On Thu, 21 Sep 2017 21:23:26 +0100, "Dave W"
wrote:

snip

I suspect the motor current will be very noisy, making any digital display
very
erratic and difficult to read.

All that would be 'damped' by sampling Dave.

It depends how often you sample, the duration of the sample window and how
many samples you send to each display reading.

Correct. You could sample every .5 seconds, put the results of 20
samples into an array and then display the average value (or something
like that anyway). ;-)


snip

Sure, analogue meters are great for showing stuff (and why I still use
them) and during the initial runs of anything I come up with may well
include some analogue versions of both Volts and Amps, just to provide
a 'simple' comparison. The problem is a moving coil voltmeter is a lot
more expensive than an electronic one (or even an electronic
wattmeter!) and it really only serves as an indication that there is
around 12V there (because you are only interested in the range 10 -
15). I did think of using a 10V zener and a 5V meter as at least then
you would have an expanded range. ;-)

Surely the cost of the meter is a mere drop in the river compared with the
cost of boat and battery?

Yes, sure.

should be driven so that when the
battery voltage is below 10V the meter is still on its zero mark, and
full scale for 15V. You are driving it from the Arduino so it can be
any old range e.g. 10mA fsd.

In this case I was going to make a straight analogue meter Dave, both
amps and volts mounted in a suitable box and to be (optionally)
plugged in series with the load. If the voltage drop at max current
affects the voltage too much I'll run a separate cable back to the
battery directly.

But you are right, I could run it from the Arduino but I was hoping to
keep this bit 'KISS'. ;-)

snip

Whilst that would vary between boats (and there are 5 we may use it
on) it might be of more use than just some arbitrary values.

You could have a float sensor to vary the calculations depending
on how low in the water the boat is, causing variations in drag.

Now that would be a step too far mate (and way too complicated to
compute). ;-)

Cheers, T i m