VDO Hall Sender.

[Kelvin12]

G'Day Jon,

That's the clear diagram of the foggy one I have and way better. OK so its a pulse generator.... now any idea of where the wires go to the tacho. I have a 2 wire diagram but haven't been game to hook it up just in case. Cooked the old one, not that it was any good but still a worry that it died. Gathering all 3 wires go back to the tacho somehow ????.

Can't tell you how many auto electricians have had a look at this and told me its a Hall Effect sender. They are fitted to Australs and Denning Coaches from the 70's to 80's driving the tacho and speedos.

Meant to tell you the hazard switch connected as you said. Good job. Unusual as they seem to be dual circuit in their connection. German engineering at its best I guess.

Dirk.

[jon_d]

I'd try this:

And run the third (missng in the diagram) wire from the third terminal to pin 4 on the tacho. (+battery) To be safe, use a low current fuse, say 250mA.

http://sydney.edu.au/engineering/aerome ... wiring.PDF

[Busman]

Hook it to your alternator and don't have the problem, if you look at the link you will see how, works for me and I have 2 tachos

[jon_d]

That's probably not a bad idea or use a proper hall effect and pick up off a face of a timing gear tooth.

From what I've read, it needs a little contact shaft to rotate the generator which might be a point of engine failure.

btw, that the switch wiring helped.

[Busman]

You will have to set it up whatever input you use. at least with the alternator I was given a starting point so I got it close, after that I was able to adjust it to be correct after I got the tachograph back from calibration.
I have no idea why you want to over complicate things, the original input on mine was from the DN50 alternator, surprised if yours was not as well, why would they add extra cost with another sender ?

[bagmaker]

Timing gear teeth would be too high Hz to use a normal hall effect sensor.
OK for speed control reading off something like a driveshaft but too many pulses on the ring gear.

[jon_d]

I don't think so. They are designed for just this.

I have one on the Isuzu running from the teeth. The switches on the back of the tacho divide it down.

This is how I calibrated it before installing.

The chuck has a laser reflector for the laser tacho. The wheel has a stud for each tooth. The lathe is spun up to the right speed and the tacho is calibrated by flicking the switches.

[Kelvin12]

I dumped the DN alt. Went with the normal alt. Way easier to replace/repair than the DN plus way easier to remove it if necessary. Even with hooking up to an alternator you still need re calibration due to pulley size and depending what its driven off, cam shaft or crank. Rather go with the original set up.

Mine was always from the cam mounted sender, same sender as in the gearbox.

Dirk

[Busman]

It doesn't matter what the alternator is, you just pick the right wire and apart from that you only need plus and negative to the tacho.
Then you set it on pulse, then you do the selection yourself, they are set up so you can self calibrate it.E.g a DN 50 you would start at 18.
It doesn't have anything to do with pulley size or anything else.
It just counts the pulses from the alt, you set the tach to pulse and then select a number and see what the tacho is reading, keep changing up or down until the revs are reading right.Idle will be around 500, fast idle around 625-650 if it is set up right. Once you have it close you can either adjust it up or down as you get the feel for what the motor is doing or get a shop one hooked up and set to that rpm.
It is all in the instruction sheet I linked to.
You don't have the original tacho so why so fixed on using the original input ? Alt is way easier
If it is the same sender you will need to put 24 v on it, the original would have been 7, that was what VDO was using at the time. One wire is ground, the other voltage, third is signal.