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Last Updated on: Thursday, November 30, 2017 07:43 AM

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Single Lead-Acid Cell Voltage Monitor,  July 7, 2012
Designed by David Johnson

The circuit below uses a a low voltage reference and a voltage comparator from National Semiconductor to monitor the battery voltage.  The green LED is controlled by a tiny charge pump type voltage converter IC from Texas Instruments.  This device efficiently converts the 1.8v from the battery into 3.3 volts.  A dual Schmitt trigger inverter IC, also from Texas Instruments, was used to latch the normal and low battery states and a Honeywell Hall switch was used as reset switch.  A small magnet held to the side of the plastic module holding all the parts would unlatch the alarm condition.  When everything was working properly, a bright green LED light would turn on.  If the battery voltage were to drop below 1.8v, the green light would switch to red and stay in that mode, until reset with a magnet.  The complete system was housed in a small plastic box, less than a cubic inch in size.  Epoxy was used to encapsulate the circuit components.

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DC Magazine, 3rd Quarter, Page 7:  Single Lead-Acid Cell Voltage Monitor


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