Is 3V enough to keep PRAM alive?

Discussion in 'PowerPC Macs' started by poiihy, Dec 8, 2014.

  1. poiihy, Dec 8, 2014
    Last edited: Dec 10, 2014

    poiihy macrumors 68020

    poiihy

    Joined:
    Aug 22, 2014
    #1
    The main question is "At what voltage does the PRAM start to die?"


    ----------Original-Post-----------

    I have a Beige G3 with dead PRAM battery. Can I wire in two 1.5v batteries in series to make 3V to keep the PRAM alive? The PRAM takes 3.6V, so would 3V be enough? What voltage does the PRAM start to die (reset)?

    ----------

    Oh, I just discovered that 3 Ni-Mh batteries (1.2v each) makes exactly 3.6 volts. I'd prefer not to use rechargeable batteries though because they leak energy.
     
  2. ctmpkmlec4 macrumors 6502

    ctmpkmlec4

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    Location:
    Lyons, KS
    #2
    Is it not feasible for you to purchase a new replacement PRAM battery?
     
  3. poiihy, Dec 8, 2014
    Last edited: Dec 10, 2014

    poiihy thread starter macrumors 68020

    poiihy

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    Aug 22, 2014
    #3
    A new lithium battery is $5-20, but two AA batteries is only 50 cents.
     
  4. comda macrumors 6502a

    comda

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    Mar 15, 2011
    #4
    I tried purchasing one of these batteries for my Beige G3 as well as my Imac g3's and Emac G4. The source wanted $20 for one and that was "apparently" the Clearance price. Walmarts price was $19. So im also wondering would 3v suffice?
     
  5. poiihy thread starter macrumors 68020

    poiihy

    Joined:
    Aug 22, 2014
    #5
    I'm going to try this when i get to it and I will report back. Saw a youtube video of someone who did this to his iMac G3 and it worked.
     
  6. Brian Y macrumors 68040

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    Oct 21, 2012
    #6
    3v should be sufficient, but once those batteries start to deteriorate it may no longer be enough.
     
  7. Intell macrumors P6

    Intell

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    #7
    Those batteries can often be found in bulk at a good price on Amazon.
     
  8. comda macrumors 6502a

    comda

    Joined:
    Mar 15, 2011
    #8
    Alright this maybe a dumb question. But what exactly am i supposed to search up to get one of these amazon batteries? The girlfriend wants to get me a gift for Christmas. figured this maybe something id ask for ;)
     
  9. poiihy thread starter macrumors 68020

    poiihy

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    Aug 22, 2014
    #9
    That's the question... at what voltage does the PRAM start to die?
     
  10. Intell macrumors P6

    Intell

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    Inside
    #10
    I think the PRAM will still be alive down to 2.7 volts.
     
  11. poiihy thread starter macrumors 68020

    poiihy

    Joined:
    Aug 22, 2014
    #11
    In that case there is only 0.3 volts space to work in, and so it wouldn't last long. It's probably better to use 3 Ni-Mh batteries to make 3.6v; that would have 0.9v margin. Or, I could connect multiple sets of alkaline batteries in parallel to increase the capacity.
     
  12. bunnspecial macrumors 603

    bunnspecial

    Joined:
    May 3, 2014
    Location:
    Kentucky
    #12
    It's a shame that mercury cells are no longer available. At 1.3v each(and a reasonably flat discharge curve) a stack of 3 would likely do a good job and last a decent amount of time. Apparently the VA here in the United States horded a bunch of mercury cells, as my grandfather had a big stash of them(for his hearing aides) still in VA envelopes with recent postmarks when he passed away-I wish that I'd had the foresight to grab them.

    You might consider stacking a pair of Silver button batteries. You would still be at 3v(or probably closer to 3.1v) but the discharge curve is a lot flatter than alkaline cells so I suspect that the "real world" life would be longer. As silver cells are often $1-2 each in bulk, however, this may put you in the same ballpark price-wise as buying "the real thing."

    I use zinc-air cells in old cameras designed for mercury batteries, as they have a similar voltage and discharge curve to Hg cells and thus will give correct light meter readings in camera with unregulated circuits designed for mercury batteries. Unfortunately, they are a less than ideal solution for a PRAM battery as once they are "opened"(by pulling off a tab on the battery to expose the electrolyte to air) they only last about a month.

    For folks here in the US, this is an exact replacement for the battery that Apple used. In fact, I've come across some(seemingly original) batteries in systems with this same wrapper. Although it's not super cheap, it is at least available on the shelf pretty much anywhere you go in the US. I'll also add that if you use the Radio Shack "battery finder" tool it will steer you toward a different p/n battery that is the same price but lower capacity(850mAH vs. 1200)

    http://www.radioshack.com/saft-ls14250-3-6v-1200mah-1-2aa-lithium-battery/2301243.html#.VIfinId4QeM

    One final thing-with as many old Macs as I have lying around, I long ago gave up trying to keep the batteries fresh in them. My computers that get used every day stay plugged in all the time, and I deal with resetting the clocks as necessary on the rarely used ones. The only ones that generally get a battery replacement are the ones that either require it for proper operation, or that get intermediate use to the point where they're not always plugged in but resetting the clock is annoying.
     
  13. poiihy, Dec 9, 2014
    Last edited: Dec 9, 2014

    poiihy thread starter macrumors 68020

    poiihy

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    Aug 22, 2014
    #13
    Would two 1.5v carbon-zinc D-cells be better than three 1.2v Ni-Mh AA batteries (2650mAh) or 2 1.5v alkaline batteries? They have higher capacity and would last longer
     
  14. bunnspecial macrumors 603

    bunnspecial

    Joined:
    May 3, 2014
    Location:
    Kentucky
    #14
    Carbon-zinc batteries have a very steep discharge curve with the only notable plateau being very brief at around 1.2. Alkalines are somewhat better in that they will hold on at 1.2v for about 2-3x the amount of time as a Carbon-zinc under the same load.

    At least for this application, I think the few extra pennies are well worth it.

    Lithiums are even flatter-plus flatten out at around 1.4v-if you don't mind to spend the money on them.
     
  15. DZ/015 macrumors 6502a

    DZ/015

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    Mar 23, 2003
    Location:
    New England
    #15
    The direct replacement batteries are commonly referred to as "1/2 AA" size. The top hit on Amazon is a 4 pack for $10.
     
  16. tampasteve macrumors 6502

    #16
    I have used these from Amazon in a number of applications including PowerMac G3/4 and alarm systems stuff. They seem to work well enough, and the price is pretty good, especially if you have Prime to ship them for free.
     
  17. weckart macrumors 68040

    Joined:
    Nov 7, 2004
    #17
    Yes, I found that if you search eBay or Amazon for 'half AA' rather than 'PRAM' you get better prices for the same batteries. VARTA batteries tend to be a bit cheaper than Saft.
     

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