Dedulfator

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, sinceI don’t have all the answers. Thanks. Alastair Couper kalepa@shaka.com http://shaka.com/~kalepa/desulf.htm

Homebrew

Lead-Acid Battery Desulfator
Alastair Couper

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.

Homebrew

©2000 Alastair Couper

I initially went to the Internet tofind any available information on the problem of sulfation. The search 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 server (www.patents.ibm.com). I found relevant patents there, using keywords like “desulfate” and “rejuvenate.” What this wealth of data shows is that there are numerousstrategies 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 a century, this is a relatively new innovation. Virtually all of the devices and patents I found have in common the use of some form of pulsing charge current. This is in contrast to the constantor slowly varying currents generated by sources like solar-electric panels. I distilled and simplified these various techniques, and came up with a basic circuit that will keep small to medium sized batteries in desulfated condition. It can even be used to bring old, sulfated units back into service. Use of the circuit has dramatically reduced the need for equalization charges in my own homesystem. Resonant Frequency The technique used in this circuit relies on a little known aspect of lead-acid batteries. They possess what is called a “resonant frequency,” at a surprisingly high frequency. The frequency is dependent on various physical details of the battery’s construction, but it is on the order of 2 to 6 megahertz, which is in the low ranges of the shortwave radio bands. Figure 1: 12Volt Battery Desulfator

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t was twenty years ago that I left my on-grid home, and my job as an electronics engineer, to begin life on an alternative energy oriented organic farm. In the intervening years, I have installed, maintained, and experimented with numerous RE systems in my area. What I have come to understand from this experience is that off-grid life tends to become very muchfocused on the battery bank and its fate.
All power sources and loads breathe through this crucial pathway. Batteries are heavy, toxic, inefficient, and—to the amazement of many—electrically very fragile. Weak or failing batteries are a very likely cause of breakdown, especially in smaller solar-electric systems. Most newcomers to renewable energy are quite familiar with using water tanks or gastanks, and naturally use this familiarity in trying to understand their battery 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. 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 minimumdaily 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...