Desulfator

Battery Desulfator Errata

In my battery desulfator article on page 84 of HP77, the value for C2

should have been 0.0022 мF, not 0.022 мF. 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

84 Home Power #77 * June / July 2000

Homebrew

Lead-Acid

Battery

Desulfator

Alastair Couper ©2000 Alastair Couper

It 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 much focused 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 gas tanks, 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 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

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.

I initially went to the Internet to find 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

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

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 constant or 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 home system.

Resonant Frequency

The technique used in this circuit relies on a little known

aspect of lead-acid batteries. They possess what is