Alternator W terminal.

[ajlelectronics]

What should I expect, voltage and waveform please?

Tachometer on the boat's starboard engine works reliably. Swapping for a new Chinese one, it will not start reading until the RPM is well above idle. It sticks at 1100 on the way back down.

I have put it onto a signal generator and it is reliable at 4v peak to peak upwards. That suggests that the W output is lacking.

One little clue may be that the original tacho has a S+ and an S- terminal, but the replacement has just a signal pin.

Rabiah Asiya

Just playing with tachometers. Original Volvo works reliably. Chinese one doesn't, yet it works perfectly from a function generator at 4vpp.

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[m_c]

I always thought the W was simply a pre-rectified feed from one of the windings, so I'd expect it to be near battery voltage, but I'm guessing it's probably got a resistor or two involved to provide protection should it be shorted out.

Best search result I can find about it is on the Arduino forum - https://forum.arduino.cc/t/reading-out-w-contact-alternator/1403594/17
Seems to also be variable voltage.

 

[ajlelectronics]

I always thought the W was simply a pre-rectified feed from one of the windings, so I'd expect it to be near battery voltage, but I'm guessing it's probably got a resistor or two involved to provide protection should it be shorted out.

Best search result I can find about it is on the Arduino forum - https://forum.arduino.cc/t/reading-out-w-contact-alternator/1403594/17
Seems to also be variable voltage.

Interesting, thank you for that.