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.

 

[dmmlyons]

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.

I have a bank of 2 batteries. Batteries had been charging on solar since I first posted. I disconnected the solar panel and I then turned the battery switch to battery number 1. No load on the battery, all breakers were off. Started the engine and after a minute or two measured the voltage across the alternator terminals with a standard multimeter set at the 20 DVC range. I got 12.7V. I measured across battery number 1 and got the same. After 30 minutes I measured again and got 12.8V across both.

 

[dmmlyons]

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.

Many thanks Ralph and all the sailors who responded! I have an inkling that the alternator is charging the battery slowly but I am never measuring 13V or 14V at the alternator and that is why I am worried. I also asked Arco by email but no response.

 

[Maine Sail]

I have a bank of 2 batteries. Batteries had been charging on solar since I first posted. I disconnected the solar panel and I then turned the battery switch to battery number 1. No load on the battery, all breakers were off. Started the engine and after a minute or two measured the voltage across the alternator terminals with a standard multimeter set at the 20 DVC range. I got 12.7V. I measured across battery number 1 and got the same. After 30 minutes I measured again and got 12.8V across both.

What kind of batteries

 

[Ralph Johnstone]

Batteries had been charging on solar since I first posted. I disconnected the solar panel and I then turned the battery switch to battery number 1. No load on the battery, all breakers were off.

So near yet so far. Without knowing the voltage of the batteries which would give you a wild guess at the "state of charge" of the batteries due to their previous solar charging, you don't know your starting point.

I got 12.7V.

Seeing that after being charged by the alternator for a minute or two you were only showing 12.7V leads me to believe the batteries were not fully charged from the previous solar charging period.

We still don't know who is doing what (including the batteries) but you must have all readings in hand before doing anything with the alternator.

Next time you are at the boat, I suggest the following :

1. completely disconnect the solar charger from the circuit
2. ensure their is absolutely NO load on the batteries
3. measure the voltage at the BATTERIES
4. start your engine so that the alternator is charging the batteries.
5. measure the voltage at the ALTERNATOR
6. run the engine for an hour and measure the voltage at the alternator every 10 min.

Post all of your readings for steps 1- 6 and we'll go from there.

MAYBE if you're not getting anywhere, you may have one or more faulty batteries. We'll look at that next time.

 

[heritage]

Before you give up on the alternator, take it to a car parts place and they will bench check it for free.

 

[dmmlyons]

What kind of batteries

The batteries are two Duralast 24MD-DL, 685 MCA, reserve capacity 140, both about 4 months since purchase.
They are sealed lead-acid batteries.

 

[dmmlyons]

So near yet so far. Without knowing the voltage of the batteries which would give you a wild guess at the "state of charge" of the batteries due to their previous solar charging, you don't know your starting point.



Seeing that after being charged by the alternator for a minute or two you were only showing 12.7V leads me to believe the batteries were not fully charged from the previous solar charging period.

We still don't know who is doing what (including the batteries) but you must have all readings in hand before doing anything with the alternator.

Next time you are at the boat, I suggest the following :

1. completely disconnect the solar charger from the circuit
2. ensure their is absolutely NO load on the batteries
3. measure the voltage at the BATTERIES
4. start your engine so that the alternator is charging the batteries.
5. measure the voltage at the ALTERNATOR
6. run the engine for an hour and measure the voltage at the alternator every 10 min.

Post all of your readings for steps 1- 6 and we'll go from there.

MAYBE if you're not getting anywhere, you may have one or more faulty batteries. We'll look at that next time.

The batteries are only a few months since purchase, purchased at the same time, Duralast 24MD-DL.
I managed to get some of these steps done - I added a pre-step

0. Voltage while solar panel is charging both batteries. Voltage the same on each battery 13.7V
1. Disconnected solar, switched to just battery 1, no load on the battery, measured voltage: 13.4V
2. Engine still off - measured voltage across alternator terminals: 13.2V,
3. Started engine -- measured voltage at the alternator, 12.8V

I didn't have time to wait for an hour, I will do that next. The results above seem to indicate some battery drain even if nothing is on. The Yanmar 2QM15 service manual engine circuit diagram indicates that as soon as you turn on the battery switch, there is voltage across the alternator and the starter motor b terminal (but not s terminal until you turn the key and press the start button)

 

[Ralph Johnstone]

With you above V readings, they still don't really tell of anything too, too, unusual. What would be very interesting to learn is : what happens to the battery voltage if you disconnect from the solar charger as above and then DO NOT attempt to start your engine for let's say 15 minutes. The rapid drop to 12.8V is likely just due to that very large A draw for a few seconds but without being there, it would be interesting to see what the voltage does as it drops from its overcharge of 13.7V down to its operating voltage of 12.8V. If you really want to get technical, take a reading every 60 seconds if the voltage is dropping. My batteries take hours to come off their overcharge of 13.5V down to 12.8V when the shoreside battery charger is yanked. I'm curious what yours do. Maybe, just maybe there's an unknown load lurking around back in there.

