Voltage drop

[Rick J]

2003 DF140.
My battery was several years old and left me stranded on the lake, so I replaced it. I checked some voltages and now I'm not sure it's just the battery that was the problem.
The new battery before starting is about 12.3 volts. When I start the motor, it jumps to 14.4 or so at any RPM which I think is perfect. But when I turn on the nav lights while still running, (one small bulb in front and back and the dash lights) the voltage drops to about 13.5 and stays there. Shouldn't it still charge in the 14.4 range, no matter what I turn on? Should I suspect some trouble with the rectifier/regulator? I read a post that claims if the tach works, which it does, there's likely nothing wrong with the charging coil. Thanks for any suggestions.

[Harper]

It depends on whether in your example you are turning on the lights immediately, while the voltage is still at 14+ or if the voltage has already dropped to 13.5 or so before you turn on the lights. The voltage regulator will by design reduce the voltage as the battery recharges, so the highest voltage will always be right after you start the motor. If you are getting a voltage drop only becuase you turned on the lights, then there might be a weakness in the charging system. But your condition doesn't really sound too bad to me, as long as it's holding at the 13.5. I'm not surprised that the 12 year old motor is showing some age, and I really don't think you have a problem yet. But my advice would be to put the battery on a charger at the end of your day, just to top it off. I've always hooked up my batteries to an automatic charger when I get home, even when everything was brand new.

[Rick J]

Thanks. The voltage is about 14.5 with the motor running and nothing turned on. With the motor still running, when I turn the lights on it drops to about 13.5. It drops a little more if I turn on the courtesy light, livewell and bilge pump. RPM's don't matter.
For comparison, I started my truck and the voltage was also about 14.5. I then turned on the headlights, radio, fan, wipers, etc and the voltage dropped only a few tenths. I know the charging system is different on the outboard, but I would think the results should be similar.
The motor is 12 years old but only has 380 hours.

[Harper]

The charging system on outboards is not as efficient as automotive alternators. That's why I always top off my batteries with a charger.

[Rick J]

I was using the voltage values as read off my Humminbird Sonar/GPS. Someone suggested taking readings directly at the battery, stating the resistance in the wiring to the dash will cause voltage drop, even with a small load.
When I took readings directly at the battery, the voltage remained virtually constant. With the motor idling and nothing turned on, voltage was 14.78. Then I turned on the lights, livewell and bilge pump, radio and courtesy light (that's all I have) and the voltage only dropped to 14.69. so, I think all is well in Minnesota and it's time to go fishing.

[Harper]

I think all is well in Minnesota and it's time to go fishing.

I agree with time to go fishing.........can't comment on Minnesota

[Moonlighter]

Fair call! I am all in favour of more fishing time!!!

However, I think what your test shows is that somewhere in your boat's wiring there could be a problem, perhaps some corrosion in the main + and - feed wires to and from the console bus bars, or poor connections somewhere. Maybe some corrosion in fuses or fuse boxes.... That's the sort of thing to check for.

Might be worth doing some checking because if the voltage drop to instruments like sounders/GPS etc on the dash is excessive, they will start cutting out or playing funny games, and that will affect the fishing!! They don't like low voltages!

[Harper]

Fair call! I am all in favour of more fishing time!!!

However, I think what your test shows is that somewhere in your boat's wiring there could be a problem, perhaps some corrosion in the main + and - feed wires to and from the console bus bars, or poor connections somewhere. Maybe some corrosion in fuses or fuse boxes.... That's the sort of thing to check for.

Might be worth doing some checking because if the voltage drop to instruments like sounders/GPS etc on the dash is excessive, they will start cutting out or playing funny games, and that will affect the fishing!! They don't like low voltages!

You're absolutely right, Grant! When he mentioned fishing, all other thought processes left me...

[Moonlighter]

I think I found your shirt Mike:

http://www.madkeen.com.au/fishing-cl...ts/mad676.html

[Harper]

I think I found your shirt Mike:

mad keen fishing polo shirt sporting clothing priorities fishing drinking women work

You got it, friend......