Light on the Outboard

[rickfant]

I've seen many dinghy outboards with a single white light attached to the top cover to provide for the required running light (white light all around). It seems to come on when the outboard is started and goes off when the engine is stopped.

I've got a Honda 20hp outboard (with generator) where I would like to install a lite attached to the outboard cover - and have the light come on only when the engine is runniing. I can wire a light to the battary - but would have to put a switch in the circuit that I would likely forget to turn-off.

I'm assuming the light is a standard 12 volt post light. Does anybody know how to wire the light so that it just comes on when the engine is running?

[ssullivan]

Hi Rick,

As an alternative, you could try one of these:

West Marine: Series 23 Portable LED Lights Product Display

See the light on the far left. It has a suction cup and sticks right on the outboard. Being that it's an LED light, it uses very little juice. I used mine for 6 months last year and never had to change the batteries once. I live at anchor and was chartering, so I ran to and from shore hundreds of times.

Good little light, no wiring or complicated project. Moisten and stick to the outboard.

[senormechanico]

You need a diode (preferably a Schottky) in series with the alternator output to the battery with the light connected between ground and the alternator output terminal. A Shottky diode capable of taking full battery charging current might need a small heat sink, but they're not expensive and are available at electronic supply houses.

Another way would be to take the output directly from the alternator windings before the internal diodes, but you would need some kind of voltage regulation for the light as it would burn out with any RPM much over idle speed.

I wish I could attach a diagram for you.

Steve B.

[AnchorageGuy]

most of these small outboards don't have alternators.

[Starbuck]

Not alternator.
Not generator.
Rectifier.

[cal40john]

My impression is that most manufacturers have chargers on their small engines now. I just checked on the Honda, Yamaha and Johnson websites, and they all have chargers on their engines down to 10 hp. The output is only 5-10 amps on this size engine.

A generator is something that produces electricity from mechanical energy. Common usage of generator, back when the earth was hot, was if you had a generator on your car, it was a device with a commutator that put out DC. Commutator (electric - Wikipedia, the free encyclopedia)

An alternator is a generator that produces AC electricity.

A rectifier is a device that converts AC to DC. It can be as simple as a single diode. An alternator needs a rectifier in order to produce DC to charge a battery. They are typically built into alternators (The kind you find on cars and inboards).

A diode is a check valve, allows flow one way, but not another. Steve's idea with the Schottky diode allows the electricity to flow from the engine to the battery when the engine is running as the voltage of the engine is higher than the battery. When the engine is off, the voltage on the engine side is lower than the battery, and so no electricity from the battery reaches the light. I believe Steve is saying to use a shottky diode because they can have a low forward voltage drop. The small outboards that I'm familar with (say old) did not have a regulator and so the voltage drop is not really a concern, but if the newer engines have a regulator, then even the smaller drop across the shottky diode will affect how well the battery charges.

................diode
engine_______|>________+ battery -
.............\_______light___________/

Is this what you had in mind Steve?


John

[rickfant]

Thanlks for all the replies; I've looked in my local marine stores and have not seen any pacakge (or individual components) that would allow the kind of diode structure described. I'll keep looking.

I wonder If I just wire the light to the oil light?

[senormechanico]

................diode
engine_______|>________+ battery -
.............\_______light___________/

Is this what you had in mind Steve?

Exactly. Whenever the engine is running, the light comes on but it can't discharge the battery at any time.

Steve B.

[SkipperCanuck]

Wow...Schottkey diodes, forward and reverse bias voltages..Yeeks. Egads, even. A sailor ain't a sailor ain't a sailor anymore.

I liked what SSullllivan ssaid. Moisten and SSStick it on. Yeahhhhh!
'Tis a joy to be sss..sss..simple.