Tach

Outboard designs up to 14'

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cusoak
Posts: 927
Joined: Sat Dec 26, 2009 8:49 am
Location: Senecaville Ohio

Tach

Postby cusoak » Wed Sep 23, 2015 7:17 am

Hi everyone here is a picture of the back of a tach that I would like to hook up to my 61 Merc 45 hp 400e outboard.
It has a mag ign. It has a charging system under the flywheel and a rectifier, which has a red wire and another wire that has 2 wires that are yellow coming out of it.
Does anyone know how to hook it up and what pluses to put it on it is a 4 cylinder
Thanks Jeff
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tach resize.jpg

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rbrandenstein
Posts: 817
Joined: Mon Mar 08, 2010 3:51 pm
Location: O'Fallon, MO

Re: Tach

Postby rbrandenstein » Wed Sep 23, 2015 7:50 am

Jeff,
I had a 75 Merc 650, and used a tach similar to yours. I was able to get it working.
Anyway, connect the signal wire to SEND on the tach and one of the yellow wires that feed into the rectifier. I don't think it matters which yellow wire you use.
Then, it is a matter of setting the switch on the tach for the right number of pulses. I found a table on the website of Faria that listed my motor. I think I had a setting for 12P, which yours does not have.
You will have to experiment with the setting if you can't find any information. It is possible it may not read correctly.
________________
Bob
Completed Malahini (launched 6/24/2012)
http://bobsboatbuild.blogspot.com/

gdcarpenter
Posts: 1325
Joined: Tue May 05, 2009 12:18 pm
Location: Raleigh, North Carolina

Re: Tach

Postby gdcarpenter » Wed Sep 23, 2015 11:59 am

Hi Jeff,

GND terminal obviously must connect to ground

IGN is for a 12 volt power supply, usually you only want power supplied when your ignition key is in the on position.

At the rectifier the red wire is the output side, should be a steady voltage output, increasing with RPM. The yellow wires are the feed from the stator below your flywheel to the rectifier. The 2 yellow leads send alternating 'pulses' to the rectifier, so connect the SEND terminal to either of the yellow wires. It shouldn't matter which yellow, but sometimes one gives better pulses than the other.

Both my Mark35A and my Mark58 have 8 pole staters, with 4 poles feeding each yellow wire. So your tach should work set on "4P".

Good Luck!
This is my first, last and only boat build.

http://www.gdzipbuild.blogspot.com

cusoak
Posts: 927
Joined: Sat Dec 26, 2009 8:49 am
Location: Senecaville Ohio

Re: Tach

Postby cusoak » Thu Sep 24, 2015 4:48 am

None of this will cause a problem with the charging system.
Does the fact that there are no 4 cylinder/ pulses settings is that ok
just pick the4 pulses setting right
Jeff

gdcarpenter
Posts: 1325
Joined: Tue May 05, 2009 12:18 pm
Location: Raleigh, North Carolina

Re: Tach

Postby gdcarpenter » Thu Sep 24, 2015 12:16 pm

That's how I have my at tach hooked up. Tach draws milliamperes, if that, off yellow lead to rectifier, just getting a 'reference' signal, no effect whatsoever on charging system. If you had a 12 pole stator you would set your tach to 6P, 1/2 of the 12. Since frequency of pulses is based on crankshaft RPM it's essentially the same as using a coil connection on a non magneto ignition system. If you had a 6 cylinder merc and an 8 pole stator you would still set the tach to 4P! Has nothing to do with the number of cylinders. Please let me know what you get for WOT RPM and MPH after your next outing Jeff.

Sometimes I wonder how I came to know what I do about Old Mercs!
This is my first, last and only boat build.

http://www.gdzipbuild.blogspot.com

cusoak
Posts: 927
Joined: Sat Dec 26, 2009 8:49 am
Location: Senecaville Ohio

Re: Tach

Postby cusoak » Fri Sep 25, 2015 4:32 am

Well let you know
Thanks for the help
Jeff


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