What is a magneto?

[mnwildpunk]

I'm putting together a 409 which in the kit can be built as a street version and a race version. On both versions it has no dizzy and uses a magneto. What is a magneto and how does one work?

[MAGNUM4342]

Magneto is proffesor X's mortal enemy! Just kidding. I'd kinda like to know as well.

Edited July 2, 2012 by MAGNUM4342

[Longbox55]

For all intents and purposes, a magneto does the same job as a distributor. The main difference is how the power for the spark is produced. With a standard distributor, the power for the spark is external, provided by the vehicles charging system/battery, and is increased to the required voltage (10k-85k volts for a street car) by the coil. This system is also commonly called "battery ignition".

With a magneto, the power is generated withing the unit itself. The coil is generally contained within the housing as well, though this isn't always the case (Model T Ford for example). The main advantage to using a magneto is that a battery or external charging system is not required for them to operate, which is why they are common on racing applications, especially drag racing. They also see use on aircraft and some ag equipment. They can be used with a vehicle that has a separate charging system and battery, but the two systems are completely independant of each other. A magneto ignition is turned off by grounding it out.

As mentioned, a magneto ignition can be used on a street car, but they would not be considered common, as in the 1:1 world, they are somewhat expensive and a regular distributor will do the same job.

[MAGNUM4342]

The main advantage to using a magneto is that a battery or external charging system is not required for them to operate

Now i'm really confoosed! Am I reading this wrong? If you have a magneto you don't need a battery or alternator?

[Fat Brian]

The magneto generates the electricity required for the spark plugs once the engine is running. Think about a lawnmower or weedeater, once you pull the string to start it the magneto keeps it running.

[MAGNUM4342]

Okay, so you still need a battery and alternator then?

[91blaze]

Okay, so you still need a battery and alternator then?

No, the magneto acts as the alternator. A weedeater or even a gokart for example does not have a battery or alternator. Instead the magneto acts to generate electricity and distribute the electricity to the spark plugs. A car, however, still would need a battery and alternator to power lights and such.

[Fat Brian]

By the time you add an alternator and battery there isn't any need for a magneto since you can run a regular distributor. A magneto is a stand alone unit that can be used when a whole charging system would be too heavy or complex like a race car or handheld tool.

[91blaze]

But in a "street car" like the OP mentioned, you would still need a battery for the lights and such, right?

[mnwildpunk]

Thank you gentleman now I have to ask is it akin to the old generators? also if I am reading out right it would be the exact opposite of an electromagnet?

[Fat Brian]

Yep, thats why no one really runs them on street cars. Since you would most likely want the covenience of starting the car whenever you like and having headlights most people run a regular charging system and it isn't cost effective to switch the spark firing to a different system.

[Fat Brian]

Thank you gentleman now I have to ask is it akin to the old generators? also if I am reading out right it would be the exact opposite of an electromagnet?

It is different from a generator which is more like an alternator in a modern charging system and yes, it is the exact opposite of an electromagnet.

[mnwildpunk]

Great now I have to pull my mower apart to play with one lol

[Aaronw]

But in a "street car" like the OP mentioned, you would still need a battery for the lights and such, right?

Yes, that is why many early cars used kerosene or carbide lamps.

Many smaller (250cc >) non street legal dirt bikes still use a magneto ignition because they can save the weight of a battery, starter and alternator and not being used on the street do not require lights.

[62rebel]

find yourself an old troybilt mower and take the ag off of it, hold the contacts and spin the drive gear.....

you'll be through "playing" with a magneto for a while. they can, will, and do pack enough kick to... kick your... rear.

ever have anybody charge a capacitor and toss it to you? something along those lines, just worse.

electricity is nothing to play with.

