Fairbanks-Morse coils should be easy to come. I have recharged the magnets in F-M and Wico mags by wrapping a spool of wire around them and giving them a shot with a 10 amp battery charger. If you have the metal working equipment required, you can build a good magnet charger.
The following includes tips on how to build and use a homemade magneto magnet charger. The cores of the electromagnet are made of soft bar steel one inch in diameter and three inches long. They are secured to a steel base measuring 5-1/4 by 1-1/2 by 5/8 inch and are provided with pole pieces measuring 1-3/4 x 1-3/4 by 5/8 inch. All contacting surfaces should be absolutely flat and square so that there will be good metalic contact over the entire surfaces. Before the wire is wound on them, the magnet cores must be insulated. A spool may be formed by placing fiber or cardboard washers around each end of the magnet cores and then wrapping the magnet cores themselves with several layers of electricians tape.
The winding for this recharger is for use on 6 or 12 volt direct current, from automobile storage batteries. Applying three layers of No. 12 double cotton covered magnet wire is preferred.
12 gauge copper thermoplastic covered type 'TW' house and building wire will give satisfactory service and results. Wind the wire around the electromagnet cores as shown in the illustrations and then wrap tape around the windings, to hold them in place. Mount the recharger on a wooden base large enough to also hold a single pole switch and a binding post. CAUTION, the switch is a must, as the recharger draws high amperage from the battery. As a result, the battery has a tendency to produce some flammable gas, and any sparks around the battery vents could cause a fire and/or an explosion. Therefore, do not connect or disconnect the lead wires from the battery when the recharger is turned on. The windings will heat up quickly when in use; therefore, the switch should be closed for only a few minutes at a time.
When a magneto is taken apart for any reason, it must be assembled with the magnets in the same relative position as formerly, otherwise their polarity may be reversed and the magneto will be inoperative. The magnets must never be left off the magneto even temporarily, without placing a steel bar across their poles to serve as a keeper. Unless this is done, they will lose their magnetism rapidly. Re-magnetizing the magnets of a magneto that has become weakened through long use is a simple process. It is important that unlike poles of the magneto magnets and of the electro magnets be brought together; i.e. The North pole of the magneto magnet to the South pole of the electromagnet and vice versa. To insure this, the current should be turned into the electromagnet and magneto magnet suspended over it on a string.
Starting at a distance of about 12 inches, slowly lower the magneto magnet. As you begin to lower the magneto magnet towards the electromagnet, the magneto magnet will automatically seek the proper polarity by swinging around and will then be strongly attracted to the electromagnet. Gas Engine Magazine is your best source for tractor and stationary gas engine information. Subscribe and connect with more than 23,000 other gas engine collectors and build your knowledge, share your passion and search for parts, in the publication written by and for gas engine enthusiasts! Gas Engine Magazine brings you: restoration stories, company histories, and technical advice. Plus our Flywheel Forum column helps answer your engine inquiries!
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The magnet is in an aluminum casting bolted to the cast iron flywheel. Kohler will not sell the magnet without the flywheel.450.00!!!!!!!! How can I remagnitize the magnet?The simple answer is, you won't be able to remagnetize it.
The more accurate answer is, you actually could, but the electromagnet you would have to build in order to supply the over 60,000 Amp-turns needed to remagnetize an alnico magnet would weigh about 250 lbs. Just the cost of the iron and copper in the magnet would be several hundred dollars. However, if you google shops that work on magnetos, one of them should have the necessary electromagnet (most won't, so you'll have to look around). The actual process couldn't be simpler. They install your rotor, adjust the pole pieces, run the current up and back down, and a few seconds later it's ready to ship it back to you. Since you say the magnet is bolted on, for that kind of money I would unbolt it and try to replace the magnet.
You may need to check for polarity (North South) on a replacement magnet. I don't know if this would make a difference but it could reverse the induced current flow and I suppose that could have an effect on you point capacitor or something. I'm not sure where you might find a replacement magnet but it seems like most anything would work better then spending all that money for a whole new flywheel. You might be able to get one from a motor shop that has a junked engine.
