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Making a W connection for Tacho to alternator
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Posted 4/17/2008 9:25 AM
amzimmy
Elite Veteran




Date registered: Apr 2006
Location: South Africa/Italy
Vehicle(s): GD300 1981, Alfa GT 3,2 V6, Alfa Brera Q4 3,2 V6.
Posts: 850
500
Making a W connection for Tacho to alternator

Just want some input to decide what to do. I have replaced the alternator to my GD300. However, the new alternator (Bosch 65A) does not have the "W" connection for the tachometer. I have been told that I have to open up the alternator and connect a loose wire to one of the three wires of the armature, surrounding the main rotating body, to be able to pick up the AC frequency that will then operate the tachometer (VDO). Has anyone of you had some experience with this?

amzimmy
#117346
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Posted 4/17/2008 5:33 PM
hipine



Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
5000
Look what I found! Convert tach from petrol car to run off alternator of diesel!

http://www.4crawler.com/Diesel/CheapTricks/Tachometer/vwdslfaq.txt

Still looking to help you out, M.  I just got really excited when I saw the above because I know others here have asked about it.

-Dave G.



Edited by hipine 4/17/2008 5:34 PM
#117397 - in reply to #117346
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Posted 4/17/2008 6:08 PM
hipine



Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
5000
RE: Making a W connection for Tacho to alternator

Well, the general concensus of info I found was that the "W" terminal is wired to one of the stator windings where it attaches to one of the diodes.  I've never done it myself.  But if I had the old alternator that DID have the W terminal there on the bench beside me, I would just open it up and see if I felt I could duplicate what I found inside.  Do you still have the old alternator?

-Dave G.

#117413 - in reply to #117346
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Posted 4/17/2008 6:30 PM
Steve D
Veteran




Date registered: Apr 2006
Location: Flowery Branch, GA
Vehicle(s): 1984 280GE cabrio; 2001 Ford Excursion diesel
Posts: 102
100
RE: Making a W connection for Tacho to alternator

I had an alternator built for a diesel with the stator wire and used a VDO tach, even with the dip switches turned down to their lowest setting my LR starts at 2000 RPMs. I have learned to look at it and automatically subtract 1500 RPMs.
#117420 - in reply to #117346
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Posted 4/17/2008 6:37 PM
hipine



Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
5000
RE: Making a W connection for Tacho to alternator

Yep.  I think that's where the trim pots come in from that article.

-Dave

#117422 - in reply to #117420
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Posted 4/18/2008 2:44 AM
amzimmy
Elite Veteran




Date registered: Apr 2006
Location: South Africa/Italy
Vehicle(s): GD300 1981, Alfa GT 3,2 V6, Alfa Brera Q4 3,2 V6.
Posts: 850
500
RE: Making a W connection for Tacho to alternator

hipine - 4/17/2008 12:08 AM

Well, the general concensus of info I found was that the "W" terminal is wired to one of the stator windings where it attaches to one of the diodes. I've never done it myself. But if I had the old alternator that DID have the W terminal there on the bench beside me, I would just open it up and see if I felt I could duplicate what I found inside. Do you still have the old alternator?

-Dave G.



Dave, Luckily I have the old alternator, I will open this one up and look inside, I will make some picks as all stages progresses so that I and especially you can see what is going on, unfortunately I am not that technical especially with electrical stuff and need here some assistance from you.

Many thanks, amzimmy

Edited by amzimmy 4/18/2008 2:44 AM
#117471 - in reply to #117413
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Posted 4/18/2008 7:40 AM
amzimmy
Elite Veteran




Date registered: Apr 2006
Location: South Africa/Italy
Vehicle(s): GD300 1981, Alfa GT 3,2 V6, Alfa Brera Q4 3,2 V6.
Posts: 850
500
RE: Making a W connection for Tacho to alternator

Here are now the sequences in which I dismatled the original Alternator.

Photo1: showing the "W" connection

Photo2: alternator dismantled

Photo3: showing the pin connected to the "W" attachment

Photo4: showing the "W" connection

Photo5: showing the fitted "W" on the holding plate

Photo6: showing the three wires and the pin protruding from "W"

Photo7, 8, 9: all three wires make a closed circuit with pin "W"

and now what? do i connect the wire of the new alternator to all of the three wires or do I connect to one and which one?

amzimmy



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#117479 - in reply to #117471
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Posted 4/18/2008 10:22 AM
fernweh
G-Class Treffens Host


Date registered: Apr 2006
Location:
Vehicle(s):
2000
Re: Making a W connection for Tacho to alternator

Michel,

I would try to find out if the stator wire connection goes directly to the "w" terminal or is there one of the big diodes between.
Definitely your new wire should not touch the ground (housing), if possible drill a hole through the back plate , insert a small plastic tube and run your new "w" wire inside of it - lots of vibrations there to shave through normal wire insulation.

