This file is raw output from pdftotext and may not be ideal for distribution. If you are a maintainer for Hackipedia, please sit down when you have time and clean this text version up. Source PDF: /mnt/fw-js/docs/Hardware/Electronics/Homebrew/Lead-Acid Battery Desulfator, Alastair Couper.pdf Like all conversions the text below should be fully readable as UTF-8 unicode text. --------------------------------------------------------------- Battery Desulfator Errata In my battery desulfator article on page 84 of HP77, the value for C2 should have been 0.0022 µF, not 0.022 µF. My mistake. I have put up a Web page that will give more details to help you build and use the desulfator circuit. I will place updates there, and will add a guestbook soon to allow comments and questions to be posted. I encourage a group effort in this, since I don’t have all the answers. Thanks. Alastair Couper kalepa@shaka.com http://shaka.com/~kalepa/desulf.htm Homebrew Lead-Acid is an energy-wasting tactic. It ultimately results in clean battery plates, but at a steep price, especially if the energy must come from a generator. Battery Homebrew I initially went to the Internet to find any available information on the problem of sulfation. The search Desulfator engines turned up several commercial sites that give useful details on the fine points of battery charging and equalization. A second resource is the IBM patent Alastair Couper ©2000 Alastair Couper server (www.patents.ibm.com). I found relevant patents there, using keywords like “desulfate” and “rejuvenate.” t was twenty years ago that I left my I on-grid home, and my job as an electronics engineer, to begin life on an alternative energy oriented organic What this wealth of data shows is that there are numerous strategies for charging and electrically desulfating batteries. Most of them were designed or developed in the last twenty years or so. Considering that lead-acid batteries have been around for more than farm. In the intervening years, I have a century, this is a relatively new innovation. Virtually all of the devices and patents I found have in common the installed, maintained, and experimented use of some form of pulsing charge current. This is in with numerous RE systems in my area. contrast to the constant or slowly varying currents What I have come to understand from generated by sources like solar-electric panels. this experience is that off-grid life tends I distilled and simplified these various techniques, and came up with a basic circuit that will keep small to to become very much focused on the medium sized batteries in desulfated condition. It can battery bank and its fate. even be used to bring old, sulfated units back into service. Use of the circuit has dramatically reduced the All power sources and loads breathe through this need for equalization charges in my own home system. crucial pathway. Batteries are heavy, toxic, inefficient, and—to the amazement of many—electrically very Resonant Frequency fragile. Weak or failing batteries are a very likely cause The technique used in this circuit relies on a little known of breakdown, especially in smaller solar-electric aspect of lead-acid batteries. They possess what is systems. called a “resonant frequency,” at a surprisingly high frequency. The frequency is dependent on various Most newcomers to renewable energy are quite familiar physical details of the battery’s construction, but it is on with using water tanks or gas tanks, and naturally use the order of 2 to 6 megahertz, which is in the low this familiarity in trying to understand their battery ranges of the shortwave radio bands. banks. Everyone knows that a bigger water tank is better than a small one. Unfortunately, batteries are not like tanks, and the result is trouble. Figure 1: 12 Volt Battery Desulfator It is definitely not true that a big battery bank is necessarily better than a small one. An oversized battery bank can be almost impossible to charge properly. Without a minimum daily exercise regimen, it can become the equivalent of a couch potato. The main culprit is sulfation, which is a gradual crystallization of the battery’s plate material, rendering it electrically inactive. Some Theory Past issues of Home Power (see Access) have gone into the details of keeping lead-acid batteries healthy, so I will only touch on the main points here. The usual practice in maintaining a battery in good condition is to apply a periodic equalization charge over and above what would be a normal full charge. Unfortunately, this 84 Home Power #77 • June / July 2000 Homebrew Figure 2: 24 Volt Battery Desulfator When Q1 is in the non-conducting state, current is drawn from the battery through L2 so that capacitor C4 can be charged slowly. Then Q1 is turned on for a brief 50 microseconds, causing the charge stored in C4 to start flowing through L1. When Q1 is turned off again, the stored inductive energy in L1 has to continue to flow somewhere, so it pulses back into the battery through diode D1. This