Circuit that disconnects an over discharged battery from the load

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edaenrico

Member level 4
Hi,

I need some help

CIRCUIT
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I got a Power Supply (+14 Volt) , a Battery (+12 Volt) and a Circuit

The power supply feeds the circuit and charges the battery

When the AC fails, the circuit is supplied by the battery.

PROBLEM
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When the battery goes below 7 Volts my circuit goes crazy.

QUESTION
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Are there any RELIABLE solutions that switch off the circuit when the battery goes below 7 Volts?

Thanks,
Enrico Migliore

Tahmid

Use a MOSFET as a switch that turns the load on/off. Use an opamp/comparator to detect the battery voltage. When battery voltage ≧ 7V, the opamp/comparator keeps the MOSFET on and load is run from battery. When battery voltage falls below 7V, opamp/comparator shuts off the MOSFET to shut off the load. Add some hysteresis so that the load isn't turned on until battery voltage reaches (for example) 8V.

Hope this helps.
Tahmid.

Ogu Reginald

Full Member level 6
Use an op amp as a comparator. In the inverting input make a reference voltage of 7V and on the non inverting input feed in the voltage of the battery so that when the battery fall below 7V the output of the op amp will be zero. Then you can use a transistor to switch ON and OFF a relay which can knock OFF th circuit as desired.

- - - Updated - - -

Use a MOSFET as a switch that turns the load on/off. Use an opamp/comparator to detect the battery voltage. When battery voltage ≧ 7V, the opamp/comparator keeps the MOSFET on and load is run from battery. When battery voltage falls below 7V, opamp/comparator shuts off the MOSFET to shut off the load. Add some hysteresis so that the load isn't turned on until battery voltage reaches (for example) 8V.

Hope this helps.
Tahmid.

The hysteresis you mean, is it by adding a feedback resistor? If yes, that is also advisable thank you.

Super Moderator
Staff member
Just for the fun of it I constructed a simulation showing how an op amp can work with hysteresis, using one resistor at the non-inverting input.

Screenshot:

mailus

Full Member level 4
Please mention your battery type. If your battery is leadacid battery means it doesn't fall below 10.5 volts.for every low voltage below 10.5V it reduces the battery life.

Ogu Reginald

Full Member level 6
Please mention your battery type. If your battery is leadacid battery means it doesn't fall below 10.5 volts.for every low voltage below 10.5V it reduces the battery life.

This is another good point worthy of note.

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