Regulator Charger, Current Limiter and undervoltage cut out.

Discussion in 'The Projects Forum' started by RodneyB, Nov 9, 2014.

  1. RodneyB

    Thread Starter Well-Known Member

    Apr 28, 2012
    I am wanting to try and make my regulator charger a more suitable unit.

    The input can go as high as 34 volts and I want a regulated 13.8 Volt 1 Amp output to charge the battery. I have the regulator working ok but want to Add 1 Amp current limiting. Also what I don't understand is if the voltage drops to say 18 Volts will the output on the regulator still be 13.8 Volts?

    What Can I do to limit the current to 1Amp. I know the LM317 will cut out if the Amperage exceeds 1.5 Amps. However if the battery is very flat it will try to draw more than 1 Amp.

    To protect the battery I would like to add a circuit that will switch out the load at 10.6 volts and only switch it back on when the battery starts to charge again , I have included a fixed 12 Volt 1 Amp output.

    Any help will be greatly appreciated.
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    You have a problem there. If you apply 13.8V to an uncharged battery it will try to draw >1A. To make it draw only 1A you have to reduce the applied voltage.
    It should be. That's what voltage regulators are for ;).
    Reduce the voltage.
    Is this the load you want to disconnect? If not, when the battery voltage is only 10.6V the regulator output will be less than 10.6V.

    Edit: BTW, you're pushing the 1N400x diodes right to their 1A rated limt. Better to use higher-current types.
    Last edited: Nov 9, 2014
  3. RodneyB

    Thread Starter Well-Known Member

    Apr 28, 2012
    Thanks for the advice. I will Change the diodes to 2 Amp diodes. Silly oversight on my behalf :eek:

    The regulator charges the battery, I want the load to cut out at 10.6 Volts because I believe this is the maximum Depth of Discharge for a 12 Volt battery. Sometimes I run a very basic LED light that just keeps drawing until the battery is down to 2 Volts. Then the battery is totally useless.

    If I was to Put a LM317 T on the output of the 13.8 Volt side as a current regulator would that make sure that the current into the battery does not exceed 1 Amp. I have had a battery swell and nearly explode because it didn't control the current
  4. Lestraveled

    Well-Known Member

    May 19, 2014
    On page 18 of the attached data sheet is a schematic of a 1 amp current regulator. Put this circuit in series with the output and the battery. It will prevent the output current from exceeding 1 Amp.
    RodneyB likes this.
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
    RodneyB likes this.