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Magnetos, Ignition Coils and Spark Plugs Discussion about magnetos, buzz coils, spark plugs, ignitors and low tension coils.

Magnetos, Ignition Coils and Spark Plugs

Single Coil Magneto Magnet Charger

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Old 09-02-2018, 03:29:00 AM
Jim Kennedy Jim Kennedy is offline
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Default Re: Single Coil Magneto Magnet Charger

Something else to consider when connecting conductors in parallel, is they should be the same material and size and they should be the same length so their resistance will be the same or currents will differ in the individual conductors.

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Old 09-02-2018, 07:52:58 PM
landreo landreo is offline
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Default Re: Single Coil Magneto Magnet Charger

I saw a magneto charger on youtube that was clearly too small to fully charge a magneto magnet but they were sure that is what they were doing. However, I also found a magnet website that sells gauss meters, magnets, etc.. and they had a charger for Alnico magnets. I believe they know what they are doing and sell quality products. This charger had 24,500 amp turns. So I believe that is still a good range. You have to consider the source of the information for charger designs. The one on youtube is clearly too small, the one on the magnetic products website is likely to be a good functional design.

A gauss or tesla is a measurement of flux density not actual flux. An Alnico magnet has a Br or magnetism flux density of around 1.2 tesla depending on the version of Alnico. Unless I am wrong, you would need at least the Br of 1.2 tesla to recharge and I expect even more. Since it is a density, the area is important. For a Wico EK magneto, the cross section of the magnet is about 2 square inches so the core, poles, movable poles of the charger will have to be at least that large in cross section if using mild steel. Bigger is OK, smaller is not.

For the winding, a longer wire length is not necessary better. If you wind a core with some wire size and use 100 feet it may have 1000 turns and draw 10 amps for a total of 10,000 amp turns. What happens if you continued to wind with the same wire another 100 feet and another 1000 turns. What is the total amp-turns?

Exactly the same!

Twice the wire length gives twice the turns but also twice the resistance and one half the current. Twice the turns but half the current gives the same number of amp-turns. The wire size and length has to be balanced with the number of turns and the current draw to give a coil that will produce the amp-turns without burning the insulation if used for a certain amount of time.

It will be interesting to see what input comes from the engineering tip forum as to the simulations.
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Old 09-03-2018, 11:26:34 AM
Ronald E. McClellan Ronald E. McClellan is offline
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Default Re: Single Coil Magneto Magnet Charger

The instructions that I got when I got my charger is to energize for 3 seconds , doing this 4 times , and allowing a few seconds between (for cool down?). The 3 seconds gives total saturation on the magnet being charged. Ron
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Old 09-04-2018, 09:20:05 PM
Boris Boris is offline
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Default Re: Single Coil Magneto Magnet Charger

Thought you would like to know the result from the magnetic engineering forum members computer sim result:

"I ran a model in 3D FEA. Assuming a 1" x 1" x 4" long 1018 CRS bar wrapped along the 4" length, producing 16000 Ampere-Turns: 3400 Gauss (0.34 Tesla) on the face of the steel. Field strength drops to 1875 Gauss (0.1875 T) at 0.5" (12.7mm) away from pole face. That probably won't be enough to properly re-magnetize your magneto."

If you want to view the full discussion, its at

So it looks like my single pole design probably isnt strong enough
If I made a second core just like the one I have, wired them in parallel as a two core vertical design, would that give me 32000 amp-turns?
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Old 09-05-2018, 01:58:56 PM
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BigGoomba BigGoomba is offline
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Default Re: Single Coil Magneto Magnet Charger

Did a quick eBay search - 250ft 12 awg magnet wire for $50 with free shipping. Almost bought 2 rolls to make 2 coils.

Decided against it. I have considered trying to make a mag charger a number of times but always decided against it because I donít have the tools machine the joints perfectly flat and square. Never looked into what it would cost to have parts for machined for me.

Great discussion btw - very interesting

One question - when you are talking about the 1/2/3 inch core - is that the diameter or circumstance ?
-Steve J
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Old 09-09-2018, 08:11:27 PM
landreo landreo is offline
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Default Re: Single Coil Magneto Magnet Charger

I think the simulations from the eng-tips forum are for an open magnetic circuit which is not what Boris had, he made a closed circuit design.

The problem with a calculator or simulator is that it is easy to believe the output even if you used the wrong equations or put in the wrong numbers. I thing I am doing the simulations correctly but my caveat is ... maybe not! I tried to pick equivalent points to measure the magnetic fields in all the simulations but I may have been off slightly but the basic magnitudes should be correct.

I ran some 2D simulations on 1x1 inch steel, 2x2 inch steel, and 2.5 x 2.5 inch section. The simulator will not do simulations for round stock but the square stock simulations should be close.

