Charging batteries without an alternator

[wbeaton]

Hi everyone, this is my first post. I've used the motor repair section before, but this is the first time I've been in the forums.

I had a conversation today with a fella at the boat launch who told me you could connect a rectifier to the coil inputs on a manual start motor and charge a marine battery without an alternator. Unfortunately I don't have enough mechanical knowledge to argue this statement.

So my question is is this actually possible?

 

[steelespike]

Re: Charging batteries without an alternator

My guess is no.I think you would here a lot more about it with some details.And I think you would see it done more.If you could do it without killing the ignition I don't think the output would amount to much.

 

[jtexas]

Re: Charging batteries without an alternator

You'd have to regulate a high voltage (maybe 150-200?) down to charging voltage - 13 or 14 - probably wouldn't get as hot as the surface of the sun, but close...of course I'm no electrical engineer...

 

[Silvertip]

Re: Charging batteries without an alternator

The stator on an alternator equipped engine has two groups of coils. Some are used to generate the voltage for the ignition. Those that make up the alternator produce the battery charging voltage. If the stator does not have those coils you would, as Steelespike indicated, have to tap into the ignition side for charging purposes which would rob the ignition system of some of its output. There is none to spare so you would very likely have a poor running engine.

 

[Texasmark]

Re: Charging batteries without an alternator

They make kits for at least Merc to allow you to charge a battery from the alternator of a manual start engine. Check with your local dealer.

Current Merc manual start engines, at least in the midrange hp arena, have an alternator for operating running lights. This kit is made especially for the person wanting to charge a storage battery.

Mark

 

[Mark42]

Re: Charging batteries without an alternator

Take one of those bicycle generators that rub against the tire to run lights, etc. Then put a 3 or 4 inch wheel on it to rub against the flywheel (you will need to do a little calculating to get the right size to reduce the rpm accordingly ) and it should put out 12-24 volts at low amperage and be able to charge a battery off of it.

 

[Silvertip]

Re: Charging batteries without an alternator

That bicycle generator would last about one trip across the lake. When it destructed it would likely cause considerable damage under the cowl. Bad idea! :/

 

[wbeaton]

Re: Charging batteries without an alternator

Thanks guys,

That's pretty much what I had thought. I couldn't see how you could rob the ignition of power and still run the motor adequately.

And thanks for the input Mark2, that is an interesting idea. However, I charge my battery with solar. I was just curious if this could be done. The fella must have been talking about one of those rectifier kits Texasmark mentioned.

 

[Mark42]

Re: Charging batteries without an alternator

That bicycle generator would last about one trip across the lake. When it destructed it would likely cause considerable damage under the cowl. Bad idea! :/

That idea is something I actually did on a minibike as a kid. I wanted a headlight and used the generator with a rubber wheel (the type used in model airplane building) about 2 or 3 inch in diameter to act as a gear reduction. It lasted a couple of seasons on the minibike, but that motor was probably only turning 4000 rpm max without the governor attached. Those were tough little generators. To bring the RPM's within its normal operating range on an outboard, a 4 to 6" wheel would probably be needed. Remember, they only had about a 3/4" diameter drive wheel to start with. My Dad was an engineer and did the calculations to figure out how to make it run at "bicycle wheel" speeds found on a 26" wheel going about 20mph.

It would be interesting to find out how small a generator could be found that can be "belt driven" off the string pull groove by a skinny drive belt ( like the ones used on self propelled lawn mowers ) and still fit under the engine cowl. If I remember right, the old Suzuki Samuari had a 35 watt alternator that was rather small. Even if a cutout in the cowl was needed, its a neat way to add independant power supply to an outboard motor.

If you want it bad enough, you can come up with something that will work and last.

8)

 

[rottenray6402]

Re: Charging batteries without an alternator

I was always going to experment with a little paddle wheel that would turn as the boat moved coupled with one of those bicycle generators but then after I quit drinking I figured it was easier and probably cheaper to do the solar thing. 8)