Page 88 - Troubleshooting Analog Circuits

Assault and Battery 75

Figure 6.6. With a solar-cell array, you can make
electricity when the sun shines.
(Photo copyright Peggi Willis.)

teristics of each type (Refs. 5-10). I couldn’t possibly give batteries a full and fair
treatment here, but I will outline the basics of troubleshooting them.
First, always refer to the manufacturer’s data sheet for advice on which loads and
what charging cycles will yield optimal battery life. When you recharge a nickel-
cadmium battery, charge it with a constant current, not constant voltage. And be sure
that the poor little thing doesn’t heat up after it is nearly fully charged. Heat is the
enemy of batteries as it is for semiconductors. If you’re subjecting your battery to
deep-discharge cycles, refer to the data sheet or the manufacturer’s specifications and
usage manual for advice. Some authorities recommend that you do an occasional
deep discharge, all the way to zero; others say that when you do a deep discharge,
some cells in the battery discharge before the others and then get reversed, which is
not good for them. I cannot tell you who’s correct.
Sometimes a NiCad cell will short out. If this happens during a state of low charge,
the cell may stay shorted until you ZAP it with a brief burst of high current. I find
that discharging a 470 pF capacitor charged to 12 V into a battery does a good job of
opening up a shorted cell. If 470 pF doesn’t do it, I keep a 3800 pF to do the job.
When you recharge a lead-acid battery, charge it to a float voltage of 2.33 V per
cell. At elevated temperatures, you should decrease this float voltage by about 6
mV/”C; again, refer to the manufacturer’s recommendations. When a lead-acid bat-
tery is deeply discharged (below 1.8 V per cell), it should be recharged right away or
its longevity will suffer due to sulfation.
Be careful when you draw excessive current from a lead-acid battery; the good
strong ones can overheat or explode. Also be careful when charging them; beware
of the accumulation of hydrogen or other gases that are potentially dangerous or
explosive.
And, please dispose of all dead batteries in an environmentally sound way. Call
your local solid-waste-disposal agency for their advice on when and where to dispose
of batteries. Perhaps some can be recycled.