Magnet Charger

I would like to build a magnet charger like the one John Rex wrote in the January 1989 G.E.M. article. I’ve wanted to do this for years but never could find a source for the wire needed. It takes 40#`s (preferably 2 20# rolls of #10 gauge heavy Formvar magnet wire. Where could the average man pick up some of this? Also, a good heavy 40 amp knife switch? I like this style charger because, as he states, it will saturate any magnet without removing it form the rest of the assembly. Any help or ideas will be very much appreciated. Thanks and you all have a Happy New Year! I’ll probably spend mine right here on Harry’s! -- Jim

I made a charger like the one you’re building. I got the wire from a place that rebuilt industrial electric motors. Told them exactly what I needed and they came up with two spools at a very good price. As for the switch, poke about in old city electric buildings or factory electrical rooms. My switch came from the electric distribution room of a local manufacturing company. They were ripping all the stuff out and tossing it in a dumpster. Traded a dozen donuts to the wrecking crew for the switch. -- Nick

Jim: I recently built a charger to Dave Gingery’s plan. Simple and easy to build, 115v converted to DC with a $5.95 bridge rectifier, 2 spools of 6lb ea #18 magnet wire from motor re-winders. It’s safe, draws 8 amps, weighs approx 50 lbs finished and with a bar across the poles when engaged, lifts it right off the bench! You can’t pull it off. It can charge most mags without dismantling. The total cost was $48.00 having had the 2" steel cores in my scrap pile. -- Fenwood

Fenwood: noted you comments about the magnet charger. I have collected all the electrical stuff and am looking for plans for the mechanical components. Where would I find Dave Gingery’s plans? -- Sherm

I just bought the book of his plans and instructions for $13.00 including shipping. An outfit out of Oklahoma marketed it as a reprint. They have many more of them and other same subject area reprints at fair prices. Glad to hear some positive feedback on these plans. It's my January project. The charger plans from the GEM are great, but I'm afraid it would pull my fillings out of my teeth! -- Will

Here’s the link to Lindsay's books, they have all kinds of cool books including the one you're looking for. Dave Gingery is a genius when it comes to building stuff from scrap! He's got a whole series of books to build a complete machine shop from scrap with minimal tools. -- Richard

Hi Folks, this is not meant to be rain on anyone's parade, but I feel it is necessary to point out a small fact about Magnet Chargers. I have been a full time Magneto Restorer/Repairman for quite a number of years and have owned a number of original Magnet Chargers built by some of the leading names in magnetos. These were units built by the manufacturers and intended for use by their own "Factory Authorized" service outlets. Without exception they have all been LARGE, HEAVY pieces of equipment. The American Bosch unit that sets on my bench at this time weighs 240 pounds. I am of the opinion that if Fairbanks Morse, American Bosch and International Harvester thought that a 25 pound charger would do an adequate job, that is what they would have built. I am sure that if all you want to do if punch up the charge on your own Mags a little, the $50 to $100 units will at least not do any harm, but if you are truly looking have a real magnet charger, take a long hard look at the one that John Rex designed. Please don't just take my word for it, ask any of the many Mag guys that are in this hobby, there are several that advertise here on Harry's site and I would be happy to put you in touch more. – Ted

Two things go into design of an electromagnet. The number of amp-turns (AT) and the magnetic permeability of the pole pieces. That will determine the maximum field you can generate to charge magnets. The AT is just the number of amps flowing through the coil of “n” turns (have to divide by the area of the pole pieces.) Having a large pole to charge a wide variety of magnets means you'll need a "Rex" -type charger with many turns carrying high current. The permeability is a characteristic number for the pole pieces used and is the ratio of the amp-turns to magnetic field strength. Some steels have higher permeability than others. BUT, Almost all steels max out or saturate at a magnetic field strength of about 1.2 Tesla. If you want to make a better charger, use Alnico steel. In some cases, bigger is not better! You may think a large BMF charger is better, but if it is operated at a current above saturation, all it will do is make a nice hand warmer in winter. It is very important that the magnets you are charging fit SNUGLY against the poles WITHOUT an air gap AND that you put a keeper on the magnet BEFORE pulling it off the poles AND that you magnetize in the same direction as the magnet originally was. I have had good luck with my charger made from two 12v truck starter solenoids. -- Paul

