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Powering DC TV off of D batteries...

Discussion in 'Electronic Design' started by SA Dev, Apr 25, 2004.

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  1. SA Dev

    SA Dev Guest

    Hi,

    I have a 9" TV that runs on DC power and it takes about 4A @ 12V. I noticed
    that when I run it off of a car starter which contains a sealed type 12V
    battery that it works great, but when I run it off of 8 D Energizers, the
    picture doesn't fill the screen and the voltage across the batteries drops
    to 7V when the TV is on. The voltage across the sealed type battery only
    drops 0.5V or so. Can a 12V 4A device be run on D batteries? With the 18AH
    life, I was assuming the batteries could power the TV for about 4 hours. Do
    I just need to add one or two more cells into the series to up the voltage a
    bit to account for the voltage loss?

    Thanks,

    SA Dev
     
  2. Joerg

    Joerg Guest

    Hello SA Dev,

    Please don't simply add two cells as this may fry the TV when for example the
    brightness is turned down and the voltage might exceed what it can stand.

    I suggest to check the load curves for the chosen D cells at the manufacturer
    web site. Most have very detailed data available. Probably the internal
    resistance of D cells is too high. I don't think D cells are meant to deliver 4
    amps. Could even be dangerous with some types but the mfg can tell you that.

    Regards, Joerg
     
  3. Ian Stirling

    Ian Stirling Guest

    I'd guess that it probably will, if you use premium quality D cells, or NiCd/
    NiMH ones.

    Lead-acid is probably the way to go.
     
  4. CFoley1064

    CFoley1064 Guest

    Subject: Re: Powering DC TV off of D batteries...
    Lead-acid *is* the way to go, because of current capability, and the ability to
    be recharged. However, if you insist on using off-the-shelf, disposable
    batteries to power your TV, you might have some luck with two 6V lantern
    batteries in series (like Ray-O-Vac 928 or 945). You can't depend on "D"
    batteries for more than an amp, and the contact resistance of 8 in series is
    going to bog you down even further.

    Good luck
    Chris
     
  5. Vlad

    Vlad Guest

    The batteries you are using are not capable of delivering the current
    required to run the TV
    Increase the current capacity, not the voltage.

    Vlad
     
  6. Tam/WB2TT

    Tam/WB2TT Guest

    hours...........................

    I can't believe that an Energizer D cell is rated at 18 AH. I hope you
    didn't multiply the number by 8 for 8 in series. Many D cells are C cells +
    fluff. A few are AA + fluff.

    Tam
     
  7. Big John

    Big John Guest

    Hi,

    IIRC alkaline "D" cells have a capacity of around 4 AmpHours not 18
    AmpHours. Four amps is just too much current for these batteries. Perhaps,
    10 true NiCad "D" cells in series would work for a short time say 30 - 40
    minutes of run time. But, as others suggested, I'd go with a lead-acid gel
    cell battery with a 10 or more AmpHour capacity. It's also probably the
    cheapest solution.

    Big John
     
  8. SA Dev

    SA Dev Guest

    Hi,
    That is what I was afraid of! Oh well, I guess I'll use my car jump start
    backup battery instead of D cells.

    Thanks for the help!

    SA Dev
     
  9. Tam/WB2TT

    Tam/WB2TT Guest

    Whoops, I spoke too soon. I saw some D cell rated at 15 AH, which is close
    enough to 18. However, if I interpret their data correctly, it is for a load
    of 100 Ohms which would be an initial current of 15 ma. Also, they consider
    the end point as 0.9 V, which might not fly.

    Tam
     
  10. SA Dev

    SA Dev Guest

    Hi,
    Thanks to everyone for their posts--I appreciate it!! I'm going to go with
    a SLA type battery...

    SA Dev
     
  11. Perhaps you could use 10 NicCads, high power type, or NiMh, and a charger.
    these things are relatively cheap, especially recharging - versus - replacing
    every few hours.
    These rechargables have MUCH lower internal resistance then normal batteries.
    Or you could consider a small sealed lead battery.
    JP
     
  12. RoD

    RoD Guest

    You might have overlooked 1 thing, Im not sure.
    If the batteries are NiCad or NiMH (rechargeables), they only deliver 1.2V
    per cell not 1.5V

    In this case (and this case only) adding 2 cells would be precisely the
    right thing to do (1.2V*10 = 2V)

    also, how do you figure that you have 18AH. When batteries are connected in
    series, their voltage increases, but their amperage stays the same. When
    they are connected in parralel, the voltage stays the same, but he amperage
    increases.

    RoD
     
  13. SA Dev

    SA Dev Guest

    Hi RoD,
    I was using Energizer Alkalines, but I didn't realize that they aren't
    capable of delivering more than about 1A very reliably according to some
    others that posted. You can get the battery specs from
    http://data.energizer.com/ by clicking datasheets, consumer/oem.

    Have a great day,

    SA Dev
     
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