Alternator & Tachs.

[captrob]

<div>I just finished installing a new Amtech alternator and Heart
incharge 3 stage regulator. The system works great. However,
there is one glitch. The tach. is driven off the alternator not
the flywheel and now it is not in claibration - at about 1600
engine RPMs the tach. is pegged. The engine is the 3QM30 Yanmar.Does anyone know if there is an adjustment on the tach. or how to
re-calibrate the instrument? I assume what the tach. does is
read pulses off the alternator and the new alternator runs at
higher RPMs than the old 55 amp one and therefore is no longer
accurate. Ideas? Experiences?Thanks,Vic Copelan
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[bschnur]

Vic, your tach is essentially a frequency meter that is reading the frequency of the AC voltage created in your alternator. You can recalibrate by looking for a "CAL" adjustment screw on the back of your tach. Use an optical tach to determine the true RPM of the engine, then turn the screw until the engine tach reads the same.
If you have a tach which has a series of switches on the back (often a 10 bit DIP switch), you could have as many as 1024 combinations to try before getting the RPM correct. Here's a shortcut. Start with all switches off (or on), whichever gives you minimum indicated RPM. Then , starting at one end of the DIP switches, flip that switch on (or off) -- you're looking for a big change in indicated RPM. If you don't get it, start at the other end. Keep going, one switch at a time, slowly creeping up on the true RPM. Any time you flip a switch and the reading goes too high, flip that switch back and go to the next in line, continuing until you're done.
Hope there's not too much data here.
Good luck...

 

[jhask]

<div>Jim, If all else fails it is possible to install a flywheel sensing tachometer.Horror story:
A few years back my alternator driven tachometer quit. The yard reinstalling the instrument messed up and replaced it with a Yanmar Tach, attaching it to the alternator as the original had been. Problem was that it was designed for a flywheel sensor. Goodbye instrument. They tried to blame me since they claimed the alternator driven tach was not standard and therefore jury rigged. Referred them to Morgan.They were not sure how to install the alternator type so I told them to install the flywheel type. The plug in the 3QM is easily accessable and easily installed. We got the sensor and installed it and a new tach. Still wasn't right Apparently there are two wire sensors and three wire sensors. My sensor was the two wire type and they ordered the wrong tach for it. The mechanic in the meantime had taken his dikes and cut the wires to the back of the tach.They ordered a new tach. The mech curt the wires again. This time it was for a different engine with more teeth on the flywheel thus producing a higher RPM. The mechanic tried to convince me that 1600 RPM was the normal idle RPM for that engine. :-( I managed to borrow an hand tach and prove to them that the RPM was wrong. They then ordered the right tack. Works fine but they tried to charge me for all the tachs they had to buy. Unreal.If you decide to go the flywheel route be sensitive to the different type of leads as well as flywheel types. Dick
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