On Fri, 22 Sep 2017 11:19:03 +0100, "Dave W"
wrote:

snip

The current can be read anywhere in the system but if there is any
significant resistance in the lead between the battery and where I
have this box, I can 'remote' the voltage mater supply / sense wires
directly to the battery terminals to remove the influence of the
voltage drop over the cables that will range from 0 at no current to
maximum (that should still be pretty low in ideal circumstances) at
full current.


OK understood. You could use the voltage between the two ends of the
current-carrying wire from the battery as input to your Arduino current
sensing arrangement. The resistance of the lead is the current shunt.

Funny you should say that ... that's exactly what I did on the
electric racing bike I built, measuring the voltage drop over the
longest battery cable and after calibration, displaying it as current.
;-)

The thing with this project though is I want to try to keep it all
modular / flexible to it would be better to keep the current
measurement 'local' to any meters etc. I'm hoping to use a hall effect
module with integrated amplifier chip to make it easier to interface
with the Arduino etc.

Also, with mostly 20mm^2 copper leads (2 x 2m) from the battery to the
outboard I'm hoping that at my typical 15A draw I'll not get
sufficient voltage drop for it to be worth measuring (although I know
I will etc). ;-)

Cheers, T i m