is this a good charger ?????

Discussion in 'General Electronics Chat' started by green90, Oct 6, 2015.

  1. green90

    Thread Starter New Member

    Sep 3, 2015
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    why use second transistor ?? can i remove it and connect 100k resistor direct to first transistor ??
    relay also is open now and separate main to cct ????? Battery-charge-controller-circuit-using-lm3241.png
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Looks like a naive circuit created by a newbie, that is missing a lot of stuff.

    Where does the battery connect?

    I see it only sensing its own internal voltage? and then shutting itself off? What restarts it for another cycle?

    What exactly are you trying to do? Might be able to provide a better circuit.
     
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  3. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    It doesn't appear to be much use as it can never be powered up, which is probably a good thing.
     
  4. green90

    Thread Starter New Member

    Sep 3, 2015
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    battery connect to pin 1 and 2
     
  5. Lestraveled

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    May 19, 2014
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    I went to circuitsgallery and found the project. http://www.circuitsgallery.com/2014/01/battery-charge-controller-circuit.html

    What is not shown is the battery is connected to the output of the power supply through a 8.2 ohm resistor. The battery supplies power to the circuit when the relay is off.

    There is a video that shows it working.

    questions:
    Is this a good charger? In my opinion it is not. You will be replacing that relay often. The concept is OK, but how it works is a poor way to do it.
     
  6. MikeML

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    It is still a stupid circuit. If the 230V gets unplugged, it will discharge the 12V automotive battery it is supposed to charge in a couple of days.
    The second BC548 creates hysteresis, so that the cut-in voltage is lower than the cut-out voltage.
     
  7. ian field

    Distinguished Member

    Oct 27, 2012
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    Auto shut-off charge sensors aren't completely rare - but there's usually a push button in parallel with the relay contacts to initialise it.

    Normally the switching would be on the secondary side, or the push button has to be a more expensive safety rated mains type.
     
  8. Lestraveled

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    May 19, 2014
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    It doesn't appear that this circuit needs a push button to initialize the charge. The threshold of the comparator is changed based on the on or off state. The charger will automatically cycle without being "started".

    My biggest complaint with this circuit is the mechanical relay. It is not a good choice as far as reliability and price. A solid state relay would have made this circuit more likeable. And, I have to admit I am starting to like this circuit a little more. If a S.S. relay was used and the turn off threshold was set to 14.5 volts at least it would complete the "bulk" charge phase of a three phase charger. That would much better than the discount charger you buy in Wally world.
     
  9. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Lets see from the beginning. The relay contacts are open, therefore the relay coil has no power, therefore the transformer has no power, therefore nothing happens ever.
    You need a switch across the relay contacts to get things going.
     
  10. Lestraveled

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    kubeek, read post #5. The battery powers the circuit when the relay is off.
     
  11. kubeek

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    A dead battery powers a relay? And it is connected to the output and the negative input of the opamp?
    Something is amiss here...
     
  12. Lestraveled

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    kubeek, the battery is not connected to the relay, it is connected to the power supply output.
     
  13. kubeek

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    Sep 20, 2005
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    Oh sorry, mixed up posts 4 and 5 and didn´t read yours.
    Well either way it is a really bad circuit and we should be discussing why you wouldn´t call this a good charger circuit.
     
  14. Lestraveled

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    OK, why would you call this a bad charger?
     
  15. kubeek

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    No charging current limit might be a good start. No way to turn it on with small Ah batteries dischargerd way close to the recommended discharge level might be another one.
    Turning on an unknown relay with a 100mA BC548, no flyback diode there...
     
  16. MikeML

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    Hook a mostly-discharged big battery to it, and you will smoke the transformer or rectifiers.

    The 1000uf capacitor does nothing.

    As I said earlier, if it gets unplugged from the AC line, it kills the battery.
     
  17. Lestraveled

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    No charging current limit might be a good start. / Hook a mostly-discharged big battery to it, and you will smoke the transformer or rectifiers.
    - There is a 8.2 ohm resistor in series with the battery. That is not bad current limiting.

    It won't start with a dead battery
    - agreed

    if it gets unplugged from the AC line, it kills the battery
    - agreed

    These are some valid and not so valid points. All could be remedied fairly easily.

    What I think is special about this charger is that it draws zero current when the battery is not charging. If the current limiting resistor were to be replaced with a switching regulator, this charger would easily meet the efficiency requirements coming into force in the near future. The concept that once the battery is charged, the charger turns itself off (from the mains) and stays alive from the battery until the battery needs refreshing again, is an excellent idea.
     
  18. InspectorGadget

    Active Member

    Nov 5, 2010
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    Sorry, but it just seems silly to beat this weird, dysfunctional circuit to death when you could make a simple constant current/constant voltage charger out of an LM317, including a passive final float charge phase. Add an MCU and you can control the 2nd phase/3rd phase switchover with exacting current monitoring. It would be much more reliable being entirely solid state, and much safer with inherent current limiting.
     
  19. Lestraveled

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    Inspector, I agree, this is a crap circuit, full of bad designs. What I find very cool is that it shuts itself off when it is not charging. It is this concept that I find innovative. California is in the process of passing laws on the efficiency of battery chargers. They are also going after energy vampires, (devices that still draw current when in the off state.) This concept perfectly conforms to those kinds of laws.

    It is a crappy circuit but it is also a great idea. Don't get caught up in the nuts and bolts to the point where you refuse to see a bigger picture.
     
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  20. InspectorGadget

    Active Member

    Nov 5, 2010
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    Good point, Les, but you could add auto-shutoff to any circuit with a couple of components.
     
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