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Old 04-19-2015, 06:27 PM   #1
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Intermittent tachometer

Recently I posted about a tachometer that didn't seem to work right and got some good advice. One idea was about a full battery and regulator in float so I ran the batteries down a bit to see if that would make a difference (It didn't). I can say all the connections are good and the alternator is connected to the tach and the tach works. When I start that engine the tachometer works fine for about one minute each time then just goes inop. It is one on the port engine( the one I start last). Perkins 120s.
Any more ideas out there?
Thanks
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Old 04-20-2015, 11:59 AM   #2
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Tachometers sometimes just break. We had Faria rebuild ours when they went south. But then I later changed to Aetna digital tachs. If the sender is good, I think replacing with new or rebuilds isn't usually difficult.


Since you say "that engine" I gather that means you've got two. Switch tachs and see if the symptoms travel or not?


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Old 04-20-2015, 02:10 PM   #3
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Any more ideas out there?
Ideas? Yes. Good ideas? We'll see...

I had a similar symptom, which turned out to be interference from the florescent ER lights. In your case it sounds you're right to suspect the alternators and/or voltage regulators. But don't forget to rule out the easy stuff, first!
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Old 04-20-2015, 02:32 PM   #4
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Maybe a failing alternator? I'm not familiar with the Perkins 120, but many tachs are alternator driven. Try swapping the port and starboard alternator and see if the problem follows.
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Old 04-20-2015, 04:23 PM   #5
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Are you getting an AC pulse out of the alternator when the tach is wired
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Old 04-22-2015, 09:33 PM   #6
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A friend made a mistake installing batteries connecting both banks together. He had the same problem I think one alternator dropped out and that tach along with it.
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Old 04-23-2015, 07:58 AM   #7
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ok i'm going to say 'a broken wire'
try getting someone to jiggle the wires that come out of the bellhousing and see if the tacho comes good for awhile.
my tacho is fine till a few minutes afterI leave the boat ramp. Sparky suggested I wiggle the wires and there the problem lies.
hope it helps
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Old 04-23-2015, 08:34 AM   #8
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Quote:
Originally Posted by Loon View Post
Recently I posted about a tachometer that didn't seem to work right and got some good advice. One idea was about a full battery and regulator in float so I ran the batteries down a bit to see if that would make a difference (It didn't). I can say all the connections are good and the alternator is connected to the tach and the tach works. When I start that engine the tachometer works fine for about one minute each time then just goes inop. It is one on the port engine( the one I start last). Perkins 120s.
Any more ideas out there?
Thanks
I had the exact same problem last time I ran my engine.
When I first noticed it I checked all the connections. All OK.

I then noticed that it was fine for first minute of startup, then did it's thing.

I wrote my boat guru, Dave Arnold and he said,
"Possible alternator shutdown due to other sources providing a charge to the house. The pulse is derived from ac ripple at the center of the Y connected stator inside the alternator. It is on the white wire that changes to yellow on your harness and ties on a post on the regulator top as it travels up to the tachometers. The voltage is around 3 or 4 to 14-16 volts ac. I remember it around 8 or so on yours. If the regulator shuts off the alternator due to solar/inverter/aux charging sources, the pulse is lost even though it is still rotating. Sometimes you can just turn off the charger breaker or shut off the charger on the inverter to make the alternator dominant, and the pulse comes back with the needed output to support the house loads."
I was running in the day time, so the solar panels were charging.

I turned on my inverter and the microwave and that solved the problem.
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Old 04-23-2015, 08:09 PM   #9
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Richard, I heard of a similar problem from David Hoar, Pacific Sapphire. He shuts his solar panels down when he's travelling for that reason, as the drawn on the batteries from the instruments, might exceed the output from the panels.


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Old 04-23-2015, 10:58 PM   #10
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Loon, I think we're getting closer.

Are you running with fully charged batteries (or nearly so) and your battery selector switch on ALL?
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Old 05-31-2015, 07:02 PM   #11
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Do you think that switching power selector to "1" or "2" would make any difference?
Thanks everyone for the input.
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Old 05-31-2015, 07:18 PM   #12
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Loon, reread post #9 from Wxx3. I'm assuming the battery selector switch on your boat controls the loads and charge simultaneously. That's how many boats are wired from the factory.

My suggestion would be to place the switch to house bank and place a relatively large electrical load on the house like a heater, microwave or coffee maker. Watch your ammeter and tach. You should see the amp output from your alternator rise to charge the battery and, hopefully, the tach will come back to life.

Let us know what you find.
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Old 05-31-2015, 07:31 PM   #13
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Down to boat Wed. Let you know,thanks.
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Old 10-30-2015, 12:27 AM   #14
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Got with the voltage regulator manufacturer on the problem. He said that the regulator comes preprogrammed with a float of 13.45 VAC and for whatever reason that was too low for my set-up. He showed me how to reprogram the VR to 13.65vAC float and solve the problem.
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Old 07-05-2016, 12:14 PM   #15
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Quote:
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Richard, I heard of a similar problem from David Hoar, Pacific Sapphire. He shuts his solar panels down when he's travelling for that reason, as the drawn on the batteries from the instruments, might exceed the output from the panels.

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I'll post more in this in another dedicated thread. My tachometer dropped out while traveling the other day and I remembered David Hoar's findings on the matter. So I turned off the breaker between my solar charge controller and the house bank and the tachometer immediately came back to life. In this particular situation the house back was fully charged and perhaps the voltage regulator got confused and stunt down the alternator which of course runs the tach.

I have an Amtech 125 amp alternator that is regulated by a Balmar Max Charge MC-612. There may be a setting on the regulator that can fix this problem but for now turning off the solar panels when the battery back is full is the course of action I will take.


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