'87 OMC 90 Tach OK Indicate That Rectifier/Regulator OK?

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Author Topic:   '87 OMC 90 Tach OK Indicate That Rectifier/Regulator OK?

Gene in NC posted 03-15-2004 11:48 PM ET (US)
Does tach OK prove that rectifier/regulator (r/r)is OK. How verify charging level. Will voltmeter across batt reading voltage increase with charging output verify that system OK?
Still trying to get ready for the 1,000 mile cruise. Need assured OK operation, at least at start.
'87 with T@T does have r/r. Our '79 100 and '83 115 with T@T have only rectifier.
jimh posted 03-16-2004 07:28 AM ET (US)
My comments in http://continuouswave.com/ubb/Forum3/HTML/005680.html are germane to your question.
Peter posted 03-16-2004 07:43 AM ET (US)
An eradic tachometer reading is usually a good sign of a bad rectifier/regulator.
Gene in NC posted 03-16-2004 09:57 AM ET (US)
Jimh, quite a post re OB charging systems. Would have been satisfied by a "yes" (a fish) but now I'm like the man taught to fish. Didn't quite get the "Omega lure" but I can build on my new level of understanding.
Conclusion is at very least I should have unregulated charging.
Chuck Tribolet posted 03-16-2004 09:59 AM ET (US)
But I suspect you could have a bad R/R and still have a good
tach reading. You need to check the output with a voltmeter.
It should show just below 12 volts with the engine off and
the battery charged. When you start the engine, it should
rise a little, and be at about 14V by 1500 RPM with no major
loads. The exact numbers are in Chapman IIRC, but Chapman is
at home and I'm not.

Chuck
Bigshot posted 03-24-2004 01:29 PM ET (US)
I have NEVEr had a R/R go bad and the tach still work right.
Bigshot posted 03-24-2004 01:30 PM ET (US)
Ps if it is the round silver one, pick up a spare, they are only like $20.
TampaTom posted 03-29-2004 04:49 PM ET (US)
Gene, sorry to jump in our your thread. Jim thanks for the info on rectifiers. I hadn't noticed your post on my thread until I saw it on this one.
Question, my Merc has two separate rectifiers (with integrated regulators) each providing about 20 possible amps to the electrical system. Could I remove one that is intermittently working (leaving two feeds from the stator disconnected) and still use the engine without damaging the stator? Then I could dissect the bad regulator and have a Merc regulator/rectifier rebuild project to post
Bigshot posted 03-30-2004 12:45 PM ET (US)
no
Sal DiMercurio posted 03-30-2004 02:45 PM ET (US)
The volage for the tach comes right from the rectifier [ grey wire ], & if the rectifier goes out, your tach wont work.
The way to check if you tach is bad is, disconnect the grey wire from the back of the tach & start the engine, if there's 12 volts in the wire, your rectifier is ok, but your tach is sick.
Sal

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Author	Topic: '87 OMC 90 Tach OK Indicate That Rectifier/Regulator OK?
Gene in NC	posted 03-15-2004 11:48 PM ET (US) Does tach OK prove that rectifier/regulator (r/r)is OK. How verify charging level. Will voltmeter across batt reading voltage increase with charging output verify that system OK? Still trying to get ready for the 1,000 mile cruise. Need assured OK operation, at least at start. '87 with T@T does have r/r. Our '79 100 and '83 115 with T@T have only rectifier.
jimh	posted 03-16-2004 07:28 AM ET (US) My comments in http://continuouswave.com/ubb/Forum3/HTML/005680.html are germane to your question.
Peter	posted 03-16-2004 07:43 AM ET (US) An eradic tachometer reading is usually a good sign of a bad rectifier/regulator.
Gene in NC	posted 03-16-2004 09:57 AM ET (US) Jimh, quite a post re OB charging systems. Would have been satisfied by a "yes" (a fish) but now I'm like the man taught to fish. Didn't quite get the "Omega lure" but I can build on my new level of understanding. Conclusion is at very least I should have unregulated charging.
Chuck Tribolet	posted 03-16-2004 09:59 AM ET (US) But I suspect you could have a bad R/R and still have a good tach reading. You need to check the output with a voltmeter. It should show just below 12 volts with the engine off and the battery charged. When you start the engine, it should rise a little, and be at about 14V by 1500 RPM with no major loads. The exact numbers are in Chapman IIRC, but Chapman is at home and I'm not. Chuck
Bigshot	posted 03-24-2004 01:29 PM ET (US) I have NEVEr had a R/R go bad and the tach still work right.
Bigshot	posted 03-24-2004 01:30 PM ET (US) Ps if it is the round silver one, pick up a spare, they are only like $20.
TampaTom	posted 03-29-2004 04:49 PM ET (US) Gene, sorry to jump in our your thread. Jim thanks for the info on rectifiers. I hadn't noticed your post on my thread until I saw it on this one. Question, my Merc has two separate rectifiers (with integrated regulators) each providing about 20 possible amps to the electrical system. Could I remove one that is intermittently working (leaving two feeds from the stator disconnected) and still use the engine without damaging the stator? Then I could dissect the bad regulator and have a Merc regulator/rectifier rebuild project to post
Bigshot	posted 03-30-2004 12:45 PM ET (US) no
Sal DiMercurio	posted 03-30-2004 02:45 PM ET (US) The volage for the tach comes right from the rectifier [ grey wire ], & if the rectifier goes out, your tach wont work. The way to check if you tach is bad is, disconnect the grey wire from the back of the tach & start the engine, if there's 12 volts in the wire, your rectifier is ok, but your tach is sick. Sal