Good luck with it

karl
#117492 - in reply to #117346
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Posted 4/18/2008 11:01 AM
amzimmy
Elite Veteran




Date registered: Apr 2006
Location: South Africa/Italy
Vehicle(s): GD300 1981, Alfa GT 3,2 V6, Alfa Brera Q4 3,2 V6.
Posts: 850
500
Re: Making a W connection for Tacho to alternator

Karl, I can't separate the plastic housing from the steel frame without ripping it apart (I will recondition the unit and keep it for spare) therefore I can not see what is behind the plastic housing . I think that I will do exactly what you suggesting, by taking the new wire through the body part with a Bakelite or similar insulation maybe even a ceramic sleeve. However the reading that I got with the Multimeter is that the "W" connection is somehow looping with all three wires......or am I reading wrongly?

amzimmy
#117497 - in reply to #117492
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Posted 4/18/2008 4:24 PM
fernweh
G-Class Treffens Host


Date registered: Apr 2006
Location:
Vehicle(s):
2000
Re: Making a W connection for Tacho to alternator

I wouldn't do ceramic......bakelite is not bad or just a nice plastic sleeve.

I have a feeling, there is a diode between the "W" post/connection and the stator wire, the diode lets the current "flow" just one-way - can't find any diagram in regard to this......

Just try it out and see what the tach is doing - .......

karl
#117520 - in reply to #117497
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Posted 4/18/2008 10:00 PM
hipine



Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
5000
RE: Making a W connection for Tacho to alternator

Sorry so late getting back to you M.  Crazy busy lately.  The circuit diagram on this site shows why you read a connection to all three windings....they're connected.

http://www.allaboutcircuits.com/vol_6/chpt_4/8.html

But what you did prove is that the W is connected to one of the windings.  You can do one more verification.  If you set your meter for "continuity test" and touch the + probe to the BAT terminal and the - probe to the W post, the meter should beep.  If you switch the leads, it should not beep.  Then touch the - probe to the case and the + probe to the W post, again it should beep.  Reverse the probes and again it should not beep.  This is telling you that the W is wired in between the two diode banks in the picture.

I'd do just what Karl suggests on your new alternator and solder the wire to one of the stator leads.  You can bench test it by pluging the alternator in to the wiring harness and using some adapters and a socket or something to spin the alternator with an electric drill that you know the full RPM of.  Make sure you turn on the key to do your testing so the alternator and tach are getting battery juice.

Make sure the pulley diameter of your new alternator matches the old one.  Your tach will be "programmed" to read out engine RPM even though it's getting it's signal from "alternator RPM"

-Dave

#117546 - in reply to #117479
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Posted 4/19/2008 2:43 AM
amzimmy
Elite Veteran




Date registered: Apr 2006
Location: South Africa/Italy
Vehicle(s): GD300 1981, Alfa GT 3,2 V6, Alfa Brera Q4 3,2 V6.
Posts: 850
500
RE: Making a W connection for Tacho to alternator

Thanks Dave and Karl, I understand now perfectly what I have to do. You both have been a great help......as usual. What can we do without your expert help and the facility to have such a great Forum?
Unfortunately, due to family matters I have to go to Europe on Monday, and have to shelve the project until the 24th May. I only be able to give you some feed back at the end of May.
Thanks again and hope to see you in June?

amzimmy
#117553 - in reply to #117546
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Posted 4/19/2008 5:36 AM
amzimmy
Elite Veteran




Date registered: Apr 2006
Location: South Africa/Italy
Vehicle(s): GD300 1981, Alfa GT 3,2 V6, Alfa Brera Q4 3,2 V6.
Posts: 850
500
RE: Making a W connection for Tacho to alternator

Dave, I have taken the time to the test with the multimeter. Set the continuity test, put the +probe to the BAT terminal and the -probe to the W post = no beep, reverse the operation = no beep. Done the second test, put the +probe to the W post and the -probe to the case = no beep, reverse to operation = no beep. What now?

amzimmy

Edited by amzimmy 4/19/2008 5:37 AM
#117558 - in reply to #117546
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Posted 4/19/2008 10:39 AM
hipine



Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
5000
RE: Making a W connection for Tacho to alternator

Our thoughts are with you for your time in Europe, M.  

