Help with an Alkaline Battery Charger circuit

Discussion in 'Power Electronics' started by Al GR, Mar 21, 2017.

  1. Al GR

    Thread Starter New Member

    Mar 21, 2017
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    I wanted to build the alkaline battery charger in the diagram below and was hoping someone could confirm a few things about the circuit. I'm not sure who the original author is.

    1. There is no connection for the Base of the transistor in the diagram ? What should it be connected to ? Directly to ground ?
    2. Would it make sense that the variable resistor is 47 Ohms or should it be 47k Ohms
    3. The circuits calls for a 9.5v AC power supply. Could I power this with 9.5V DC knowing that the second 1.5v charging circuit ( lower in the diagram ) would not work.

    Thank you

    Charger.gif
     
  2. crutschow

    Expert

    Mar 14, 2008
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    You do realize the alkaline batteries are not meant to be charged, and if you try, will likely only provide a slight recharge, if any?
     
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  3. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    And the batteries may object to being charged by leaking electrolyte.

    The base of the transistor is supposed to be disconnected. Used this way they don't conduct until the voltage reaches a threshold value and they conduct and dump the charge stored in the capacitor into the battery as a pulse. Read here.

    I don't know whether this would work well with a DC supply. Someone may be along shortly to do a simulation.
     
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  4. tcmtech

    Distinguished Member

    Nov 4, 2013
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    Unless its a purposely designed rechargeable alkaline battery you wont get anything for your efforts but a ruptured battery which typically destroys the charger or the device it's in via chemical reactions with whatever metal is near it.
     
  5. ian field

    AAC Fanatic!

    Oct 27, 2012
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    You can get acceptable results with pulse charging methods as long as they're not discharged too far - there were rechargeable alkalines released onto the market, but probably weren't much good, I haven't seen any on the shelves for a while.

    There's a very old plan for charging zinc-carbon cells; as simple as a transformer with half wave rectifier - the diode is shunted by a resistor so a small back flow occurs between the forward conduction half cycles.
     
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  6. tcmtech

    Distinguished Member

    Nov 4, 2013
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    I had a bunch of those for a while. The first generation of them were fair but life expectancy was way short of advertised.

    Next generation that came out turned out to be rather fair. I found they lasted a decent run time and took way more charges than the first ones I had.

    Last ones were the new eco friendly and were crappier than the first generation os since then I gave up on the idea and went with the NiMH ones. Still have them and they still work well when needed even after two years and more!
     
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  7. ian field

    AAC Fanatic!

    Oct 27, 2012
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    High frequency pulse charging works brilliantly for reviving old Ni-Cd cells - but doesn't do Ni-Mh any good.

    I was experimenting with a modified AT PSU to try to improve on the pulse method for alkaline - the results on alkaline were unimpressive, but astounding with Ni-Cd.
     
  8. Al GR

    Thread Starter New Member

    Mar 21, 2017
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    Thanks for all the replies and info. I didn't know transistors could be used that way as a pulse generator. I kinda figured the results wouldn't be fantastic recharging alkalines and am aware of the possibilities of leakage even if "properly" charged but I'm going to give the circuit a try just for fun. I'll post back with the results. Thanks.
     
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