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[OM] Re: OM-1 mercury cells / adapter / recalibration

Subject: [OM] Re: OM-1 mercury cells / adapter / recalibration
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
Date: Tue, 19 Apr 2005 07:26:03 -0400
Yes, exactly what Charlie said.  The reason for the recommendation of 
silver oxide batteries on OM's is that they have the same type of stable 
voltage characterisitic as mercury cells did.  The voltage drops nary a 
bit until the battery is near death.  Alkaline batteries, however, do 
not have a stable voltage level.  It begins to drop immediately.  That's 
why we're all admonished to use only silver oxide (and preferably 357's) 
and never alkaline or even lithium.

That said, the simple Schottky diode modification that JH does during a 
CLA or (the same) that you get from a CRIS-Cam MR-9 adapter is not 
perfect.  My recollection is that the meter can be off by a small amount 
at the extreme ends of the brightness range.  Tim Hughes has written 
extensively on this in the archives in his quest to develop the perfect 
silver oxide, mercury battery simulator.  (I didn't want to call it an 
ordinary adapter).  Maybe Tim will weigh in here.

I guess the answer for you depends on how long you expect your mercury 
battery stash to last.

Chuck Norcutt

Karl-Hans Lehnet wrote:

> Simon,
> an adapter reduces the voltage by 0.2 V from 1.55 V to 1.35 V with a 
> Schottky diode (1N6263 o.a. ) and does not any kind of voltage 
> stabilization. So if the voltage of  the silver cells drops down to 1.5 
> V,  the adapter delivers 1.3 V. On the other hand, the voltage-over-time 
> characteristic of the silver cells are similar to the quicksilver cells, 
> both deliver a very constant voltage over their lifetime, and this is 
> the reason you can use the adapter with the 1.55 V silver cell for 
> replacing the quicksilver cell.
> Charlie L.

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