> I dont understand what you are saying. Of course they
Apparently.
> are not dead at 1.1 volts under load, what I said is
> any nimh battery is nearly gone ( almost dead as a percentage
> of the total capacity it gives or gave ) once
Capacity in terms of what? Energy or mAH... they're not the same
thing. Check a book on physics... one is Joules, the other is
Coulombs.... the amount of charge a cell can provide says nothing about
how much work it can do until you know the voltage it provides it at.
> you go below 1.2 vdc on the cell regardless of load.
> If you are getting another 0.1 volt drop on these cells
> with a .350A load, the total additional series R is only about
> 0.3 ohms which is still quite low for a AA cell if that is
> what we are talking about here. In any case, I dont think
> most AA cells will give you the full maH rating under a 0.35
> amp load, its just too much and I believe the maH ratings
> are done with a much smaller drain current to be fair
> to the battery makers. And your last statement is only true
> under high load conditions because the internal resistance
> is a much lower loss factor under normal or low load conditions.
> And what your seeing as "higher internal impedance" is not
> fixed, it varies as the cell discharges. Your not saying you
> only get 1.1 VDC output on these cells at the start of the 0.35A
> discharge
> cycle are you?
> jco
<skipping confusing drivel...>
Cell capacity is defined in terms of the "C-rate." That's the
amount of current they can provide for 1-hour. Actually, as you say, the
test is typically done at the C/10 rate... in other words the C rate is
10x the current the battery can provide for 10 hours.
Some battery constructions (even with the same fundamental
chemistry like e.g. NiMH) can provide significantly different output
voltages under the same loads. If the voltage-current (i.e. power)
integrated over time (i.e. energy) is lower, the energy output is lower.
Batteries are NOT rated in terms of energy.... mAH has nothing to do with
energy until a voltage is defined.
Now, if you cannot wrap your argumentative self around these
things, please either keep it to yourself or be willing to be educated.
-Cory
>
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of
> Cory Papenfuss
> Sent: Thursday, January 25, 2007 6:50 PM
> To: Pentax-Discuss Mail List
> Subject: RE: about NiMH batteries (was: aliasing/moire)
>
>
> On Thu, 25 Jan 2007, J. C. O'Connell wrote:
>
>> If I am not mistake, NIMH batteries all have
>> appox the same internal resistance and its very
>> low compared to Nicad for example. specifically
>> what kind of load are you draining them at and what
>> is the output voltage of the cells under that load?
>> Once a nimh drops below the rated voltage of 1.2 VDC the charge is
>> nearly gone regardless of load... jco
>>
> I'm using a LaCrosse BC-900 charger. It will cycle individual
> cells under a constant current charger or discharge, while integrating
> the
> total charge/discharge mAH capacity. As such, it's a constant current
> charge/load... not a constant resistance.
>
> The cells I'm referring to are Powerex 2150 mAH (IIRC), and I
> did
> the cycle at 700mA charge, 350mA discharge.... That's roughly C/8
> discharge rate, and I obtained approx 2000mAH before dipping below 1.1V.
>
> On these cells, they're not dead at that rate until they get between 1.0
>
> and 1.1V... on the Energizer cells it's much closer to the 1.2V you
> specifiy.
>
> Bottom line: Cheap cells illustrate a higher internal impedance
>
> than higher quality cells... even at the same mAH rating. That means
> they
> don't last as long before the camera thinks they're dead.
>
> -Cory
>
>
--
*************************************************************************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
*************************************************************************
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