Paul, I'm thinking of using the coil assembly from K type railroad relay, and reconfiguring the positioning to have the end that originally moved the relay armature marry up to the magnet poles. K relays seem to have a lot of magnetic pull, given the design of the armature, and the weight of the coils. My major question is how critical is the mass of the saddle piece across the unused ends of the magnetic coils? -- Franz

Hi Ted, I have an Allen heavy duty magnetizer that will really do the job. It is very heavy and is powered by 110 volts. I also have made one from windings from Delco starter solenoids that will charge but nothing like the Allen. -- Ed

A $5.95 bridge rectifier and 2 spools of 6lb ea #18 magnet wire at 8 amps is going to work like a toy compared to the big chargers. You can pretend that you charged the magneto or you can charge hell out of it to last forever. Note the size of the Wico EK compared to the coils. This one was at least 200# and cost almost $2 per pound. It works! -- Harry

My decision to build the Gingery plan charger was primarily based on the electrical engineering calculations outlined. IE 100 turns (heavy) @ 60 amps. 600 turns (#18) @ 7.5 amps, both give you 6000 AMPERE TURNS AND THE SAME EFFECT AT THE POLES. The Gingery plan claims "Quote" that at 1600 total turns at a max of 10 amps the charger will provide 12,000 ampere turns of magneto motive force, at least twice what is required to saturate an ordinary magneto magnet. I felt that was adequate to my needs and it will accommodate a fully assembled Wico EK quite nicely. – Fenwood

True, ampere turns do the job, but I still wonder about the actual mass of the iron. I'm no magnet expert, so I'll forgo the fineries other than to be proud of my Weidenhoff. – Harry

Harry: I do envy your Weidenhoff and yes, mass plays a substantial role. On the Gingery the cores are 2" dia x 6" mild steel mounted on a 4" x 10", 1" thick mild steel plate! The $5.95 DC rectifier is a state of the art, full wave bridge rectifier rated to 30 amps. The oldies (chargers) of course are scarce as hen’s teeth so I recommended the Gingery based on cost, standard readily available components, step by step clear instructions and drawings and the electrical calculations that support the unit’s performance. A great project and confidence builder for the do-it-yourselfer. -- Fenwood

My question is, where can you get the pieces of mild steel, or preferably soft iron without having to buy a large piece of material. I read somewhere that soft iron was best because it doesn't stay magnetized well and separating the magnet from the magnet charger is a little easier. With the mild steel, do you have any strong residual magnetism after turning off the power? I have always thought that you can have less turns and more current, or more turns and less current in the magnet windings and still do the same amount of work. That is as long as the volts times the amps, comes out to the same value. Say 10 volts times 100 amps, versus 100 volts times 10 amps, which in both cases equals 1000 watts of power, or energy. The number of turns in the coils, and the wire size, or gauge has to be proportionate. Any thoughts? -- Russ

Russ, my question is what do you ask for? Soft Iron? Is there only one kind? Are there different types? If so, which is best? If I knew what to ask for, for certain, I would see who wants some and order a bar and cut it to length for those interested. I wouldn't want to get stuck with something no one wanted though. -- Bill

I guess I knew what I was thinking, but maybe I didn't express it too clearly. I am not a metallurgist, so my knowledge of these materials is limited. I have read that soft iron, whatever that is, makes a better electromagnet because when you turn off the power to it, the magnetism decays rapidly. I understand that the laminated pole pieces in transformers, motor field windings and any other similar coils used with alternating current have to be soft iron so the magnetic flux can be reversed at whatever frequency it is operating at. This may not be as important on a magnet charger as the polarity is constant in one direction. I have come across a number of projects in "Do it Yourself" articles for making electromagnets where they always say use soft iron for the pole pieces. I'm thinking of the large magnets they use to pick up scrap metal in a junk yard. They have one of these near me that I have watched on and off. They use a gas engine driven welder on the back of the crane to supply the magnet power. When they turn off the power, almost everything falls away from the magnet rather quickly. It is amazing to see an engine block jump a couple feet or so off the ground when the magnet gets close. Now that is power! On the other hand, you mentioned using mild steel for the pole and base pieces. The question then becomes, what happens when you remove the power. Is the decay of magnetism satisfactory? If mild steel is satisfactory for the pole and base pieces, then I can probably get it here locally in the smaller quantities. I have already obtained a couple rolls of heavy magnet wire from a surplus outlet, which has since gone belly up, for the project. I have checked with a couple local steel suppliers and my problem with obtaining the soft iron is that not much of it is ever used locally, so it is not stocked here. The minimum special order required to ship it in was more than I was willing to pay for such a small amount of material. The problem with many of these small projects is finding the right materials. Some people are fortunate to be living in places where these supplies are more common than here in the small city boondocks. (The chamber of commerce will kill me if they read that!) Thank you for your comments. -- Russ

