Well fellow listers I have some minor news on the Gauge thang. After
replacing the temperature sensor the fuel gauge went up. I suppose that
this is due to the weird and wonderful voltage stabilizer. The
resistance on the old sensor was well above the ~1kOhm measured for the
new gauge. This means that significantly less current was being drawn
through the stabilizer and so it was probably swithcing slower and
producing less voltage. I am going to experimant with the LM317 I have
kicking about. It is not rated for temps below 0 deg Celcius but then
I don't plan to drive it in the winter so no big deal. There is an
LM317A that is rated to -40 deg Celcius for those who care.
As far as the temperature stability goes, the LM317 is very stable with
low current draw. According to the spec sheets the output voltage will
drop only 0.2% with a 0.5 Amp draw at 150 deg C and a little over 0.4%
at 1.5 Amps. This is given for no output capacitor, Vin=15V and
Vout=10V <- how convenient. Want numbers? At 0.5 Amps the output will
drop to about 9.98V ans at 1.5 Amps to 9.955 V. This seems quite
stable. As for being stuck under a dash in the hot summer sun... we'll
see. I do have a fair sized heat sink to bolt on. As for the
resistance values I'm goint to use 1k between Vout and Adj and 6.5k from
Adj to Gnd. The formula is:
Vout = 1.25 * (1 + (R2 / R1)) + Iadj * R2
NOTES
======
1) Iadj is typically 50 microamps but can venture as high as 100
microamps.
2) 1 uF on the Vout and 0.1 uF on the Vin is recomended.
I'll report on funcionality later. Also I'll try the LM340-T10 that
was recomended when I get my hands on one.
Thanks to all who responded. What a fantastic forum!
Mark Dickinson
Calgary, Alberta
1980 Spitfire
1967 911S <- in many pieces but complete
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