Some claim you can re-magnetize a magnet by rubbing it with a powerful neodymium magnet. Worth a shot. If not, maybe you could machine a recess for a small neodymium, compared to old iron magnets they are immensely powerful so even a small one should work.Unfortunately, the 'B-H curve' of a magnet is such that it isn't possible to remagnetize an alnico magnet this way. However, the B-H curve isn't symmetric, which means it.is. possible to demagnetize it, so keep your neodymium magnets away from this. The original poster did just what he needed to do, and found someone with an appropriate electromagnet.
I have magnetized many magnets, mostly field magnets in tachometer generators but on occasion outboard motor magnets similar to the one described and a few antique motorcycle magnetos. It doesn't require anything like 250 pounds of iron. You make a core that has a greater cross sectional area than the magnet so it will carry the magnetic lines of force to saturate the magnet and the minimum length required to join its poles. The RFL magnetizer I used in the local GE shop just had a single buss bar that went through the space between the core and the center of the magnet. The magnetizer had a capacitor that was charged to 600V and discharged by an ignitron through the buss bar. Later I made my own using 66,000 mfd charged to 150V and discharged by a size 4 contactor.
Both these systems generate a huge current pulse that only has to persist for milliseconds to align the magnetic domains. The core I made for GE 5PY59 tach generators had three turns of 4 ga wire around it and a hole for the shaft on the armature. After I magnetized it, I used the armature to push the core out so that there was always a complete magnetic path, preserving the magnetism. By bumping the field up to near saturation, the output of the generator would too high. Then I ran it at a constant RPM and waved a magnetron magnet past it to bring the output down. I was able to calibrate them closer than the GE factory. You can remagnetize an alnico magnet with a stronger one.
Tapping it with the magnetism applied helps. You can also demagnetize or reverse ceramic magnets, but they don't like to be changed to to a different axis. I probably should not say this, because I wouldn't want anyone else to try it, but in an emergency I have run a jumper cable through the gap and banged it across a 12V car battery. Perhaps not very smart, but it worked. Bill Last edited by 9100; at 10:35 PM. Reason: addition. The RFL magnetizer I used in the local GE shop just had a single buss bar that went through the space between the core and the center of the magnet.
The magnetizer had a capacitor that was charged to 600V and discharged by an ignitron through the buss bar. Later I made my own using 66,000 mfd charged to 150V and discharged by a size 4 contactor. Both these systems generate a huge current pulse that only has to persist for milliseconds to align the magnetic domains.Yes, you can trade high voltage for smaller amounts of iron and steel. But, instead of paying for the metal (which is relatively inexpensive), you pay for the 600 V power supply (which typically is more expensive). I agree that it only requies a very short pulse to accomplish the remagnetization, although there's no harm in applying a field for longer. You can remagnetize an alnico magnet with a stronger one. Tapping it with the magnetism applied helps.
We're just going to disagree on remagnetizing an alnico magnet with a stronger one. It's physically impossible (B-H curve). I should add, though, if the alnico you're working with has been largely demagnetized, you can recover some of the magnetism using a stronger magnet, so this is likely the effect you saw. You just won't be able to get to even half its properly magnetized value. Also, tapping it with a magnet does no good whatever.
The domains either have enough magnetic force on them to reverse, or they don't, and the mechanical force imparted by tapping is negligible compared to the forces required. Tapping the magnet while an old magneto was on the charger was something people were told to do in automotive books of a half-century ago, and the incorrect thought that it does some good persists with many people to this day. I just got back from the local UPS store. I sent the magnet to McWhorter's antique Iron repair. They rebuild and restore about 25 brands of magnetos, mostly from old tractors and stationary engines and have the bit of kit to recharge my magnet.
They will do it the same day and send it right back. I am told it will be as good or better than new and will last many years. When it returns I will report back.Well I got the magnet back on Saturday and bolted it on. Cranked it over.
