[Elecraft] Kx3 lithium batteries life

[Rich Heineck]

Bob,

I think you forgot to multiply by 24hrs/day for your annual energy 
consumption, but your conclusion is still valid.  Even at a ~440 mAH for 
one year, the battery drain can be ignored for practical purposes.  Most 
of the current is consumed by the shunt regulator and the resistor 
dividers on the +12V line.

The LED does blink faintly as an 'alive' check when KX3 power is off, at 
a 1/2 second period.  This is how often the microcontroller wakes up to 
check power status.  Maybe an adventurous individual will put a scope 
across the resistor in series with the LED to measure average current, 
and the result may be surprising on how little it takes to produce a 
visible blink.

73,
Rich  AC7MA


On 03/16/2013 11:07 AM, Bob wrote:
> Some earlier posts have referred to a LED on the charger/clock board
> that seems to blink 24/7.  So there may be more load than just the
> clock on the internal battery.  I haven't noticed anything glowing or
> blinking on mine.
>
> Still your message made me curious, so I measured the drain from the
> internal batteries (8 NiMH cells).  With the radio turned off, it was
> about 50 microamps.  This was surprising to me as clock chips usually
> pull much less than that (a factor of 30 less give or take).
>
> So I pulled out the schematics and found the KX3 uses a Microchip
> PIC24F16K101 as the time keeper and charge controller.  The chip spec
> puts the real time clock drain at 350 nano amps, and says that the run
> mode currents should be 8 uA or so.  Sure enough, there is a Yellow
> LED shown on the schematic (D2).  But like I said, I don’t see it
> blinking on mine.
>
> Given the 50uA current draw I experienced, that is still only 18 mAH
> over an entire year.  If you are talking 2800 mAH for a Energizer
> Ultimate Lithium, that is less than 1% of its capacity.  So that can't
> explain the early demise of your batteries.  You would expect those
> cells to say above 11 volts for almost their entire life, which would
> be about 12 hours of KX3 receive, and about 6 hours at with occasional
> transmit at 5 watts.
>
> Now you mentioned that you keep the radio powered by a external supply
> and really only use the Lithium batteries for time keeping.  If that
> were the case then you would need to have an external supply that was
> always above about 12.4 volts to keep the Lithium batteries from
> partially discharging.
>
> 73, Bob, WB4SON
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