Does a magneto charge the battery

[Leahcim]

Hi experts!

My first post.

I recently bought a boat with a 1967 Merc 650 (65hp) short shaft. The model I have does not have a alternator/generator, just a magneto. The motor is not running now so I can't test to see if I'm getting 14 or so volts across the battery terminals when it's running. Does this motor have a charging circuit? Will it charge the battery?

Also, what the heck is a magneto?

 

[ufm82]

Re: Does a magneto charge the battery

A magneto is a self-exciting current generator that provides the voltage to produce a spark. The magneto works by passing a magnet through a field and this generates a current. Then the current is interrupted and the field discharges. If you hold a magneto in your hand ( like an aircraft type unit) and you spin the shaft, it will bite you. The Flywheel on the engine has the magnets and the stator underneath the flywheel provides the field. (I may be parapharsing per my understanding but that's basically how it works.) The magneto does produce enough current to charge a battery. My 150 has no "alternator" on it- the current is produced by the flywheel/stator combination and provides 40 amps of charging ability. Most small outboards will provide 6 amps or so. The 65hp you have may be more but I don't know that off the top of my head. Electric start engines were equipped to be able to charge the starting battery so it will charge provided everything is working properly. Some outboards use no regulator and rely on the battery to act as the regulator while others do have a regulator.

You should have 12.7 volts or close battery voltage and it will rise to 13.7 or better when the engine is running.

UFM82

 

[Leahcim]

Re: Does a magneto charge the battery

Thanks Chief!

 

[jeffnick]

Re: Does a magneto charge the battery

Does this mean that you can't have one without the other...spark & battery charge?

 

[ufm82]

Re: Does a magneto charge the battery

Not at all. Many small outboards have no way to hook up a battery. My 15 hp Chrysler had no wires to attach to a battery. Little outboards only produce enough spark to power the plug- no more. The 6hp Johnson in my attic has no way to hook up a battery. Like I said, any electric start outboard will charge a battery, although it may be a very small charge. Flywheel magnetos are extremely common- weedeaters, lawnmowers, chainsaws, etc. All use a magneto to power the plug. And none of those charge batteries.

UFM82

 

[merc850]

Re: Does a magneto charge the battery

Here's a view of the magneto with covers off and some info on point gap etc. No this magneto will not charge a battery - the bolt on the side is for a wire that grounds the magneto (kills it) when the key is turned off do not hook + power to this terminal!

Since the battery only starts the engine it can be attached to a charger, maybe solar, to keep it up; the motor can be started by pull cord even with a dead battery.

 

[Leahcim]

Re: Does a magneto charge the battery

Yikes, ufm82 says it will charge the battery and merc850 says it won't.

Here's the motor I have. I think it is the 650S model but I am not sure.

http://store.eastcoastmarineservice.com/category_s/853.htm

So two questions.

1. Did they produce electric start motors that did not charge the battery? (seems like a dumb thing to do since there is no pull rope)

2. How do I tell for sure that I have the model without an alternator?

 

[merc850]

Re: Does a magneto charge the battery

Here's the wiring diagram for most 4 cylinder engines.
Check the serial Nr. located on the clamp bracket between the thumbscrews this will help with parts etc.
Take the cowling off and look on the right side (viewed from back) you should see two yellow wires coming down from under the flywheel and hooking up to a rectifier at the front of the engine. This is a rectangular box with two yellow and one red wire connected to it. Apparently there was a market for non-charging motors doesn't yours have a pull handle on the top cowling?

 

[JB]

Re: Does a magneto charge the battery

Most electric start outboards have an additional winding in the stator, called a "charge coil" with the sole duty to charge a battery. It is electrically independent of the magneto ignition system. The bigger ones are called alternators.

It is not the magneto that offers the charging current, it is the "charge coil" which happens to use the same magnets as the magneto.

I think it was an 5HP Elgin I had back in the 60s that had what the book called a "Lighting coil" under the flywheel whose purpose was to provide power for nav lights when operating at night. If I recall (it has been a long time and I am pretty old) it made 6volts AC.