[aprssig] Shunt for battery current / APRS Telemetry

Robert Bruninga bruninga at usna.edu
Thu Feb 23 19:17:58 EST 2006

Easiest way is to put a 0.02 ohm resistor in the negative
lead of the battery.  Then connect the battery terminal
through a 10K resistor to an analog input and protective
5v zener.  When 12 amps is flowing through that
resistor, the voltage will be 0.24 volts and the (0-5v) telemetry
will be a count of 12 (out of 255).  This is of course only
1 amp resolution. 0-12 and is not taking full advantage of
the 0-255 range of the A/D, but it is simple.   de Wb4APR

>>> ad6nh at arrl.net 02/23/06 6:13 PM >>>
I am in need of assistance with building a shunt circuit to measure the 
charging amperage of my solar-powered digi.  I have found some vague 
references on the web, but none that tell me how to figure out what 
values of what components I need in order to achieve my desired goals.  
For reference, if it makes things easier, I believe the maximum current 
will never get above 12.7 amps.  Therefore, dividing the 255 max 
telemetry range in half gives 127.5, or 12.75 amps.  That makes the 
calculations easier - now, how do I build this circuit?  I have already 
done the voltages with the divider circuits - that was easy.  Thanks in 

Phil Pacier - AD6NH

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