Marine power sucks.

The x79 power system consist of 1) Tohatsu 6HP saildrive/sailpro with "alternator" and 2) 100Ah car battery, plus the normal consumers of power.

Everything is nice and easy, wired through suited circuit breakers. The alternator is connected to the battery behind the main switch, so it always charges when running even if the switch is off. (good idea?)

Of course I've done the normal fuckup of trying to run the electronics straight from the alternator without a battery hooked up. Voltage will spike to 20+ volts, and you either fry stuff or things complain endlessly (hello dsc vhf) about over-voltage. Good thing to avoid.

Even with the battery connected, I'm suspecting there to be transient power spikes. I don't have concrete evidence of this, but something is odd.

This went as far as I went on an ebay rampage last year and bought transient diodes (P1.5KE18) that in theory should dump any excess voltage to ground when bad things happen. I haven't installed these yet, mostly because I have no clue if it is a good idea or not. (any EEs want to chime in, please do)

Picking up this since now that the season is about to start again, I'm combing through the internets on this, and I came upon a forum post on sailnet. (yes, very authoritative)

It seems that the Tohatsu Saildrive strictly speaking has a magneto generator. It produces AC that is subsequently rectified to DC.

Some background on generators, alternators and magneto generators can be found on

Based on the Tohatsu webpage, my MFS6 engine should be equipped with (3GR-06128-0) Alternator Kit 12V 60W and a (3GR-76160-0) Charging Rectifier Kit. Finding a datasheet for the rectifier would be nice.

The battery can handle dirty charging voltage, but I'm not so sure about the electronics I try to fill the boat with. Perhaps it would be easiest to find a nice DC-DC converter that doesn't run off with too much juice when it is running.

I wonder how the LiFePo4 crowd handle being charged from such a current source. Can I get the magic part of their charging controllers, somehow?