How to build a battery tester, including wiring schematic, calibration, monitoring, list of materials, lamp interpretation figure, parts layout
by TJ Byers
May/June 1982
Add to My MSN

Content Tools

Related Content

Folks who depend on battery power for their daily needs obviously have more than a passing interest in the state of charge of their storage banks. And although that level can be checked with a hydrometer, doing so is a time-consuming, messy chore. Fortunately, there's an alternative that will make the burdensome task less of a bother.

As battery charge drops, so does battery voltage. In fact, voltage can provide an accurate gauge for evaluating battery condition. Fig. A shows a curve of voltage, plotted against the percentage of charge, for a 12-volt battery. But rather than asking you to consult the graph and a voltmeter whenever you want to check your system, we've wrapped the whole procedure ( plus some fringe benefits) into a neat little electronic package.

MOTHER'S Battery Monitor is essentially nothing more than a very easy-to-read voltmeter. The voltage of the battery being tested is indicated by one of ten LED's (light-emitting diodes). The scale of the readout is arranged so that each of the consecutive lamps represents 1/2 volt. The first indicates a charge of 10.5 volts, the second 11.0, the third 11.5 ... and so on up to 15.0 volts.

The lights are switched on and off by an integrated circuit (designated LM3914), which is actually a large collection of transistors in one package. In addition, the lights are color coded to indicate the urgency of the situation. Lamps between 12.0 and 14.5 are green, while the 11.0 and 11.5 items are yellow, and the 10.5 light is red . . . indicating that the battery is almost entirely discharged.

At the other end of the scale, the 15.0 is also red . . . since excessive charge voltage can cause a battery to boil. (This situation might occur if the temperature control in your voltage regulator goes haywire.)

Finally, to be sure you'll be warned of a potential disaster, both the lowest and the highest readings are hooked to a piercing alarm. Whenever voltage drops too low or soars too high, integrated circuit 2 (known as 4011 CMOS) will call for help.

The monitor has been designed for easy assembly, and all the parts are readily available (for under $20) at Radio Shack outlets or similar electronics stores. You can either prepare your own circuit board, or purchase one, ready made, from the source included in the List of Materials.

Post a comment below.


Subscribe Today - Pay Now & Save 66% Off the Cover Price

First Name: *
Last Name: *
Address: *
City: *
State/Province: *
Zip/Postal Code:*
(* indicates a required item)
Canadian subs: 1 year, (includes postage & GST). Foreign subs: 1 year, . U.S. funds.
Canadian Subscribers - Click Here
Non US and Canadian Subscribers - Click Here

Lighten the Strain on the Earth and Your Budget

MOTHER EARTH NEWS is the guide to living — as one reader stated — “with little money and abundant happiness.” Every issue is an invaluable guide to leading a more sustainable life, covering ideas from fighting rising energy costs and protecting the environment to avoiding unnecessary spending on processed food. You’ll find tips for slashing heating bills; growing fresh, natural produce at home; and more. MOTHER EARTH NEWS helps you cut costs without sacrificing modern luxuries.

At MOTHER EARTH NEWS, we are dedicated to conserving our planet’s natural resources while helping you conserve your financial resources. That’s why we want you to save money and trees by subscribing through our earth-friendly automatic renewal savings plan. By paying with a credit card, you save an additional $5 and get 6 issues of MOTHER EARTH NEWS for only $12.00 (USA only).

You may also use the Bill Me option and pay $17.00 for 6 issues.