Yanmar Alternator

[Daverw]

Hi, I seem to have issues with my alternator not charging, I've had it checked by auto electrical guys and they say it was ok. However it does not seem to be, the charge light is always on and I've checked the wiring and all is as per the drawing.
I'm I correct that the two wires to the rear plug as as follows, one feed 12v when ignition is on and the second feeds via the lamp, when the output difference is large the lamp is on and as the output v rises the v difference between then stops lamp illuminating, I've measured the difference and it's always about 4 volts so build always on glowing.

Have I got this correct and if so assume that the output is low and unit faulty even though they say it's OK.

 

[RichardS]

If we're talking about the T connector on a Hitachi alternator I also think that one terminal connects to the lamp and the other sense wire to a good 12V source which represents the actual state of charge of the battery like +ve battery terminal or the battery side of the starter solenoid.

I've no idea what one terminal should be doing in relation to the other in voltage terms though.

Richard

 

[VicS]

Hi, I seem to have issues with my alternator not charging, I've had it checked by auto electrical guys and they say it was ok. However it does not seem to be, the charge light is always on and I've checked the wiring and all is as per the drawing.
I'm I correct that the two wires to the rear plug as as follows, one feed 12v when ignition is on and the second feeds via the lamp, when the output difference is large the lamp is on and as the output v rises the v difference between then stops lamp illuminating, I've measured the difference and it's always about 4 volts so build always on glowing.

Have I got this correct and if so assume that the output is low and unit faulty even though they say it's OK.

I would have diagnosed your problem as a faulty alternator ............... ...... or broken drive belt!

The lamp will be on when there is a large enough difference between the battery volts and the alternator output volts As the alternator volts rise towards the battery volts the light will dim and finally go out when the two are equal. ... It appears that you have no output from the alternator.

I have not properly thought through the reason for asking but is your warning light a filament bulb or an LED ?

 

[Topcat47]

If the alternator checks out, it's most likely a problem with the wiring harness. If there's a break between the charging wire to the battery and the alternator, you just won't get anything going in. As eney fule no, I'm no electrical guru so hopefully a good boat spark will be along soon but I've had a lot of alternator problems recently, culminating in the rewind of my original Hitachi. The first thing to be checked out was the harness.

 

[Daverw]

The bulb is normal filament. Looks like I will have to take it out again and have it looked at by someone else. Not sure how they tested it as OK

 

[Daverw]

Harness is OK, wiring only about 6' to panel so easy to check, about the only thing that is.

 

[Topcat47]

Harness is OK, wiring only about 6' to panel so easy to check, about the only thing that is.

Wiring to the panel is only part of the harness. On my harness, the feed to the panel isn't thick enough to carry charging current which is a separate heavier duty cable.

As an aside, I have the workshop manual and the wiring diagrams are no help whatsoever. Luckily I have a mate who's a dab hand with a multimeter.

 

[savageseadog]

Usually wiring problems. Check connections for corrosion.

 

[JumbleDuck]

What voltage are you seeing at the alternator output when the engine is running?

 

[Daverw]

Tide dependant I'm going to check voltages tomorrow, unfortunately were on mud berth and going towards neaps so may not be able to fun until next week

 

[CJU]

I have just fitted an Argo FET charge splitter to my Yanmar charge system. To start with I had no charge but it mentioned in the instructions that some alternators will need a 12v I/P from the Argo FET to the L lead (red with 2 silver dots) on the T connector on the back of the alternator, as the alternator would now be isolated from the 12v batteries.
This new feed is to provide a small current to start the excitation of the electromagnet windings. After I cabled a dedicated wire from the charge splitter to the alternator all worked OK.

So it might be worth testing that you do get 12v on the thin red wire on the alternator and perhaps flashing 12v on to it to see if it starts to charge.
Also I would use a 12v bulb on flying leads to check for continuity. It is easy to see voltages but the cct wont always carry any current if there is a high resistant joint somewhere.

Good luck.

 

[Daverw]

I've checked for voltage at the plug but check with a bulb to make sure current is a good idea. There are only 3 connection from the ignition switch and that includes switch and alternators connection so not much to really go wrong. I've just st today taken the alternator off the boat, stripped and clean slip rings and plan to get it bench tested tomorrow hopefully.

Have today checked for voltage drop, earth connections etc and none found and no resistance issues. In one way I hope it's the alternator as it's sending me a little mad.

 

[Topcat47]

I wouldn't wish that on you. Marine Power in Bursledon want ~£800 for a replacement. I bought a chinese rip off from a specialist firm in Birmingham but although it was rated at 35w, it was actually producing 55 and the 1gm10 couldn't swing it when cold.

 

[De.windhoos]

Had this problem in the past. Finally figured out that the belt was slipping slightly that was causing the problem.