What does the TD "W" alt. terminal actually output

[Mardak]

Hi guys.  I'm using an A2 TD cluster for my mTDI Caddy swap, and was hoping to use Megasquirt to drive my tach.  I found a circuit to build to take the Megasquirt "ECU" type tach output and condition it to drive a gasser tach (that normally gets driven off the ignition coil), but that won't work for the TD cluster since it gets it's signal from the "W" alt. terminal.

Anyone know what the output of the "W" alternator terminal looks like?

Thanks!

Mark.

[Vincent Waldon]

It's a sine wave that represents one of the three phases of the AC signal upstream of the diode bridge... it's at approximately 12X the frequency of the  equivalent gasser tach signal and a different amplitude so not trivial to convert.... more so to upconvert since you'd need a frequency multiplier.

I'm not sure I understand where the Megasquirt enters into your mTDI conversion... you have a diesel engine and a diesel cluster... all you need is a diesel alternator (or open up your gasser alternator and add the W terminal) and you're good to go ??

Or am I completely missing something ??!!!

Vince

[Mardak]

It's a sine wave that represents one of the three phases of the AC signal upstream of the diode bridge... it's at approximately 12X the frequency of the  equivalent gasser tach signal and a different amplitude so not trivial to convert.... more so to upconvert since you'd need a frequency multiplier.

I'm not sure I understand where the Megasquirt enters into your mTDI conversion... you have a diesel engine and a diesel cluster... all you need is a diesel alternator (or open up your gasser alternator and add the W terminal) and you're good to go ??

Or am I completely missing something ??!!!

Vince

Nope, I was the one missing something...  The alternator I have doesn't have a "W" terminal labeled.  The two "terminals" connected to the connector are labeled "DF", and "D+" (european sourced alternator - "DF" = "W"?).  The other alternator I have doesn't have any labeling, other than the B+ terminal (it's a Valeo brand from France).  From the bleary eyed late night research I've just done it appears that most of the 90's VW alternators have a "W" terminal, so I'm assuming one of the wires in the alternator connector is indeed the "W" output...  I'll do some more digging tomorrow - I gotta get some sleep...

Later,

Mark.

[Vincent Waldon]

No worries... we're all on the same page now.

Gasser alternators have 2 wires/terminals, and diesels have three.

Pretty sure on the alternator you have "DF" is the *field* wire that goes to the alternator light on the dash, and "D+" is the battery post (is it a really heavy post in comparison to the other ??)

On your Valeo the B+ is the battery post.

The diesel alternators have a third terminal, usually a spade lug but sometimes a small stud, "W", that drives the alternator.

If the above is true you have a couple of options:

a) get a diesel alternator.... ideally you need one anyway because it has a higher output than the gasser alternator
b) pull the back off the alternator and wire in your own W terminal.  I've got a generic schematic I can post if you go this way...

One other thought... if you post the part numbers some smart person with ETKA may be able to tell you exactly what alternator you have.

[Mardak]

No worries... we're all on the same page now.

Gasser alternators have 2 wires/terminals, and diesels have three.

Pretty sure on the alternator you have "DF" is the *field* wire that goes to the alternator light on the dash, and "D+" is the battery post (is it a really heavy post in comparison to the other ??)

On your Valeo the B+ is the battery post.

The diesel alternators have a third terminal, usually a spade lug but sometimes a small stud, "W", that drives the alternator.

If the above is true you have a couple of options:

a) get a diesel alternator.... ideally you need one anyway because it has a higher output than the gasser alternator
b) pull the back off the alternator and wire in your own W terminal.  I've got a generic schematic I can post if you go this way...

One other thought... if you post the part numbers some smart person with ETKA may be able to tell you exactly what alternator you have.

I put the numbers into ETKA, but I don't see any information to determine whether or not the "W" terminal is included.  The range of vehicles that the alternator came on is pretty wide.  Here's the part number off the 120amp Valeo - 037 903 023G.  According to ETKA it's been replaced by: 028 903 018 A.  Maybe I just don't know where to look for the info in ETKA...

Thanks,

Mark.

[Mardak]

Here's a pic of a bosch alternator that looks like both of mine.  It labels one of the two wires in the connector as "W".  Can anyone confirm this?



BTW, the web page this pic came off of has some really good info on servicing these alternators:

http://www.rangerovers.net/rrupgrades/electrical/boschalternator.html


Later,

Mark.

[hillfolk'r]

"w" leads can be put into any "vw alternator" in about 20 mins
you need to solder a wire  to one of the stator leads before  it goes to  the diodes
its an ac signal,like the ac that comes out the wall(120vac,60hz in the us) :wink:
but i remember checking the voltage on one a long time ago,and without lookin at the tach,id say i had around 7 vac at 3000 rpms
but the tach really doesnt care about voltage,it reads frequency(hz)

[Baxter]

http://www.brick-yard.co.uk/VehicleSpecific/T3/info/DIN.htm

A list of DIN numbers that may be of use.