[mnwildpunk]

I was an eletronics major in college I was almost finished when I had to drop out because of my transplant. Yes I know eletricity is nothing to p play with and you respect it. But,thank you for the warning

[Art Anderson]

OK, anyone up for a bit of a science lesson here? (actually, I learned this in 7th grade electrical shop class--Dr Lloyd Neher, Dean Emeritus of the College of Technology at Purdue University, was our teacher back then, fresh out of Purdue himself);

Pass an electric current through a wire, and a magnetic field is created around that wire (think Direct Current here). With direct current (which is what your car's battery and starter use, BTW), an old rule called "the right hand rule" will show you the direction of that magnetic field, by simply wrapping the fingers of your right hand around a wire (no electrical current is required for this demonstration, in fact it's NOT recommended AT ALL!) with your thumb laying along that piece of wire. Your thump points in the direction that DC current would flow, your fingers wrapped around that wire shows you the direction of the magnetic field created.

Now, if you "create" a magnetic field around a loop of wire (by spinning that wire loop between the two poles of say, a "horseshoe magnet), doing so with create a magnetic field around that loop of wire, and that will send electric current THROUGH the wire. That is how a Magneto, even an old-fashioned DC generator works. Now, both a Magneto and a DC Generator will create more voltage of electricity the faster you turn their armature (which is nothing more than a whole lot of wire loops wound around the segments of the armature). Both a magneto and a generator do the same thing, produce direct current, but the magneto puts out lots higher voltage, where the generator puts out more amperage (volts are a measure of "pressure" -- think pressure in a water pipe or compressed air line -- while amperes are the measure of capacity, or how much electricity can be produced).

Early automobiles relied on magneto's to provide electricity for the ignition system, which was OK in the years before electric lights, electric starter came about, and the introduction of storage batteries into the automotive equation. Magnetos are actually quite simple, just that concept of spinning a loop of wire between the two poles of a magnet in order to create current. The faster the mag spins, the higher the voltage (and it's voltage that creates spark at the sparkplug), which made magneto's the electrical generation of choice for early automobiles. Ford Motor Company likely made the most magneto's of any carmaker: 15 million plus Model T Fords ALL used magneto's to provide electricity for ignition--Model T flywheels contain dozens of bar-type permanent magnets, which spun in close proximity to a wire coil which surrounded the flywheel, creating direct current which was routed by means of a "timer" (a primitive sort of "distributor") to a type of induction coil called a "buzzer" coil, one for each sparkplug. That ensured a hot spark for each plug in time with the cycle of each of the 4 cylinders. When Ford adopted electric lighting, and an electric starter, a generator, a cutout (early type of voltage regulator) and a battery were added, but from 1908 until June 1927, EVERY Ford car used magneto ignition.

Race cars of all types relied on magneto ignition until electronic ignition systems came into use in the 1960's, that's the simplest, and often most reliable way to ensure that no matter the engine RPM's, the spark generated at the plug is the highest voltage, the fattest, hottest spark that could be had.

In a street automobile, one can use magneto ignition, but if the car is to be driven on the street, and relies on an electric starter motor (as opposed ot either a hand-crank or remote power starter) then a generator and storage battery are also required. The same is true if a magneto ignition automobile has electric lights--a mag would simply blow out head and tail lights once the engine rpm's reached a certain point.

Another use for magneto's, and one that has seen an awful lot of screen time in movies and on TV, is the old "hand-cranked" wall telephone. While those phones relied on 6-volt "dry cell batteries" to provide the low voltage necessary for talking and listening on those phones, a way to let the operator know you wanted to be connected with your Aunt Mabel across town had to be available. Enter the magneto! You picked up the receiver, wound the magneto crank a few rapid turns, and a "door bell Briiinnnngg!" went off at the operator's switchboard. She'd see the light on her board of YOUR phone, plug in, and ask "Number Puleeeze?".

I hope I've helped you understand what those old-style magneto's did, why they were used and so on, along with the difference between a magneto and a generator or alternator.

Art

[Greg Myers]

What is a "dizzy" and how does it work ?

['08SEAL]

Magneto is proffesor X's mortal enemy! Just kidding. I'd kinda like to know as well.

Thats what I thought too!

[Guest G Holding]

Greg, a dizzy is a simple switching mech that directs the coils spark to the proper plug at the correct time. Notice a top fuel car...dual mags, no battery or starter

Edited July 2, 2012 by G Holding

[2002p51]

What is a "dizzy" and how does it work ?

