Both Tachs stopped Working

[Shrew]

1999 MAinship 350 Trawler (Dual Helm)
2011~2012 Yanmar 6LPA-STP2

Sunday, the tachs stopped working while underway. At first I noticed the one at the upper helm was bouncing, then it died. The tach at the lower helm also died. The volt meter showed I was at 14.4 Volts, so the alternator was still working.

I know the tach is off of the alternator. Last year, the alternator was not putting out voltage, so I swapped it. At the time the new one was also not putting out voltage, so I was suspecting the exciter wire. At that time I noticed the tach was also not working.

After fiddling with the wires on the connector to the alternator, the tach came back as did voltage to the batteries.

I left the new alternator installed and put the used one in a box in storage since I felt it wasn't the alternator that was the issue.

Now I find the tach. dead and the alternator itself putting out voltage.

Where should I start troubleshooting and how?

 

[jleonard]

The alternator should have an R terminal that sends signal to the tachometer.

 

[koliver]

Shrew
I feel your pain. I have twins. The alternators excite the tachs.
For several years now my port tach hsn't given rpm,, though it still counts off the hours. I have learned to rely on the vibrations, trying to synchronize the engines, but recently the starboard tach has switched off too. It sometimes comes on, but goes off again. Its hour meter keeps ticking along.
On the Flybridge, another pair, more failures.
This weekend I was enjoying a beverage with a friend, on the rear deck of his boat, while he explained what he was presently working on....the exact same problem. His approach was a pair of electronit tachs that he was trying to put in service, thus avoiding the ones on his dashboard completely.
I have a pair of $35 electronic tachs that I bought a few years ago, but they haven't risen on my list to the "must do now" level.

 

[Shrew]

The alternator should have an R terminal that sends signal to the tachometer.

My Yanmar has a 3 wire male going to a female connector on the alternator. IF I have an R terminal (link a post for a ring terminal) could it be as easy as running a new line to my tack from there?

 

[Gdavid]

I would locate where the engine harness grounds to the engine and make sure it is clean and tight.

 

[PhilPB]

I had a similar problem and part of the problem was a loose wire on the tach from the lower station.

 

[catalinajack]

This is a common problem, that is, relying on the alternator for the signal to the tachs. Sometimes, when the alternators shut down cuz the batteries are full, the tachs no longer receive signals. Our Lehman 120s had a mechanical port to which a signal generator could be installed. This is the same drive port that is used by Glendinning synchronizers. Totally reliable with a constant number of pulses per revolution. Paired with programmable tachs, the result is highly accurate intrumets.

 

[Gdavid]

This is a common problem, that is, relying on the alternator for the signal to the tachs. Sometimes, when the alternators shut down cuz the batteries are full, the tachs no longer receive signals. Our Lehman 120s had a mechanical port to which a signal generator could be installed. This is the same drive port that is used by Glendinning synchronizers. Totally reliable with a constant number of pulses per revolution. Paired with programmable tachs, the result is highly accurate intrumets.

I actually appreciate the alternator signal tach because if my tach is behaving normally, I know my the belt for my coolant circulation pump is in intact and not slipping.

 

[socalrider]

Do you have solar by chance? In my case, once the batteries were full the solar would push the house bank voltage high enough that the alternators stopped charging the batteries and my tachs would cut off.

Solution is to install a shutoff switch for the solar, or do what CatalinaJack recommended (which is what I did as well) if your engines have the option.

If you don't have solar, you could check to see if the tachs come back to life if you switch on some electrical loads - that might provide a clue.

 

[catalinajack]

I actually appreciate the alternator signal tach because if my tach is behaving normally, I know my the belt for my coolant circulation pump is in intact and not slipping.

Wouldn't your voltmeter tell you the same?

 

[Barrie]

I had this and traced it to my Balmar voltage regulator. Cleaned the terminals and sprayed with a moisture repellent contact cleaner. Tach problem went away.
Barrie

 

[jleonard]

My Yanmar has a 3 wire male going to a female connector on the alternator. IF I have an R terminal (link a post for a ring terminal) could it be as easy as running a new line to my tack from there?

It was like that on my Cummins could be the same.

 

[Gdavid]

Wouldn't your voltmeter tell you the same?

Yes, to a much smaller degree, I think. The alternator output connects to the battery so if it stops putting out a charge, it would drop from about from about 13.5 volts to ~12.8, less than a volt of difference. My tack needle would go from 1700 to zero and the gauge is twice the size, so I would notice it much sooner. Just my thought.
If I were running a twin engine boat, I would probably more concerned over the accuracy of my tach and may not appreciate the limitations of a alternator driven signal.

