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Battery Deep discharge protection Cut Off Circuit

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krishg1974

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Referring to old thread https://www.edaboard.com/threads/209214/
In KAK's circuit, if the charger is on, the relay will not be energised whatever the battery voltage because the collector of Q2, and therefore the base of Q3, will be at 0V.

The circuit below will energise the relay if the charger is on, or the battery voltage is greater than about 19.3


deepdischargeshut-off.gif

Thanks for providing this circuit, I tried this with 12V battery and 8V zener. Everything seems good till the battery voltage reaches 9.4 V. The relay starts chattering heavily. I put one capacitor(50mfd) parallel to relay coil, though heavy chatter came down still the contacts chatter a bit before complete disconnection. Same haappens with heavy load only that, the last minute chatter in little less time compared to the normal load for which I want this protection circuit.
Please advice some solution.
 
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FvM

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That's expectable behaviour of a cut-off circuit without hysteresis. If the battery is disconnected, the voltage will immediately rise again due to it's internal resistance, cause reconnection and so on.

The circuit isn't well considered, I suggest to review battery cut-off circuits suggested in the similar threads first.
 

KlausST

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Hi,

about the circuit:
As long as the relay is ON, it will draw current. This decreases lifetime of the battery. I´d rather use a MOSFET circuit.
But surely it depends on your application.

Klaus
 

krishg1974

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That's expectable behaviour of a cut-off circuit without hysteresis. If the battery is disconnected, the voltage will immediately rise again due to it's internal resistance, cause reconnection and so on.

The circuit isn't well considered, I suggest to review battery cut-off circuits suggested in the similar threads first.

Thanks for your quick reply on this. You are right it is due the gain in voltage of the battery, so reduce this chatter I used 470mfd in parallel to the coil and another 470mfd from base of Q3 to ground. This helped in reducing the chatter to almost zero, only that if the load is less battery gains the voltage and the on/off continues for longer time, if load is high the on/off happens for a shorter time and then complete disconnect.

Could you please help me in adding hysteresis to this circuit. Any sample or idea would be great.

Thanks
 

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