Author Topic: Tach (Read 121977 times)

Mark(The Miser)UK · « **Reply #30 on:** March 03, 2006, 03:25:45 pm »

Subject to the weather and my time and my being able to find my 1950's oscilliscope out in the shed; I'll see if I can note pulse frequency to rpm on the tach...Edited [over the weekend] :oops:

Busdriver · « **Reply #31 on:** March 03, 2006, 09:06:07 pm »

This is slighty off subject, but I found a generic 6000 rpm tach that has 3 terminals on the back, positive, ground, & signal. It also has a four position switch, 4, 6, & 8 cylinder, and the 4th position is marked "12 pole alternator". Will this "12 pole alternator" switch position accept the signal from the "w" wire from the VW alternator?

regcheeseman · « **Reply #32 on:** March 06, 2006, 06:20:19 am »

Tried to test the modified circuit board on the weekend,

Rigged up the altenator on the bench but I've had major problems getting my altenator to do anything. }

spent a few hours checking and double checking before stripping the altenator and checking all the internals. I cleaned some contacts and rebuilt it.

Still no joy.

I got my spare petrol alt out and ran that up, it was fine. So I started to swap bits from one alt to the other (needing a working one with a W terminal).

Anyway I went to connect the brokeen alt up and thought 'whoa not that way round and went to swap battery terminals' - it was then I noticed......

For some reson I had been connecting the 'broken' alt up to the battery wrong and when I swapped alt I also swapped terminals.

so I connected it up fine and suddenly my broken altenator is 100%

Anyway I connected the modded tacho up and span the alt up - the needle moves!!! not much but it moved...maybe up to about 1000rpm? (no face or needle on tacho)

The alt has a ratio of 1:2.4 from the crank and my drill runs 3000 rpm with no load giving an maximum effective crank speed of about 1250rpm.

Facking sweet - looks like its a go!

I have removed some of the previous images as I have made further modifications and will produce the new artwork soon.

biobill · « **Reply #33 on:** March 06, 2006, 09:31:56 pm »

I'm just starting into a diesel conversion on a '93 Cabriolet. As the car comes with a tach I found this topic to be very interesting. Turns out, however, that I've got a few different challenges. First, I've got the Motometer gauges (like jonny and other Europeans?). Also, probably because the engine is "run by a computer" in 93, the back of the gauges looks very different (I just ripped the dash apart today and discovered this) something of a ribbon cable covering the entire rear and top of the instrument cluster with a row of resistors on the top. No 555 chip here. I'm guessing all of the "smarts" are in the computer. Unless someone has some good suggestions (electronics is not my specialty) I'm thinking I've gotta use the older gauge cluster to make anything work (and it has no tach). Hummm... Any ideas?

PS If those pictures don't show up (I'm new at this) you can go directly to
http://www.renewableenergyworks.com/transportation/dieselcabby.html
to see the gauge pictures and more.

regcheeseman · « **Reply #34 on:** March 08, 2006, 04:54:27 am »

Biobill,

Depends entirely on what diesl you are using.

But your guages sound perfectly normal - the ribbon on the back (membrane) is common to all clock assemblies.

You need to take the clocks apart to get to the guts of the tacho - which is where you should find the board with the chip (SAK215) is....... maybe. :?

biobill · « **Reply #35 on:** March 08, 2006, 10:15:45 am »

Thanks! I guess I was expecting to see something different. I'll keep digging and let everyone know what I find!

I've got a 1.6 NA diesel from a 1981 Rabbit to put in. The fun has just begun!

regcheeseman · « **Reply #36 on:** March 08, 2006, 11:03:14 am »

Ok, here we go...

The original gasser schematic

Re-worked into diesel w terminal version

The gasser board before (click to enlarge)

replace R1 with 100 ohm
leave R2
replace R3 with wire link
replace R4 with 191 ohm
replace R5 with wire link
replace R6 with 10K
replace R7 with 15K

replace C1 with 10nF
remove C2
leave C3
remove C4
replace C5 with 47nF
fit C6 3.3uF in vacant spaces next to tacho motor (red and blue) wires or desolder wires from board, fit cap and then solder wires to cap wires/board.

adjust RV1 to mid range

The final working board.

