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Tachometer Wiring Ideas

13135 Views 6 Replies 4 Participants Last post by  Mr. Sharkey
Continued from the EV Calculations Thread

KiwiEV, the 1.5 volts that you're supplying to the tach isn't really what the gauge needs. It is just a coincidence that 1.5 volts moved the tach to 4,000 rpm. A conventional 4 stroke piston engine will send a signal (a 12 volt signal IIRC) to the tach one time for every 2 rotations of the crank. I have heard of people placing inductive pick-ups on the front shaft of a Warp8 or similar double shaft motor, but that would send a signal to the tach twice as often as needed. I guess it depends on the car as to whether or not the tach would like that signal. How is it possible to divide the number of pulses by two?
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So what are the chances of an average person with limited mechanical knowledge finding one of these on a trip to the wreckers? Would there be one on every abs car? or just on an audi? or just on those audis?
 

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So does the voltage increase with RPM or does it just let out a pulse every time a tooth (is one of the teeth still called a tooth on a sprocket or is that just mouths?) goes past? I'm trying to guess how it works by its different names "induction" and "variable reluctance" sound to me like it was just an electromagnet and a sensor that measures the induced eddy currents in the spinning wheel which would probably cause increasing voltage with increasing rpm BUT judging by the way you described that tachometers work i could also guess that as the surface of the sprocket moves closer and further away as the teeth move past the induced voltage would get greater and smaller giving you a signal that looked more like AC i.e. pulsing which would be easier to hook up directly to the tacho. So i guess the second option, am i right?
 
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