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Circuits designed by David Johnson, P.E.
Last Updated on:
Friday, March 12, 2010 12:08 PM
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Lead-acid Battery Low
Voltage Indicator
Lead-acid batteries should not be discharged below a certain voltage. Discharging a
cell below about 1.8v and can often damage it, which will result in a lower amp-hour
capacity. Large battery banks are critical in off-grid energy storage systems.
One bad cell in a series wired string will weaken the whole bank. The circuits below
are designed to be connected across either a single 2 volt cell or a 6v three cell battery
bank. It will alert the user of a weak cell by turning on a red LED when the cell
voltages drop below 1.8v. The circuit takes advantage of a low voltage LMP2231 op
amp from Nation Semiconductor and a LM385 voltage reference in the first circuit. In that
circuit the red LED must have a forward voltage of about 1.6v at 5ma, in order to operate
properly. In the second three cell bank circuit, a TLV3701 voltage comparator is
used. The circuits are simple enough that they could be placed on a postage stamp
size circuit board. |
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| 2v Lead-acid Cell |
6v Lead Acid Battery |
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Click on Drawing
Below to view PDF version of Schematic |
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Master Schematic
Category List -
David A. Johnson, P.E.
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