IM-17 Batteries

[Garey Barrell]

Bob -

It doesn't look like an alkaline battery would last even 10 hours
at a 10 mA load before it's terminal voltage drops to less than
8.5V.  A lithium is a little better, but even it would only last
about 40 hours at a 10 mA load before dropping to 8.5V.

The alkaline drops 0.5-1V quickly , then slopes down at a
somewhat slower rate.  End of life for an alkaline is 4.8V!

Probably the closest approach would be to use 8-10 AA cells and
regulate to 8.4V.  Not really a viable solution unless it's a big
product.!

73, Garey - K4OAH
Atlanta

Bob And Bettina Groh wrote:
> Regarding 'low drop out regulators' - there are a bunch of them today
> that will (at 'light' loads) that will regulate well with only 50 mV or
> so across them. You would need one of the adjustable one's with some
> precision resistors (or a pot) to set the output voltage.  Should work
> great and, with SMD devices, could be built up in quite a small space.
> Good point about the discharge characteristics.  If any other info
> needed, I would be glad to look into the matter and provide a 'paper'
> design.
>
> 73
> Bob Groh, WA2CKY
>
> Garey Barrell wrote:
>
>> John -
>>
>> There really isn't a good replacement for a mercury cell.  There are
>> many ways to get 8.4 V from a 9V battery, but the absolute voltage isn't
>> the problem.  All batteries EXCEPT for the mercury battery have a
>> "slope" discharge curve.  i.e., the voltage starts to decrease almost
>> immediately, and continues until it reaches the minimum that will
>> operate the equipment.
>>
>> On the other hand, a mercury battery has an almost flat discharge
>> "curve" until just before end of life when it drops like a rock.  This
>> is important for things like watches, light meters for photography,
>> voltmeters or anything else that relies on a stable voltage.
>>
>> Photographers have gone to great lengths to make accommodations to keep
>> their light meters accurate.  The only "good" answer is a voltage
>> regulator, but not many regulators will regulate with less than a volt
>> to work with.
>>
>> 73, Garey, K4OAH
>> Atlanta
>>
>>
>>
>> John Barkow wrote:
>>
>>> Anyone know of a replacement for the 8.4V mercury battery for this
>>> unit other
>>> than a 9V battery?
>>> Thanks, John kd6pt
>>>

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