Tach electrical question

[Seattle Scott]

My 20 year old tach on my yanmar does have any voltage at the terminal ends going to the sending unit screwed in above the flywheel.With the key on, I get 12 volts at the various terminals on the tach at the panel. So is there a disconect or bad connection somewhere in between? If working fine, I should get 12volts at the sending unit, right? The tach got lazy, meaning read low or delay in getting a reading, then died dead with no needle movement, thus my question. Did you see our local snow on Monday Night Football? Only about every 5 years here in the Emerald City.

 

[Dan Johnson]

Terminals...

Scott, I had the same problem on my H34 last summer. Pull all the connectors between the panel and engine apart and clean each pin and socket one at a time. Clamp down on the slide-ons at the sending unit with a pliars to increase the friction contact after cleaning the two spade terminals on it. There isn't any voltage at the flywheel sensor. As a "sending unit", each time a magnet on the flywheel passes the sensor, it induces a small current to flow, which is interpreted by the tach head into an RPM reading. Cleaning all the connections in between will ensure that this signal gets through.

 

[Dan Johnson]

MNF...

Forgot...watched 3 quarters of the game...last year in November while working out of Linwood I had to help a co-worker find a rain coat. This year I would have had to find him a wet suit with a matching shovel...quite a shock!

 

[scott]

Thanks Dan

re sending unit info.PS, 16 plus inches of rain in November in Puget Sound area, a dubious record.

 

[Fred Ficarra]

Glug-glug!

Oh, I'd start with the sending unit terminals. That's the most likely cause of your problem. Also, for info, the tach gets its signal via the flywheel starter gears. It's called the 'Hall effect'. No magnets. Same method used in many ignition system distributors.And we built our home on a hill for a reason,,,,,

 

[Landsend]

I'll fax you the specs on the tac and sender.

Call me....Karl 1-386-447-1838

 

[Dan Johnson]

Thanks, Fred!

I was going to mention the "Hall Effect" as the description for the process, but didn't want to add to the confusion. I thought there was an imbedded magnet in the flywheel to create the inductive effect. If no magnet, what creates the signal at the sensor? Same deal with a knotmeter or an OB electronic ignition.

 

[Dan Johnson]

Funny word

"Deion" somehow showed up instead of description. Must have been the NSA again!

 

[Dan Johnson]

This is nuts!

I wonder what is causing d_e_s_c_r_i_p_t_i_o_n to appear as "deion"?

 

[Seattle Scott]

Still busted

I got some fancy electrical terminal grease and greased up the terminals on the sending unit and put the spade or whatever they're called connectors back on and wiggled them around. Still dead at the instrument. So is there any test of the sending unit to determine if inop?