Re: mercury 15 alternator
If it is like the 25 hp, the engine already has the alternator winding and somewhere on the engine wiring harness is a connector that your boat's wiring can connect into. It's made to run the lights on the boat.
Lights don't care if it's AC or DC power so you don't need the rectifier; but a battery does care.
The "kit" probably is nothing more than a rectifier and maybe another short cable/connector, and some instructions. You need to convert the AC to DC to charge your battery. Since the amperage is so small, there is prbably only a rectifier, not a regulator also.
Call your nearest Merc dealer for part numbers and availability.
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Buttttttt
Now here's some speculation, based upon my electrical/electronics knowledge and what my 90 hp looks like. I have 2 yellow wires coming out from under the flywheel which are the alternator output wires.
If your engine has an alternator ......you could go to radio shack and buy a "Bridge Rectifier" rated at say 25 amperes; 15 amperes would probably do also; amperage not important as long as you have enough. The DC Working Voltage rating needs to be 50V or more.
For reliability reasons I wouldn't go below 15 even though the alt is only supposed to put out 5A at WOT rpm's.
The rectifer has 4 terminals: ~, ~ (Identical looking terminals which are AC inputs from the alt), + (Pos DC output, goes to battery + terminal), and - (Neg DC output, goes to battery - terminal).
Wire it up with 14 ga automotive wire (auto parts store) and mount it somewhere convenient, preferably somewhere there's some metal. The metal will help to pull the heat out of the unit; however, with only rectifiers and such a low current, there won't be much heat.
Might put a 10 amp fuse in line, between one leg of the alternator and the rectifier, so that if something shorts out you won't burn up your alt and get another pair of connectors (male-female) so that you can disconnect from the boat if you want to remove the engine for some reason.
On the color of the alternator output wiring: Don't know what color yours will be (mine are solid yellow on a 90 hp) but you will have 2 wires of the same color (probably solid color) and a couple other wires (which will probably have a white stripe with color codes that are different from each other) which are used for triggers to your ignition system.
Lastly the alternator may not put out any voltage at idle; the 25 doesn't.....may be the same alternator. So if you hook it all up and want to test it, get rev your engine up a little.
Testing is simple. With the engine offl, measure the terminal voltage at the battery. For a fully charged battery it should be around 12.75 Volts.
Start the engine and rev it up a little (2000 rpm ok, not WOT). The meter will now read more than 12.75 and as you watch, it will slowly climb as it is charging the battery. Max you will get out of the thing should be about 14.5v but the battery would have to be fully charged to get that.
HTH,
Mark
