Tachometer Trouble On Shore Power?

[jviss]

I haven't fully verified this yet, will do so today. But commissioning my boat this season it's the first time I've ever run the engine while plugged into shore power. The tach only works when the engine is rev'd up real high. Could it be that the shore power charger is keeping the battery voltage high enough that the alternator regulator isn't pumping any field current and the alternator isn't 'generating,' hence no pulses to the tach? Just my current theory (no pun intended). I'll unplug and try it today.

 

[Davidasailor26]

Interesting situation, and a plausible theory. But if the regulator isn’t pumping field current at low RPMs why would it start pumping at high RPMs? Also, was the charger just in float mode at 13.3ish Volts? If so it seems the alternator would still start working to get the batteries into the 14’s. At least that what mine usually does in similar situations.

 

[Leeward Rail]

. Could it be that the shore power charger is keeping the battery voltage high enough that the alternator regulator isn't pumping any field current and the alternator isn't 'generating,' hence no pulses to the tach?

The tach on a diesel should be getting the pulse from the windings in the alternator BEFORE it's rectified to DC and sent to regulated output. As long as the alternator is spinning it should get pulses.

 

[Stu Jackson]

and the alternator isn't 'generating,' hence no pulses to the tach?

It's not a theory, it's a reality. I can't count the number of "My tach isn't working when I'm plugged into shorepower!!!" questions this and other boating forums have seen over the years. Why is this even a question from someone with 50 years of boating experience? This assumes that the tach signal is from the alternator and not a separate mechanical source.

 

[Leeward Rail]

This assumes that the tach signal is from the alternator and not a separate mechanical source.

Made me wonder.. are there any diesels that use an oem hall effect sensor for a tach ?
Obviously you can buy one aftermarket.

 

[Leeward Rail]

I can't count the number of "My tach isn't working when I'm plugged into shorepower!!!" questions this and other boating forums have seen over the years

Are they connected after the diodes and regulator ?

I always assumed they were connected to the stator, for the AC pulses, but admittedly haven't had to confirm it or pay attention to that, other than reconnecting the same way.

 

[dlochner]

Don't you have a Yanmar?

The Yanmar tachs do not work off the Alternator, unless the boat has been modified. There is a sensor that counts the teeth on the ring gear as the engine is running. The tach is basically an AC Voltmeter. The sensor generates a small AC current which drives the tach, the faster the engine is running the higher the voltage. If there is more than designed resistance in the circuit, it will take more voltage to overcome that resistance. Try cleaning the connections or replacing the wire, as usually Yanmar skimped on wire size.

 

[Ralph Johnstone]

Made me wonder.. are there any diesels that use an oem hall effect sensor for a tach ?
Obviously you can buy one aftermarket.

The VDO Vision Series 333-163 ( which I used as a replacement for the original Yanmar tach) can use anything and everything including your pacemaker and TV remote to generate a signal to their tach :

 

[jviss]

Don't you have a Yanmar?

If you are directing this question to me, no, not a Yanmar, but a Westerbeke based on a Mitsubishi diesel. It's the Westerbeke 38B-FOUR.

 

[dlochner]

If you are directing this question to me, no, not a Yanmar, but a Westerbeke based on a Mitsubishi diesel. It's the Westerbeke 38B-FOUR.

Yes it was to you. You can ignore my comment as it is relevant to Yanmar diesels not Westerbeasts.

 

[jviss]

Why is this even a question from someone with 50 years of boating experience?

As I said, "it's the first time I've ever run the engine while plugged into shore power." So I never noticed or cared before. Not that I'm going to go far while plugged into shore power, anyway.

I plug in maybe once ever few years, if I have the chance to top off the batts, and to run power tools, etc., while commissioning, instead of using the inverter.

If I ask they'll launch me on a Friday and leave me "at the bulkhead," a dock near the seawall/bulkhead by the crane. Convenient to load stuff, do some work, etc.

 

[jviss]

Westerbeasts

No, that's "Westerbreaks."

 

[jviss]

You can ignore my comment...

I would never ignore your comment, Dave! I enjoy your contributions and the conversation.

 

[Rick486]

I haven't fully verified this yet, will do so today. But commissioning my boat this season it's the first time I've ever run the engine while plugged into shore power. The tach only works when the engine is rev'd up real high. Could it be that the shore power charger is keeping the battery voltage high enough that the alternator regulator isn't pumping any field current and the alternator isn't 'generating,' hence no pulses to the tach? Just my current theory (no pun intended). I'll unplug and try it today.

