Re: NiMh voltage?

Discussion in 'Digital Photography' started by Martin Brown, Oct 23, 2013.

  1. Martin Brown

    Martin Brown Guest

    On 22/10/2013 15:26, bugbear wrote:
    > I have a (old) Canon A630 camera.
    >
    > I can get very few shots/use out of a freshly charged set of
    > NiMh AA batteries, and yet when I put them in a halogen
    > bulb torch, the torch will run for hours.


    It is a common problem with some of the older cameras. They have logic
    to shutdown the camera when the terminal voltage of the presumed primary
    cell battery pack drops below a certain fixed value under load.

    There is also a possibility that you have a single weak cell developed
    in a pack and that will spoil the entire sets capacity.

    You can't tell which is which unless you can load them with about 500mA
    and measure the terminal voltage (typical current draw for an older but
    not massively old camera). Unloaded voltage is no guide to the fitness
    of a cell or otherwise - you need a load based battery tester.
    >
    > I assume it's related to voltage, not Ah capacity.
    >
    > Do brands/models of NiMh battery vary in voltage,
    > and (if so) can anyone recommend a high(er) voltage type?
    >
    > BugBear


    Sadly no. They have lower internal resistance than primary types, but
    although when freshly charged they have terminal voltage of ~1.4v it
    quickly falls below the older cameras panic and shutdown threshold of
    ~1.3v. Even the primary alkaline cells are not giving all they could and
    such batteries will have a fair residual capacity left even when the
    camera rejects them. More modern cameras tend to have their "give up"
    threshold set to below the 1.2v discharge plateau of rechargables, but
    the early ones didn't. This graph shows the battery discharge
    characterisitics for eneloop(blue), NiMH(black) and alkaline(pink)

    http://s3.media.squarespace.com/pro...s/2010/03/eneloop-discharge-curve-540x380.gif

    A lot of them now use other battery technologies in custom packs.

    The advantage of AA cells is you can buy them most places.

    I keep my once used AA cells for use in other low current drain
    applications where terminal voltage is non-critical. I do use and get
    decent life out of my NiMH in a Pentax istD but I have matched the sets
    and periodically weed out failing cells. I carry a set of alkaline
    spares too as high self discharge is a problem with most NiMH.

    --
    Regards,
    Martin Brown
     
    Martin Brown, Oct 23, 2013
    #1
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  2. Martin Brown

    nospam Guest

    In article <>, Daniel W. Rouse
    Jr. <> wrote:

    > I think the hotter the charger makes the battery, the less it lasts not just
    > in a single charge, but overall for the number of charges.


    yep, heat is *bad*.
     
    nospam, Oct 27, 2013
    #2
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  3. Martin Brown

    Robert Coe Guest

    On Sun, 27 Oct 2013 01:09:37 -0400, nospam <> wrote:
    : In article <>, Daniel W. Rouse
    : Jr. <> wrote:
    :
    : > I think the hotter the charger makes the battery, the less it lasts
    : > not just in a single charge, but overall for the number of charges.
    :
    : yep, heat is *bad*.

    I have a feeling (not backed by any actual knowledge) that it may be more
    complicated than that. I have a Radio Shack charger (two actually: one at home
    and one at work) that leaves the charged batteries too hot to touch. I usually
    stand them up on a formica counter to cool for 15 or 20 minutes before putting
    them away. But the batteries seem to accept the treatment, as I haven't seen
    any degradation of their performance over time.

    But while those chargers work fine on Radio Shack and Enercell batteries (the
    latter a brand sold by RS), they refuse to charge "Impact" batteries (which
    are a B&H house brand, I believe). The model claims to be a "high speed"
    charger, and it does seem to do its job relatively quickly. My suspicion is
    that the charger knows (or thinks it knows) which batteries can stand the high
    heat of being charged that way and which ones may not.

    I have an older RS charger that does charge the Impacts, but it doesn't claim
    to be a high speed model.

