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Voltage Threshold Sensing Relay

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holabr

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I need a circuit that will close a relay (to sound an alarm) when the voltage in a 24 volt battery (2 - 12 volts in series) drops to a predetermined voltage. I'd like to be able to adjust the threshold voltage. I also plan to add a timing circuit to sound the alarm for a defined period of time. This is to remind me to plug in a battery charger on a handicap wheelchair that doesn't get used very often. The manufacturer recommends not leaving it on charge but only recharge when the voltage drops at least 1/4 full charge. Any ideas or examples to start me down the road?
 

Key words to start with:- :idea:

12V DC Relay
Resistor Divider Network
OpAmp Comparator Circuit
555 Pulse Generator Circuit
Buzzer
Transistor as a Switch circuit to drive the buzzer and relay
 

See attached a very simple voltage trigger alarm using TL431.

You may add a timer module using for example the CD4060 circuit, to trigger the alarm in short beeps, followed by an adjustable stop time period and circuit restarting automatically over a period of time to keep monitoring as a remainder for charging the batteries.
 

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