D cell versus lead-acid battery

Discussion in 'General Electronics Chat' started by Lightfire, Jun 25, 2011.

  1. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
    690
    21
    Hello,

    My radio needs four pieces of D cell type battery connected in series in order to work. My radio has a holder itself for it.

    But I am wondering if what if I use a 6 volt, 6 ampere-hour lead-acid battery instead of a four D cell type battery? Will the radio explode?

    I guess it won't as the radio will consume only the ampere it needs not the whole ampere that battery produces.

    But I need clarification.

    Thank you for the help.

    Lightfire
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,394
    1,606
    6 volts is 6 volts, your radio doesn't care how it gets it.

    Just don't give it MINUS 6 volts. That lets all the magic smoke out.
     
  3. tom66

    Senior Member

    May 9, 2009
    2,613
    214
    Well, not quite true...

    A 1.5V cell might be 1.55V peak. So 6.2V maximum. Probably fine.

    But a lead acid can be charged up to 3V per cell! That could mean 9V. Not sure if it could take that.
     
  4. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    I disagree with you on the lead acid can be charged up to 3V per cell. The limit is pretty close to 2.5V per cell. When the charger is removed the voltage gradually drops back to about 2.1 volts per cell.
     
  5. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469
    I recently measured a batch of mn1300 D cell Duracell batteries. The initial voltage was 1.61 VDC on all cells. Then, as soon as any load was put on them (even briefly) the voltages dropped and then (with no load) were indeed at about 1.55 VDC. They never went back to 1.61 VDC, even with no load and waiting a long time.

    So, I think any device will handle more than 1.61 VDC per cell, and probably significantly more than this considering design margin. Hence, it should be safe to assume 6.4 - 6.5 VDC will be fine. Also, a 10 % margin is not unreasonable to expect, making 6.6 VDC a likely allowed spec. But, more than that will have some risk. And, 6V lead acid batteries can be more than 6.6 immediately after an initial charge. However, one is free to not charge the battery fully, or to charge fully and then put a load on it for some time to bring the voltage into spec.

    Most likely, there should be no issue at all, but I think none of us want to see the OP blow the radio, so we are being conservative.
     
  6. WellGrounded

    Member

    Jun 19, 2011
    32
    2
    Overvoltage is not a problem since most devices or PCB circuits have built in voltage regulators or a voltage "range". "D" cells and lead acid batteries(especially) are almost always overcharged(maximum voltage charge).

    When you observe the Voltage(y axis) versus Time(x axis) discharge graph of a lead acid battery on a constant load you see a reverse "hockey stick" curve where the voltage drops quickly then smooths out when it reaches its normal operating voltage.

    Danny
     
  7. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
    690
    21
    Actually, my radio both works in AC and DC.

    To work in DC, it needs " 6V UM-1 UE "D"1.5X4 "
    And to work in Ac, it needs " 220V/50 Hz

    Any help?

    What do you mean by MINUS 6 volts?

    Thank all.

    Lightfire
     
  8. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Putting the batteries in backwards would be considered -6V. Polarity is relative.

    If you were to create 12V with D cell battery packs and put a connector on them you could wire it two ways, one would be considered +12VDC, and the other - 12VDC.
     
  9. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
    690
    21
    Ah I see, so if the voltage are for example +6v. Means, they are connected correctly. And if -6v, connected wrongly?

    Thank you so much.

    Lightfire
     
  10. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    There are circuits that require both. Op amps are a type of electronic circuit that routinely uses a ± power supply.
     
  11. iONic

    AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    (4) New D Alkaline's will begin their life at about 6.44V
    (1) 6V Lead-Acid battery charged and at the recommended float charge will give you 6.85V That's a difference of 0.41V. I see absolutely no issue here. Also, as the Lead-acid battery sits for a day or so prior to use it will dwindle down towards 6.35V, which is actually lower than the D batteries at full capacity. Even if the Lead-Acid charger only charges to the end of the Bulk phase (14.2V - 14.4V) and it maintains this voltage (which it should not) the battery will be damaged and the charger should be thrown away...in my opinion. Irregardless of this, as soon as you remove the charging voltage the battery will very quickly drop to under 7V and farther and faster still as soon as a load is attached. If you have any fears that it will be an issue, just add a diode in series with the battery to drop 0.6V - 0.7V.
     
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