Why would you do that? I would never think of doing such a thing. To me that would be taking a chance of causing an electrical problem for no reason.

 

[jviss]

Why would you do that? I would never think of doing such a thing. To me that would be taking a chance of causing an electrical problem for no reason.

I'm not following you, Rick. Why wouldn't one start the engine, for whatever reason, while plugged in?

 

[Rick486]

I'm not following you, Rick. Why wouldn't one start the engine, for whatever reason, while plugged in?

I would never do that simply because the two systems are not designed to be simultaneously running. There is no requirement for simultaneous running. when the boat is plugged into 110 she is presumably tied to a dock and the engine is not required. Were I developing requirements for the ship's systems I can't imagine a situation where running the engine while drawing AC would be required. If a configuration is not typically required the chances are that the designers would not include that capability, it would not be a stated capability, and would not be tested thoroughly. So, anything could happen....pretty simple. This is similar to running a genset while the main engine is running. Typically that is a configuration included in the design, but to run that line up requires certain switches to be set so the engine provides DC voltage and the genset provides AC, so there is no conflict, depending on the boat.

 

[Davidasailor26]

Don't you have a Yanmar?

The Yanmar tachs do not work off the Alternator, unless the boat has been modified. There is a sensor that counts the teeth on the ring gear as the engine is running. The tach is basically an AC Voltmeter. The sensor generates a small AC current which drives the tach, the faster the engine is running the higher the voltage. If there is more than designed resistance in the circuit, it will take more voltage to overcome that resistance. Try cleaning the connections or replacing the wire, as usually Yanmar skimped on wire size.

The YM series Yanmars do use a signal from the alternator to drive the tach. I have traced the wires and measured that with an oscilloscope to confirm. And I’ve never seen my tach drop out regardless of battery SOC, so I don’t know what signal they use but it seems unaffected by that characteristic of alternator driven tachs.

Yanmar alternator tachometer wire signal at idle -

 

[Davidasailor26]

I would never do that simply because the two systems are not designed to be simultaneously running. There is no requirement for simultaneous running. when the boat is plugged into 110 she is presumably tied to a dock and the engine is not required. Were I developing requirements for the ship's systems I can't imagine a situation where running the engine while drawing AC would be required. If a configuration is not typically required the chances are that the designers would not include that capability, it would not be a stated capability, and would not be tested thoroughly. So, anything could happen....pretty simple

But all of those systems do need to be designed to handle charging when other charge sources are present, for example Solar + engine, or wind + shore. Engine + shore is just another combination. All the alternator knows is the voltage at its output and sense wire, and it regulates its field current to keep the sense wire voltage at the intended output voltage accordingly.

 

[jviss]

I would never do that simply because the two systems are not designed to be simultaneously running. There is no requirement for simultaneous running. when the boat is plugged into 110 she is presumably tied to a dock and the engine is not required. Were I developing requirements for the ship's systems I can't imagine a situation where running the engine while drawing AC would be required. If a configuration is not typically required the chances are that the designers would not include that capability, it would not be a stated capability, and would not be tested thoroughly. So, anything could happen....pretty simple

Rick, I have no reason to believe that there's any issue with running the engine while plugged in. Perhaps you are suffering from fear of the unknown? Can you point to a single owner's manual that say not to do this? That said, the only "connection" of note is at the battery, the shore power charger and the alternator connection, and this is no different than leaving your solar panels connected when you're plugged in - they just don't care. I am happy to learn something, though, if you can tell me why this is a problem, other than fear, uncertainty, and doubt.

 

[dlochner]

I would never do that simply because the two systems are not designed to be simultaneously running. There is no requirement for simultaneous running. when the boat is plugged into 110 she is presumably tied to a dock and the engine is not required. Were I developing requirements for the ship's systems I can't imagine a situation where running the engine while drawing AC would be required. If a configuration is not typically required the chances are that the designers would not include that capability, it would not be a stated capability, and would not be tested thoroughly. So, anything could happen....pretty simple

It is not unusual for a DC system to have multiple charging sources at one time. We often have the engine running while connected to shore power and have the solar panels working without issue. The electrical system really doesn't care where the power is coming from as they are all wired in parallel. Collectively they will provide as much DC power is needed.