current pulse can get as high as 6 amps. The use of an inductor to supply this pulse is what makes it possible to restore badly sulfated batteries with a high internal resistance. The peak voltage drop across the battery can initially be as high as 50 volts. With continued treatment, this peak voltage will decrease as the battery’s internal resistance gradually declines. This resonance is just like that of a stringed musical Figure 2 shows the version for use in 24 volt systems. instrument, where a pluck of the string creates a Its only additional feature is the use of a 79L12 voltage vibration of a specific tone. In the case of the battery, regulator (component U2, Digi-Key part number sulfur ions dissolved in the electrolyte take the place of NJM79L12A-nd) to convert the 555’s input voltage the string. A sufficiently energetic electrical “pluck,” or down to 12 volts. Also L3 (Digi-Key part number pulse, will cause a similar vibration of these ions, back DN4518-nd) is increased in value over L1 in the 12 volt and forth throughout the electrolyte. unit, to compensate for the higher terminal voltage. When this vibrational state is occurring, there are uncountable Lead-Acid Battery Desulfator Parts List collisions between the ions in the electrolyte and the battery plates, Item Component Description Cost (US$) as the back and forth vibration Q1 IRF9Z34 P channel MOSFET 1.82 continues. It is this rhythmic beating U1 LM555CN Timer IC 0.42 of the plates which causes the U2** 79L12 12 V regulator 0.36 breakup of the crystalline deposits, D1 GI826CT Fast recovery diode, >6 A, 100 V 0.77 slowly but surely, for as long as the electrical pulsations are applied. C1 30 µF, 16 V Electrolytic 0.23 C2 0.022 µF Disk ceramic 0.38 It is not unlike sandblasting a rough C3 0.047 µF Disk ceramic 0.54 surface, but on a micro-physical level. This is an advantage of C4* 100 µF, 16 V Electrolytic, low impedance type 0.44 electrical methods over the use of C5** 10 µF, 35 V Electrolytic 0.23 chemicals like EDTA. Rather than C6** 100 µF, 35 V Electrolytic 0.49 dissolving the sulfate deposit and R1 470 kΩ 1/4 W 0.15 allowing it to settle on the bottom of R2 22 kΩ 1/4 W 0.15 each cell, as with EDTA, the pulse R3* 330 Ω 1/4 W 0.15 technique returns the sulfate back into solution again. R4 330 Ω 1/4 W 0.15 R5** 1 kΩ 1/4 W 0.15 Circuit Details L1* 220 µH (nominal) Ferrite inductor, 6+ A peak 2.08 The circuit is in essence a very widely used form of switching DC- L2 1000 µH Ferrite choke, 100 mA 3.12 to-DC convertor, which can take a L3** 330 µH Ferrite inductor, 6+ A peak 2.08 DC voltage and step it up to a Case Aluminum project box 5.44 higher level. Figure 1 shows the Clip leads Alligator type, insulated (RS) 1.00 version which is specifically for 12 Board material 0.1" spaced copper pads 3.00 volt systems. The basic pulse rate is set by the venerable 555 timer Total for 12 V Unit $19.84 * For 12 V unit only. chip, U1, which switches the Total for 24 V Unit ** For 24 V unit only. $20.48 MOSFET Q1 at a 1 kHz rate. Home Power #77 • June / July 2000 85 Homebrew If an oscilloscope is available, it is easy to observe the into account the circuit’s behavior at different ringing wave form across the battery terminals. It is frequencies.) likely that more than one frequency will be apparent, One way to keep the external equipment from shunting due to all the wiring and other details of the setup. It away the current pulse would be to take some ferrite should be possible to see a small spark jump from the toroid cores and slip them over the battery leads as leads of the pulse generator as it is connected, a result they leave the bank. This will increase the high of the high peak voltage available (keep this in mind if frequency impedance without affecting the DC your batteries are not well ventilated). Depending on performance of the circuitry. the case, and the type of inductors used for L1 and L2, a faint audio tone can also be heard when the circuit is The circuit as shown, with its approximately 6 amp peak operating. Digi-Key part number DN4516-nd will work capacity, is probably strong enough to maintain a bank for L1, and DN7437-nd will work for L2. of several hundred amp-hours. If you want to use the circuit with larger banks, it will be necessary to select There is no reverse polarity protection in this circuit, so D1, L1, and L2 for higher current capacity. You will also make sure that the leads are clearly marked. A mistake need to vary the pulse width from the 555 accordingly, will result in damaged components. Also, it is not a so that Q1 is allowed to stay on for a longer period of good idea to expose the 12 volt circuit to more than 16 each cycle. If you want to power the circuit from an volts at the terminals. auxiliary voltage source, so that the battery being See the parts table for a detailed component list. But treated remains trickle charged, simply remove R3 and don’t get too attached to using exactly these place 12 volts across C1. components, or to buying new