>The IC regulators that are out there are spec'ed to work over the
"industrial"
>temperature range, that's usually -40 to 85 degrees C. Within that range
the
>accuracy of the voltage output depends on the goodness of the resistors you
use
>to set the output voltage, so a few pennies (or quarters, at low volumes)
spent
>here means you don't need adjustments.
>
>As far as over/undervoltage spikes go, a good reference here is SAE J1211.
I was
>planning to provide a clamp diode to trigger at 50 volts or so (which is
the
>maximum that the regulator I had in mind can stand). The diligent
experimenter
>will be able to find ways to exceed that voltage, but that kind of stuff
will
>also damage other components in the car's electrical system, and the
instrument
>regulator will then be the least of your worries.
>
>A dual output with adjustments on both is something that I was specifically
>trying to avoid, since most folks are still using stock sensors and gauges
>(correct me if I'm wrong here), and having adjustments would just mean that
>everyone would then be dependent on the goodness of their voltmeter. My
plan was
>to offer a bolt-in (or solder-in, for those of you that like to tinker)
>solution, no adjustments, no frills. Frills cost engineering time, and that
>means everyone gets to pay more.
>
>Theo
Theo,
I have done a layout circuit board for just he Instrument regulator that you
are talking about. I have had it working for about 4 years and several
thousand miles now and had no problems with voltage spikes or anything else
for that matter. You will need to put dual adjustable controls IF you want
calibrated instruments. If not, a fixed voltage is quite adequate. I used a
dual system since the gas gauge and the temperature gauge required different
voltages to read "correctly" at one point. You will find that the
instruments were intended to be for indication only, but CAN be calibrated
at ONE point on the dial. I chose 2 gallons on the gas and 190 degrees on
the temperature. Any reading close to those points is plenty adequate (even
with the errors due to tracking unbalance). Lucas (IMHO) did not do a very
good job of matching the dial calibration with the sending units resistance
curves. One other added benefit is that the LM317 has an internal current
limit protection built-in for the possible inadvertent short circuit
protection which limits the current to approximately 2Amps. The under dash
temperature is not a problem either, since I built mine into a cast aluminum
box with lid that acts as the heatsink for the regulators. I like
battle-ship types of designs (they don't cost but a few pennies more and
provide a lot of mental happiness). The calibration is quite simple. For the
gas gauge: disconnect the hose from the engine side of the fuel pump while
on level ground. Connect a hose to a catch gas can, turn it on until the
pump won't pick up any more gas and runs "dry". reconnect the original hose
connection and pour exactly 2 gallons of gas into the tank. Adjust the
voltage on the gas gauge voltage regulator until it reads 2 gallons on the
meter. This will be somewhere between 9 and 10.5 volts typically. To adjust
the temperature regulator circuit, loosen the hose clamp on the radiator
inlet side and slide an Iron-Constantine (or equivalent) thermocouple
junction into the water flow, retighten the clamp. Start it up and bring it
up to operating temperature. Adjust the voltage regulator for the
temperature to the same reading. This voltage should be somewhere within the
previously mentioned range. I'll bet money that the two voltages are NOT the
same. I use a 165 degree thermostat with four small (1/8") holes drilled
into the perimeter of the thermostat. It runs a little on the cool side, but
I live in an area where the ambient is a little on the Hot side, so they
sorta cancel each other out. Steve had asked me to write up an article about
this, and I guess I have just written the outline for that here. Mine cost
somewhere in the neighborhood of $20-25 as I recall to build. If you want to
produce them, by all means do so, I highly endorse them.
Cullen Bennett
Tempe, Arizona USA
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