outboard battery charging

I am building a boat and recently started my new Yamaha outboard for
the first time. While the engine was running I measured the voltage at
the battery and the reading was 15.5 volts. I have a 100 amp hour AGM
starting battery and the battery manufacturer reccommends a bulk charge
voltage of between 14.1 and 14.5 volts. Is there a way to reduce the
outboards charging voltage? Will this damage the battery? I think the
outboard puts out about 10 amps.

fritz

"gaffcat" <gaffcat DeleteThis @hotmail.com> wrote in
news:1123566716.521862.310500@z14g2000cwz.googlegroups.com:

> Will this damage the battery? I think the
> outboard puts out about 10 amps.
>
>

Two possible answers. The rectifier from the simple charger puts out
pulses, not DC. This drives some DVMs crazy. Try measuring it with an
analog VOM and see what it says.

My other answer is that Yes, 15.5V will certainly destroy a 6-cell battery.
However, this voltage, if real, is only temporarily applied when the motor
is running. With the 10A limit, I doubt it will overheat 10A x 15V = 150
watts distributed over the whole battery.

Is the battery bubbling madly and getting hot as you are underway? This
would indicate overcharging. Is it using any electrolyte requiring you to
refill it with distilled (only) water? This indicates overcharging over a
longer period. Modern batteries use little water charged normally, so
little they don't even put caps on them any more and require maintenance
over their lives.

I bet your meter is reading the peak of the charging pulses....

--
Larry