stuff. The homebrew It’s best to construct the unit in a shielded case. ethic is based on an ability to make do, come up with Otherwise it is likely to generate a fair bit of radio alternatives, and recycle. My first trial units had quite a interference. The use of the shortest possible lead bit that was clipped out of old junk circuit boards. length is also a good idea. All the components are Usage available from any general electronics distributor. Radio It should be emphasized that pulsing energy to and Shack is as good a place as any for getting the case, from the battery happens at less than 100 percent clip leads, circuit board, and other components. efficiency. This circuit draws about 40 mA from the Does It Work? battery while in operation (less than 1 amp-hour per If badly sulfated batteries are treated, it is convenient to day), so some additional charging source is needed. use a trickle charger of one or two amps. In this case, For reconditioning a sulfated battery, I simply clip the the simplest way to see that the circuit is having an circuit across the battery terminals in parallel with a 30 effect is to note that the terminal voltage actually drops watt solar panel. each day as the batteries slowly charge. This is a result In my initial testing, it took a month to partially reclaim a of the internal resistance of the cells decreasing as the pair of golf cart batteries that had been allowed to sit, plates become slowly cleared of the sulfate, and more discharged, for almost a year. They had such a high useful plate area comes in contact with the electrolyte. internal resistance that a very small current would take Also, the specific gravity of the cells begins to rise the terminal voltage over 16 volts. slowly, evidence that the sulfate is going back into solution. For use in a functioning power system, you can clip the circuit across the main battery terminals, using as short To further check the progress, you could do a discharge a lead length as possible. When external equipment, test, using a known load, to determine the useful such as an inverter, is connected across a battery bank, capacity. This would involve measuring the length of then additional low impedance paths are formed. The time taken by the load to drop the battery voltage from desulfator’s current pulses will happily flow down these a high level to a low level. If you repeat this test, a paths as well, and it serves no purpose for the pulses to gradual lengthening of this interval should be noted. flow into the inverter. In one system I worked with, at first the batteries would I had initially thought that this shunting, or dilution, of not power even a small load. After treatment, they were the current pulses away from the battery would be a able to run loads in the neighborhood of 5–10 amps for problem. This has not proven to be the case, however, a few hours. This is far from “like new” condition, but it because the impedance of typical inverters at was sufficient for them to be returned to use in the small frequencies above 1 megahertz is not very low. (Note: PV system they were taken from. I expect that further impedance is just a fancy word for resistance, taking treatment would have helped. It seems that the process 86 Home Power #77 • June / July 2000 Homebrew is inherently slow. Lead sulfate is just not very willing to Mouser Electronics, 11433 Woodside Ave., Santee, CA return into solution. 92071 • 800-346-6873 or 619-449-2300 Fax: 619-562-8796 • sales@mouser.com Healthy Batteries www.mouser.com I have used this circuit in my main system for over a year, and have not seen the need to equalize in that Radio Shack, 100 Throckmorton St., Fort Worth, TX time (I do not own a generator). All of the cells’ 96102 • 800-843-7422 • 817-415-3011 electrolyte levels remain in step with each other, and Fax: 817-415-3240 • support@tandy.com there has been no problem with starting big loads—a www.radioshack.com sure sign of battery health. Patience is required in Web sites of interest: reclaiming weak and tired batteries, and no amount of www.batterybes.com • www.innovativeenergy.com desulfating will help a battery with a shorted cell, or one that has lost plate material through excessive use. Home Power articles: Batteries: How to Keep Them Alive for Years and The device is especially useful for automotive batteries Years…, by Windy Dankoff, HP69, page 46. that sit for long periods. If you use a generator for equalization, this technique is a must. When you live Batteries: What We Know About Them; How to Use off-grid, silence is golden. Them, by John Wiles, HP58, page 66. Access Preliminary Notes from the EDTA Trenches, by Stan Author: Alastair Couper, Kaupo, Maui, HI 96713 Krute, HP 21, page 36. kalepa@shaka.com New Life for Sulphated Lead-Acid Cells, by Richard Suppliers: Perez, HP20, page 23. Digi-Key, PO Box 677, Thief River Falls, MN 56701-0677 • 800-DIGIKEY or 218-681-6674 Fax: 218-681-3380 • sales@digikey.com www.digikey.com Home Power #77 • June / July 2000 87