1980 H33 Yanmar 2QM15 Alternator Anomaly

[dmmlyons]

Hi Folks, I'd appreciate your take on the following:

* A previous owner had replaced the alternator on my 2QM15 with an Arco 84135 alternator which I understand is a replacement for the LR135-31 12V-35A alternator that was original equipment. The Arco 84135 has no L terminal so I could not check when the alternator was charging. I looked at battery voltage before the engine started, about 12.6V on both, and after it was running, and they were the same, Belt tension was good so I assumed .. faulty alternator.
* I replaced it with an Arco 84150, the replacement for the LR 155-04 12V-55A that was the original equipment upgrade. Again no L terminal. Used a pry rod to get good belt tension for the replacement.
* Battery switch to just number 1 battery and ran the battery down to 11.9 first by loading it as much as I can. I leave all the battery load in place and start engine (it was already warm). Battery voltage jumps over 30 seconds to a minute to 12.4V and stays there for the next 35 minutes - no increase beyond that. Engine still running, I turned off all the load and voltage jumps to 12.6 but does not increase beyond that. Certainly not to 13V which is what I see when I have my solar panels charging the battery with no load.

Appreciate any feedback on whether you think the alternator is working and why I don't see 13V on the unloaded battery or anything silly that I am doing to see these measurements.

thanks!

 

[Ralph Johnstone]

Engine still running, I turned off all the load and voltage jumps to 12.6 but does not increase beyond that.

If the batteries started out at 11.9V, they may still be looking for a lot more amperage to come up into the 13.2V region. I won't use the words bulk charge as the alternator does not have smart regulation.

I don't know what your house bank is like but remove one battery and see if there is any increase in output voltage. Don't get any bright ideas about removing all both batteries or you'll need ANOTHER new alternator.

Keep us updated.

 

[heritage]

Measure the voltage at the alternator. Put one lead of your multimeter on the positive post of the alternator and the other on the engine for ground. Voltage should be well over 14v. If that checks out, then the problem is downstream.

 

[Davidasailor26]

How are you measuring the battery voltage? 13V sounds low for the solar if it’s in bulk mode, so I suspect your voltage readings may all be low. If your solar is really charging in the low 14’s then maybe your alternator is really in the mid 13’s, which sounds reasonable for a deeply discharged bank. You’ll need a volt meter on the battery posts (and/ir alternator as heritage suggests) to see what’s going on.

 

[Ralph Johnstone]

Voltage should be well over 14v.

Unfortunately, if the battery(s) are still pulling heavy amperage and the actual alternator output is down around 15A (the measured output of a hot 55A Hitachi LR155-20B alternator) you will have a wait of several (5-6hrs.) hours to see a voltage increase if the battery started out at 11.9V. This also depends on the battery's rated AHrs as to how long it will take to "fill" this empty battery.

Until the alternator is capable of producing more amps than the battery is able to accept, you will not see much of an increase in voltage anywhere in the charging circuit. Once the amperage draw by the battery(s) has significantly declined, the internal voltage regulator of the alternator will rise to its set point of 14.2 - 14.3V. With the alternator at 14.3V and the battery at 14.3V, there is no voltage differential hence no amperage flow.

Nothing can be said about this alternator until it has has been charging continuously for at least 6 hours. This is where an external alternator regulator and battery monitor would really pay for themselves.

 

[Ralph Johnstone]

Battery voltage jumps over 30 seconds to a minute to 12.4V and stays there for the next 35 minutes - no increase beyond that.

I should mention that while the alt. was cold, it's max. output would have been around 30A. As it heated up, its output would quickly drop to about 15A which is why the voltage climbed quickly over the first minute and then stopped increasing. It was increasing, but so slowly, you wouldn't be able to see it. You will eventually see it after about 6 hrs.

If you had a battery monitor in place, it tells the full story of voltage and amperage in the battery as you check on it every hour or so.