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Old 13-07-2020, 10:14   #1
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New Alternator Connected Tachometer cuts in and out

As a reward for rebuilding my Westerbeke 40, I bought new gauges. I deserved it. However,my new alternator connected tach is behaving EXACTLY like my old one-that is it cuts in and out. Runs beautifully for hours and then poof-no more tach! What’s going on? I have a 100 amp power line alternator, solar panels on a Morningstar mppt controller and a wind gen.
Once I resolve I will have a spare to mount over my bunk
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Old 13-07-2020, 12:24   #2
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Re: New Alternator Connected Tachometer cuts in and out

When the alternator "sees" that the batteries are charged, the regulator lowers the output to the point where the tach doesn't get a good signal.

Try turning on some high-draw DC system and I'll bet it comes back.

I replaced mine with mechanical tachs. Well worth the effort.
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Old 13-07-2020, 13:06   #3
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Re: New Alternator Connected Tachometer cuts in and out

Thanks Cap. Kind of figured that was what was happening. I also have a xantrex ARS three stage regulator-can monkey with the settings on that to see if there is a work around. I tried to find a mechanical tack as I have the takeoff on the Perkins, but no luck. Do you remember where you found yours?
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Old 13-07-2020, 15:14   #4
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Re: New Alternator Connected Tachometer cuts in and out

Jim, Jewel I is a great stop. On weekdays, that is. Weekends can be a bit crazy.

I fed the sender directly to the Noland RS-11 analog-to-NMEA 2000 box, so the tach display is on my chartplotter and/or a multi-function gauge.
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Old 14-07-2020, 09:12   #5
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Re: New Alternator Connected Tachometer cuts in and out

I did exactly the same thing last year with my 1981 Westerbeke 40, and I have exactly the same problem, so I am watching this thread with interest......
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Old 14-07-2020, 10:18   #6
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Re: New Alternator Connected Tachometer cuts in and out

I had some problems with my Tach on my Yanmar2GM20. I replaced it with a "Tiny Tack for Diesels". Under $100. It clips a sensor to one of the fuel injectors lines. It runs on 12 or 24 volts. Easy install. It gives a very accurate digital RPM readout. It tracks engine hours, has countdown timers so you track maintenance (i.e. oil change).

To find out all the features you can google "Tiny Tack for Diesels.

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Old 14-07-2020, 11:49   #7
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Re: New Alternator Connected Tachometer cuts in and out

I believe this happens when the field current is cut to zero when the charge parameters are met. I think (but am not positive) that modern regulators keep a tiny amount of current flowing so that the tach still works.

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Old 14-07-2020, 11:56   #8
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Re: New Alternator Connected Tachometer cuts in and out

Batteries are typically in float stage when tach cuts out. The regulator is a xantrex ARS (think they may be out of business). Something other than an alternator driven tach is in order I think
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Old 14-07-2020, 12:12   #9
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Re: New Alternator Connected Tachometer cuts in and out

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Originally Posted by jpendoley View Post
Batteries are typically in float stage when tach cuts out. The regulator is a xantrex ARS (think they may be out of business). Something other than an alternator driven tach is in order I think

Could be, but the suggestion of turning on a load will simply stop that from happening. You don't need a large load, a couple of lights (incandescent not LEDs which draw zilch) or even your autopilot, if so equipped, will do. Turn on your steaming light on a sunny day!


Not necessary to go to that expense, but Your boat, your choice.



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I believe this happens when the field current is cut to zero when the charge parameters are met. I think (but am not positive) that modern regulators keep a tiny amount of current flowing so that the tach still works.
Chuck, don't know for sure, vaguely remember that being a promotional aspect when they first came out. I'll check my Balmar MC-612 manual later today. Good point. Whether a xantrex regulator does so, too, dunno, but they pretty much bought everything from Ample/Heart and have no clue what's under the hood, nor do they seem to care.
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Old 14-07-2020, 14:04   #10
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Re: New Alternator Connected Tachometer cuts in and out

My apologies for dictation which will no doubt enhance errors. However I'm on my phone and not my computer. I'll come back later and fix it.

however, the answer is to have a 100 ohm resistor in line to your tach feed.

I have not done that on mine yet, but it is on my to-do list. I discovered that when I went searching in other forums. It's as noted elsewhere in the thread that a small load should keep it alive...
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Old 14-07-2020, 15:28   #11
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Re: New Alternator Connected Tachometer cuts in and out

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Originally Posted by skipgundlach View Post
My apologies for dictation which will no doubt enhance errors. However I'm on my phone and not my computer. I'll come back later and fix it.

however, the answer is to have a 100 ohm resistor in line to your tach feed.

I have not done that on mine yet, but it is on my to-do list. I discovered that when I went searching in other forums. It's as noted elsewhere in the thread that a small load should keep it alive...
I have the same issue with my tach. I like the idea of putting a resistor in the tach feed line but would like to understand how it would work. If this issue is caused when the field drops when the regulator senses that the batteries are full, what difference would the resistor in the tach feed line make?
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Old 14-07-2020, 15:31   #12
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Re: New Alternator Connected Tachometer cuts in and out

Had autopilot on most times it cut out and a cabin fan-I dunno, maybe the wind gen was making up the difference and alternator cut back. Will try the resistor idea- Or a mechanical tach it is. Not a bad out come as the W40 mechanical tach takeoff is a source of leaks when not in use.
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Old 14-07-2020, 22:28   #13
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Re: New Alternator Connected Tachometer cuts in and out

I think that the wind generator or solar panels are the problem. When the batteries are full they are putting out a high voltage which fools the alternator controller into shutting down which eliminates the alternator pulses for the tachometer.
I put in a switch to turn off my solar panels which I use when running the engine. You could also use a relay. It has the benefit that the batteries charge faster with the alternator than with the panels. You are running the engine anyway and the alternator load's effect on fuel consumption is minimal. I remember a friend telling me that while crossing the Atlantic, he could only get his alternator to work at night and his small panel could not power his autopilot during the day. The panel was the culprit. Depending on regulator settings even a small solar panel can fool the alternator regulator into shutting down. With only the alternator charging, when the batteries are full, the alternator controller will go into trickle mode which requires some current from the alternator so there should be pulses.
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