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Old 25-04-2019, 13:27   #1
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Yanmar 2GM20F Alternator Output Voltage?

My alternator output voltage is 15.5 when the batteries are at about 12.2v. Output is the same for 1st, 2nd, or both batteries using the switch. I believe the alternator is the standard one for the Yanmar 2GM20F diesel.

The battery charger output voltage is 14.4 when the batteries are at about 12.2v. The charger is wired to charge both batteries at the same time.

Batteries are lead acid Interstate Deep Cycle Marine. #1 battery is 3 years old and #2 is 2.25. I normally sail on #1 and start the engine and run on both. When sailing on #2, it seems to hold the charge a little better. The water doesn't seem to be boiling out and hasn't been low on either batteries.

Can anyone give me an opinion if the regulator is not working properly and needs to be replaced? Maybe battery #1 needs to be load tested and replaced?

Thanks,
Bob
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Old 25-04-2019, 14:59   #2
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Re: Yanmar 2GM20F Alternator Output Voltage?

Please specify some detail about how when where your V measurements are being made.

While charging, there is a circuit voltage that should be the same at both ends, less any voltage drop from the wiring / connections, which should be kept to a minimum.

The battery's **resting** voltage has little to do with that of the circuit while charging.

The voltage settings of each charge source should match the recommended charge profile of the target batteries, as per mfg published specs.

Thus different sources feeding the same bank are usually pretty close.

Over 15V is a bit high, but again more detail is needed as to where you're getting the number.
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Old 26-04-2019, 07:54   #3
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Re: Yanmar 2GM20F Alternator Output Voltage?

The analog volt meter is part of the 12V panel. It is wired to a bar that is connected to the hot side of the circuit breakers. By selecting battery 1, 2, or both at the selector switch the voltage is shown on the meter. I have checked the voltage with a digital meter at a 12V accessory plug and the voltage is almost the same as the analog meter which is running thru a little more wire and the circuit breaker.

I didn't understand most of the response and not sure what all the mfg specs say.

The batteries may just be very low on amps, as I rarely turn on the battery charger and only run the engine a limited amount. There are enough amps to start the engine, but maybe the starter draw is enough to cause the alternator to spike the volt up to increase the amps?

Anyway, I guess my plan is to turn on the battery charger for at least 24 hours to ensure both batteries are fully charged and see what the alternator puts out. Next will be to remove both batteries and have then load tested.

Thanks in advance for any comments on my plan and comments on the previous post.

Bob
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Old 26-04-2019, 09:02   #4
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Re: Yanmar 2GM20F Alternator Output Voltage?

if the batteries are 12.2 then they are 25% (or less) charged .. so the alternator is probably giving them everything it can. i would test when they are better charged.
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Old 26-04-2019, 10:08   #5
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Re: Yanmar 2GM20F Alternator Output Voltage?

Be sure to measure the voltage at 2 places when the alternator is running. Directly at the battery terminal and directly at the alternator output. When using the battery charger measure again directly on the battery terminal and at the output of the battery charger.

The wording of your first post is rather ambiguous and that's why John was asking for clarification.

Let us know what you find.
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Old 26-04-2019, 11:31   #6
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Re: Yanmar 2GM20F Alternator Output Voltage?

Quote:
Originally Posted by bobmcreynold View Post
I didn't understand most of the response and not sure what all the mfg specs say.
If you meant mine, do please try to parse it again, and ask clarifying questions will try to help.

You need to use a DMM for measuring at specific points, not rely on a central gauge.

Your batteries may (or may not) be OK, but that issue is separate from the symptoms you're trying to describe. Definitely need to do better at keeping them at 100% Full as much as possible, otherwise you're drastically shortening their lifespan, aka murder by PSOC abuse.

Link to your model batteries, many have data sheets online.

Do your charge sources offer the ability to adjust voltage?

Again, clarify what the system state is while you are reading each reported voltage, e.g. which switch position, bank is under load (how much?) vs at rest isolated, vs charging (which source?)
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Old 26-04-2019, 14:23   #7
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Re: Yanmar 2GM20F Alternator Output Voltage?

I've got the 110v battery charger turn on to get the batteries fully charged.

