Carl, my ammeter installation is fused at the engine side of the firewall
before the current is routed into the cockpit.
Needless to say, I carry a spare fuse with me, and also carry a short
emergency jumper wire with alligator clips on it so that I can quickly
bypass the ammeter if it fails (opens up). However, it wouldn't take more
than ten minutes to loosen the screws on the back of a bad ammeter, remove
the meter, patch the wires together, tape 'em up, and be on my way, if need
be.
I also devised a circuit for measuring current that uses a solid-state Hall
effect sensor from Allegro Corp.. Using it means that heavy-current wiring
doesn't have to be routed into the cockpit. The Hall effect sensor is
mounted near the starter solenoid. It generates low-level signals that are
sent to a signal conditioning circuit. It, in turn, routes low current to a
milliammeter inside the car.
I tested the Hall effect sensor on the bench here, and also simulated the
circuit using Electronics Workbench Multi-Sim circuit simulation software
running on my PC, and the circuit proves to work.
However, I wound up installing an old fashioned zero-center automotive
ammeter in my Healey just because it's much easier to do, and doesn't call
for circuit elements that need to operate over wide temperature ranges. In
contrast, my Hall effect circuit needs a military-temperature range
operational amplifier (op-amp) chip, a voltage regulator chip, a circuit
board with discrete components (resistors, capacitors), and a zero-center
milliammeter. The old fashioned KISS approach using an automotive ammeter is
much better---and likely much, much, much more reliable.
The other day, list member John Miller (Amateur Radio operator N4VU)
mentioned using a current shunt, and then routing lower-current wiring from
the shunt into the cockpit. I've never tried that, but with suitable
calibration, that should work too, and is somewhat like my Hall effect
system. BTW, both the Hall sensor and a shunt add a small "burden" or
voltage drop to the overall car's circuit.
IMHO, it seems to me that using a shunt or a Hall sensor is analogous to the
complexity of a BJ8's tach compared to a mechanical tach on earlier cars.
It's okay if done in a mass production car, and debugged at the factory, but
is probably too much trouble for the average car owner to duplicate.
== Alex in Maine
1960 BT7 "Blue Mainie"
Former owner 1957 100-6, 1967 BJ8
Amateur Radio AI2Q
http://users.adelphia.net/~alexmm/ai2q.htm
.-.-.
-----Original Message-----
From: owner-healeys@autox.team.net
[mailto:owner-healeys@autox.team.net]On Behalf Of Dr. Carl Rubino
Sent: Thursday, April 15, 2004 3:13 PM
To: healeylist
Subject: voltmeter vs. ammeter voting
19 votes cast todate: Ammeter got 11 and Voltmeter got 8.
There were several concerns about wiring and fire with an ammeter-kind of
scares me so I am going to think a little more about it.
Carl
BN-4L
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