Let us know those readings as well as the charging for one hour from the alternator maybe every 5 minutes.

 

[Davidasailor26]

2. Engine still off - measured voltage across alternator terminals: 13.2V,
3. Started engine -- measured voltage at the alternator, 12.8V

That’s a concerning pair of measurements. The Arco alternator is internally regulated so it should be blindly pushing into the low 14’s unless the batteries are at such a low state of charge that it can’t manage that. The batteries being over 13V before starting means they’re close to full, so the alternator should have no problem getting higher than that. If bring the alternator to a shop to have it bench tested. If it tests bad I’d look at the rest of your charging configuration to figure out how it got that way, considering you just installed it.

 

[dmmlyons]

Let us know those readings as well as the charging for one hour from the alternator maybe every 5 minutes.

Well, ARCO finally reached out and I spoke with them. No schematic/instructions came with my ARCO 84150 alternator and apparently ARCO support don't have access to schematics either! However, they were able to tell me that the alternator would not work with only battery plus and negative connections. I connected the alternator that way because that's the way the ARCO 84135 I was replacing was connected when I bought the boat. Apparently the alternator never worked long before I owned the boat! Lucky I had shore power for a few years and then a good solar charger since though that meant I never thought to check the alternator until recently!
Any, here is the solution, for posterity. In addition to the ''nut" connections on the back of the ARCO 84150 (and the old 84135) alternator for battery plus and minus, there is a T shaped socket with two male spade connectors. One is the light connector and the other is an ignition (Batt + switched through the ignition key) connector. Either or both have to be connected for the generator to work. I have a light connection which was never connected - the original equipment LR135-31 alternator had a 'nut' connector for light and whoever put in the replacement ARCO 84135 did not realize it has a spade connector for light and will not work without it being connected. I can't complain too much about whoever that was because ARCO themselves could not tell me which of the two spade connectors was the light -- they did not have access to a pin-out for the socket! We both searched and both found the same diagram in another sailing forum (Alternator wiring question - Cruisers & Sailing Forums) and I attach it again here since it seems like a rare find. I connected the light to the radially most inwards of the two spade connectors and all works as expected now, plus I have a charging light that works as well. The alternator is putting out 15.4V which doesn't vary much with load. Thanks to all who followed this story and gave me hints about what to do!

 

[Ralph Johnstone]

The alternator is putting out 15.4V which doesn't vary much with load.

Nothing succeeds like success.

Sorry, but I don't remember after all these posts what is controlling your alternator voltage but I believe 15.4V is a bit on the high side for a bulk charge on a smart alt. controller. According to my ARS-5 external regulator, 14.7V is the desired voltage for lead acid batteries. If your alternator is internally regulated, time for more research before this can be put to bed. Also, if your alt. is internally regulated (not smart) you may damage your batteries if they are up to 100% state of charge (SOC) and your regulator is still pumping 15.4V into the batteries without any load on the batteries.

Sorry if this presents any further headaches.

 

[dmmlyons]

Nothing succeeds like success.

Sorry, but I don't remember after all these posts what is controlling your alternator voltage but I believe 15.4V is a bit on the high side for a bulk charge on a smart alt. controller. According to my ARS-5 external regulator, 14.7V is the desired voltage for lead acid batteries. If your alternator is internally regulated, time for more research before this can be put to bed. Also, if your alt. is internally regulated (not smart) you may damage your batteries if they are up to 100% state of charge (SOC) and your regulator is still pumping 15.4V into the batteries without any load on the batteries.

Sorry if this presents any further headaches.

I'm glad you said this. I was worried about the high voltage but I might have been tempted to use the boat a while before checking into the problem. Instead I connected up the R connector and now I see 14.5V. I guess my L (D+) connection is enough to excite the alternator into charging but not a very good voltage reference. Its been a journey, thanks!