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  Tachometer Compatiblity with OMC Engines

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Author Topic:   Tachometer Compatiblity with OMC Engines
montauk steve posted 05-17-2006 02:58 PM ET (US)   Profile for montauk steve   Send Email to montauk steve  
What tachometers are compatable with the older Evninrude outboard motors, such as 1983 to be exact? I read Teleflex are not compatable with Evinrude motors. Right now there are Faria tach, volt and trim.

None of them work but will find out this weekend why.

I don't want to spend a bundle on a tachometer and volt meter.[Give me a brand or model] suggestion. I would like to hear them

Also, on the back of the tachometer instrument, there is a switch and it is set to position 12--Is this the correct position for a V4 90-HP two-stroke with T/T?

Thanks

ratherwhalering posted 05-17-2006 04:15 PM ET (US)     Profile for ratherwhalering  Send Email to ratherwhalering     
Steve, try setting (6). 12 and 6 should both work with that engine. Any volt meter will work with any engine. The trim gauge should be manufacturer specific, so get the serial numbers and check them with Faria's web site.
ratherwhalering posted 05-17-2006 04:25 PM ET (US)     Profile for ratherwhalering  Send Email to ratherwhalering     
Scratch that...setting must be 6.
montauk steve posted 05-17-2006 05:09 PM ET (US)     Profile for montauk steve  Send Email to montauk steve     
Ratherwhalering,

Thanks for the info on the switch setting.

will check the setting, the rectifier or the combination there of.

Now if the tach is no good, are the teleflex tachs compatable??

jimh posted 05-17-2006 05:37 PM ET (US)     Profile for jimh  Send Email to jimh     
Tachometers are just about universally compatible. The signal that drives them generally is derived from the same output, the permanent magnet alternator of the motor as it is applied to the rectifier. For more detail read:

http://continuouswave.com/whaler/reference/PMA.html

Many outboards use a 6-pole alternator.

jimh posted 05-17-2006 08:28 PM ET (US)     Profile for jimh  Send Email to jimh     
If a tachometer is driven from the stator coil of a permanent magnet alternator--and this is the case for a very high percentage of all outboard motors--the power stroke configuration of the engine--two-stroke or four-stroke--makes no difference because the pulses are derived from the mechanical rotation of the engine's crankshaft, and the alternator cannot tell if the mechanical energy creating that rotation came from a two-stroke or a four-stroke engine. So the questions of two- or four-stroke does not come into consideration with these types of alternators.
montauk steve posted 05-17-2006 09:59 PM ET (US)     Profile for montauk steve  Send Email to montauk steve     
Jim,

in regards to your last post.

yes that makes sense. unless the the signal cam from the cams like in most cars. then the signal would be divided by two to make up the difference in the cycle.

hopefully this weekend i can get things dialed in.

OH, by the way, i called a local Evinrude dealer and they said that the switch on the tach should be on 4. just to put that out there. I am going to try position 6 first and then check the voltage on the grey wire, and so on and so forth.

Which brings me to my next question: when I check the grey wire that provides the signal for the tach, does the grey wire come from the rectifier??

And I am looking for 12Vs right?

now if the signal comes from the grey after the rectifier then it is a DC signal, unlike some of the posts that I have read saying to put the multi-meter on the AC volts and check it like that. Unless its to check for pulses on the AC mode.

Steve

jimh posted 05-17-2006 11:24 PM ET (US)     Profile for jimh  Send Email to jimh     
In really simple circuits, the tachometer signal comes off the stator coil at the input to the rectifier. The rectifier is connected to ground and the battery positive. The action of the rectifier affects the signal at the stator:

--the stator voltage is clamped to about one volt greater than battery positive at its most positive

--the stator voltage is clamped to about one volt less than ground at its most negative

It fluctuations between those voltages at a frequency determined by

--the engine speed

--the number of poles in the alternator

If you connect a voltmeter to the tachometer signal lead, you will get some average voltage. It is hard to predict exactly what voltage you'll see, as it will depend on the characteristics of the meter.

It is possible that in some motors the tachometer signal undergoes a bit more processing, so the voltage levels might be different than I described above, but they should be about those levels.

jimh posted 05-17-2006 11:27 PM ET (US)     Profile for jimh  Send Email to jimh     
I am skeptical about the advice to put the tachometer calibration on "4", if that implies "four-pole alternator." Maybe it is a marking that corresponds with the V4 engine. My guess is that the alternator has more than four poles. But, heck, maybe it is a four pole alternator.

The calibrating control on the tachometer is a way to adjust the tachometer to work with alternators having different numbers of poles and thus producing a tachometer signal of a different frequency at a given engine speed.

ratherwhalering posted 05-18-2006 03:02 AM ET (US)     Profile for ratherwhalering  Send Email to ratherwhalering     
I believe that a 12 pole alternator gives off 6 pulses, and thus the setting must be 6. If it is an OMC <70 Hp engine, it has a 10 pole altenator, and thus gives off 5 pulses, and the setting should be 5. By no means am I an expert on this, I just read a great article, after I changed my answer above. Of course, now I can't find the article :-(
montauk steve posted 05-18-2006 11:19 AM ET (US)     Profile for montauk steve  Send Email to montauk steve     
rahterwhalering,

That is textbook. if you find the article let me know I would like to see the info.

steve

ratherwhalering posted 05-18-2006 01:17 PM ET (US)     Profile for ratherwhalering  Send Email to ratherwhalering     
Here is a good link to tachometer applications:

http://faria-instruments.com/site_manuals/IS0012i_doc.pdf

Still looking for that article...

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