Note the two resistors joined together are because I could not find a 191 ohm resistor so joined a 180 and a 10.

C6's value is not critical, I used a 2.7 instead of a 3.3, it works fine without this cap altogether and I believe is only there to stop needle flutter (I didn't have a problem with or without this fitted)

Job done!

fatmobile · « **Reply #37 on:** March 09, 2006, 01:40:28 am »

Next we do it to a Rabbit Gti instrument cluster.

johnny · « **Reply #38 on:** March 09, 2006, 04:00:38 am »

In the last week I discovered VW jused a lot of different setups on the tachs. Even the same brands can be found with different setups. Last week I bought a original '90 GTD cluster to replace the tach into my gas-cluster but found out this was not possible because here they used the main printcircuit for the tach and not a stand alone on the tach.

I'm now trying to compare my '86 gastach from motometer with the vdo of regcheeseman. I don't know much about electronics but I can see different resistors, capacitors and a different IC on the printcircuit.
I will post a pic of my motometer and hope someone can help me out.

regcheeseman · « **Reply #39 on:** March 09, 2006, 04:33:32 am »

Quote

Next we do it to a Rabbit Gti instrument cluster.

Mine started out as a Golf GTI cluster..... is it not the same?

vwmike · « **Reply #40 on:** March 09, 2006, 04:46:59 am »

Quote from: "regcheeseman"

Quote
Next we do it to a Rabbit Gti instrument cluster.

Mine started out as a Golf GTI cluster..... is it not the same?

In the US we got US made Rabbit GTI's. They are very different. Here is mine:

And here is the instrument cluster:

mortskeg · « **Reply #41 on:** March 09, 2006, 04:55:59 am »

Hey guys,
Well the westmoreland style tach like in the 83-84 gti's is a bit different. We've got a big pink box looking thing and some other chicklet gum looking things... haha. You've inspired me though, cheeseman.

Here's my feeble attempt at doing the above with the westmoreland gas tach circutry. Unfortunately the flipside of the board is white, so the yellow lines were hard to see, so I made them blue. I couldn't tell with the solder if some of the areas near the trim pot were maybe connected? They kinda looked like it but it doesn't really make sense to me. Anyhow, everybody feel free to correct what is wrong, or use this image how you wish. Keep up the good work and let me know if there is any info you need regarding the US tach. Cheers!

regcheeseman · « **Reply #42 on:** March 09, 2006, 07:00:49 am »

I'm on it Morts!

The big pink thing, has it got an adjustment screw?

I'll need numbers, colours, values whatever I can't make out on your images....

Let me just annotate the image and knock up a schematic first....

regcheeseman · « **Reply #43 on:** March 09, 2006, 08:15:53 am »

Mods for westmoreland clocks...

First the schematic as is..

The annotated board..

A lot of similarities with the original VDO circuit, I'll wager the SAK chip is the same and converting to the diesel tacho circuit should work..

Make R1 = 100ohm
replace R2 with 72ohm
replace R3 with wire link
replace R4 with 191ohm
replace R5 with wire link
replace R6 with 10K
replace R7 with 15K

replace C1 with 10nF
leave C3
remove C4
remove C?

make RV1 = 22K
remove RV2 and replace with 47nF cap

If you can get a 3.3uF across the needle output wires then do so....I've no idea why, guess the blokes at VDO just liked drawing capacitors!

God am I bored at work today!

RabbitGTDguy · « **Reply #44 on:** March 09, 2006, 10:20:37 am »

I've got a fun one for you then...

I was using the optical setup that roger brown advertising in conjunction with the Westmoreland style GTI cluster, works well...but isn't as "clean" as I'd like the setup to look this time around.

I'm also having to change directions a little bit with my mTDI project and without getting into details I'm going to use an early cluster. I was able to get the early tach with it as well and I pulled the board today to see how it compared to the boards already up here and it looks different...so, yet another variation... think we could make it work off the W terminal? My setup will be using the serpentine belt MK3 style, non a/c etc.... the alternator on the MK3 also has the W provision there as well. Should be accurate with serp too because of the fact that they are harder to slip...

So, now I want to post a pic of the board for all to see but it seems that the fiancee must have take my digi camera to school for some pics today! Will post pics later then i guess.

Its a motometer tach from '78 MK1 or so...

Joe