    Bob
     
    Robert Coe, Oct 27, 2013
    #3
  4. Martin Brown

    nospam Guest

    In article <>, Robert Coe
    <> wrote:

    > : > I think the hotter the charger makes the battery, the less it lasts
    > : > not just in a single charge, but overall for the number of charges.
    > :
    > : yep, heat is *bad*.
    >
    > I have a feeling (not backed by any actual knowledge) that it may be more
    > complicated than that. I have a Radio Shack charger (two actually: one at home
    > and one at work) that leaves the charged batteries too hot to touch. I usually
    > stand them up on a formica counter to cool for 15 or 20 minutes before putting
    > them away. But the batteries seem to accept the treatment, as I haven't seen
    > any degradation of their performance over time.
    >
    > But while those chargers work fine on Radio Shack and Enercell batteries (the
    > latter a brand sold by RS), they refuse to charge "Impact" batteries (which
    > are a B&H house brand, I believe). The model claims to be a "high speed"
    > charger, and it does seem to do its job relatively quickly. My suspicion is
    > that the charger knows (or thinks it knows) which batteries can stand the high
    > heat of being charged that way and which ones may not.


    high speed charging means pumping a lot of current into the battery to
    charge it quickly, which heats it up. that reduces its useful life.

    if you charged them at a normal rate, they wouldn't be hot to the touch
    and they would last a lot longer.

    some chargers can report the actual capacity of the battery, and you'd
    see that decreasing over the lifetime of the battery.

    are you in that much of a rush that you need high speed charging?
     
    nospam, Oct 27, 2013
    #4
  5. Martin Brown

    Martin Brown Guest

    On 27/10/2013 04:55, Daniel W. Rouse Jr. wrote:
    > "Martin Brown" <|||newspam|||@nezumi.demon.co.uk> wrote in message
    > news:kiL9u.17125$4...
    >
    > [snip...]
    >
    >> The advantage of AA cells is you can buy them most places.
    >>
    >> I keep my once used AA cells for use in other low current drain
    >> applications where terminal voltage is non-critical. I do use and get
    >> decent life out of my NiMH in a Pentax istD but I have matched the sets
    >> and periodically weed out failing cells. I carry a set of alkaline spares
    >> too as high self discharge is a problem with most NiMH.
    >>

    > Not only too high a self discharge, but also how the charger does a charge
    > on the NiMH batteries. Some chargers make them burning hot to the touch,
    > while others do not.


    Fast chargers tend to run the batteries seriously hot. That is the price
    you pay for high charging currents. I try not to do this since battery
    chemistry tends to be more nearly reversible when done slowly.

    A good fast charger should never take the battery outside of its rated
    operating conditions but a cheap and nasty one probably will.
    >
    > I think the hotter the charger makes the battery, the less it lasts not
    > just in a single charge, but overall for the number of charges.


    I haven't done the experiment but I also believe that fast charging
    accelerates the loss of capacity.
    >
    > Not sure if this is a Fry's Electronics only brand, but I've had mixed
    > results with Lenmar branded NiMH AA batteries. Some lasted for much
    > longer than AA alkaline. Others lasted less than 1/4 the time of a AA
    > alkaline. On the other hand, Lenmar AA (and AAA) are very cheap in price
    > to replace even if one or more batteries become defective.


    In the UK Aldi/Lidl supermarkets sometimes have unexpectedly good low
    self discharge NiMH batteries (already charged when supplied) on offer.
    They are much cheaper than better known brands and almost as good. The
    batch I got were all in a red finish and still going strong.

    The odd cell does go duff with time developing a high internal
    resistance and needs weeding out. You have to test terminal voltage
    under load to find them. Open circuit the voltages are all very similar.

    --
    Regards,
    Martin Brown
     
    Martin Brown, Oct 28, 2013
    #5
  6. Martin Brown

    J. Clarke Guest

    In article <Myqbu.81757$4>,
    |||newspam|||@nezumi.demon.co.uk says...
    >
    > On 27/10/2013 04:55, Daniel W. Rouse Jr. wrote:
    > > "Martin Brown" <|||newspam|||@nezumi.demon.co.uk> wrote in message
    > > news:kiL9u.17125$4...
    > >
    > > [snip...]
    > >
    > >> The advantage of AA cells is you can buy them most places.
    > >>
    > >> I keep my once used AA cells for use in other low current drain
    > >> applications where terminal voltage is non-critical. I do use and get
    > >> decent life out of my NiMH in a Pentax istD but I have matched the sets
    > >> and periodically weed out failing cells. I carry a set of alkaline spares
    > >> too as high self discharge is a problem with most NiMH.
    > >>

    > > Not only too high a self discharge, but also how the charger does a charge
    > > on the NiMH batteries. Some chargers make them burning hot to the touch,
    > > while others do not.

    >
    > Fast chargers tend to run the batteries seriously hot. That is the price
    > you pay for high charging currents. I try not to do this since battery
    > chemistry tends to be more nearly reversible when done slowly.
    >
    > A good fast charger should never take the battery outside of its rated
    > operating conditions but a cheap and nasty one probably will.
    > >
    > > I think the hotter the charger makes the battery, the less it lasts not
    > > just in a single charge, but overall for the number of charges.

