Thread: alternator's w wire & digital multimeter?

W wire is usually just a tapping from one of the windings just before the diode, which means its AC. I'm not sure how you'd calculate the frequency, but if you have a multimeter with frequency measurement you should be able to read it with that.
There should be plenty of circuits on the Arduino forums etc showing how to measure AC frequency.

Steve

I'm doing exactly that with an arduino on another project.
I rectified the wave with a diode to make a 7v pulse and used that to blow up my arduino.
Bought a new arduino and built a voltage divider to halve the signal to 3.6v. About to try again.

The one I found last night for measuring 240vac frequency used an optocoupler. Might be an option and keep the alternator isolated from the Arduino.

Steve

Originally Posted by steveG

The one I found last night for measuring 240vac frequency used an optocoupler. Might be an option and keep the alternator isolated from the Arduino.

Steve

That's expensive over-kill. It's a ~7v analogue signal you're talking about. Not 240 VAC.
I killed my first arduino because I thought it might handle 7v. But no. Anything over +/-5v and it's toast.
A simple voltage divider to take the +/-7V ripple down under 5v and you're good.

I wouldn't be that confident about those 7V. Or you used some special sort of diode? Could you share your schematics? part numbers? The thing is the higher the rews, the higher should be your voltage (otherwise you wouldn't need voltage regulator, right?). Or W wire is just after the regulator? 14v p-p, thus positive semiperiod is 7v?

here's my alternator. It's lucas, A133/80
so basically it should be one pulse per rotation?

IMG_20140325_144351.jpg

can anyone explain what are all these wires?
I wonder why those engineers used that complex schematics for instrument cluster? I am afraid of putting it apart. Speedo unit utilizes magnets?

optocoupler costs less than a dollar. should the voltage regulator fail for any reason, the optocoupler would be a sacrifice that would save your arduino ;-)
btw, you baked the whole chip or just one port of it?

Originally Posted by russotouristo

I wouldn't be that confident about those 7V. Or you used some special sort of diode? Could you share your schematics? part numbers? The thing is the higher the rews, the higher should be your voltage (otherwise you wouldn't need voltage regulator, right?). Or W wire is just after the regulator? 14v p-p, thus positive semiperiod is 7v?

here's my alternator. It's lucas, A133/80
so basically it should be one pulse per rotation?

IMG_20140325_144351.jpg

can anyone explain what are all these wires?
I wonder why those engineers used that complex schematics for instrument cluster? I am afraid of putting it apart. Speedo unit utilizes magnets?

The 7.something v is half of your charging voltage. For me this is about 7.2v. I have used a voltage divider with equal resistors to cut this voltage in half to ~3.6v.
This will give me plenty of space before it could get over 5v and damage the arduino.

I don't know exactly what failed on the arduino, but the LCD output is now gibberish and it won't load new instruction sets from the PC.

so the voltage regulator is inside the alternator and is BEFORE the W wire, right? I am not that confident
did you know that before using electronic v regs land rover utilized tricky assembly based on bimetallic plates to close or open the battery circuit depending on the voltage generated by the alternator, and the cutoff voltage wasn't that steady and predictable as nowadays? the battery could easily receive 20V, though, for rather short period of time (matter of seconds)