It is a 3 stage charger, which I believe outputs 30 amps, 20 amps, and 10 amps as the batteries are being charged. There is no voltage adjustment that I know about. There should also be no load on the batteries as they are charging, as everything is turned off. I can change the A-B-Both battery switch to each position and the voltage reads the same on the analog meter. The charger has 2 12v leads, one to each battery and one neg lead (i think). In all positions, voltage should be the same.

With the 110v panel turned off, the engine will start at 12.2v with the battery switch set to Both. Once the engine is started, analog meter reads 15.5V. Nothing on the 12v panel is turned on, so I assume no load. There is no amp meter, but starting the engine causes a big amp draw. Changing the battery switch to each position shows little difference in the 15.5v voltage output. I probably should have let the engine run a little longer than 3 minutes to see if the output voltage drops as the batteries were being charged.

The comment on 25% of less charge in the batteries and probably 650 amp batteries x 2 means to get them fully charged with 110v charger or 55 amp (I think) alternator will take many hours.

As to the condition of the electric system, both the 110v and 12v panels, breakers, wiring, terminals, battery switch, battery charger, electronics, etc are all new. Batteries are 2-3 years old.

I'll provide an update after the batteries are fully charged and a few more tests are complete. Thanks to everyone that responded.
Bob
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Old 26-04-2019, 14:46   #8
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Re: Yanmar 2GM20F Alternator Output Voltage?

Quote:
Originally Posted by bobmcreynold View Post
I can change the A-B-Both battery switch to each position and the voltage reads the same on the analog meter
AKA shore charger.

What is the low voltage in the early stage, as opposed to after they're Full? Ideally also note down the peak "Absorb stage" plateau in between, before it drops to Float.

Then with no load nor charging, wait a few hours overnight even better **if no loads** then note "resting" V

> With the 110v panel turned off, the engine will start at 12.2v

Do you mean that is the bank V, before or after, or during cranking?

> Once the engine is started, analog meter reads 15.5V

OK that's alt output, and likely needs dropping. Bank spec and a DMM to check V drop from wiring needed first.


> Nothing on the 12v panel is turned on, so I assume no load.

Hmm. Better to know, put an ammeter at the bank.

> to see if the output voltage drops as the batteries were being charged.

V should rise as SoC climbs in Bulk stage, then plateau peak Absorb, then (if 3-stage) Float, in theory only after Full.

> The comment on 25% of less charge in the batteries and probably 650 amp batteries x 2 means to get them fully charged with 110v charger or 55 amp (I think) alternator will take many hours.

At least 5, likely 7, regardless, why shore charging is (should be) left going overnight.
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Old 26-04-2019, 15:06   #9
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Re: Yanmar 2GM20F Alternator Output Voltage?

John, I know you are trying to help and know much more about electric systems than I do. I'm a CS guy and should have been more into EE. Maybe it would be easier to discuss over the phone to avoid my poor writing skills? My number is 361-960-9139. I live in Rockport, TX and you are welcome to call at anytime.

Chances are that I should have just made a simple post of "Is the Yanmar 2GM20F standard alternator within spec to output 15.5v on a low battery?".

Thanks again,
Bob
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Old 26-04-2019, 15:24   #10
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Re: Yanmar 2GM20F Alternator Output Voltage?

I would say very unlikely, as that is higher than any lead battery should receive in normal cycling, and would certainly damage say a GEL bank.

But perhaps it was tuned to compensate for a long run of wire causing voltage drop at the bank?

More likely the VR needs looking at.

Many are adjustable, so best to find out what your bank's mfg specs are beforehand.
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Old 26-04-2019, 16:11   #11
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Re: Yanmar 2GM20F Alternator Output Voltage?

Quote:
Originally Posted by bobmcreynold View Post
John, I know you are trying to help..............
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>


Chances are that I should have just made a simple post of "Is the Yanmar 2GM20F standard alternator within spec to output 15.5v on a low battery?".

Thanks again,
Bob

Bob,


You're right, but sometimes he talks in shorthand.


Short answer: NO


15.5V AT THE BATTERY BANK is a least an entire volt too high.


It is superb that you noticed this.


What John is recommending is: measure the V at the back of the alternator AND at the battery bank (in addition to your panel gauge) TO SEE IF THERE IS A DIFFERENCE. That's all.

Many alternator regulators are NOT adjustable.