Nice hot bright blue spark on both plug wires. I put it all back together, runs great. 15.00 to re charge the magnet, or or over 400.00 for a new flywheel.
Not a hard decision to make. It is very easy to re-energize a magnet. You need to make a coil of wire with about 1000 turns of #24 enamel coated copper wire. Get 1 or 2 large electrolitic capacitors. I am using 2 capacitors 7400 mfd 200 vdc each in parallel. I have a bridge rectifier connected to 120 vac to get 170 vdc to charge the capacitors.
When the capacitors are charged, I disc charge them into the coil. The tiny magnet in the picture will lift 1/2 lbs of steel. After recharging the magnet it will lift about 300 lbs for 2 seconds. Magnets have a half life of about 2.5 seconds. After 2 seconds 300 lbs drops to 150 lbs, then 75, then 37, then 18, 9, 4, 2, 1, etc. It takes about 15 seconds for the magnet too loose the super charge and return to almost normal. A magnet levels off and holds at a steady power rating for a long time but even then it is always loosing power that is why OLD magnets get weak.
This device will restore a magnet as good as new. I have an old antique telephone generator I recharged the U magnets on it. I recharged the magnet on an old antique engine. I have a lot of fun experementing with things.
I can reverse the magnet field on a magnet too. With a special set of coils I can put 2 to 6 North Poles and south poles on the same magnet or I can switch the poles from the ends to the sides of the magnet and back again. It's interesting to read this thread and contrast the general technical opinion (which is correct) with the anecdotal (which is not incorrect). The OP wanted to fix his magneto so he sent the magnets it off to a place that had the right equipment to fix his magnets whereas the anecdotal references talk about ' did this magnet,' 'did that magnet' without the specifics about magnetic field strength attained. There are several interesting tutorials and descriptions of magnetic hysteresis that show distinctly the general problem of trying to remagnetize a previoulsy strong magnet with not enough juice.
The question will always revolve around how strong. Cheers, Rich. It's interesting to read this thread and contrast the general technical opinion (which is correct) with the anecdotal (which is not incorrect).
The OP wanted to fix his magneto so he sent the magnets it off to a place that had the right equipment to fix his magnets whereas the anecdotal references talk about ' did this magnet,' 'did that magnet' without the specifics about magnetic field strength attained. There are several interesting tutorials and descriptions of magnetic hysteresis that show distinctly the general problem of trying to remagnetize a previoulsy strong magnet with not enough juice. The question will always revolve around how strong.
Cheers, Rich Very well said. Opscimc - lots of us appreciate good info like you provided. I had no gauss meter to check the magnet with so before I sent the magnet I tried to pick up different sizes of wrench. Before sending it to be recharged it would just pick up a 7/16 wrench, it will now pick up a 15/16. I have never seen a magnet on a small engine flywheel go bad before. I do have a dial indicator magnetic base that came with a piece of steel that was supposed to be kept on it to prevent loss of magnetism. If you buy a new rotor for the alternator on a 60s and 70s Triumph, BSA, or Norton motorcycle it comes with 2 steel bits, each wrapped half way around it.
The engine had no spark, and did not run. The only change was to recharge the magnet. Now it has spark and runs. I have one question.
I have worked with small engines that use flywheel magnets and magnetos for at least 40 years and have not run across a magnet that became weak and couldn't produce a spark for the ignition. Have I been lucky or is 40 years not long enough? Most people don't have a magnetometer so have no way to determine if their magnets have lost strength, and by how much. Also, I'd wager the output of a stator on a British motorcycle could slowly drop over the years from 120 W to 60 W and most owners would never notice, nor have the knowledge and tools required to measure it.
Heat and shock are the enemies of magnets. Although under typical conditions an alnico magnet will outlast whatever it is attached to, it is possible to defeat it by untypical methods, like pounding with a hammer to loosen it from a tapered shaft.
Also, it's possible the OP's system uses the field to generate a trigger signal as well as the spark energy, and a reduced field fell below the threshold needed to trigger the spark.