alternator-tachometer interface

[jhgullett]

Last Spring we added extra batteries for a house battery bank and upgraded to a new Delco 95 amp alternator. The alternator needed a bracket adjustment and different belt.

Afterwards, the Nissan electric tachometer didn't read right. Come to find out the original alternator with the Nissan 6LD engine was a "5 or 6 phase" [can't remember which just now] and the new Delco is "7 phase". The Nissan tach has different inputs for either 5 or 6 phase but none for 7 phase. Seems the phase of the alternator has to match the phase of the electric tachometer.

Has anyone solved this equation before ? My tach, in the Nissan cluster, could use some freshening. Is there someone who rebuilds tachs and could convert my Nissan tachometer to receive 7-phase signal from the Delco alternator ?

The alternator shop said they could get me a 95 amp, 6 phase alternator but it would be $300. I just ran the boat locally with the Delco and did without the tachometer info last summer but would like to get the alternator and the tach to play together.

To me it would seem ideal to overhaul my tach to 7 phase spec and continue with the off-the-shelf Delco alternator that would be easy to service and cheaper to replace.

Advice anyone ? I am an electrical babe in the woods; have a friend who is good but doesn't know what the best solution could be. Could always go back to the old alternator but wanted the extra juice.

Many thanks,

John

[Beta Don]

Ample Power (a company which markets all sorts of marine charging equipment) says that if you've converted to a high power alternator, it's a good idea to convert your tach to operating from an engine sensor, rather than a signal from the alternator because once your batteries are full, and the regulator cuts back the output from the alternator, you're going to lose the tach signal no matter what you do

http://www.amplepower.com/primer/tach/

I'm not sure where on the Nissan engine you would install the sensor - On my Yanmar, the sensor counts the teeth on the flywheel I think, so maybe have a look there and see if there's a threaded hole meant for that sensor. Some research about where the Nissan Maxima diesel got it's tach reference might be a good place to start

Don

[jhgullett]

Dear Beta Don,

Thank you for this info and link. Tiny Tach <www.tinytach.com> looks like a sensible and direct solution at $95.00.

It seems the Nissan Maxima Diesel took its tach info from a tap into the EGR valve which marine diesels do not have.

With a flywheel sensor it might be possible to run the old Nissan tach and preserve the original dashboard.

There seems to be a plug on top of the housing at the aft-stbd end of the engine. Have not tried yet to unplug it, but wonder if anyone else has tried it out ?

Many thanks,

John