electrical/electronic gurus

MadScientistMat said

What's the minimum voltage the trip computer needs to operate? A small lead acid battery is a good choice if using a diode as the charging demands are simpler. Another option might be to take two USB phone battery banks and wire them in series - they would supply 5 volts each, so that could work if your device works on 10 volts.

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The phone batteries sounds like what I want to do. I don't know the minimum voltage requirement for the computer, but the trouble shooting page lists a possible problem if the voltage to the unit drops below 5 volts during engine cranking. I would assume 10 volts would be ok as an emergency backup. The unit needs to be calibrated to the vehicle.
1: pulses per mile
2: fuel flow meter to actual fuel usage
3: size of the fuel tank
4: clock time
If memory power is lost these all need to be recalibrated
The more you drive the more accurate the outputs become, as you can "tweek" the calibrations.
There are several different versions. I have a ZT-1 with cruise control, a ZT-3, and a ZT-4 which is on my 64 Valiant.
I also have a Direct Connection P4349443 performance timer, that was made by Zempco.
This is similar to the units I have. 1979 Zemco ZT-3 Driving Computer NEW OLD STOCK Complete MPG MPH Fuel | eBay