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ScratchBC 20-05-2006 20:09

Tachometer connection

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

GordMay 21-05-2006 02:51

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.

Gord May

SkiprJohn 21-05-2006 10:39

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--

Rick 21-05-2006 12:14

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.

SkiprJohn 21-05-2006 17:50

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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