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Battery under voltage protection circuit

Discussion in 'Power Electronics' started by canactech, Mar 11, 2013.

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  1. canactech

    canactech

    38
    2
    Jul 7, 2009
    I have a problem with a mobil unit that is feed by a 12V/200A AGM battery plugged on an inverter. To protect the battery when the charger is active I've installed a relay that cuts the power to the inverter. But now I should install a protection circuit that will cut the power to the inverter when the battery reach 12V and reconnects the circuit when the battery is charged at around 13.5V.

    I've found this circuit on Internet but I need to replace the switch by a circuit that will restart the system at 13.5V. low-voltage-cutout-for-12v-sla-batteries-2.jpg
    I also want to know if its better to replace the LM358 op amp by a LM339 quad comparator because I've read that a comparator is more stable than an op amp. if yes can I install the comparator directly (with respect to the pins) or if I should modify the circuit?

    Thank you.

    Canactech
     
  2. Electrobrains

    Electrobrains

    259
    6
    Jan 2, 2012
    Hello Canactech
    Just a couple of questions and comments:
    1. How much DC current does your load (the inverter) draw (maximum)?
    2. The circuit diagram you show must be a bit old. There are much more efficient MOSFETs than MTP3055 around now.
    3. If you base your control unit on the suggested circuit diagram or a changed version thereof, you should not change the IC. The OP-Amp (LM358) is already working as a comparator!
    4. I did not calculate on your circuit, but it might well be that you could adjust the hysteresis to fit your 12V and 13.5V limits. Probably by manipulating the feed-back resistor (the 10k from the OP-Amp output) and the 22k at the transistor base.
    5. Also, you might need to filter the circuit a bit more, so that it doesn't start oscillating if you switch a high current load.
    6. The unused inputs of LM358 should be fixed.
     
    Last edited: Mar 11, 2013
  3. canactech

    canactech

    38
    2
    Jul 7, 2009
    Thak you Electrobrains for your answer.
    The inverter is actually controlled by a relay that cut the power to the inverter when the charger is plugged. The relay need 169mA to be activated and it's that element that the circuit will control.

    As you can see I don't need a strong circuit. So if you have any circuit to suggest me I will apreciate it. The circuit should be simple and activate the relay when the tension of the battery fall to around 12V, and release the relay when the tension reach 13.5V. I plan to put it in a "Black Box" so the users cannot play with it.

    Back to the circuit on my previous e-mail, I've choose this circuit because that's the one who seem to be the closer to my needs. Actually I'm just looking for a protection circuit and, after I will see if it's possible modify the circuit.

    Thanks again for your help.

    Canactech
     
  4. Electrobrains

    Electrobrains

    259
    6
    Jan 2, 2012
    Try the circuit you found!
    It's simple and cheap and you sure can put it together on a bread board within an hour.
     
  5. Prashant mahi

    Prashant mahi

    1
    0
    Jan 23, 2015
    Dear Sir,
    i got the design form internet site. i am working on a 50W Inverter design. for low battery cut off i am using the below design.
    but the circuit does not switch off the mosfet...can you please help me.


    Regards
    Prashant mahi



    upload_2015-1-23_13-1-45.png
     
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