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DiscoverCircuits.com -- Hobby Corner
Last Updated on:
Tuesday, June 01, 2021 03:06 PM
Hobby Circuits List
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12v Battery Load Cutout Circuit
-- August 23, 2009 |
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Lead-acid batteries should not be
discharged below a certain point if they are to last. Also, you don’t want
certain 12v powered devices, which might be plugged into a car’s cigarette lighter
outlet, to drain the car battery down to a point where the car’s engine will not
start. To prevent battery damage or a dead battery, the circuit below
disconnects a load from the battery when the voltage dips below a fixed but
adjustable voltage and will not reconnect the load until a reset button is pressed.
To keep the whole circuit efficient and compact, a medium current rated p-channel
FET forms the power switch. |
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| A 8.2v zener diode forms the voltage
reference while a second 15v zener diode acts as a transient voltage protector.
This hobby circuit uses one half of a popular LM393
dual voltage comparator to monitor the battery voltage and the adjustable reference
voltage. If the battery voltage drops below the adjusted level, the comparator
changes state. One half of a popular CD4013 dual flip/flop latches the on/off
condition. A reset button must be pressed to reestablish power to the external
load.
A rather long 5 second time constant filter is used
in the voltage comparator circuit. This allows the circuit to ride out the dip
in battery voltage, which always takes place when the car’s engine is started. |
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Click on Circuit Below to view PDF of Schematic |
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eMail David A.
Johnson, P.E. about this circuit |
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