magneto to charge battery

[Actovon]

Hello, I was wondering if it was at all possible to charge my boat battery using the magneto from the outboard motor. unsure of voltage and current from magneto. The outboard is a 85 HP Force. If there is any info you may need, please let me know. Thank you in advance for the help.

Mike

 

[Nigel Goodwin]

Hello, I was wondering if it was at all possible to charge my boat battery using the magneto from the outboard motor. unsure of voltage and current from magneto. The outboard is a 85 HP Force. If there is any info you may need, please let me know. Thank you in advance for the help.

As far as I'm aware, the magneto is for the ignition, and provides the high voltage pulses directly - so you can't use it to charge a battery.

This is certainly what I understand a magneto to be, they used to be used on old petrol engines, motorbikes, cars etc. - probably pre 1960's.

As a kid, they were great fun for giving people shocks 8) half a turn of the magneto provides a huge great spark!.

 

[hantto]

The generator is a part of the magneto. There is different coils inside the magneto, one for the spark and another for electricity and maybe even more. Maybe it isn't like this in bigger engines but in my 15hp outboard it's the way i described.

It's made for charging a 12v lead-acid battery, a rectifier in between the coil and battery is enough.

 

[stevez]

Some small 4 cycle engines used on lawn and garden equipment have what you might call dual magnetos. One is what some of us recall - and Nigel described - purely for the ignition. The other is more or less the same thing - a magnet on the flywheel passes a coil but instead of a high voltage spark it provides lower voltage to charge the battery. It's crude but eliminates the need for a separate generator or alternator. It would seem that adding something like this could be a challenge in a mechanical sense but it could be done. You'd have to experiment to get the right output voltage.

 

[Klaus]

Charge coils or "magnetos" were an optional accessory on most smaller OB engines. They do need a rectifier block as the coil's output is AC. They rarely put out more than 10 Amps and that only at WOT (wide open throttle). My 9.9 Mercury only puts out 6 Amp max but at normal running revs its more likely around 3 Amps.

For a 85Hp motor I would have thought there is something more substantial, like an alternator, fitted. The reason is that these size motors most likely have an electric starter and associated battery.
Whatever charging method it is, you cannot reliably measure the output voltage unless there is a load connected. A battery makes a good load. You can measure the current with an Ampmeter.

Check under the motor cover or look into the manual (at the library, if you don't own one) to see what kind of charging system is available for your motor.

Klaus

 

[Actovon]

Thank you all for your response and sorry I have not been back to respond sooner. I was on vaction and unable to get to a computer.

I looked under the hood on the motor and there is a wire from a terminal block marked magneto. I did not have time to trace it back through the motor to see if there was a rectifier in line. The wire does go through the main wire harness to the key switch, it is not connected to anything there after. When time allows I will look into it further and post my findings.

Again, Thank you for the quick responses.
Mike

 

[ChrisP]

That wire is most likely the kill lead for the magneto. Most magneto ignition systems are shut down by grounding the kill lead. This is usually accomplished by grounding the kill lead via the "ignition" switch. It is for this reason that magneto systems use a different switch type than battery ignition systems do. The magneto ignition switch has one terminal (the MAG terminal) that goes "closed" (to the switch housing and/or the GND terminal) when the switch is in the "OFF" position. These switches will thus also (usually) have a "GND" terminal to facilitate the grounding of the kill lead, as the switches are sometimes mounted in non-metallic or isolated panels, and thus cannot rely upon the switch housing to provide the ground path.

Battery-sourced ignition systems are shut down simply by opening the battery feed to the coil. Without battery power, these ignition systems cannot and will not produce a secondary spark, as the battery current in the coil primary is the ultimate source of the secondary output.

Magneto ignition systems, used on many small engines (and on most gasoline-fueled aircraft engines as well) do not have this dependency on battery supply. The magneto is the ultimate energy source in these systems. As a result, these systems can't be shut down by simply disconnecting the source. Instead, they are shut down by grounding a lead that is in parallel to the breaker points. This has the net effect of keeping the points "closed", which prevents secondary spark output -- no break in primary current equals no collapse of the coil magnetic field, which in turn equals no secondary spark output.