Meters and Heaters
I got the Cruising Equipment E-Meter and shunt the other day
along with heater parts. EcoElectric carries the E-Meter and you can get more
information, including specs
and a nice wiring
diagram, from their home page.
The photo shows the meter in a dashboard switch panel that had a square opening otherwise
perfect for the meter. A little cosmetic touchup (with 5 1/4" floppy plastic again)
around the edges and it looks like it was born there.
The E-Meter measures voltage, current, and keeps track of other usage statistics
one of which is translated into how much fuel remains. A shunt is required for
current measurement and since we are talking the neighborhood of 500-600 amps, the
shunt is no small affair. A shunt is a piece of metal with a known (albeit low)
resistance. This way when X amount of current flows through it, there is a corresponding
and linear voltage drop. In the case of this shunt 500 amps produces 50 millivolts.
By hooking up an ammeter to this you can calibrate it so that every time it gets
50 millivolts it points to 500 amps. In the case of the E-Meter the display
is digital and there is an A/D which translate the analog voltage into digital
signals that the E-Meter circuits can understand and manipulate.
That's the shunt on the right, with big screws for the battery current to flow through
and the smaller screws for the E-Meter to tap off of. On the left side is a high
current contactor. This particular one is rated for twenty amps at 125 volts and
will be used to supply power to the ceramic heater. It is controlled by 12vdc and there
will be a combination of fan power and heater switch interlocks which determine
when the heat is on.
You'll remember the two images on the right showing the old heater core and the box
that houses the core and related controls for heating and cooling. The image
on the far left is the electric ceramic heater. I'm fabricating a box with roughly the
same dimensions of the old core which the ceramic heater mounts to. The images above
don't share common dimensions, the ceramic heater is 4.5w x 4.5h x 2.5d inches,
the old core and the hole it needs to fit in is 6.5w x 7.5h x 3d inches. Only the wire
for the heater will come into the dash area, the contactor and fuses will all be in the
engine in a common electronics area.
Next: A battery of boxes
© Copyright 1995-2002 Jerry Halstead