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 wrote:
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

The voltage would probably drop as the battery became fully charged.

"gaffcat" wrote in
oups.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

gaffcat wrote:

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.


Reduce the rpm of the motor?

How accurate is your test meter?

The voltage is probably high because the battery is charged, and is
resisting the charge current. If the battery was low, and accepting
current more readily, the voltage would be lower with the same motor
and rpm, etc. Your outboard motor probably does not have a very
fancy regulator on it, typical.

What is the "float" voltage for the battery? A bulk charge implies
a discharged or partially discharged battery.

If your situation does not change, as I suspect it will with a
little use, the only damage would be water consumption in the
battery. Keep it topped up with distilled water and keep the
battery tops clean and dry.

Terry K

Fritz,

In my humble opinion 15.5VDC is too high a voltage. Does your charge
circuit have a voltage regulator or is the output going straight into the
battery without a voltage regulator?

Depending on the horsepower of your outboard, 10 amps seems like a lot of
power going to the battery. It would probably be nice if you could control
the charge current to divert power from the engine to propulsion instead of
charging the battery, if desired.

Best Regards,

Bert

Bert van den Berg
CruzPro Ltd.
www.cruzpro.com
35 Keeling Road, #A4
Henderson 1008
New Zealand
Tel: 64-9-838-3331
Fax: 64-9-838-3332




----- Original Message -----
From: "gaffcat"
Newsgroups: rec.boats.electronics
Sent: Tuesday, August 09, 2005 5:51 PM
Subject: 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" wrote in message
oups.com...
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