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Old Nov 23, 2006, 9:17 PM   #1
K J
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I have two 4xNi-MH Sanyo 2500 and after 8 months of usage and 10 recharges (of each 4pack) I see that they tend to self-discharge in less than 2 weeks even when rarely used. I only use them in my digicam (4 at a time) and fully recharge them only after camera can't operate anymore. I find it disappointing since Sanyo seems to be highly renowned and claims "Lasts two times longer than a normal Ni-Cd battery" :?:
I will appreciate any comments and suggestions.
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Old Nov 23, 2006, 9:38 PM   #2
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What make/model charger are you using?
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Old Nov 24, 2006, 7:54 AM   #3
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KJ,

The Sanyos are a lot better than that. Have you tried running a reconditioning cycle on them? I don't know if your 9168 charger has that capability (my German isn't very good).

the Hun

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Old Nov 24, 2006, 8:08 AM   #4
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All NiMH batteries self discharge (I assume you know that). What I do is to put cells into a charger just before I need to use them, to top them up. I also use a battery tester to make sure each cell is fully charged. I have three different chargers and I find none of them will consistantly give a full charge to all cells. So it may be that one or more of the cells you are using is well below the others and the weakest cell will determine the useability when in the camera.

Oh, I also use Sanyo cells.
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Old Nov 24, 2006, 9:54 AM   #5
K J
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My charger has 'Battery Care' function... but I believe Ni-MHs are supposed to be immune to 'memory effect' ? My Sanyos used to last up to a month (didn't wait longer) when I bought them, only now they started to behave this way. So maybe I should try reconditioning (I haven't try it yet) - could you give me some tips on that or maybe some link, do I need to fully discharge them before reconditioning cycle, how it works etc. Of course I know that all NiMH batteries self discharge but that's way too fast. Speaking of measurement, I checked voltage manually and all four show 1,58V +/-0,01 just after charging is complete - yet I don't know if voltage is a significant measurement. When any drop below 1,3V there are only few camera shots left. But generally they keep consistant voltage up to 1,3V.
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Old Nov 24, 2006, 12:39 PM   #6
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K J wrote:
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Speaking of measurement, I checked voltage manually and all four show 1,58V +/-0,01 just after charging is complete - yet I don't know if voltage is a significant measurement. When any drop below 1,3V there are only few camera shots left. But generally they keep consistant voltage up to 1,3V.
Well, if your DVM is accurate, you've been vastly over charging your Sanyos so it's not surprising they now have bad self-discharge. I've never, ever, seen a NiMh cell have such a high voltage immediately after charging. 1.42v to 1.48v would be more normal.
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Old Nov 24, 2006, 5:08 PM   #7
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@SteveB, it's rather very simple multimeter DT-830B looks more less like this:arrow: http://www.hongyan-e.com/images/taojian2/830B.jpg
From my observation, the initial 1,58V drops in few hours to something like 1,46V (at least according to my DT-830B). My charger, that I mentioned earlier, uses -dV to control charging and it takes ~4 hours to fully charge my Sanyos. According to manual: Charge current for AA =800 mA; Trickle current =80 mA.
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Old Nov 25, 2006, 2:38 AM   #8
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K J wrote:
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@SteveB, it's rather very simple multimeter DT-830B looks more less like this:arrow: http://www.hongyan-e.com/images/taojian2/830B.jpg
From my observation, the initial 1,58V drops in few hours to something like 1,46V (at least according to my DT-830B). My charger, that I mentioned earlier, uses -dV to control charging and it takes ~4 hours to fully charge my Sanyos. According to manual: Charge current for AA =800 mA; Trickle current =80 mA.
The meter could be the problem, it's not exactly a calibrated instrument by the look of it, but on the other hand your voltage dropping to 1.46v after a few hours sounds about right so the meter is probably OK. I still say 1.58v fresh off the charger is a sign that your batteries are being overcharged though. Perhaps someone else on the forum can take some measurements as a comparison.

Do the batteries get hot? It's normal for them to get fairly warm, verging on hot at end of charge, but not for very long (a few minutes?, I've never measured it) if the charger is detecting end of charge correctly. I believe that's how -dV detection works, the battery voltage falls a little when it heats up and this is detected and the charger changes over to a trickle charge.
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Old Nov 25, 2006, 10:24 AM   #9
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Hello KJ,

There seems to be some problems with some of the batches of Sanyo 2500 cells. We are hearing of scattered reports that they seem to work well off the charger, but self discharge to nothing in a couple of weeks. Your cells may be bad.

I also think that your volt meter is reading high. NiMh cells come off the charger at around 1.45 volts per cell. This voltage will increase to around, or just slightly over, 1.5 volts per cell after 100 - 200 cycles. A few hours off of the charger will see them stabilize at around 1.35 volts, and when they get down to just under 1.2 volts, they are nearly empty.

It looks like you are reading 0.1 volts high.

Tom
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Old Nov 25, 2006, 2:23 PM   #10
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SilverFoxCPF wrote:
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I also think that your volt meter is reading high. NiMh cells come off the charger at around 1.45 volts per cell. This voltage will increase to around, or just slightly over, 1.5 volts per cell after 100 - 200 cycles. A few hours off of the charger will see them stabilize at around 1.35 volts, and when they get down to just under 1.2 volts, they are nearly empty.
All NiHi batteries have a terminal voltage of nonimally 1.2Vfalling off rapidly towards the end when they become discharged.

The important thing that determines whether a battery is charged or not is NOT the terminal voltage BUT just how much current it can deliver; when fully charged a NiHi battery should be capable of delivering in excess of 5A.
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