6BTA Alternator 15SI – Failed?

[Stephen Oliver]

Hi Guys

Finally started using our boat again after a crazy busy year (Aus seems to have just got busy and not too troubled by COVID .. yet.. )

Halfway through a 2 hour trip starboard rev counter dropped to Zero. Volts held up so i thought we were ok… on restart a few days later still zero RPM and this time voltage was down at 12v.. i assume battery voltage. As it was low the VSR hadnt opened so was showing actual true voltage so I assume the alternator wasnt charging.

I checked the simple things, belts wires fell off etc.. nothing. Checked the lamp on the instrument panel. Lamp doesnt light with ignition on (the Port side does) Bulb is fine and swapped holders etc around so know they are good. I have a diode between the lamp and the start button which I thought was bad, but changed it and no change.

Lamp doesnt light when running either which I thought it would if the alternator had failed?

Any diagnostics I can perform on engine to the alternator? Do I assume the alternator is shot?

Alternator is 15SI Model 20-113-1

Wiring diagrams as below

Topic

[Stephen Oliver]

Hi Mike

The more the merrier.. mine was a sudden fail which is why I checked everything else out.. I’m planning on doing the 160deg thermostats while im replacing it as you are almost there with the removal of the alternator..

I wasnt planning on replacing the belt.. but now you have me thinking I should.. !

Steve

[Mike Uliasz]

Hoping I can jump in and get some advice on this post. Port alternator is going and I’m going to replace. Tach not working, it read right on the 12V line out on last trip, weak batteries after the trip. For a while the tach was not working at start up, but would come to life when coming up to cruising speed and work the rest of the day, even at idle.

Plan on changing the belt too. Is there any other maintenance to consider while in the process of replacing the alternator?

Looks like the 15 SI, 12V, 3-Wire, Alternator with Pulley, green belt configuration.

Next projects are the digital volt meters for the 2 engine and 3 house batteries and the 160 thermostat. Upgraded to the SMX seawater pump & removed the fuel cooler last year.

Thanks

[Stephen Oliver]

Hi Phillip

Lamp was one of the first things checked and funnily enough the over temp lamps wasnt working but it was a crappy holder.. i swapped things around between engines to prove what was and wasnt working..

I have a new alternator now just need to fit it which will no doubt be a pig to do as its between the engine and the fuel tank.. joy! Hopefully thats the issue though!

Steve

[Philip]

Might want to check the indicator light… if it doesn’t work when the key is on then why should it work when the alternator fails…

[Stephen Oliver]

Thanks Tony

Understand that the tacho out has nothing to do with charge – it was the indicator that something was wrong so included it in the wiring (i’ll be changing to the mag pick up soon)I was surprised that the ALT light didnt light up.. but it doesnt even on ignition.. but does on the port engine.. so assuming the alternator is stuffed. I’m going to replace it and then see if the old unit is worth repairing to keep as a spare..

Thanks for the wiring diagrams.. to clarify the second image with the lamp / resistor, do you mean it has a lamp and a diode or the lamp / resistor can be replaced by a diode (mine has a diode and lamp.. but not in series as you show.. I probably need new standard engine harnesses as they are custom things I think.. )

Steve

[Tony Athens]

Take your alternator to a shop and have it tested or replaced,

As to your wiring–Make no sense to me. The ACV phase tap for the tach has NOTHING to do with the charging circuit although when it does not work, usually the alternator went poo-poo.

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Mike Uliasz

[Author]

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