I'm still on the fence for June.  The 2600 mile drive is daunting, and I don't really want to fly in.  Maybe the thing to do is to make it about a 2 week vacation and visit lots of friends around the west.  I am building up a lot of available time off from work, and working too much.  June might be just the time to escape for two or three weeks.  I'll keep you posted.

All the best,

-Dave G.

#117577 - in reply to #117553
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Posted 4/19/2008 10:44 AM
hipine



Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
5000
RE: Making a W connection for Tacho to alternator

Looks like your multimeter won't overcome the threshold voltage of the diodes.  It takes some voltage to get across them even in the "right" direction.  No worries.  You're on the right track.  If I remember correctly you had near zero resistance from the windings to the W post.  That's a good sign that there isn't circuitry in between them so I'd just try taking a wire from one of the stator windings to your alternator.

-Dave G.

PS - I see the switch on your meter is in AC mode.... it should be on DC for these tests.  Shouldn't make a difference, but just good practice.

PPS - been thinking about this and I think "W" might mean "wave" as in the sine-wave voltage that comes out of the stator directly from the windings... or maybe W means "winding"....  Or maybe it means we should drink some "Wine" to help our brains figure out how to "Wire" it? 



Edited by hipine 4/19/2008 10:58 AM
#117578 - in reply to #117558
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Posted 4/19/2008 12:39 PM
amzimmy
Elite Veteran




Date registered: Apr 2006
Location: South Africa/Italy
Vehicle(s): GD300 1981, Alfa GT 3,2 V6, Alfa Brera Q4 3,2 V6.
Posts: 850
500
RE: Making a W connection for Tacho to alternator

Thanks Dave for your thoughts, it won't be a holiday, life always throws you a curved ball when least you expect!
You got me in stitches about the "W" (I like the wine bit) I, myself, don't really know what it stands for. On my return I will surely give it a try.
I sincerely hope that you will make the treffen in Oregon!

amzimmy

Edited by amzimmy 4/19/2008 12:41 PM
#117585 - in reply to #117578
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Posted 7/2/2008 3:39 AM
amzimmy
Elite Veteran




Date registered: Apr 2006
Location: South Africa/Italy
Vehicle(s): GD300 1981, Alfa GT 3,2 V6, Alfa Brera Q4 3,2 V6.
Posts: 850
500
RE: Making a W connection for Tacho to alternator

Here I am back again in SA. First thing to attend to, my "W" connection of the rev counter to the alternator.

Opened up the new alternator (Bosch 75 Amp), soldered with silver solder a piece of silicone insulated wire with an extra heat protection sleeve, to one of the three windings terminal, put the casing back together, placed the new wire through the casing with a rubber sleeve, fitted back the alternator, connected the wire to the rev-counter, started the engine ......... and ........voila, my rev-counter was back in operation

Thanks guys for all the help and suggestions, yet an other job successfully done!

amzimmy
#125770 - in reply to #117585
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Posted 7/2/2008 10:42 AM
mgrays
Regular


Date registered: Oct 2007
Location: UK, Scot, Aberdeen
Vehicle(s): 300GDSt 1988
Posts: 81
50
Re: Making a W connection for Tacho to alternator

Watch out on some alternator.... most have 3 windings like the ones shown.. I came across one the other day that was 4 windings instead of 3 (on a Rover 400 with a PSA(Peugeot) 1.9td .. and then the frequency will be wrong.. hence Steve D's problem with the rpm not matching on the rev counter.. sounds like the wonders of (Land) Rover+Bosch using 4 windings instead of more normal 3 windings.
#125786 - in reply to #117346
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Posted 7/2/2008 12:58 PM
amzimmy
Elite Veteran




Date registered: Apr 2006
Location: South Africa/Italy
Vehicle(s): GD300 1981, Alfa GT 3,2 V6, Alfa Brera Q4 3,2 V6.
Posts: 850
500
Re: Making a W connection for Tacho to alternator

Mine had definitively only three windings and its working correctly, checked with magnetic revolution counter on the crank-pulley. About LR's ....well they always have to have something different to create some difficulties!

amzimmy

Edited by amzimmy 7/2/2008 12:58 PM
#125793 - in reply to #125786
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Posted 7/2/2008 4:00 PM
hipine



Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
5000
Re: Making a W connection for Tacho to alternator

Refresh my memory M.  Is yours a factory G tach, or an aftermarket one?

-Dave G.

#125800 - in reply to #125793
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