Supposed to automatic solar charge disconnect

Discussion in 'General Electronics Chat' started by mrel, Nov 22, 2014.

  1. mrel

    Thread Starter Active Member

    Jan 20, 2009
    97
    1
    Hello
    I found this solar charge circuit on the internet.
    It suppose to be when battery fully charge from the solar panel transistor BC548 will disconnect the LM317 from charge the battery.
    Has anybody build (test) this circuit does it work?
    Does anybody know where in this circuit can put an led to show battery no longer take a charge from the solar panel?
    Enclosed is schematic of the circuit mention in this thread.
    I posted as jpg file because i don't know how to post schematic drawing to thread.
    mrel
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    looks like it should work.
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    It is a circuit designed by a novice. It overcharges the battery by allowing the battery voltage to repetitively go to 6.8+0.65 = 7.45V, or 2.48Vpc, which is too high. A SLA should not go over 2.40Vpc (7.20V for three cells) at room temperature during intial charge-up. If the battery is already charged, the charger should revert to a float voltage of only 2.3Vpc, or 6.9V for a three cell battery. This charger would hit a charged battery with too high a voltage every day. (BatteryUniversity)

    The Voltage tolerance of a 6.8V Zener is +-10% if you buy a cheap one, so the overcharge could be even worse...

    A solar panel is intrinsically current limited, so a small solar charger like this one does not need current limiting as provided by R3. Since R3 is inside the voltage feedback loop to the '317, R3 makes the charger take three times longer to recharge the battery.

    All in all, I hate this circuit. Can you tell?
     
    Last edited: Nov 22, 2014
  4. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    3,554
    2,504
    Your circuit says "Transistor T1 and and zener diode ZD act as a cutoff switch when the battery is full. Normally T1 is off and battery gets charging current"
    If that works as it's supposed to, you could simply add the LED you want between the back of the zener diode and ground:

    Capture.JPG

    Edit: change the 1K resistor for a 470Ω one and the LED will burn brigher.
     
    Last edited: Nov 22, 2014
  5. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    3,554
    2,504
    On the other hand, Mike's right... If this is a school project, then this circuit will do the trick. But if it's for more serious applications, I'm afraid it's oversimplified and would probably damage your battery in the long term.
     
  6. mrel

    Thread Starter Active Member

    Jan 20, 2009
    97
    1
    Are you saying don't need r3 in the circuit?
    Since you say you hate this circuit ,Do have better circuits than this one and easy to put together?
    mrel
     
  7. mrel

    Thread Starter Active Member

    Jan 20, 2009
    97
    1
    instead putting led behind zener diode if put led at the output of the lm317 with resistor does make any sense or wrong place to put led.
     
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Gopher, the circuit you linked is a constant-current source. There is nothing to limit the battery voltage once the battery has reached the final charge voltage. It will dry the electolyte out of a sealed lead-acid battery. It is only useful for very occasionally "equalizing" a flooded lead acid battery with caps where the electrolyte can be replaced. Do not use this circuit on an SLA!
     
    GopherT likes this.
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,981
    3,710
    Quite right, trying to make it as simple as possible but failed by making it too simple. I deleted the post to avoid problems.
     
Loading...