t8 alternator

[fisher_i_am]

Not sure if my Yamaha t8 alternator is working. How can I check. Problem started when I spent a couple of hours trolling with both graphs on a radio playing. Starting battery ran low. I charged at home an went out again. Noticed voltage on graph stayed about same with and without t8 running (+/- 0.2v) and saw voltage climb slowly with 115hp motor running. Any thoughts.. I thought all t8s had alternators....maybe mine is bad..any sure way to tell.

[PJM]

Fisher_i_am

The alternator charges at I believe at 6 amps @ WOT, so it you were just trolling and with your livewell running and electronics on the motor was not keeping up with the demand. Does your T-8 have electric start and power tilt

[fisher_i_am]

Yes it has power trim and start

[nwpaconcours]

My T8 shows 14+ volts on dephtfinder when trolling (near idle). Same off the main motor. I only have 12.4 volts or so when both motors are off.

Sounds like you have a charging issue.

[Lundexp]

Originally Posted by nwpaconcours

My T8 shows 14+ volts on dephtfinder when trolling (near idle). Same off the main motor. I only have 12.4 volts or so when both motors are off.

Sounds like you have a charging issue.

Mine is exactly the same way. I often will run my T8 up to 6 hours straight and run 2 fishfinders and the livewell at the same time and all are off the starting battery. Never had any issues.

What voltage are you seeing when the T8 is running?

[fisher_i_am]

was out again and I definitly think it's not charging.

Anyone run into this problem or have suggestions other than a dealer / mechanic to fix.

Thanks

[yarcraft91]

A regulated charging system should hold a good, fully-charged battery at 14+ volts when the motor is running at mid to WOT rpm. If yours won't do that, there is either a heavy electrical load or a charging system problem.

If there are fuses in the charging system, check to make sure each one is good. Trace the wires from the T8 to the battery and make sure the connections are good. Trace the wiring in the T8 charging system and make sure all connections are good. At that point, the cheap fixes are about done.

If that doesn't locate a problem, you may be at the point of replacing parts. The rectifier/regulator may be the easiest to replace at roughly $100 parts cost. Consider if you're willing to risk replacing a perfectly good $100 part without having a shop test the motor.

[fisher_i_am]

thanks Yar.

My main motor keeps voltage up around 14V, so I think it's definitly something with the T8.

I did locate the rectifier and wires, all look good but could really use a wiring diagram to help test rectifier.

The rectifier has a red, green, green/white wire coming out of it and also a ground. Anyone know where to get wiring diagrams for these.

Jason

[yarcraft91]

A factory service manual will have the wiring diagram. A third-party manual, like Seloc, might also. If the T8 complies with the current marine wiring color code, red = 12 volt mains output wire (connects to battery + terminal). I can only guess at the green and green/white. One of them is likely the AC voltage output from the alternator to the rectifiers, the other is the feedback wire to the alternator field wiring to regulate alternator voltage.

[fisher_i_am]

I did a little more trouble shooting. I measured ~5 V between the red wire and ground at idle and it went even lower at WOT. Then measured ~25V between the green and green/white wire at both idle and WOT.

I'm guessing the alternator is doing its job but rectifier is not. I real close to buying a new rectifier ($100). Any more thoughts?

Thanks