Thread: RRC Engine RPM signal

Originally Posted by fraser130

Does anyone here happen to know how many pulses the alternator w terminal outputs for each rotation of the engine?

Ta,
Fraser

And without hijacking your thread Fraser, could some explain how this works ?

The AC voltage from the W terminal has 6 cycles per alternator revolution as that is how many poles it has. Multiply this by the ratio of pulley diameters, crankshaft to alt.

Originally Posted by bee utey

The AC voltage from the W terminal has 6 cycles per alternator revolution as that is how many poles it has. Multiply this by the ratio of pulley diameters, crankshaft to alt.

Unfortunately I don't have a RRC handy to check that on, I'm just trying to make up a circut to simulate the engine doing approx. 1000RPM, and need the frequency to set the circut up.

Thanks but, I'm getting closer!

Fraser

Guess about 3.5:1? When I get a minute and my mate turns up I can measure his.

Originally Posted by bee utey

Guess about 3.5:1? When I get a minute and my mate turns up I can measure his.

Thanks bee utey, that would be fantastic.
So I may be looking at around 350Hz.........

Cheers,
Fraser

Originally Posted by pop058

And without hijacking your thread Fraser, could some explain how this works ?

From what I gather Pop, it's just a "feed" from one of the phases in the alternator taken before the diodes, and it's used as an engine rpm signal on lots of vehicles, usually diesel (but not always).
Obviously the Tachometer needs to be calibrated to give an accurate reading as the alternator runs much faster than the engine speed, and it varies depending on how many poles the alternator has, and the pulley sizes too!

Fraser