    >
    > I haven't done the experiment but I also believe that fast charging
    > accelerates the loss of capacity.
    > >
    > > Not sure if this is a Fry's Electronics only brand, but I've had mixed
    > > results with Lenmar branded NiMH AA batteries. Some lasted for much
    > > longer than AA alkaline. Others lasted less than 1/4 the time of a AA
    > > alkaline. On the other hand, Lenmar AA (and AAA) are very cheap in price
    > > to replace even if one or more batteries become defective.

    >
    > In the UK Aldi/Lidl supermarkets sometimes have unexpectedly good low
    > self discharge NiMH batteries (already charged when supplied) on offer.
    > They are much cheaper than better known brands and almost as good. The
    > batch I got were all in a red finish and still going strong.
    >
    > The odd cell does go duff with time developing a high internal
    > resistance and needs weeding out. You have to test terminal voltage
    > under load to find them. Open circuit the voltages are all very similar.


    That's good information--I hadn't thought of Aldi as a source for
    batteries, next time I go in I'll have to see if they have them in the
    US.
     
    J. Clarke, Oct 28, 2013
    #6
  7. Martin Brown

    Robert Coe Guest

    On Sun, 27 Oct 2013 18:57:48 -0400, nospam <> wrote:
    : In article <>, Robert Coe
    : <> wrote:
    :
    : > : > I think the hotter the charger makes the battery, the less it lasts
    : > : > not just in a single charge, but overall for the number of charges.
    : > :
    : > : yep, heat is *bad*.
    : >
    : > I have a feeling (not backed by any actual knowledge) that it may be more
    : > complicated than that. I have a Radio Shack charger (two actually: one at home
    : > and one at work) that leaves the charged batteries too hot to touch. I usually
    : > stand them up on a formica counter to cool for 15 or 20 minutes before putting
    : > them away. But the batteries seem to accept the treatment, as I haven't seen
    : > any degradation of their performance over time.
    : >
    : > But while those chargers work fine on Radio Shack and Enercell batteries (the
    : > latter a brand sold by RS), they refuse to charge "Impact" batteries (which
    : > are a B&H house brand, I believe). The model claims to be a "high speed"
    : > charger, and it does seem to do its job relatively quickly. My suspicion is
    : > that the charger knows (or thinks it knows) which batteries can stand the high
    : > heat of being charged that way and which ones may not.
    :
    : high speed charging means pumping a lot of current into the battery to
    : charge it quickly, which heats it up. that reduces its useful life.
    :
    : if you charged them at a normal rate, they wouldn't be hot to the touch
    : and they would last a lot longer.
    :
    : some chargers can report the actual capacity of the battery, and you'd
    : see that decreasing over the lifetime of the battery.
    :
    : are you in that much of a rush that you need high speed charging?

    Yes. At least I was until very recently, when I bought a lithium battery pack
    and spare battery. For a long photo shoot I was charging 48 NiMH AA's. So yes,
    charging speed was important to me.

    Bob
     
    Robert Coe, Oct 30, 2013
    #7
  8. Martin Brown

    nospam Guest

    In article <>, Robert Coe
    <> wrote:

    > : are you in that much of a rush that you need high speed charging?
    >
    > Yes. At least I was until very recently, when I bought a lithium battery pack
    > and spare battery. For a long photo shoot I was charging 48 NiMH AA's. So yes,
    > charging speed was important to me.


    jeezus. how the hell did you keep track of them all?

    did you at least get an 8 cell charger? i don't know if they make 16
    cell ones but they probably do.
     
    nospam, Oct 30, 2013
    #8
  9. Martin Brown

    Robert Coe Guest

    On Tue, 29 Oct 2013 21:03:17 -0400, nospam <> wrote:
    : In article <>, Robert Coe
    : <> wrote:
    :
    : > : are you in that much of a rush that you need high speed charging?
    : >
    : > Yes. At least I was until very recently, when I bought a lithium battery
    : > pack and spare battery. For a long photo shoot I was charging 48 NiMH
    : > AA's. So yes, charging speed was important to me.
    :
    : jeezus. how the hell did you keep track of them all?

    Carefully. When getting ready for a shoot, I tried to make sure to charge each
    set of four exactly once. :^}

    : did you at least get an 8 cell charger? i don't know if they make 16
    : cell ones but they probably do.

    I have three 4-cell chargers. I keep one at work and two at home.

    Bob
     
    Robert Coe, Nov 3, 2013
    #9
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