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Convert AC to DC?

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New Member
I have a 9.9 hp boat motor that has a lighting coil on the flywheel that produces 80watts @ 12v AC. This is peak output, as rev's go down so does output.

The rectifier and voltage regulator are missing from the motor and are discontinued parts. I've searched, and no one can tell me any specifics on the parts either.

I do not know what the Amps are from that lighting coil, but the repair manual schematic shows a 20Amp fuse after the rectifier if using the DC power directly from the rectifier. It shows a 15Amp fuse if using a regulator after the rectifier.

I will be using the circuit to charge the (2) 12V/7 AH 'lights only' batteries. It has all LED lighting.

1. If buying a manufactured rectifier, are they all the same when it comes to voltage and amperage? Any links to a product I could use?

2. I know basic electronics and can build a Rectifier. Is it economically worth it?

3. Is the regulator necessary if I'm just charging the battery?

4. Any way to leave my batteries in parallel conection and charge them together?

5. What should I look for in a regulator. Volts, Amps, etc...

I'm documenting the build on this boat and I'm trying to make 'cost' an important factor. Any ideas are appreciated in building the components I need. Maybe an all in one rectifier / regulator assembly?

Thanks in advance for any help.


Well-Known Member
Most Helpful Member
1. Rectifiers come in many voltage and current ratings. You would need at least a 10A, 25V device. The diode will need to be on a heat sink.
Does the generator have one output wire or two? If it has two you could use a bridge rectifier for a full-wave conversion.

2. The cost would be relatively small to build. Rectifiers are cheap.

3. A regulator is needed to avoid overcharging the battery.

4. If the batteries are the same brand, type, and age, then paralleling them should be ok.

5. The regulator should be a low dropout type with an output of about 14V. The current rating depends upon how much your lights draw. The maximum would be about 7A.

Don't know if there's any single unit device that will meet your needs but a solar battery regulator such as Brunton Solar Controller- 12 volt battery charger regulator :: $29.95 :: peak62.com should work from the voltage at the output of your rectifier. You may have to add a large electrolytic capacitor at the rectifier output so that the regulator sees a relatively smooth DC voltage.


New Member
Carl, Thank you for the help!

The generator has 2 wires. So should I google "Bridge rectifiers" to find one?

The batteries are the same type & age. They came out of 2 new APC UPS's. If I leave one in the UPS box, so I have an inverter on the boat, can I run an external charge to the batteries? More or less 1 in 1 out. Or will that charge go thru the battery into the UPS and do damage? Probably a dumb question, huh?:)

My lights will draw 2 amp max but I'd rather go high if it's safer? Is it better?

With a full wave conversion are there simple and small regulators? Also, my leds have a 13.5 volt max. Will a 14v regulator burn them out when it's charging and the lights are on?

Thanks again.


Most Helpful Member
Check with your local lawn and garden service place and and ask for a small engine voltage regulator.
The one you need is for the Onan engines. They are a standard two wire AC input with a single regulated DC output with the case as common negative.
They are 20 amp rated and are very versatile and rugged and are specifically designed for use with unregulated permanent magnet type alternators.
Expect to pay about $30 - $40 for one. Often far less online too!
All they need is to be mounted where they can get air flow over the built in heat sink. Usually thats on the ducting that takes the cool air that blows over the engine cylinder.
Just ask for a picture of where they go on the Onan engines and you will see what I am talking about.


Well-Known Member
Thanks for the tip on the lawnmower regulator! I was gonna suggest basically the same thing, but with a small motorcycle regulator. Many of the small cheap motorcycles use a 12v single phase rectifier/regulator, basically a 4 wire package; 2 white wires go to the AC input, then red/black wires are the 12v (14.5v) regulated output. Most motorcycle wrecking yards have units for sale for a few $$.
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