Mixing non rechargeble batteries

Discussion in 'General Electronics Chat' started by Gdrumm, Feb 20, 2014.

  1. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    I got an old Knight Transistor and Diode checker from ebay for cheap.
    It has a 22 1/2 volt battery that looks similar to a 9 volt.

    The battery is still available, but with shipping it will cost me about $40.00.

    Can I link two 9 v and one AAA battery box with three 1.5 volts in series to get the 22 1/2 volts I need to run the tester.

    Again, I will only be using the tester occassionally, and I would be using non-rechargable batteries.

    I read another post that seemed to imply that re-chargables would be a problem, (but perhaps non- rechargables would be ok? my read) .

    As long as they are all the same type, say Alkalines?

    Any thoughts appreciated. I just hate to shell out $40.00 for a tool I won't use that often.

    Thanks,
    Gary
     
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    You can get three "9V" NI-Cad rechargeables that are actually 7.5V nominal each. Three of those will be 22.5V.
     
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  3. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    A pair on Ebay is $32.00, but perhaps I can find them elsewhere for less.
    Thanks for the tip.
     
  4. bountyhunter

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    Sep 7, 2009
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  5. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Excellent,
    I found a 4 pack of NiMH with charger, for $20.00.
    Would that work?

    Thanks for the Harbor Freight tip.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    Two 9V alkalines and three 1.5V AAA's in series should work fine for you. If you are only using the device occasionally, I see no need to go with recharageables. Recharageables will likely self-discharge faster than the discharge from your usage.
     
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Another option: you can open up 9V alkaline batteries which have six cells each inside them. use two 9V batts and open one up and just salvage three of the six cells inside. I have done it many times. That way, all the cells in series will have the same A-hr capacity.
     
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  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    If they are six cell batteries with 7.5V rating they would work. It's true rechargeables may drop out if not used for months. Alkalines are better for rarely used devices.
     
  9. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    I have several fairly new 9v batteries.
    I think I will try what Bountyhunter suggested.
    Thanks All
     
  10. #12

    Expert

    Nov 30, 2010
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    If you don't like peeling them open, just use a zener diode to waste the extra voltage from 3 alkaline 9's.
    Better not to risk leakage from a (usually) very reliable battery.

    I'd like to add a R.I.P. for the 22.5 V batteries. They were very convenient when you needed them.:(
     
  11. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Thanks #12, please tell me what a R.I.P. is.
    I'm guessing Resistor in parallel?
    I'll check the board & Google this morning.

    How would the Zener diode be hooked up?
    Would it just be hooked up in line between two of the 9v batteries?
     
  12. bertus

    Administrator

    Apr 5, 2008
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    #12 likes this.
  13. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    May I say Duh! to me, and my goofy question.

    When I re-read # 12's comment now, it makes perfect sense.

    I thought he was referring to some obscure, little known secretive trick he did with resistors, in parallel.

    What can I say.

    Thanks for the link also, the price is a lot more reasonable.

    I still want to play with the 9v batteries however.
    I have 4 of them setting on my table, with a exp. date of 2017.

    Hey! I woke up this morning, maybe not 100%, but at least I woke up.

    Thanks all, I'll try to slow down a read stuff more carefully.
     
  14. alfacliff

    Well-Known Member

    Dec 13, 2013
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    why dont you just try the two 9 volt in series, the voltage might be enough to work. older stuff like that was designed to work with batteries that sometimes were partially discharged.
     
  15. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Would the same be true of three 9v in series, in case two are too weak?

    Would three 9v (27V) be too much? The unit looks pretty robust inside.

    It has a switch (that looks like it could withstand 120v)
    A Potentiameter (also rubust)
    A couple of resistors, and a guage that reads (L-R 0 - 2 - 4 - 6 - 8 - 1)
    A PNP socket and an NPN socket,
    +/- sockets for the leads and for Diodes.

    It looks 10 times more robust than my Harbor Freight Multimeter.

    I will give it a try with two 9v, and report back.

    Thanks
     
  16. #12

    Expert

    Nov 30, 2010
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    The 22.5V batteries that look like 9V rectangular used to be available in every hobby shop and hardware store. I guess I'm getting old.:(
     
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  17. takao21203

    Distinguished Member

    Apr 28, 2012
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    use a dc/dc converter.

    If you only need low currents, they can be built as simple as just a joulethief.

    Adding feedback makes the circuit more complicated however, you can also shunt it with a zener diode, if you dont use it often (the efficiency will not be so good).

    There are also ICs for such purposes.
     
  18. crutschow

    Expert

    Mar 14, 2008
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    You too? ;)
     
  19. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Okay,
    Of course there was no users manual, perhaps I can locate one on line.

    The Diode test didn't seem to do anything, I tried it one way (anode to positive), then the other way, and the needle didn't move either time.

    But a Transistor in the NPN slot pegged the meter, when I engaged the Leakage / Gain switch in the Gain direction.

    I took a couple of pictures.

    If you have time to share insights on how this works, let me know please.

    Thanks,
    Gary
     
    Last edited: Feb 21, 2014
  20. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    I have some Zener diodes, whould I just place it in line to the positive side of the device, then connect to the battery?
     
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