Simple and cheap NiCd charger

Discussion in 'The Projects Forum' started by spencer_manzon, Oct 20, 2011.

  1. spencer_manzon

    Thread Starter New Member

    Dec 26, 2010
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    hello :D

    is there any way to build a charger to charge a 12v 1.5AH battery?

    i have a 24vdc @ 0.417A ac/dc adapter and a 12vac @ 0.4A adapter.



    please and thank you :)
     
  2. #12

    Expert

    Nov 30, 2010
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  3. wayneh

    Expert

    Sep 9, 2010
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    Always good advice there, but the OP asked for simple and cheap. He didn't mention "accurate" or optimal. Depending on the details of his adapter, it might in fact be ideal for the simple and cheap criteria. A strategy taking a nominal 12v battery to 12v, as you noted, doesn't give a full charge, but it's close and unlikely to overcharge. That may be good enough. On the other hand, his adapter might be 12v at rated current and more like 16v or so at open circuit. Devil in the details.
     
  4. k7elp60

    Senior Member

    Nov 4, 2008
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    I assume that the battery is 10 cells so the maximum voltage for charging would be 10 x 1.5V or 15V. If you use the 24vdc adapter, us a LM317 as a constant current charger @ AH x .095(1.5 x.095=0.142A) you would not have to disconnect the charger as the battery would not overcharge.
    The resistor for the LM317 would be 1.25V/.142A= 8.8Ω I would use a heatsink on the LM317 and a 10Ω 2W resistor.
     
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  5. Adjuster

    Well-Known Member

    Dec 26, 2010
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    One "cheap and dirty" method involves the use of a small tungsten light bulb placed in series with the battery.

    A DC supply is required, of at least a few volts higher than the battery voltage expected on charge. This supply does not necessarily need to be regulated.

    The lamp bulb needs a bit of experimenting. Its voltage rating could be that of the battery, or for safety a bit higher to allow for a stone-dead battery. The lamp power will need to be chosen to get a suitable charging current, which should be a bit less than the bulb's normal rating unless the battery is extremely flat.

    This is a very crude method, but with a suitably chosen lamp the current obtained will be more stable than with an ordinary resistor, because of the positive temperature coefficient of the lamp filament.

    Well, he did say "simple and cheap"!
     
  6. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Charging a battery to 12V or even keeping it at 12V is pretty darn ridiculous in my opinion.
    It's like basic life support for a nearly dead battery. Sulfation will be a constant and soon the battery will not have the potential to supply squat for current.

    Without an actual measurement of his supplies it will be difficult help him. If the supplies do provide more than 12V, perhaps 15V, you could use the PB137 Vreg to keep it charged but never overcharged.
     
  7. wayneh

    Expert

    Sep 9, 2010
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    He's charging a Ni-cad. Taking a Ni-cad cell to 1.2v or ten of them to 12v, is not so ridiculous, IMHO, if the charger is "typical" (unregulated) and actually gives something a bit more than 12v at low current.
     
    Last edited: Oct 21, 2011
  8. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Yeah, your right, I got the chemistry wrong and suggested a float charger voltage regulator for a Lead-Acid Battery! Thus the sulfation issue is not present and 14V - 15V is fine.
     
  9. spencer_manzon

    Thread Starter New Member

    Dec 26, 2010
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    thank you very much everyone for your reply! :D

    it is a drill battery, so the post of k7elp60 was appropriate for my case. :)
     
  10. k7elp60

    Senior Member

    Nov 4, 2008
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    If you need more help or information please let me know as I have built many similar chargers.
    Ned
     
  11. spencer_manzon

    Thread Starter New Member

    Dec 26, 2010
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    will the constant current LM317 charger work for a drill battery? is this charger a 10 hours charge?

    is there a schematic? i'm not really sure how to wire it..
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Electric drill batteries generally incorporate a thermal switch that indicates to the charger when the battery pack is getting too warm. The switch connection is generally separate from the battery terminals; there are 3 terminal connections to the battery.

    Charge time depends on the AH rating of the battery, the charge current, and how deeply the battery was discharged.

    Schematic of the battery? Or the current regulator?
     
  13. iONic

    AAC Fanatic!

    Nov 16, 2007
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    The 7815 Voltage regulator is ideal for your requirements.

    [​IMG]
     
  14. k7elp60

    Senior Member

    Nov 4, 2008
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    I disagree with your circuit. The current will be limited to 15/8.2=1.83A.
    It is not suitable for his charger.
     
  15. k7elp60

    Senior Member

    Nov 4, 2008
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    The attachment has the schematic of the charger. I have found through practice that if the charging current is limited to AH x .095 that the NiCad and Nmih batteries will not ever over charge. With the circuit shown it may take longer than 10 hours to fully charge the battery and as such the voltage across the pack will seek is value at it charges. My original calculation for the 10 ohm resistor was incorrect, a 1/2W is adequate.
    The heat dissipation of the LM317 will be approximately 2W so a heat sink of about 1" high and about 1.5" wide will be necessary.
     
  16. iONic

    AAC Fanatic!

    Nov 16, 2007
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    With this configuration, 1.83A from a 1.0A regulator???

    Perhaps R should be 100 ohms....!
     
  17. SgtWookie

    Expert

    Jul 17, 2007
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    Ionic,
    The circuit you posted just won't work properly.
     
  18. k7elp60

    Senior Member

    Nov 4, 2008
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    The output current can be affected by a number of factors. One is the input output differiential, another is the temperature of the 7815. Although it is classed as a 1A regulator there are conditions when the output current can be greater. The way you have it wired the output voltage will be somewhere around 9V as the there will be about 15V dropped across the resistor connected between the adjust terminal and the output terminal. There will also be a voltage drop between the input and the adjust terminal.
    The regulator has internal circuitry that monitors the input/output differiental, the temperature and the load current among others and protects the regulator from overload with the internal circuitry.
     
  19. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Cheap & dirty? 12 V AC= about 16.25V when rectified, add 56Ω @ 2W gives 200 mA charge for Ni-Cds. It has worked in practice; in 1980 made a 7 slot 5 cell D size Ni-Cd charger using a 12V? supply, & resistors.Was still in use when I retired in 1986. Or usec 24V DC with 56Ω @15W.
     
    Last edited: Oct 25, 2011
  20. spencer_manzon

    Thread Starter New Member

    Dec 26, 2010
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    thanks guys! i'll be trying out your ideas :D
     
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