Troubleshoot auto cut-off battery charger circuit

Discussion in 'The Projects Forum' started by Faareast Mk, Aug 20, 2015.

  1. Faareast Mk

    Thread Starter New Member

    Aug 20, 2015
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    i have built exactly the same circuit based on this video on youtube

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    the circuit and components are as follows: [​IMG]

    the problem is, as soon as i turn on the power supply, it will trigger the relay therefore the power will be cut off. no charging happened and the light will be turned on.

    i used 19V psu with 4.5amp.

    attached here are my project pictures:
    [​IMG] [​IMG]
    https://www.facebook.com/faareast/posts/1001765233226932?pnref=story
    the video will be uploaded soon..

    pardon me for bad grammar. but please kindly help me in this project
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Your posts don't work.
    Use the "Upload a file" button at the bottom of the posting window.
     
  3. Faareast Mk

    Thread Starter New Member

    Aug 20, 2015
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    ok.. will do
     
  4. Faareast Mk

    Thread Starter New Member

    Aug 20, 2015
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    this is the components used and the project pictures cutoff_zps097889d1.png
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    As soon as the input voltage gets to 14.1v or above the relay will click on, reverse the change over contacts, so the charger gives out the dc, and when it gets below 14V input the relay drops out.
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    PS: I just went and looked at the circuit again, and it is totally wrong in concept! It is measuring the voltage of the input power supply; not the voltage of the battery! Whoever put that on the internet is an idiot! I'm my opinion, 90% of the DIY electronics on YouTube and Instructables is garbage.


    Do you have a 12V Lead-acid battery in the circuit when testing it. If not, the relay will pull-in instantly when power is first applied.

    Measure the initial (precharging) battery voltage. If the battery has been sitting around, it should be between 12.0V and 12.6V. The idea is to charge the battery until its terminal voltage comes up to ~14.2V to 14.4V, and then the relay is supposed to pull-in, disconnecting the charger from the battery. Ideally, the circuit might automatically drop-out the relay when the battery voltage sags below ~13.0V, restarting the charging cycle.

    This circuit is poorly designed, obviously created by a naive newbie; it has no hysteresis except as provided by the mechanical properties of the relay itself, so the relay will quite rapidly cycle from on to off near the initial trip point voltage.
     
    Last edited: Aug 20, 2015
  7. Faareast Mk

    Thread Starter New Member

    Aug 20, 2015
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    the battey i used to charge has 6.6V left.. is it to low?
     
  8. Faareast Mk

    Thread Starter New Member

    Aug 20, 2015
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    what do you mean by "reverse the change over contacts"? swap the NC and NO terminals on relay?
     
  9. Faareast Mk

    Thread Starter New Member

    Aug 20, 2015
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    yea, there is battery attached.. 6.6V left..

    btw, did u have better but easy circuit for me? maybe i can try it
     
  10. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    A 12V SLA that has been discharged all the way to 6.6V is likely junk at this point, and needs to be replaced. During normal cyclic use, a 12V SLA should never be discharged below 11.5V!

    Re-read post #6.
     
  11. Faareast Mk

    Thread Starter New Member

    Aug 20, 2015
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    i have another 3 lead acid battery laying around.. cant i revive this battery?

    btw, would you guide or give me the link on another better solution on charging a 12v battery (diff capacity).. this is my preparation for flood season.. need to set up my portable amateur radio station..
     
  12. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    The design has no hysteresis, so it cant give a clean switch off, you can reverse the n.o and n.c contacts to make it work, but it won't monitor the battery voltage ⚡.
     
  13. Faareast Mk

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    Aug 20, 2015
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  14. MikeML

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    Oct 2, 2009
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    Read this forum thread. It deals more with maintenance of occasionally-used batteries, rather than rapid recharging.

    For occasional rapid recharging of storage and automotive starting batteries, I use an old HP rack-mounted linear power supply that has independent voltage and current settings. I set the short-circuit supply current to ~10A. I set the open-circuit supply voltage to 14.5V, and then connect the supply to the battery.

    Initially, the supply goes into current-limiting, putting out the preset 10A. As the battery voltage increases to near 14.5V, the supply goes into voltage-limited mode, and keeps the voltage constant at 14.5V as the battery current slowly decreases from 10A to a few hundreds of mA.

    It would not be good to leave the supply connected to the battery indefinately beyond a few hours after the current tapers. To "float" charge the battery after the initial recharging, the supply voltage must be turned down to <13.5V, which can be left connected for long periods. This will prevent the battery from self-discharging, just sitting around waiting for the next "emergency".

    Note that the process I described above is the "three state lead-acid battery charging algorithm" described at Battery University. Modern commercial battery chargers implement it using an inexpensive microcontroller like a PIC or Atmega.
     
    Last edited: Aug 20, 2015
  15. Faareast Mk

    Thread Starter New Member

    Aug 20, 2015
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    the float charge circuit u posted, can it charge let say from 9-10V left? wouldn't it will overdraw current? what i understand (im newbies), float charger suitable for maintaining the charge, not recharge? or am i wrong?
     
  16. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    In that posting, I rely on the intrinsic current-limiting built-into a wall-wart (plug-in) transformer to limit the initial current in-rush when the charger is first connected to a discharged battery. The current-limiting is essential to protect the transformer (not the battery). A regulated power supply (like your 19V SMPS) may or may-not blowup due to being overloaded by the initial high battery current.

    Even a one-state 1A float charger will recharge a mostly discharged LA battery; it is just that it will take ten to twenty times longer than a fancy three-stage high-current charger can do it. The electro-chemistry works the same either way.
     
  17. Faareast Mk

    Thread Starter New Member

    Aug 20, 2015
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    ok tq for your kind replies... will do some reading again.. i dont have electric or electronics background.. but kinda need this thing for my hobby
     
  18. ian field

    Distinguished Member

    Oct 27, 2012
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    Yuasa battery Co published a "Little red book" on battery charging, with a few sample circuits among the pages.

    To summarise; a sulphated battery should be charged with a voltage limit of about 29V and current limited to 1/3 of the Ah capacity of the battery. As the sulphation is displaced, the battery will start to draw charging current and pull the voltage down. When it gets down to 10.8V the charger should switch to constant voltage charging - I forget the exact voltage as it varies with battery technology within lead acid type.

    Chargers like the Optimate have a pulse charging mode at about 30 ish volts for sulphation, they bulk charge at about 14.4V, then cut back to float charge at about 13.6V - this is for minimum need to keep topping up the electrolyte over long float charge.
     
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