Alternator help needed

[barunal]

Dear All,

I have the stock 80A Hitachi alternator on my Yanmar 4JH2-HTE.
The alternator stopped working/no output at all.

Here is my findings:
- When ignition key is at "ON" position, the ALT/charge warning light on the panel doesn't come on. (it used to light up before engine start, at key ON position, and it should)
- After the engine start, the ALT/charge warning light doesn't come on, plus there is no output on the alternator. (it should light up if/when there is a charging issue)
- Before & after the engine start, I can read the same voltage as my battery at the ALT output terminals: positive and GND.
- I checked the two ALT/charge warning lights (one on the panel, one behind the panel) and they are both fine.

What would you suggest for further testing to identify the problem?

Many thanks.

[Shenandoah52]

As silly as this sounds, in some charging systems when the warning light on the panel burns out the charging system no longer works due to the bulb being burnt out. The circuit needs the bulb to function properly. Pull the bulb out and check to see if it is good. If you have a spare, just stick the spare in the bulb socket and go from there.

[barunal]

Hi Shenandoah52.
Thank you for your input.
I checked both bulbs and they are fine. (one on the panel, and the other one hiding behind the panel)

[wingssail]

Originally Posted by barunal

Dear All,

I have the stock 80A Hitachi alternator on my Yanmar 4JH2-HTE.
The alternator stopped working/no output at all.

Here is my findings:
- When ignition key is at "ON" position, the ALT/charge warning light on the panel doesn't come on. (it used to light up before engine start, at key ON position, and it should)
- After the engine start, the ALT/charge warning light doesn't come on, plus there is no output on the alternator. (it should light up if/when there is a charging issue)
- Before & after the engine start, I can read the same voltage as my battery at the ALT output terminals: positive and GND.
- I checked the two ALT/charge warning lights (one on the panel, one behind the panel) and they are both fine.

What would you suggest for further testing to identify the problem?

Many thanks.

The stock alternator has a wire for the lamp (L). If it is not lighting then either you have no power to the field (F, assuming that the internal regulation is still present) or the alternator is burned out internally.

If you have external regulation then either there is no power to that device or it is burned out.

[Shenandoah52]

My apologies, I see you had that in the original post. A good reason to check the warning light circuit, bulb, socket, and wires, is because your alternator has 3 circuits 120 degrees apart as it spins and if one fails the other two phases will still show it's charging. Same with two out. It won't charge for diddly, but it will send voltage to the bulb. No light could mean a totally bad alternator or a bad warning light bulb or circuit.

It's also the cheapest fix so a good one to look before before you start throwing money at the problem. A multi meter is your friend here, but you may be well past that already I have no idea. Is the warning light circuit good?

[smac999]

Normally yanmar have 2 small wires on the alt. Red and blue. Both should have 12v when the key is on. Check that. One is lamp and one is ignition.

If you have 12v on both wires and the main pos wire. The alt is probably shot.

[barunal]

Shenandoah52; bulbs are fine but I should do further checking on that circuit.

Smac999, thanks for the input. Both small wires (red & blue) have 12v on them when the key is on.

[GordMay]

Alternator Testing
➥ https://dam-assets.fluke.com/s3fs-pu...00_ENG_A_W.PDF

[Wotname]

Originally Posted by barunal

Dear All,

I have the stock 80A Hitachi alternator on my Yanmar 4JH2-HTE.
The alternator stopped working/no output at all.

Here is my findings:
- When ignition key is at "ON" position, the ALT/charge warning light on the panel doesn't come on. (it used to light up before engine start, at key ON position, and it should)............

What would you suggest for further testing to identify the problem?

Many thanks.

IMO, troubleshoot the above first.
Until the ALT warning light come on initially, all else is wasted effort. The circuit is quite straight forward and if all the external components test satisfactory, the fault most likely will be in the internal regulator. If the regulator is shot, that would explain why the alternator is no outputting.

The attached circuit is from the 4JH2 manual and is for the 55 amp Hitachi alternator - I suspect the 80 amp will be the same.

[barunal]

Wotname, thank you very much for the input.
I will go through the warning light circuit first.

[smac999]

If there is 12v at the alt on the lamp wire. Then the problem is inside the alt. Pull it off and take to an alt shop for testing and repair.

[barunal]

smac999; well noted, thank you.

[Wotname]

Originally Posted by smac999

If there is 12v at the alt on the lamp wire. Then the problem is inside the alt. Pull it off and take to an alt shop for testing and repair.

Originally Posted by barunal

smac999; well noted, thank you.

To be pedantic, smac999 is correct when the alternator is stationary; if the alternator is spinning and working normally, there will 12V on the lamp wire.

[barunal]

When the ignition key is ON, I get 12V on both red & blue wires that come in a T-plug to connect to the alternator.
However, the charge warning light is still off by then, which should light up.
Warning light stays off after the start as well, and there is no output on the ALT.

[Wotname]

Originally Posted by barunal

When the ignition key is ON, I get 12V on both red & blue wires that come in a T-plug to connect to the alternator.
However, the charge warning light is still off by then, which should light up.
Warning light stays off after the start as well, and there is no output on the ALT.

Is that with the T-plug connected to or disconnected from the alternator?