Surging voltage

[hlev00]

Starting our Yanmar this spring we noticed that the sound was not steady at idle. After a while it seemed to settle down. today (our second day out ) it behaved the same way but never settled down. I happened to Notice that the voltage fluctuates in sync with the engine sound. No tach. The voltage is between 14 and 15. I checked the batteries and they were bubbling away. I removed the batteries over the winter but no other electrical changes.

Is this clearly a bad regulator or might there be a loose or corroded connection I should look for?

Thanks, Harry
Beneteau 423

[Kettlewell]

Something is obviously wrong with the regulator if it is allowing up to 15 volts. Did you by any chance disconnect a small sensor wire that runs direct from the battery bank to the regulator in order to allow it to sense battery voltage?

[hlev00]

Originally Posted by Kettlewell

Something is obviously wrong with the regulator if it is allowing up to 15 volts. Did you by any chance disconnect a small sensor wire that runs direct from the battery bank to the regulator in order to allow it to sense battery voltage?

That's what I was thinking but that is all handled through the harness and seems to be intact. What doesn't seem right though is that there are two wires out of the alternator that appear to be the sensors. They appear to be to ground which would explain the high voltage. But it makes no sense how it got that way. So I think I must not be looking at what I think I am.

[Kettlewell]

If you have a standard Yanmar Hitachi alternator you may find the diagrams in this thread handy.

[hlev00]

So, I was a bonehead when I first tested the sense wire - the key was off. Doh!

After subsequently studying the diagram in the service manual for the alternator it was obvious that the key had to be on. That crossed my mind originally, but finding the sense wire at ground instead of floating/open is what threw me. I turned the key on, the light came on and the sense wire was at battery level.

Starting the engine, the voltage went to 14.5 then up to 15+. Voltage still fluctuates between about 14..5 and 15.5 at about 1 - 2 Hz. All connections seem to be clean and secure.

I went through several on-boat diagnostics and it seems to point to the regulator, so I pulled the alternator and am taking to an alternator shop. I will be disappointed but not surprised if it comes back testing fine telling me I still missed something.

I also checked the spec gravity of the cells. A couple seemed a little iffy. The alternator shop thought that the regulator is the problem, but also suggested load testing the batteries.

More to come,
Harry

[hlev00]

The alternator shop confirmed that the alternator is putting out 15+V so they are going to rebuild. It is tempting to have them put in the ability to switch between the internal regulator and an external one.

[Cheechako]

Dont rely on teh Yanmar panel to tell you what the voltage is... it could be fine. Where are you reading it? Not sure what the voltage would have to do with the engine surging anyway.... unless the regulator is kicking in and out... but the voltage should vary more if that's happening... right?

[hlev00]

Originally Posted by Cheechako

Dont rely on teh Yanmar panel to tell you what the voltage is... it could be fine. Where are you reading it? Not sure what the voltage would have to do with the engine surging anyway.... unless the regulator is kicking in and out... but the voltage should vary more if that's happening... right?

Thanks for the input. Yes, the surging symptom bothers me. The surging was first noticed by the sound of the engine and then by the voltage on the DC panel. I also confirmed at the R (or IG) wire at the back of the alternator, and at the batteries. The surging engine RPMs would result in fluctuating voltage but I still think it shouldn't go above 13.5-14 V. The alternator shop says the alternator tested bad, well over 15V. I hope they aren't just trying to get a rebuild out of me.

[hlev00]

Well the 2nd shop first said it was good even though it was putting out 15+V, but he said "that was normal for these, they run high." That didn't instill a lot of confidence. Anyway, when I went to pick it up he said he had tried it again and now it was a steady 14.2. He put it on the bench for me and sure enough, rock solid at 14.2. I guess that's the new normal. Anyway, it seemed okay at that point.

I put the alternator back in the boat. Before the first test, the bank was at 12.49. I started then engine and the voltage went to about 13.8 and held there for a while. Then it crept up to 14.2. Then finally it moved up to 15 then started bouncing between ~14 and ~15. I cleaned grounds and also ran an ignition wire directly from the battery - no change. Every time after that first time, the voltage went straight to 14-15. I'm thinking maybe it is a heat induced problem in the regulator. The alternator wasn't hot but it was warm.

FWIW, here is a video of the volt meter on the panel. The first bit is from when I was toggled to the start battery that wasn't being charged. This is from after all the ground checks and other tests. I get the same results from the start battery.

Charging problem - YouTube

[Paul Elliott]

Measure the voltage at the battery terminals. You might have a bad cable or connector.

[hlev00]

It turns out it was my alternator after all. One rather important data point I forgot to obtain was how did the alternator behave at different RPMs. The oscillation between 14.1 and 15.2 occurred when the engine was at idle, around 900 RPM. When I moved the RPMs up to 1,600 the voltage stayed right at 14.3. I bought an aftermarket replacement from Rare Electrical and installed it today. Now the voltage stays at 14.4 whether at idle or anywhere else. I'm going to get the original fixed. Had I done the above test, I could have taken care of this with the first trip to the alternator. Live and learn.

BTW, I did check the the voltage drop across 12V and Gnd while either alternator was running - only 0.15V.

[Greatketch33]

I suspect my yanmar hitachi 55amp as a problem because the charge light is on at all times.

How can I check? Is it just a letter of putting a volt meter on the starting battery to see if there is a change?

I read the tech manual and L and R terminal tests are not clear to a newbie on motor electrical matters.

Thank you for your advice,
Deric

[Cheechako]

Originally Posted by Greatketch33

I suspect my yanmar hitachi 55amp as a problem because the charge light is on at all times.

How can I check? Is it just a letter of putting a volt meter on the starting battery to see if there is a change?

I read the tech manual and L and R terminal tests are not clear to a newbie on motor electrical matters.

Thank you for your advice,
Deric

If you are asking how to tell if it's charging or not... yes , it's that simple... should read up into 14+ volts if charging... make sure all your terminals are clean if it's not ... they loosen sometimes or get cruddy... sometimes they look clean but are wet/cruddy inside the mating surfaces.