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Re: [OM] [OT] Calling on the list's electrical engineers

Subject: Re: [OM] [OT] Calling on the list's electrical engineers
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Tue, 02 Dec 2008 08:25:40 -0500
Thanks.  It never occurred to me that the internal battery resistance 
cold be part of the design assumptions.

Chuck Norcutt

Frank van Lindert wrote:
> If the camera or flash is designed in such a way that the internal
> resistance of the battery also limits the current, rather than the
> impedance of the device alone, then a battery with lower internal
> resistance could indeed lead to a larger current flowing through the
> device. IMHO this is to be considered as bad design, but it was often
> used in the past.
> 
> I think that this is the reason for the warning (or rather disclaimer,
> I would call it). It is impossible to say if using NiMH cells could
> indeed damage the camera or not.
> 
> Frank van Lindert
> Utrecht nL.
> 
> 
> 
> Tue, 02 Dec 2008 07:41:39 -0500, Chuck Norcutt
> <chucknorcutt@xxxxxxxxxxxxxxxx> wrote:
> 
>> A friend just purchased an old Ricoh FF-90 film P&S camera.  He wants to 
>> use NiMH batteries but the user's manual (which can be found here)
>> <http://www.butkus.org/chinon/ricoh/ricoh_ff-90/ricoh_ff-90.htm> states:
>> ------------------------------------------------------------
>> * Do not use Nickel Cadmium batteries. "Use of rechargeable Ni-cad 
>> batteries is not recommended. Due to higher internal amperage, the 
>> electronics in your Ricoh camera/flash unit may be damaged. If damage 
>> due to use of Ni-cad batteries occurs, the warranty will be considered 
>> null and void"
>> ------------------------------------------------------------
>>
>> Can someone explain why this is?  I can understand problems with NiCad 
>> or NiMH possibly not delivering enough voltage for proper operation but 
>> I don't understand just the *capability* of the batteries to deliver a 
>> higher current as injurious.  In fact, my limited knowledge of 
>> electronics (Ohm's law: I=V/R) would say that the fixed resistance of 
>> the camera's circuits would cause a lower current draw with lower 
>> voltage batteries.  Without understanding why I suspect that the flash 
>> is the problem since the flash, during recharge, is that only thing that 
>> normally draws a high current.  If that's the case could NiMH be used if 
>> the flash is turned off?
>>
>> Thanks,
>> Chuck Norcutt
>>
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