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Old 05-15-2012, 06:12 PM   #1
boltbustingtorq
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Default Can you data log a "local" power voltage using the SCT analog input?

Can you (or has anyone tried to) data log the voltage of an incoming power wire? I'm assuming the SCT analog inputs want the signal to be between 0 - 5V so could you use some resistors as a voltage divider (say a 10k ohm and a 3.3k ohm) to scale the voltage down 1/4th and data log the result?

Or will there be too much noise or ...?

The hope is to be able to monitor voltages at different locations on the car -- for example whether you are seeing low voltage at the FPDM (to see if you do or do not need to wire upgrade things).


Thanks,

--Tim
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Old 05-16-2012, 05:42 PM   #2
02sonicGT
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Quote:
Originally Posted by boltbustingtorq View Post
Can you (or has anyone tried to) data log the voltage of an incoming power wire? I'm assuming the SCT analog inputs want the signal to be between 0 - 5V so could you use some resistors as a voltage divider (say a 10k ohm and a 3.3k ohm) to scale the voltage down 1/4th and data log the result?

Or will there be too much noise or ...?

The hope is to be able to monitor voltages at different locations on the car -- for example whether you are seeing low voltage at the FPDM (to see if you do or do not need to wire upgrade things).


Thanks,

--Tim
Although I have not tested, I see no reason why using resisters to step the voltage down would not work.

I only question the fact that you are running wires to monitor the voltage so why not just add the relay and fuse to bump the voltage. It is a fact the voltage from the fpdm is lower to the pump than if hard wired.
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Old 05-18-2012, 06:06 PM   #3
Joe@Trick Tuners
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sure you could do that, but I'm not sure that it will provide much useful info. There is a parameter in the ECU that describes the voltage drop to the FPDM and I believe it is around 1.7V on the 2V and around 0.9V on the 03-04 cobras (due to thicker wire). If the pump is pegged, do a wire upgrade to the FPDM and to the tank and it will get you a bit more DC, sometimes around 2-10%.
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Old 05-23-2012, 01:16 PM   #4
boltbustingtorq
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I ended up adding some leads and measured it with a volt meter sitting on my dash (granted it's doing some "averaging") but I was able to see the BAP output voltage was a constant 17.1-17.2 volts (even when the fuel pump duty cycle was 100%)

--> So bigger wires wouldn't help in this case (initially the thought was the voltage was dropping enough to get the KB BAP out of voltage regulation (< 11 V input).
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Old 05-23-2012, 09:50 PM   #5
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Nice! I remember when I street tunes a 408ci fox with a volt meter. Crazy! The bap wire is fine, but there is probably some drop from the fpdm to the pump.
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