However, and here is a curveball for you, if yours IS adjustable, some PO may have adjusted it upwards to "cover" this peculiarity with Hitachi alternators that came with Yanmar engines.

I understand that your're a CS not an EE, but none of was born an electrician, we all learned. Seriously, buy a boat electrical book. Or read some of these: Electrical Systems 101

And learn about how batteries get charged. Almost every single external regulator manual all available online, explain how, even if you don't get a book. Go to www.balmar.net and download the MC-614 manual. I know you don't have an external regulator a nd I'm not suggesting you get, just for learning purposes.



Here's the Hitachi alternator discussion: (don't know if that's the one you have, but most Yanmars do, or did)

Hitachi/Yanmar Alternators: (by Maine Sail)

Some alternators though, such as those made by Hitachi and found on Yanmar diesels, are dumber than a pound of beetle poop. Actually, to the alternator, they are pretty smart but to your batteries and the speed of charging they are flat out stupid. Why?

Hitachi alts with dumb regulators, and some others, limit voltage but also reduce voltage based on alternator temperature. This is a self protective feature installed in the internal dumb regulator to prevent the alternator from cooking itself. Remember voltage is the pressure that allows more current to flow. So, if we reduce the absorption voltage, then we also reduce the current the alternator is supplying.. The battery simply will not accept the same current at 13.4V that it did at 14.4V and as a result the alternator will run cooler. What do you suppose this does to your batteries over time.......?

The problem is that when cold you will get 14.3V to 14.4V out of the Hitachi but as the alternator heats up the dumb regulator begins to reduce the CV/voltage limit based on the alternators internal temperature. It is not uncommon to find a Hitachi alternator at 13.4V when hot. This is REALLY, REALLY DUMB....

If you have a dumb regulator, and notice the voltage dropping, it is likely a temp compensated dumb regulator. Get rid of it or plan to buy new batteries more often.

If you have a temp compensated alternator or a Hitachi alternator on a Yanmar you really are in dire need of external regulation if deep cycling a larger battery bank.

This is from:

http://forums.sbo.sailboatowners.com...d.php?t=125392

and these, too:

Hitachi Alternator and Smart Regulator Instal Question


Most practical way to upgrade Yanmar alternator?
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Old 26-04-2019, 16:20   #12
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Re: Yanmar 2GM20F Alternator Output Voltage?

Relevant
Internal alternator regulator or external
Hitachi Alternator and Smart Regulator Instal Question
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Old 27-04-2019, 13:54   #13
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Re: Yanmar 2GM20F Alternator Output Voltage?

The problem must be the regulator. Output voltage at the alternator is 15.43 on a DMM with the engine running at idle. Battery #1 started the engine and is showing 15.38v with the DMM. The analog meter at the 12v panel reads a little high at about 15.6v.

I found the Yanmar GM shop manual on the internet and it shows the output voltage should be 14.2-14.8 at 2500 RPMs. I didn't try the higher RPM, as it might raise the voltage even higher.

After charging the batteries overnight and with the charger off, both batteries read 13.3v on the analog meter. When starting the engine on 1, the voltage drops to about 10.7. Starting on 2 the voltage drops to about 11.5. Starting on both, the voltage drops to about 12.5. I'm thinking battery 1 may need to be replaced or at least load tested.

I'll make another post after the alternator is serviced and is re-installed. Replacing the regulator is probably something an alternator shop needs to do, as suggested in the shop manual.

Thanks again,
Bob
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Old 27-04-2019, 16:55   #14
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Re: Yanmar 2GM20F Alternator Output Voltage?

Yes you're on track, in more ways than one, great work.
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Old 27-04-2019, 17:00   #15
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Re: Yanmar 2GM20F Alternator Output Voltage?

Quote:
Originally Posted by bobmcreynold View Post
The problem must be the regulator. Output voltage at the alternator is 15.43 on a DMM with the engine running at idle. ...........
.................
.............................


I'll make another post after the alternator is serviced and is re-installed. Replacing the regulator is probably something an alternator shop needs to do, as suggested in the shop manual.

Bob,


Good move. It's always important, critical, necessary, helpful, essential, etc. to find a good alternator shop. Emphasis on GOOD. I found one when I lived in California, old place, old guy with his son ran it, really knew their stuff, bits&pieces all over kinda place. I loved it. Like going to a museum!


Best of luck, keep us posted.
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