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Old 04-21-2015, 12:43 AM   #21
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+1 on the Tiny Tach. I love it.
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Old 04-21-2015, 08:27 AM   #22
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Quote:
Originally Posted by FF View Post
Alt driven tachs are always off. No way for them not to be.

IF accurate RPM is required ask the engine builder how to hook up a tach sender , and purchase a tach that can read the sender.

After adjustment , this gives most accurate readings .

How does an alternator-driven tach get signal to the display? Doesn't it use a sender of some sort?

-Chris
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Old 04-21-2015, 09:14 AM   #23
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Tach gets signal from the AC part of the alternator, its really a 3phase alternating current generator, and a connection is given directly to the AC windings. The frequency on this tap is proportional to rpm.

All alt driven tachs should have a fine cal screw to dial in readings.
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Old 04-21-2015, 10:11 AM   #24
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Quote:
Originally Posted by Ski in NC View Post
The frequency on this tap is proportional to rpm.
Does that mean generally only accurate at a specific RPM level?

Our original analog Faria tachs were adjustable -- sorta -- but the result was that they were accurate at the set point (2000 RPMs was what we tried for), and then not as accurate at the 600 RPM idle and 2600 (actually about 2700) RPM WOT levels. That was using a magnetic sender...

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Old 04-21-2015, 11:03 AM   #25
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A good tach once dialed in will maintain its accuracy within a few percent across the rpm range. All it needs to do is display a reading proportional to the signal frequency, regardless of the source.

A cheap tach often can only be dialed in to be accurate at one rpm. Farias are not known for high quality.
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Old 04-21-2015, 12:51 PM   #26
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My alternator driven tachs have an adjustment on the back to select the number of stators. I believe mine are set at 8 stators and my RPM at 1800 indicated is actually 1840. I can live with that 2% level of accuracy.
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Old 04-23-2015, 08:04 PM   #27
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Tachometer adjustment

I was able to calibrate it just fine with the laser tachometer and the set screw at the back of the tach. It's close enough to within 2%. With the imprecision of the throttle adjustment, together with the analog tachometer dial, it's close enough, IMO.


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