batteries overcharging

[blake115Yami]

I just rebuilt a 17 mako with a 91 yamaha 115.My friend did all of the rewiring.I am noticing that 1 battery is charging up to 16.5 volts and the other one wont go past 12 volts(this reading is coming from my garmin 188c).The one that is at 16.5 goes right back to 12 when the motor isnt running.Could this be a wiring problem or a bad alternator?If its an alternator could someone please link me to a new one on this site because i couldnt find one.Thanks for the help

[Ken]

blake,
I don't know how your buddy has the batteries wired, but the 115 is designed to charge only one battery at a time - unless they are hooked up in parallel, and I don't recommend that.
Sounds like you have a bad rectifier/regulator assembly - should charge up to a max of approx 14.5 volts. You should confirm the voltage reading with a digital voltmeter before replacing any parts. Here's a link to the part you need:
http://www.boats.net/yamaha/partsyst...114bd0118b2548
Item number 13 - rectifier/regulator assy.
This is in the online catalog (above) of boats.net, sponsor of this forum.
Good luck [img]smile.gif[/img] ,
Ken K

[CharlieK1988]

Blake, Having the same problem with my 1987 Yamaha 50. The voltage was normal (13.8) until the motor warmed up so I mounted the rectifier below the air intake. I saw that Yamaha did that in a later year. Voltage still ran high. Then I ran an electric *****ing motor with the battery which discharged it some. After that the battery charged normally. I was out for a couple hours, mostly at full throttle, and it never got above 13.8 volts

I ordered a rectifier / regulator and a new lighting coil for a 1995 Yamaha 50. If I run into the high voltage problem (16.5 volts) I'll install them.

By the way Ken is a great help with these type questions.

[CharlieK1988]

The answer is a voltage con*****er. I use a FlexCharge NC25A-12 It's made for solar collectors and outboard motors. Perfect for unregulated charging circuits. Cost is $95.00 at www.solerseller.com

If you don't want to go that route you can buy a DC to DC regulator from Jameco. It only handles 30 watts (2.1 amps), but you can use it for your instruments (tach fishfinder GPS ect) and at least avoid blowing them out. It puts out 12 volts with an input of 9 to 18 volts. Works great.