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Old 20-05-2006, 21:09   #1
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Tachometer connection

Hi

I have beta marine BZ482 13.5hp diesel motor. I want to hook up the tachometer because the guy who installed the engine never did. First off is the alternator a reiable way t get tach reedings? Secondly which of the three unused screws on the alt is for the tach? Is there another tach pickup on the motor, if so where.

thx Alex
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Old 21-05-2006, 03:51   #2
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Alternator Tachometer Connection:

On diesel engines the tachometer signal can be generated by (one of) several different means, including:
1) the alternator
2) the magnetic (Hall) sensor, which counts gear teeth
3) a tachometer signal generator that is spun by a mechanical take-off

Alternator Tachometers operate off the “AC Tap”* connection on the engine alternator. As the engine speed increases and decreases it varies the AC output reading to the tachometer. These units offer a stable reading, are reliable and virtually maintenance free. It is however important to ensure correct alternator belt tension is maintained. Belt slippage will result in a low and/or erratic reading. Tachometers require calibration when first installed, normally performed with a hand held tachometer, reading from the crankshaft.

The AC Tap(s) could be marked: AC, AUX, S, R, TACH, STA, W, X, N, or P.
Some alternators have more than one tachometer tap.

HTH,
Gord May
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Old 21-05-2006, 11:39   #3
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Wow, that is great information!! Thanks Gord. I have an old Mercedes engine, an alternator from a Perkins and have been wondering the same question. I do have a hand held tach to do the calibration. Can you recommend a brand of permanently mounted tach that can be calibrated or are they pretty much the same? Regards, --John--
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Old 21-05-2006, 13:14   #4
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alternator driven tach pitfalls

Please note that virtually all new engine installations use Hall effect pickups from the engine. If you convert your alternator to an external 3-step regulator in order to properly recover a deep-discharge battery then an alternator driven tach will not function when transiting from acceptance to float and may be intermittent at float from then on.
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Old 21-05-2006, 18:50   #5
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Rick and GordMay. Thanks. I've also discovered that my alternator has only a Bat Terminal so I'm not certain I can use an alternator tach. Any advice? Rick, I used to keep my Garden Ketch in Bremerton ('84,'85)
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