Jim, Here's your wire source www.swwire.com - reply to Mark Benzio. A 40 pound spool of 10 RD HPT is $2.94 lb. There's a $ 30.00 re-spool charge if you want it broken up and that’s per spool, so (2) 20lb spools is an extra $60.00. This company is out of PA. HPT is a better wire for the job than Formvar and has a higher temp coating just in case you leave it on too long. Also, Formvar is getting obsolete. As for dave Gingery’s charger I have one word for it (TOY). If your going to take the time to build something do it right the first time. You won’t be disappointed in the charger you are thinking of making. -- Ed

I agree! We went down that road with the small magnet chargers and while they will put somewhat of a charge on the magnets, we decided to build the one featured in the GEM instructions that are also available on Bill Lopoulos’ website. It worked out great! It took about 2 hours to locate a supplier for the wire and the only other trouble was finding some high amp rated diodes. But, it's all together now and boy does it sock the juice to the magnets and it weighs in the 200 lb. range. -- Denny

The "REX" type charger is the way to go and I am building one now. I talked to a local motor rewind shop about winding the coils so I don't have to buy small spools of wire. Theirs is in 5 gallon buckets and very heavy. The steel for the core is CR 1018, very common. Lots of on-line companies sell steel buy the inch, buy what you need. Rex's charger is 20,000 ampere turns. -- Doug

I like your suggestion about using a motor rewinding company to make the coils. I know of a couple of these firms nearby. They might also solve the tedious chore of counting turns so you know what you have ended up with. Fabricating the pole pieces for someone else to wind shouldn't be much of a problem. A thought just came to my mind, does the smaller in length turns near the center of the coil contribute as much to the strength of the magnet as the longer length turns near the outside of the coil? The smaller length turns carry the same current, but they do it over a shorter distance. Just a general thought. -- Russ

Russ, Turns are turns, close to the core or far away. -- Norm

Russ, I went and looked at the motor rewinders machine to see how they would grip the core to wind it. The machine has a type of four jaw chuck to grip most anything. The wire sits on a scale so they just wind until it gets 20 pounds lighter. The wire goes through a tension device to keep it tight. They will also wrap the outside coil and seal it to make it "purdy". -- Doug

After following this thread, I just have to build me a 200 pounder "REX" Magnet Charger, to replace my toy one that weighs about 20 #. Anybody in NJ want to build one. Send me an email. Gonna really have some fun now. -- Paul

I am nearly finished with my own design (made from stuff I had laying around) to charge EK mags. It consists of one 1"x 2"x 5 1/2" mild steel with two 1"x 2"x 2 1/4" tapped and bolted together to form a wide, flat "U" shaped core. I have taken the four field coils from a Ford auto starter and I am in the process of mounting them on the short legs of the "U". May work, may not. Should I bother finishing it to see? -- Wayne

Just thought I would throw my two cents in. I work at a place where we built solenoids, valves, LVDT's, etc, for aerospace and such. With a team of 3 electrical engineers and myself (mechanical Eng.), we designed a magnet charger that weighs 35.5 lbs. We used a special alloy wire used for aerospace, and a core material of silicon C, with all gaps welded and annealed. This charger will super-saturate any magnet or magnetic material in 3.5 seconds, using 110DC. We actually have cracked a magnet, something went haywire with electrons or something in the magnet they said. It is almost too much for the old magnets until we install a rheostat. So a good charger can be done under 40lbs, it is the turns that count, not the weight. Technology has changed a lot from the 20's, 30's, & 40's. -- Mike

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