On Sun, 29 May 2005 13:30:07 GMT, "Mark Holden"
wrote:

I'd love to hear from people who have successfully installed a bunch of
panel meters on a boat or similar system.

First post here and probably no help because of the common rail or
some other part that I've missed but:

Years ago I designed, built and raced an electric 'motorcycle' (more
like stretched moped). It had 2 x 12V car batteries wired in series
and I used a single panel meter (and additional components) to
display:

Voltage on battery 1
Voltage on battery 2
Total voltage
Total current
Speed.

The voltage was just a matter of calibrating the meters (with a
potential divider) to read a max of 199.9 volts.

The current was the voltage drop across the longest main battery cable
(to 199.9A).

Speed was done magnetically by sensing teeth on a drive gear within
the donor mopeds final drive unit then using a frequency to voltage
converter chip to display mph (to 199.9). [1]

The voltage was fairly easy to calibrate using a couple of good
(calibrated) DMM's and the current with an accurate high power bench
PSU. The 'speed' was resolved imperially and mathematically down to
'pulses / mph' and then an oscillator used to set / calibrate the
speedo. There were no affordable GPS units available in those days. I
didn't need all that level of accuracy but it was nice to have.

That was later tested against a Police RADAR gun. Mine showed 45.7 mph
and theirs said 46!

I can't remember how I got round the common link between powering the
unit and the sense inputs. Knowing it only had to last an hour or so
probably using a PP3 battery and an on/off switch but I guess all but
the Battery 2 voltage could have been done using the same common
ground point

I don't suppose it helps but has reminded me it might be handy if /
when I find a suitable electric outboard for my 12' Porta-Bote.

T i m

[1] I assume I could even make use of the speed function using a
marine log / transducer?

p.s. I came back to my machine after the lunch break to find a '1st'
rosette stuck to it? It turns out the IEEE had some judges there that
day and my award was for 'Technical innovation (apparently for my
electronics stuff). That was a nice surprise!