# Circuit to Catch voltage off flywheel magnets.

Discussion in 'General Electronics Chat' started by bundick, Dec 24, 2007.

1. ### bundick Thread Starter Active Member

Dec 19, 2007
97
1
I want to get some voltage off the Flywheel magnets in my little outboard motor.
I think I can use a piece of Ferrite, wrap some turns of wire around the Ferrite and stick it up close to that whirling flywheel.

As the Ignition magnets embedded in the flywheel go by, the lines of flux should penetrate my little invention and upon collapse, I'd get some kind of voltage reading out of my circuit.
I could charge a Battery or a Capacitor and use the voltage for some work.

I'm wanting 12V @ .5a....

I'm not sure how to determine the strength of the field. Anybody have any ideas or experience of some way to measure that strength?

2. ### Papabravo Expert

Feb 24, 2006
10,021
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Almost surely a great waste of time and effort.

3. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
Papabravo refers to the likelyhood of 6 Watts from the home-made generator, not to the measuring of a magnetic field.

Current induced into your winding will diminish by the second power of the distance of your winding from the magnets. Windings and magnets have to be quite close in order to generate useful power.

4. ### Papabravo Expert

Feb 24, 2006
10,021
1,757
If you ever have the opportunity to take an electric motor apart pay particular attention to the separation between the stator and the rotor as well as the extraordinary strength of the permanent magnets in a typical motor. It can be a real knucklebreaker putting one back together correctly.

5. ### bundick Thread Starter Active Member

Dec 19, 2007
97
1
Well...the attitude was depressing enough!

I think I understand Thingmakers statment. He's saying the Air gap (distance) between the Coil/Ferrite and the Rotating magnets cannot be much or my experiment wont do anything!

If I cant get the Ferrite or the coil to a distance of .030 or less, I'll not be picking up much in the way of flux. So not much in the way of power.

So if I were going to persist in experimenting, what size wire would I use?
A smaller wire with lots of turns. #22 for instance, or maybe 5 or 6 turns of #14 House wire?
What would be the noticable difference between those two?

6. ### SgtWookie Expert

Jul 17, 2007
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You could try doing things the easy way, and just get a compact alternator from a car in your local junkyard. Put a small V-pulley on top of the flywheel, fashion a bracket, and hook up a vee belt to the alternator's pulley.

But let's just assume you're a masochist for the moment.

Were I to attempt something like this, I'd obtain a scrap/salvage transformer and grind one end in a concave radius to match the radius of the flywheel where the magnets are, winding up with a "W" shaped gizmo with the top of the "W" having the concave portion. This would provide for multiple flux variations in each coil for each pass of each magnet.

I would then fashion some sort of very stiff bracket that would bolt on to either unused threaded holes on the crankcase/head or other existing engine bracketage (there are usually quite a few unused accessory mounts) keeping in mind that precise adjustment of the air gap between the flywheel magnets and the edge of the converted transformer is vital.

I'd probably start with as many turns of 20 gauge wire that would fit on each leg of the "W", but keep the number of turns in each coil the same. I'd also keep in mind that the polarity of magnetism across each coil would be changing multiple times per revolution of the engine, so I'd need to wire up a three-phase full bridge rectifier assembly, requiring no less than six power diodes.

I'd then mount the thing to the bracket, and use a couple sheets of paper between the converted transformer and the flywheel to set the clearance. I would make absolutely certain that at no point could the flywheel come into contact with my converted transformer, as striking magnets with any degree of force will weaken them.

Then I'd see what kind of voltage I was generating. You won't get much (if anything) at idle, and possibly too much at full throttle. Then you're into regulators, etc.

Sure would've been easier to just use a compact alternator. Dang, why didn't I think of that....

7. ### Papabravo Expert

Feb 24, 2006
10,021
1,757
I think it is presumptuous to read attitude into any of my posts. I expressed my opinion in a succinct and objective manner. I apologize if I've offended your tender sensibilities.

8. ### bundick Thread Starter Active Member

Dec 19, 2007
97
1
OK, We'll assume your dealing with a Masochist. stubborn too.
Years ago I had the idea of Hooking up a large RC airplane engine to a small Alternator.
I hunted on a large lake that didn't allow Gas engines. so I used a small Electric and a battery. The Battery would only last a day or so in that cold weather.

I thought I could make a Voltage monitor to watch my battery. When it dropped below 11.5V that little Gas engine would start up. I was going to hook the Pully up to a small motor with a V-belt to use as a remote starter. Grandiose plans for the day. (1972)

Al Gore hadn't invented the internet then. No forum like this to get help with ideas.

One more question, or try, with this Current robber idea. What if I could find room inside the Flywheel for a coil/Ferrite assembly about 1" wide. The foot of this Ferrite would be almost touching the magnets as they went by. Would that work better?

I havent gone as far as Regulation yet.

