BATTERY CHARGER: DUMB QUESTION OF THE DAY

[Larry H]

One more thing;

Outboard motors usually do not have a field circuit or coil in the alternators. Outboards have a series of permanent magnets in the flywheel and generate current when the flywheel turns. This current generation is continuous if the motor is running, and is an AC current, as Bob mentioned. That AC current is rectified to DC current and may be regulated.

If the voltage 'tops out' at 13.6-14.0 or so after charging the batteries(motor running), then it is regulated. If the voltage continues to climb above 13.6-14.0 after the motor has run for some time, then the alternator is NOT regulated. If you have a non-regulated alternator in your motor, you will need to turn on some load(running lights, stereo, etc) to control the voltage. The older outboards from the early 1990's were mostly non-regulated. It is not good for lights, batteries, or electronics, to let the voltage climb into the (15.0-16.0) or higher range.

[thataway]

Larry is correct for the small and midsize engines. I left this out for simplification. However the ranger tugs do have alternators which are simlar to the automotive. I know that the larger Mercs use the belt driven Arco alternator, (Arco is in Pensacola from us, and I am friends with the owner)
I am not sure, but some of the other larger outboards may also be running integrated alternators vs the magnets/ coils The Suzuki's go up to 54 amps--and The larger Hondas are running a 90 amp alternator. These larger alternators do have regulators--and in the Suzuki large blocks they are water cooled.

In my experience with Yahama 115, Honda 130 and Suzuki 150's the voltage has not gone beyond 14.4 volts, so that the newer engines do seem to have much better regulation than the older outboards. I have run all of these engines, with a fully charged battery to start with, and after running over 8 hours constantly, with minimal current draw (depth finder, VHF on receive and chart plotter, I have yet to see voltage over 14.5 volts...it would be better on the battery if I were to see only 13.7 volt when running long times (as I did with adjustable regulators on my cruising boats). As Larry says, some of the older and smaller engines do develope excessive voltages (which will cook gel cell batteries).

[Larry H]

Bob,

Yes, I was talking about small to mid size outboards. Interesting that Mercury now uses belt driven alternators.

I agree that if voltages do not rise above 14.5 that there is a regulator. I does seem that a steady voltage of 14.5 would 'cook' the battery eventually.

Larry H

[Jazzmanic]

Thanks Dr. Bob. Perfect explanation for my question as usual.

Peter