first circuit. LDR and charger.

Discussion in 'The Projects Forum' started by Dentsu, Jul 29, 2011.

  1. Dentsu

    Thread Starter Member

    Jul 7, 2011
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    this is my first ever circuit and need some of your opinion and if you could double check if it will indeed work. the circuit is made of two part. one being the 9v nimh battery charger and the second is a simple photoresistor ciruit. i got the schematic from googling and i made some changes so wondering if it this will effectively charge my battery and do i need to add in safety feature like reverse charging and overcharge? i have taken a look at some LDR setup and most of them uses a transistor so wondering if it would be necessary on mine. new to electronic and multisim so appreciate any feedback. i posted the multisim file in case it is needed. :)

    input source is a DC 9V <1A
    battery is 9V 300-400 mAh. charge current at 50mAh so about 6-8hrs
    photoresistor need to go on when in low light

    infrared led being used
    LENS TYPE:WATER CLEAR
    REVERSE VOLTAGE:5.0 V
    DC FORWARD VOLTAGE:1.5-1.7V TYPICAL
    DC FORWARD CURRENT:20~30mA
    VIEWING ANGLE:+/- 15 deg
    LEAD SOLDERING TEMP:260oC for 5 second
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    T1, D1 and C1 are OK.

    The regulator is not able to regulate anything, as there is no real current path from Vout to ADJ, which is how it determines the amount of current needed from Vout to keep Vref at 1.25v (nominal). Then, the current path from ADJ to GND is via R5 and the base-emitter junction of Q1.

    I don't know what you are doing with Q2 or Q1, because they are not really able to do anything purposeful.

    XMM2 has its' leads shorted, so it won't measure anything.
    X3, the 12v 10W lamp, is too much of a load for the battery you want to use.

    I guess R2 is supposed to be your LDR? It should be controlling a transistor's base or MOSFET's gate instead of supplying current to the LEDs directly.

    Why don't you post a link to the original project/schematic that you found?
     
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  3. Dentsu

    Thread Starter Member

    Jul 7, 2011
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    the original one uses a ic7805 but have been replace with a LM317AH due to not being available in multisim. the rest of the component and setting should be correct.
    [​IMG]

    forgot to mention that the load(X3) will be a device that uses 9v/200mAh.

    the goal is that it need to be simple and reliable using those cheap component i have outline in my first post. updated schematic attached.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    The LM317 is not a substitute for the 7805 in this circuit; they are different regulators.
     
  5. Dentsu

    Thread Starter Member

    Jul 7, 2011
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    thanks sgt. ill stick with the 7805 then and i see that its max output is 5v and my battery is a 9v so will that be a problem?
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    The charger puts out a limited current, but the charge voltage is only limited by the power supply's output voltage - so you would need a way to stop the charging.
     
  7. Dentsu

    Thread Starter Member

    Jul 7, 2011
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    how would you go about putting a charging cap thingy? i have a limited budget. anything for under $2? also can you use the power directly while it is being charge? if not then i guess it would be a matter of relocating my LDR?
     
  8. iONic

    AAC Fanatic!

    Nov 16, 2007
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    If you charge the 9V battery at about 1/10 of the rated battery capacity then end of charge circuitry might not be necessary.

    Example:
    The cheapest way to charge a nickel metal hydride battery is to charge at C/10 or below (10% of the rated capacity per hour). So a 400 mAH battery would be charged at 40 mA for 15 hours. This method does not require an end-of-charge sensor and ensures a full charge. Modern cells have an oxygen recycling catalyst which prevents damage to the battery on overcharge, but this recycling cannot keep up if the charge rate is over C/10. The minimum voltage you need to get a full charge varies with temperature--at least 1.41 volts per cell at 20 degrees C. Even though continued charging at C/10 does not cause venting, it does warm the battery slightly. To preserve battery life the best practice is to use a timer to prevent overcharging to continue past 13 to 15 hours.

    You will need aprox. 9.6V across the battery to charge it fully and haven't a clue how a 7805 can do this as 5V will not charge a 9V battery.
     
    Last edited: Aug 17, 2011
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  9. Dentsu

    Thread Starter Member

    Jul 7, 2011
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    maybe i am missing something but woundn't a 400mAh battery charged in 10hr on a 40mA and is it possible to use two 7805 together and have them output 10V?
     
  10. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Nope, 15hrs. is the recommended time.
    With two 7805's you will have twice the dropout voltage and a LM317 would serve you better as far as a linear regulator solution.
     
    Last edited: Aug 17, 2011
  11. Dentsu

    Thread Starter Member

    Jul 7, 2011
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    thanks for sticking around and helping a newbie like me and if anyone have any suggestion do share. i just uploaded a update HERE and hope the gate is what i am looking for to get it running from two source. what is needed in order to replace the 7805 with a 317 in my circuit? :confused:

     
  12. iONic

    AAC Fanatic!

    Nov 16, 2007
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    All I can say that without doing all the math you are getting very close to not having a sufficient charging voltage for the 9V battery. You will need just short of 10V for fully charging the 9V battery. A 15V supply would be better.
     
  13. Dentsu

    Thread Starter Member

    Jul 7, 2011
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    i found this while googling and seem more appropriate for what i want and skill level. i made some adjustment to the original. the x1 would be the 400mAh 9v battery. i have to work around a 12v source until i know how to use a transformer or something similar. my budget for the charger is <$10 USD and have already bought some part already. hoping to finish this soon with your help.
     
  14. Chygoz

    New Member

    Apr 27, 2011
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    Why not use 7812 regulator instead? It should provide 12v output which is sufficient to charge the battery.
     
  15. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Because with a 12V supply you can't regulate to 12V with a 7812. You will need 2V or more for the regulator to actually do it's job. Plus, 12V on a 9V battery will be too much without any end of charge detection.
     
  16. Chygoz

    New Member

    Apr 27, 2011
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    Thanks for the info. I didn't know that. Then 7810 regulator should do then.
     
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  17. iONic

    AAC Fanatic!

    Nov 16, 2007
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    It might. It would be close. Ideally a regulator with a lower Drop Out Voltage would work the best.
     
  18. Dentsu

    Thread Starter Member

    Jul 7, 2011
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    do i just replace my lm317 on my charger or on the simple charger diagram? i can not seem to find any 7810 nimh charger on google. getting more difficult by the day now. any other option given my scenario?
     
  19. iONic

    AAC Fanatic!

    Nov 16, 2007
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    You seem to have redefined your project somewhat. What is your goal. Do you want to charge a 9V battery or do you want to run a 9V bulb with a 9V battery?
     
  20. Dentsu

    Thread Starter Member

    Jul 7, 2011
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    the goal is still the same and in both schematic i know i have used a light bulb but their is no light bulb that i want to lit. so i see where it can get confusing. ill try to be clearer with my schematic next time. so again i need to charge and use a 9v battery (400mAh) with a 12V (2.1/5.5mm) source. the x1 bulb in the "simple 9v charger picture" is the 9v battery.
     
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