Alternator seems not to be charging

reworb

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Apr 22, 2011
234
Beneteau 311 Ft Myers Beach
I have a Yanmar 2GM 20 in my 2004 Beneteau. For a while I had been suffering from the dreaded push the start button and nothing happens syndrome. I read all the threads and I have the service manual with the wiring diagram. The wiring diagram show no connections after the 30 amp fuse at the engine to either the white or red wire so I decided to run new wires (proper tinned marine wire #10, not like the junk in the Yanmar harness) from after the fuse to the key and starter button. Did that and now the engine engine starts first time every time even when the boat boat has not been on the dockside charger for several days.

In an abundance of caution I started the engine and checked the voltage at the meters on the below deck panel, the meters so no change in voltage after I start the engine, also the charge warning light on the engine panel at the helm does not come on when the key is turned to the on position, the other warning lights come on and the warning buzzer sounds. Other than removing the alternator and taking it to a shop (its hot and humid and I really don't want work inside a hot cabin if I don't have to) any ideas for me to check?
 
May 24, 2004
7,129
CC 30 South Florida
Check for voltage at the battery posts with a digital multimeter. Allow for battery to discharge some by running a few lights and perhaps a fan for a while and then with the engine running check the voltage. A reading of 13+ volts would be indicative it is putting out charge. Disconnect the wire to the oil pressure sender and if the alarm buzzer still comes on when you turn the key it will mean the warning circuit to the alternator is working and it is just the lamp that is fouled up.
 
Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
Here is the diagram and this one shows what yours is missing.

I am not certain about the Hitacihi alternator in your setup however if the charge lamp is burned out the alternator will not excite and so there will be no charging.

Charles
 

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reworb

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Apr 22, 2011
234
Beneteau 311 Ft Myers Beach
Good to know if the bulb is not lighting there is no charge.
That's the wiring diagram I have. I checked the bulb yesterday and it does not appear to be burned out.
 
Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
OK If you are sure the lamp works.

The circuit shows the alternator lamp gets 12v + at key on (red/black). 12v - is supplied via the alternator itself at key on (blue/black). So at key on the lamp lights. When the motor starts the alternator begins charging and 12v - no longer is present. The lamp turns off.

So either there is no 12v + to the lamp at key on or the alternator does not furnish 12- at key on and in that case it needs attention - at the alternator shop.

EZ to test with your VOM at the alternator lamp socket. Do tell us what happens

Charles
 
May 24, 2004
7,129
CC 30 South Florida
Good to know if the bulb is not lighting there is no charge.
That's the wiring diagram I have. I checked the bulb yesterday and it does not appear to be burned out.
No, if the bulb is not lighting when you turn the switch it is either burnt out or not getting 12V power from the battery. It needs to be fixed before it can properly be indicative of whether the alternator is working or not. Since you messed around with the harness from engine to panel go back and visually inspect the harness specially as it goes around sharp fiberglass edges. With hull flexing over time the wires in the harness can get chaffed and you may get some open circuits. Look for worn or peeling insulation. You seem to have fully charged batteries so postpone your concerns about the alternator until you fix the warning lamp problem and I have doubts that the two would coincidentally fail at the same time.
 

reworb

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Apr 22, 2011
234
Beneteau 311 Ft Myers Beach
I braved the heat and humidity some more. The lamp is definitely getting 12+ from the red/black. So I'm assuming it's not getting 12- from the blue/black. I have the inspected the entire cabling from the alternator to the lamp I can not see any damage. I was wondering how I could check the continuity of the blue/black with a VOM as the distance from one end to the other is obviously much further than my leads will stretch. Or should I just run a temporary "jumper wire"?

Thanks for all your help I'm not much at diagnosis I can run wires and install new stuff but that is about the end of my skill set.
 
Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
Try the charge lamp socket at key on. VOM + to one socket lead VOM common to the other. If you show 12 v. then blue/black is operative and the bulb is bogus. If not then follow blue black to the alternator. There is a connector(s) proximate to the starter motor take apart and make contacts spiffy. There is a white plastic push-on plug at the alternator backside. Pull off and make clean. You can also jumper to these points to test for any break.

Charles
 

reworb

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Apr 22, 2011
234
Beneteau 311 Ft Myers Beach
Thanks everyone.

I tapped into the blue/black at the alternator end and the bulb end and ran a temporary wire between those two taps. When I turn the key the charge light lights up and then when I start the engine the light goes out and the alternator functions fine as battery voltage increases to about 14.3 to 14.5 volts. As I tapped into the blue/black and it's also non-tinned wire I will just run a new wire.

What puzzles me is why when the charge light wasn't coming on the alternator would "not start" and now it does?
 

pateco

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Aug 12, 2014
2,207
Hunter 31 (1983) Pompano Beach FL
I posted this in an older thread today, 1GM10 Charge Light ON, Batteries Charging because I did not see this one.

I have the same problem but different symptoms. My Yanmar 2GM charge light goes on when started, but it does not go out. Instead it gets brighter with increasing RPMs. I am getting good charging at 14.2V, and good regulation (for a Hitachi). Higher amps with a lower SOC and then decreasing as the battery comes up to 100%

What could be the wiring issue?

Sorry to be so confused. I understand that the lamp provides field power to the alternator at starting once the ignition key is on, but what normally would make the light go out once the engine is started and running? The sense wire, or something else?
 
Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
Thanks everyone.
What puzzles me is why when the charge light wasn't coming on the alternator would "not start" and now it does?
Your particular alternator is essentially automotive and internally regulated. The alternator must 'excite' to charge. The excite current runs from the ignition switch through the warning lamp and then to the alternator via blue/black. In your case blue/black is broken thus the alternator cannot receive excite current and so will not start charging. You replaced the broken blue/black, restored the excite path, so now it charges.

Isn't this stuff exciting?

Charles
 
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reworb

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Apr 22, 2011
234
Beneteau 311 Ft Myers Beach
Thanks for the explanation, makes sense now. So if the bulb were to burn out the alternator wouldn't charge?
 
Mar 2, 2008
406
Cal 25 mk II T-Bird Marina, West Vancouver
If you have the Yanmar manual, you will see that the Hitachi LR136-31 alternator with LR1Z-28 internal regulator has a resistor wired internally in parallel with the external charge lamp to supply the excitation current should the bulb not work. Also the charge lamp is basically wired between the alternator output and the battery so that when the alternator is charging both sides of the lamp are at the same nominal +12 volt level with another resistor to the battery common/ground.
looks like some of you have big wiring problems.
Sorry, I tried to attach a copy of the manual but it is too big.
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
If you have the Yanmar manual, you will see that the Hitachi LR136-31 alternator with LR1Z-28 internal regulator has a resistor wired internally in parallel with the external charge lamp to supply the excitation current should the bulb not work. Also the charge lamp is basically wired between the alternator output and the battery so that when the alternator is charging both sides of the lamp are at the same nominal +12 volt level with another resistor to the battery common/ground.
looks like some of you have big wiring problems.
Sorry, I tried to attach a copy of the manual but it is too big.
Pretty much spot on. There is a diode in there, a zenner IIRC, that creates unequal voltages and allows the lamp to light while the alt is only in key-on or rotation is too slow to bring alt voltage above battery voltage. When alt voltage exceeds bank voltage the diode can now open and both sides of the lamp become at essentially parity voltage, this extinguishes the charge lamp. You can also get low idle situations, or high loads at idle, where the alt can't produce enough current to get voltage high enough. In this case the diode stops flowing and the charge light will come back on but if you increase revs it will again go out.. The alt should still excite without the lamp but it is a good idea to keep it working.
 
Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
I like fact so last question

The facts are, he had no joy with lamp to alternator L path broken and 100% success with lamp to alternator L well connected. So apparently there is no excite absent the charge lamp path on the unit he is wrestling with despite what "should' happen according to the diagrams we have at hand.

Is it possible the unit he has is not Hitachi LR136-31 (probably LR135-31) or maybe not LR135-105 either?

Charles
 
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reworb

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Apr 22, 2011
234
Beneteau 311 Ft Myers Beach
I don't think I have the stock alternator. (I can not read the label on the alternator without removing it) The previous owner installed a much larger alternator and then when I had a lightning strike I believe the boatyard replaced the alternator with the same specs as the one that was installed. But as Charles said, no lamp lighting up at key on, no charge at engine run. When I "jumpered" the blue/black wire at key on the light came on, at engine runnning the alternator was charging.

Perhaps after I have cataract surgery in several weeks I will be able to read the alternator label and maybe that will shed some light (pun intended) on the issue.
 
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pateco

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Aug 12, 2014
2,207
Hunter 31 (1983) Pompano Beach FL
Pretty much spot on. There is a diode in there, a zenner IIRC, that creates unequal voltages and allows the lamp to light while the alt is only in key-on or rotation is too slow to bring alt voltage above battery voltage. When alt voltage exceeds bank voltage the diode can now open and both sides of the lamp become at essentially parity voltage, this extinguishes the charge lamp. You can also get low idle situations, or high loads at idle, where the alt can't produce enough current to get voltage high enough. In this case the diode stops flowing and the charge light will come back on but if you increase revs it will again go out.. The alt should still excite without the lamp but it is a good idea to keep it working.
This makes sense, But why then on my 2GM does the charge light go on when engine is started, but not go out. Instead it gets brighter with increasing RPMs and dims to almost out at idle? I am getting good charging at 14.2V, and good regulation (for a Hitachi). Higher amps with a lower SOC and then decreasing as the battery comes up to 100%
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
This makes sense, But why then on my 2GM does the charge light go on when engine is started, but not go out. Instead it gets brighter with increasing RPMs and dims to almost out at idle? I am getting good charging at 14.2V, and good regulation (for a Hitachi). Higher amps with a lower SOC and then decreasing as the battery comes up to 100%
Could be many reasons but the charge light should go out if everything is working properly and wired properly. Do keep in mind that many of the cheap aftermarket alts do not use the same internal circuitry that Hitachi does. I have had a few "eBay grade" "direct replacements" burn out in less than a few weeks due to lacking some of the internal self protective features.. Perhaps your panel wiring has been messed with or your alt may not be stock..
 
Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
If the blue black/wire is grounded (shorted to 12 v -) the lamp will not go out. Check the instrument wire loom to be sure blue/black is not chafed to a neighbor wire or to anything else either. Also check the 2-wire plastic plug at the back of the alternator to be certain it is clean.

If all is well with the signal wire call the local alternator shop and ask whether an internal failure will cause this symptom. If so take the unit out and they will test it, verify what has failed, and fix it.

If the cost to fix is not to your taste - or if you want a far more reliable and useful alternator - this would be a good time to consider a unit like a Compass Marine 100 amp alternator.

http://sbo.sailboatowners.com/gear/gear.php?task=showad&id=5542.

Charles