VDO tacho/hourmeter callibration

[gtsouchlos]

Hi to everyone
I have just bought 2 new VDOs (model N02 012 165) tachos with hourmeter to fit with my KADs 42 and it is impossible to find the pulse number that comes from W wire of alternator.
I saw that there was a relavant question in April 2010 with some useful hints (as the code, ratio, nr of teeth etc) but there was not the answer for the famous pulse number. If the instrument was vdo-volvopenta, then the code 8 is in use but if the vdo's are universal then we need a pulse number. With respect the number of teeth and ratio I have tried (among others) 90 and 22,5 but no luck.
Can anyone help so I can see them work ??

Thanks
George

 

[VicS]

I cannot find any info on the VDO number you quote . Are you sure they are the correct type of tacho for connection to the W terminal.

 

[earlybird]

I think VicS is pointing to the reason for your problem.
I'm fairly sure that some Volvo/ VDO tacho's. sense from an inductive pick up on the block. Probably the ring gear teeth and perhaps around 90 to 100 pulsed per rev. if they're anything like the Yanmar GM engines. The frequency from the W terminal will be much lower, maybe around 8 pulses per engine rev. Don't know if that would drive your particular instruments though.

 

[gtsouchlos]

Hello guys and thanks for your interest
According to the wiring diagram, these VDO's have an 8 contact socket (2 rows of 4 contacts) with 5 contacts in use.
Contact #1 & #5 for illumination, #2 +12V, #3 ground & #4 for W (diesel alternator or signal from ignition coil for petrol engines)
There is also a knob at the back and if it is already pressed when you turn on ignition there is the choice of either "pulse" or " adjust". Pulse needs the nr of pulses and adjust is for fine rpm adjusment. So what I'm looking is the number of pulses.
The preset nr was 22,50 but no luck. Because Volvo Penta has a chart for it's vdo tachos (code 8 for KAD42) I have tried combinations of 45 (nr of teeth), 90 (ratio 1:2) and even measure diameters of pulleys of crankshaft, water pump & alternator coming to a final ratio of 1:2,40 which gave me the number of 180 (2,4X45) but no luck.......

 

[VicS]

I think references to number of teeth are irrelevant when using the "W" terminal. It refers to picking up pulses from the teeth on the starter ring gear or similar as they pass a sensor

Relevant factors when using the "W" terminal are the relative diameters of the pulleys and also the number of poles of the alternator.

( it'll be a low number, 6 or 8 ?, for the number of pulses per rev from the alternator. Multiply that by the overall ratio of the pulley diameters and you get the number of pulses per engine rev. 12 or 16 if your ratio is right.


Sorry probably no help.