I ran a 1X1 core and 2x2 poles charger simulation going to a 1X1 inch cross section magnet, a 1X1 charger going to a 2X2 magnet. Did the same for the 2X2 charger and 2.5X2.5 charger. All with differing amounts of amp-turns in the single coil.

I thought I had found a reference years ago for the field intensity needed to charge magnets but could not find it again. However, you will need, as a minimum, the coercivity field amount, Hc.

For tungsten steel, Wico EK, old horseshoe style magnets, the Hc is around 5500 amps/meter. For cobalt steel around 5000 to 19000 depending on the type. For Alnico the Hc runs from 35000 to 50,000 for Alnico 1 to 5.

There is no reason to have a core size smaller than the magnet being charged, all you do is lose field intensity. You can go smaller at the magnet being charged, that actually will increase the intensity. So a 2X2 core can charge a 1X1 magnet size but a 1X1 core will not charge a 2X2 magnet.

Some simulations:

1X1 core size, 2X2 poles, 1x1 magnet, 16000 Amp-turns gives an Hc of 27,000 and 1.9 tesla, enough for a 1X1 tungsten or cobalt steel magnet.

1X1 core, 2x2poles, 2x2 magnet gives an Hc of 1270 and 1.15 Tesla, not enough for tungsten steel.

2x2 core, 2x2 poles, 2x2 magnet, 20,000 amp-turns gives an Hc of 19,000 and 1.9 Tesla.

A 2x2 core and poles with a 1x1 magnet gives 132,000 for the Hc and 2.19 Tesla.

2.5x2.5 core and poles to a 2.5 magnet, 20,000 amp turns gives an Hc of 17,400 and 1.9 Tesla.

A 2.5 x2.5 core and poles charging a 1x1 magnet with 20,000 amp turns gives and Hc of 120,000 and 2.17 Tesla.

To get into the higher Alnico range for a larger magnet, 2x2 or so, you are going to need the magic 60,000 amp-turns as recommended by Lucas magneto.

I also simulated using magnet wire vs THHN wire with an insulation thickness for the THHN of 0.02 inches which I think should be reasonable.You will lose around 1.25 percent of amp-turns effectivness for each layer of THHN wire compared to magnet wire.

Boris's design should work for the Model T magnets he is charging, they have a small cross section and should be tungsten steel. That charger may not be able to fuly charge a Wico EK set of magnets since the cross section is larger.

The common 20,000 amp-turns standard recommendation is still a reasonable target although it depends on the size, cross section, of the magnet being charged.

Keep the core and pole cross section at least as large as the magnets you want to charge.

Single core or double core design did not seem to make any significant difference in my simulations.

Magnet wire vs THHN wire? Doesn't really matter is you take in account the percentage loss of amp-turns.

Magnets will charge is milliseconds, no need for a longer pulse time than 1 second. There may be some advantages to doing a few short pulses for some magnet materials. Despite what is on Youtube, there is no need to tap the magnet, chant over the magnet, or wave a dead chicken over the magnet. Just a few short pulses is more than enough.

When the current is released, an inductive spike will go through the charger, a diode, resistor, or just an auto taillight bulb is more than enough to catch that spike.

You can use a starter solenoid to activate the charger as Boris did or I just use a push starter button from NAPA or Tractor supply made for tractors. That eliminates the solenoid.

Lots of ways to design and build a magneto charger but you can't ignore the basic physics behind electromagnets. As I said before, you can charge a 12 volt battery with an 8 volt charger but only to 8 volt. You will need a 12 volt charger to fully charger the battery. Same idea with magnets.

The data from the simulations should give folks some starting points for designing their own charger.

Last edited by landreo; 09-09-2018 at 08:21:21 PM. Reason: spelling
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Old 09-11-2018, 10:21:48 PM
Boris Boris is offline
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Default Re: Single Coil Magneto Magnet Charger

This is what we need: actual calculations that show when a larger core is important. A lot of ideas and info available on magnet chargers that are not backed up by facts. Thanks landreo!

I would caution against using just a starter switch. The starter solenoid can easily switch several hundred amps; I doubt a starter switch can switch a lot of current.
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Old 09-12-2018, 08:46:15 AM
landreo landreo is offline
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Default Re: Single Coil Magneto Magnet Charger

This is the type of switch I was referring to. Should be good for 100 amps or more. These are used to switch starters directly without using a solenoid.
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Old 09-17-2018, 12:52:09 PM
Dempster Dempster is offline
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Default Re: Single Coil Magneto Magnet Charger

Knife switch is used because first time that solenoid or other switch sticks the coil or coils will be burned up before you can get the power supply unhooked.
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