m52 power! said:
So previously I had an LM35 temp sensor on a MAC motor so I performed hte LM35 sensor mod to my CAV3 ...
Now I am running a crystalyte 4065 which has a 10K NTC thermistor. I started to convert my CAV3 temp sensor input back to stock but OF COURSE I've lost that tiny stock 4991 surface mount resistor. I was able to source another surface mount resistor in the 4.7K range so I installed it.
...
RIght now the bike is sitting at 23C but the CAV3 is reporting it as 65C! I'm assuming this is due to the resistor I used.
m52 power! said:
Well - there are only two parts in play here: the thermistor and the pullup resistor:
What is the resistance of the thermistor at room temperature?
(We know it should be 10K at 25degC.)
- If it measures 10K then the pullup resistor may be damaged.
- If it does not measure ~10K then the thermistor is either damaged or is not the proper part
m52 power! said:
So I was wondering what my options are? Can I do a custom sensor calibration in the CAV3? How do I know the other values? OR should I just simply source hte correct 4991 resistor?
As far as the 5K resistor is concerned, you can just parallel two thru-hole 10K resistors across the NTC and +5v pads. There's really no reason to tinker with SMD on the crowded PCB (unless you're very comfortable doing that). 10K parts are readily available. Or stack a couple of 10K SMD parts...
You cannot switch the V3 to linear mode and calibrate it to work properly using a 10K NTC device because the linear mode expects a PTC device and entry of negative coefficients is not supported. That is, with an NTC (Negative Temp Coef) device the resistance decreases with increasing temperature. For example, if you go to the SETUP TEMP SENSR screen you should see a voltage of about 3.33v for 25degC and about 1.48v for 65degC.
In any case, you can do the math, but the small difference between your substituted 4.7K part and the specified 4.99K resistor cannot account for the large error you are seeing....