger in conjunction with my 650W generator, to charge up my batteries fast. My understanding is that if I monitor the voltmeter and wait for the system to reach its terminal voltage and shut down, then it will not harm the batteries and will also save gas and time because the 16.0 volt charger does not have the same tendency to taper off, when the battery approaches full charge, as do the lower voltage chargers... Please elucidate. Sincerely, Kathy Compagno, POB 903, Redway, CA 95560 Hi, Kathy. You can use the Todd charger. In fact, its design is best suited for operation from your small generator. If you monitor the voltage as you mentioned, then no harm will come if you shut off the charger at around 14.5 to 15.0 VDC depending on battery temperature. You will get the fastest recharge possible and thereby reduce your generator's operating time. However, if you space out the charger and let it "cook" the batteries at over 15 VDC, then you can damage 12 Volt appliances that may be on line during the recharge period. While lead-acid cells love a good equalizing charge (and this can go up to over 16 VDC at a C/20 charge rate if the cells are cold), they don't like chronic overcharging at high current rates. The 35 Amp Todd will put over a C/10 rate into your particular battery. This is OK for a fast recharge, but when the battery is almost full (state of charge greater than 85%), this rate is too high. For equalization and/or recharging above 15 VDC consider a C/20 rate to be the maximum. Richard Grid Use How about using the "grid" as a battery? Sell power to the grid during week days, when not at home, so no AC or heating. At nights and weekends, buy it back. Power companies currently see residential customers as a burden and businesses as their most profitable arena. This would turn the tables and make residential customers a "source" instead of a "sink" and create an atmosphere of cooperation where energy efficiency becomes a plus in their corporate reports. John and Pam MacDonald, RR1 Box 133 CC Connor Sta. Rd., Finchville, KY 40022 You bet! Actually the US Federal Government passed a law known as the Public Utilities Regulatory Policies Act of 1979 (PURPA, for short). This act states that public utilities must buy power from individuals if the power comes from a renewable source of energy. The government says the utility must buy our RE sourced power, but it doesn't say that the utility has to make this deal easy or profitable for us. For example, the utility is required to pay you only its "avoided generating cost" for the power you sell them. This means between 1.5¢ to 3.5¢ per kWh. The hook-up and licensing procedure commonly takes several years and at least one hundred pounds of paperwork. In spite of these warts, more and more folks are putting renewable energy back into the utility grid. The current best prospects for a PURPA system are sourced by hydro, the bigger the better. Also large wind systems. Right now, PV electricity is too expensive to sell back to the power companies and still make a profit. If the price of PV modules can come down in price by a factor of three, then we are looking at America's favorite form of roofing. PV-based PURPA systems will be as common as lawns. Richard Retirement Dear Home Power; My seven year old 980 amp-hr lead-acid battery bank is clearly showing its age. Can you offer a rule of thumb to help decide when to replace old batteries? Any discussion and description you could give concerning the heartbreak of aging batteries would be welcome. Keep up the good work! Dan Reeve, RFD2 Box 347, Belfast, ME 04915 Well, Dan, deciding when the ole' batts are done is hard. In my case, I've ridden them until I had an out-and-out cell failure (either open or short), then the decision is obvious. If the battery is still working, then an ampere-hour meter. like the new Cruising Equip. models, will give you an idea of the efficiency of the aged cells. This is really the main issue in battery replacement. New cells are around 85% efficient. As deep cycle, lead-acid cells age, their self-discharge rate increases radically from about 5% self-discharge per week when new, to over 25% per week when old. If you battery is not storing enough power to get you through the dark days of winter, then its time for a replacement. The common band-aid used on aging batteries is running the generator for frequent recharges. In our experience, this wastes gas, does the batteries no good, and wears out the generator to boot. Seven years is about the age when most lead-acid batteries begin to show diminished capacity, increased self-discharge, and decreased efficiency. Richard DC to DC Dear Home Power Crew; As a family living completely off the grid we have always looked forward to your excellent magazine. Also, we have a technical problem that we hope you can be of some help with. Our 6 Arco 40-watt modules have to be located about 400 ft. from our house due to exposure. Obviously we need to wire our panels in series in order to transmit the power that far. Question; How do we transform high voltage DC to low voltage DC (12-15 V)? We are having a very hard time answering this question and would much appreciate your help as we are tired of moving our batteries back and forth in the wheel barrow! Thank you for your time and trouble and for your excellent magazine! Bill C. Gomes, 5184 Sauk Valley Rd., Concrete, WA 98237 „ 206-853-7553 There are several ways of running the PV array at higher voltages than the battery. You have discovered one obvious reasonŠ voltage loss. You can use a Bobier LCB20 in conjunction with a Bobier ECM-1, see HP#25, page 16 for a technical article describing this type of system. Or you can use a Todd charger as described in this issue, page 34. And there are more "switching" power supplies, called Maximum Power Point Trackers (MPPTs) on the horizon. Richard Earth Tube Dear Home Power; I'm interested in an "earth tube" or a "cool tube" to help regulate the temperature of my home. If you or any of your readers have information about them, please write Jim Rosen, Rt 5, Box 494, Malvern, AR 72104, or call 501-623-2050. I will be happy to pay for the call. Hello, Jim, it sounds like you are talking about a ground coupled heat pump. These devices work like a regular heat pump, but instead of using ambient air, they draw either heat or cold from the earth. The ground coupling pipes can be buried horizontally at a depth of ten to fifteen feet. Or the pipes can be vertical and sunk down a drilled "well". Since the interior temperature of the ground is constant at around 55” F, the ground coupled heat pump has access to heat in the winter and cold in the summer. Other "passive" schemes such as heat pipes and phase change materials are also used to couple a home thermally to the ground. I have no hard data on the more exotic schemes, but I do know that the ground coupled heat pumps work well in very severe climates. Richard Big & Little I would like to find out how to hook up multiple size battery groups to be all charged at the same time - it seems the smaller unit charges up way faster than the larger unit. Mr. & Mrs. J.W. Sebranke, 4305 212th S.E., Bothell, WA 98021 Charging dissimilar cells is alway very vague. As you have discovered, the smaller capacity cells fill first and then the larger ones. In general, this does the cells no harm. It does, however, overcharge the smaller cells if they are routinely cycled with larger capacity cells. If you are doing this, then make sure that the system has tight voltage regulation to prevent overcharging. See my article on Battery diagnostics, page 36 in this issue for particular voltage regulation points for lead-acid and nicad cells. Richard Natural Gas Vehicles Dear HP; Recently I wrote you concerning literature on methane generation and natural gas vehicles. I have a correction to make about the American Gas Association's 'Natural Gas Vehicle' newsletter. The newsletter is available free to local or state government agencies or local school districts. Requests for subscriptions must come from the agency or school. Write: A.G.A. Membership Services, 1515 Wilson Blvd., Arlington, VA 22209 „ 703-841-8400 I hope you are able to provide this information to your readers. Thank you. Sincerely, L. J. Aurbach, 2811 McGill Terr. NW, Washington, DC 20008 Stirling Opportunities I am interested in methane generation and other bio-mass fuels. I'd like to connect with any local people who'd be interested in a methane project. Also, if anyone's interested in Stirling Cycle engines or refrigerators, I have worked in the field and I'd be glad to share my experience with local folks. Kelpie Wilson, POB 1444, Cave Junction, OR 97523