 

[Shrew]

This is interesting. I installed an ACR and remote battery switches. However, prior to that I had 2 8D batteries and a battery switch. Whatever the switch was set too, that is the active battery for both start and house. I never had the tach. kick out if the active battery was fully charged.

 

[Shrew]

OMG!!!

So I've been on anchor since Sunday. A short time ago I heard the ACR kick off, so I know the battery dropped below a certain voltage and the ACR isolated the house bank from the starting battery. (I haven't run the generator since breakfast).

I decided to fire up the engine based on this conversation. Low and behold!!! Tach is working perfectly again.

OK, I can't have the tach die everytime the batteries reach full capacity.

Anyone mind revisiting my options??

 

[High Wire]

OMG!!!

So I've been on anchor since Sunday. A short time ago I heard the ACR kick off, so I know the battery dropped below a certain voltage and the ACR isolated the house bank from the starting battery. (I haven't run the generator since breakfast).

I decided to fire up the engine based on this conversation. Low and behold!!! Tach is working perfectly again.

OK, I can't have the tach die everytime the batteries reach full capacity.

Anyone mind revisiting my options??

Is there a load like the refrigerator, that you can run on 12v while cruising? If not, incandescent running lights? It doesn’t take much to keep the alternator charging.
When we were making long runs the batteries would top off just after lunch and the tachs would shut down. The chart plotter draws a hair over 3 amps so adding 3 NAV light bulbs would bring the load up to a steady 7 amps. Enough to keep the alternator charging all day.

 

[Shrew]

Is there a load like the refrigerator, that you can run on 12v while cruising? If not, incandescent running lights? It doesn’t take much to keep the alternator charging.
When we were making long runs the batteries would top off just after lunch and the tachs would shut down. The chart plotter draws a hair over 3 amps so adding 3 NAV light bulbs would bring the load up to a steady 7 amps. Enough to keep the alternator charging all day.

I have 2chartplotters, novakool fridge and freezer, autopilot, and a stereo all running while underway.

When the tachs stopped working I checked house battery through inverter and it was showing 14.4, so that told me the alternator was still working at the time.

 

[Barking Sands]

Here is an option. This is what I did and its been working great. and its very inexpensive. The hall effect sensor is now hooked up to an Aetna Engineering tach and is very very accurate and does not need the Dakota adapter. If your tach has a wide range of adjustment capability you may not need the Dakota adapter.

 

[Sailinggod]

Both Tachs stopped working

Just checking to make sure, as on my 6lYA-STP the tach comes off a sensor on the flywheel. I had the same problem, although only a single engine, the sensor needed to be adjusted closer to the flywheel to pick up the magnetic signal. All is good now. so just in case your tachs aren’t driven by the alternator.
Cheers, and good luck with it.

 

[jespchee]

temperature sensors on the alternator or batteries will do the same thing.

 

[Nepidae]

Tachs

On our boat, and I haven't gone the route of troubleshooting the problem due to the known problem of running tach's off the alternators.

While underway I will notice that after leaving the dock, etc, the tach's will stay active for a period of time. Then they will fluctuate for a period of time. The use of the tach's is only when we are leaving or arriving at a dock so I know what our speed is.

To make sure I have the tach's when arriving, I will have the mate go down to the galley and start the microwave with a pan of water in it, for an allotted amount of time I think it will take to dock.

The tach's will kick back in because of the drain on the batteries that will excite the alternators to start working.

You say that you know that the tach's are working but do you know what the output is? A spinning alternator doesn't mean it is outputting enough to get the tach's to work,

IF anyone has an alternative to a spinning alternator tach, please let me know.

 

[Panama Dave]

I had the same issue. It turns out my spade connection on the exciter wire at the alternator had a loose fit. Tightened that up and problem solved. The weird thing is that it would work if the batteries were drained enough. I used to purposely run the batteries down some before starting up. Then I would run every load I could while underway. The tach would still drop out after a couple of hours run time. Now I can just disconnect shore power and go with no issues.

 

[gerilla]

Just checking to make sure, as on my 6lYA-STP the tach comes off a sensor on the flywheel. I had the same problem, although only a single engine, the sensor needed to be adjusted closer to the flywheel to pick up the magnetic signal. All is good now. so just in case your tachs aren’t driven by the alternator.
Cheers, and good luck with it.

My twin yanmar 4lha-ste MS350 has the same flywheel tach sensors. Alternator not charging does not knockout the tachometer.