Finicky Tachometer on port motor?

Two days ago the port engine tach meter quit working. my son and I investigated the issue starting at the alternator and found a broke wire from inside the alternator to the exterior nut that sends the signal north to the gauge. We replaced the wire and it started working again for a few minutes and then stopped. Now here’s the funny bit, it only works when the starboard engine is off. Once it is on the port tachometer stops working. Obviously a fault of some sort or an isolater unit the sends the signal to the gauge? Any thoughts? They are Volvo penta TAMD41’s and in excellent condition, and the alternators look brand new.

I don't know any specifics on VPs, but generally there should not be any cross-ties of wiring between twin engines other than:


Engine start battery cables emergency cross tie.
Negative battery cables
A Balmar Centerfielder if you have one.


Check behind the dash panel for co-mingled black wires for the gauges and panel lights.


Also try shutting off any battery chargers and putting a 12 DC load the port side battery on like a spotlight or refrigerator

If the batteries are very very charged, it is common for one alternator to turn off. Try adding a heavy load and see if it turns back on. If it does, then you know why.


Ken

kchace said:

If the batteries are very very charged, it is common for one alternator to turn off. Try adding a heavy load and see if it turns back on. If it does, then you know why.


Ken

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I have TAMD41s. My Port alternator turns itself off.
I have a "Smart" regulator on the port side, attaching the 120 amp alternator to the charging system. Stb side has the original 50 amp Alt attached only to the start battery, through its own internal regulator.
You likely have something similar going on.

I have learned to syncronize the engines on harmonic vibrations and temperature.

If you find a way to keep the port tach turned on, please post your solution.

kchace said:

If the batteries are very very charged, it is common for one alternator to turn off. Try adding a heavy load and see if it turns back on. If it does, then you know why.


Ken

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+1 Same issue on my twins when both alternators are sharing a charge via combiner to the same bank and the bank gets above 90-95%. The dominant alternator (the one with the higher V) will take over the charging and the lesser alternator will stop charging and lose stator tach output. Adding a load to the bank will return the indication. Turning off the combiner will also fix the issue on my vessel.

FlyWright said:

+1 Same issue on my twins when both alternators are sharing a charge via combiner to the same bank and the bank gets above 90-95%. The dominant alternator (the one with the higher V) will take over the charging and the lesser alternator will stop charging and lose stator tach output. Adding a load to the bank will return the indication. Turning off the combiner will also fix the issue on my vessel.

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Adding a Balmar Centerfielder will obviate one alternator dominating the other. In fact, that is its only purpose. It works and wiring it to the smart regulator is quite straightforward.

Jack, I think it requires 2 Balmar regulators, right? My boat only has one Balmar. The other side is an off the shelf internally regulated 60A Napa alternator for the start bank.

FlyWright said:

Jack, I think it requires 2 Balmar regulators, right? My boat only has one Balmar. The other side is an off the shelf internally regulated 60A Napa alternator for the start bank.

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Yes, I think you are correct. Without two and with a compatible alternator I rather doubt you can solve your problem. Call Balmar tech support. They will answer your question in short order.

Wow you were right. I loaded up the drain on the batteries. Both kicked on. I don’t like that so think I’ll have to look into separating that or adding an engine sync. I can’t really hear them well enough on the flybridge. Usually I drive twins by ear regardless of what the tachs say. But yep. The load was causing the port to turn off. Thanks guys.

So I am curious about installing a fly bridge engine synchronizer, however all the gauges i see require inputs from the tachometers. I’m wondering, since the port tach stops working when the battery bank is full then how do I get constant signal to the gauge if not from the tach or alternator? The ignition system, maybe the starter solenoid or ignition coil?

Diesel engines do not have electrical ignition systems at all so no to all those.

On other engines the tachs are driven by a sensor that reads the flywheel tooth count.

In your case the alternator signal may need to be tricked.

Try putting a load on the alternator that is constant of a few amps so the alternator does not shut down. I would just temporarily connect a 12v load directly to the alternator output terminal. If that works then the "load" could be connected/disconnected by an oil pressure switch so the engine MUST be running to connect the load. Just fuse it .

I'm trying to think of something and can't that would be a 4-5 amp load for a test that can stand continuous use . Maybe someone else has a brain wave.


You apparently have already done this as a test to prove/disprove the shutdown being the tach failure cause. It's just a matter now of finding a suitable load. I have a few heaters around and they would certainly do a job but the voltages needed are way too high. They do not need to produce a high temperature, just let a few amps through.

maybe One 12V light bulb of about 50watts would do as a test. They are or used to be available at chandleries. Just be aware it will be hot and would not likely be suitable for continuous use but as a test for a couple hours would give you an answer. For this it could be switched on manually once the engine is running and after the alternator has shut down losing you the tach signal. DOne like this it may not need the 50W so even a 25W might be enough. I'm thinking the light bulbs as they can be changed to check the minimum needed relatively cheaply and easily and need minimal effort to test..

Once the minimum wattage has been determined then a better load can be set up that will auto switch on/off , not get dangerously hot and be able to run continuously.
That could be done with high power resistors
An example is shown below:

https://canada.newark.com/vishay/rh0503r000fc02/wirewound-resistor-3-ohm-50w-1/dp/01F9899


This is not the one I'm suggesting , just an example of the type. But the light bulb test needs to be done to determine if it will work AND the minimum wattage needed.

I know this isn't the solution for everyone, but I was able to buy a direct-reading tach sensor on the after market for my Perkins engines. Obviously this is dependent on the engine make and model, but if it's an option, I'd highly recommend it. This was easily one of the best modifications I've made, and relatively easy and inexpensive.

Is it even possible to use the alternator tach outputs for syncronizing? All belts slip and it seems to me very unlikely that 2 different alternators would "slip" exactly the same.


Edit - I just looked up the Glendinning manual and they sell mechanical tach adapters for many engines.



Ken

Thanks for the info.

Thanks all for the information I obviously have some good choices for my winter dry dock maintenance. I’ll let everyone know what I come up with.

Finicky Tachometer on port motor

So while conducting my first oil change today on my twin TAMD-41As. I decided to turn off the combiner on the battery box. Left the port on the starboard on and the gen-set on. The tachometer on the port came to life. I didn’t have to run the fridge and all the other electronics. Now does that mean that the combiner being off that the batteries aren’t being charged or am I mid understanding what the combiner does?