9. ### SgtWookie Expert

Jul 17, 2007
22,182
1,728
I really couldn't tell you if it would work better. I haven't worked on magnetos in awhile; my 1927 Johnson 1 1/2 HP outboard is sitting at my folk's place about 1,100 miles from me.

I had a 1956 Johnson 7.5hp outboard many years ago, but I can't remember much of what was under the flywheel. Seems like there was a coil wrapped around stamped sheet metal plates that were formed to the inside of the flywheel, points and condenser under a lid.

Well, if you have room in there you could try doing something. I don't think ferrite would work nearly as well as a transformer core that was stamped out of sheet metal plates, but hey - it's your project and you're welcome to try it

If your goal here is to charge up a lead-acid deep cycle battery, you're either going to need a lot more than 0.5A output, or a LOT of gasoline to run the motor long and fast enough to charge it up. Even with 5 amps output, you're going to be running the motor for several hours.

A lead-acid battery is considered fully discharged when it reaches 10.4V. Most vehicles charge a battery at 13.8 to 14.2 output from the alternator. It takes a good bit of current to maintain that kind of voltage into a discharged battery.

You're going to have to rectify your output, as it's going to be AC. Your options for regulation of the output are going to be rather slim, because unlike an alternator, you can't control the field winding because there IS none. You'll still have to monitor the output anyway, and disconnect it from the battery if/when it becomes fully charged.

10. ### Papabravo Expert

Feb 24, 2006
10,021
1,757
I use deep cycle marine batteries to run my mobile amateur radio station for contesting. The batteries are charged from between 2 and 12 amps derived from the mains. It takes 12-14 hours for a full charge. One battery lasts about 10 hours powering a 100W transceiver, a laptop, and a DC FAN for the operator. So I always bring two for a twelve hour contest.

11. ### bundick Thread Starter Active Member

Dec 19, 2007
97
1
OK, now we are gettin somewhere.
Thanks for both tips.
The 2a for 10 hours is a good estimate. I read that somewhere else as well. That means if I did get this idea working the guy would be operating at full RPM for 10 Hours which is out of the question for most guys.

And Papa says the Transformer core would be better than the Ferrite. Good again. I'll look around for an old Doorbell transformer and give it a whirl.

The inside of the Evinrude is much like you said. There is a Coil wrapped around the flat plates, with the ends of the plates right up within .030 of the whirling magnets.
The Breaker points open the primary so the secondary fires off to the plugs. Two sets, one for each Cylinder.

A question popped into my mind as I read Papa's post. Do the magnets in the flywheel have a Pole set 'up n' down' or 'fore n' aft'?
Now I have to look and see if there is two magnets or just one magnet and one counter weight.
I'll get a magnet or a compass and check all that out.

My idea was to charge a capacitor, and use it as a storage battery which will drain through a small coil.
If I slow down the discharge rate with a Resistor, I should have a Cap. staying charged up as long as the little engine is running to keep it charged.
When the engine quits, the Cap. will drain off.
The little coil was holding up an armeture, storing spring tension, and allowing fuel to flow.
When the charge in the coil drains off it will let the armeture drop and shut off the fuel supply.

If I make the armeture out of plastic, wrapping a piece of Tin around the Plastic to act as the metal armeture, the Plastic will melt if anything goes wrong and I shouldn't have a fire.

12. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
Tin is not magnetic. Your solenoid will only attract iron, nickel, or cobalt.

Be sure to take into account the minimum current required for your solenoid, and the resistance of the solenoid winding, when making your calculations. I predict you'll need one heck of a capacitor.

13. ### bundick Thread Starter Active Member

Dec 19, 2007
97
1
Hmmm, Thanks for the tip on the Tin.
I dont remember how to make those Calculations any more. I'll go get a book and re-make all my crib sheets.

14. ### SgtWookie Expert

Jul 17, 2007
22,182
1,728
Hmm... you might want to check with some of your local outboard motor repair places; see if they have an old magneto coil from a motor similar to yours. It would already be ground/stamped to the correct shape to fit the inside of your flywheel; you'd just strip off the old windings and replace it with your new winding(s), and drill mounting holes for it in your magneto plate.

15. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
Minimum Voltage Across Solenoid Coil = Minimum Solenoid Coil Current * (Solenoid Coil Resistance + Resistor Value)

Capacitor Discharge Time Constant = Capacitor Value * (Solenoid Coil Resistance + Resistor Value)

Then refer to the chart: http://interfacebus.engineer.googlepages.com/time_constant

Instantaneous Voltage Across Coil = Instantaneous Capacitor Voltage * Solenoid Coil Resistance / (Solenoid Coil Resistance + Resistor Value)

I continue to predict you will need a very big capacitor.

16. ### cheddy Active Member

Oct 19, 2007
87
0
Your definition of a waste of time has little objectivity.