It's an "internet forum word" for people who are too lazy to type out "distributor".

[Greg Myers]

It's an "internet forum word" for people who are too lazy to type out "distributor".

Yep, I taught High School Auto Shop for eight years, and demanded the proper terminology. ain't nottin' "Dizzy" about this.

Edited July 2, 2012 by Greg Myers

[2002p51]

Yep, I taught High School Auto Shop for eight years, and demanded the proper terminology.

Thank you, I wish more people cared about the language, especially on forums such as this one.

(Don't get me started!)

[Ace-Garageguy]

Here is an answer I posted to this exact question on another forum a few months back. I hope it will clear up some mis-understandings.

I've posted this before. I currently build 1:1 period hot rods for a living, and I'm an engineer. This is the true and complete answer from someone with 40 years of actual experience working with magnetos, etc.

Mags were / are commonly run on period street / strip cars. They made a fat, hot spark at relatively high RPM before the days of capacitive discharge. A fair number of 'teens and '20s cars came with magnetos, and many early race car mags were adapted from AIRCRAFT parts. Small aircraft engines STILL use magnetos that look very much like those on '40s-'60s competition cars, and they use them because the engine will continue to run even if the rest of the electrical system fails. Small airplanes have batteries for starting, and charging systems ( generator OR alternator ) to run accessories and to keep the batteries charged for starting.

TO RUN A MAG on a street / strip car, you'll need a generator OR alternator, and a battery , and a starter. You will NOT need a coil or distributor, of course. The advantage to using an alternator is that it will provide more current at lower RPM. They work better at running loads like air conditioning and lights at idle, or while sitting in traffic. Alternators began to become common in production cars in the early '60s. They appeared first on police cars because of the high electrical demands of the communications radios. Interestingly, most small aircraft alternators are adapted from CAR parts.

The guys above are correct in that:

1) The magneto has an internal generator (sort of), points, "coil" (sort of) , and distributor cap, and provides its own spark to fire the plugs

2) A magneto does not provide enough energy to keep a starting battery charged, or to run any accessories

3) For STREET use, battery and starter motor will be required to start the engine. Old race cars (that didn't have batteries or starters for weight-saving) were push started, 'cause the mag has to be spinning to make any juice, and without a battery and starter, no spin, no juice.

4) A charging system will be required ( generator OR alternator ) to keep the battery charged and run accessories.

AMT Chevy 409 specific:

The mag in that kit isn't really very accurate. It sorta has a distributor cap molded on. Some mags had this, and you wire them to the plugs like you wire a distributor. No coil wire though. More common mags had little numbered "buttons" on top of the "cap", and the plug wires came out on the side grouped together. Do a google image search for "vertex magneto".

You will see that what you need to do is file the nipples on the AMT Chevy magneto almost flat. Paint the "cap" black or red and the remains of the nipples silver. Also paint the body of the mag silver. They were all aluminum. Route your plug wires like in the photos on google. For a push-start car, you only need one small ground wire going from the mag to a kill switch inside the car. The only way to "turn off" a magneto is to ground it. For a battery start, street driven car, you could also simulate a starting-voltage booster with a small hot wire running to the mag. These would be two very small wires, much smaller than plug wires, coming out under the "cap", well away from the plug wires. The small hot wire could run to a little box on the firewall.

There was also a unit called the Spalding Flamethrower, basically two, four-cylinder coil-type ignition systems in a single, usually red, case. It looks like a mag, but isn't. It had two groups of 4 plug wires on either side. Do a google image search for that. It was fairly common on really hot street cars, as was the Vertex ( Scintilla, Joe Hunt, etc.)

Plan your work, work your plan.

In closing, a mag won't blow out lights as posted above, because it's constructed so that it's spark discharge is directed to a SPECIFIC spark plug as the magnetic field collapses, and not into the car's general electrical system.

The spark is created in a magneto when the magnetic field rapidly collapses inducing a high voltage in the adjacent wire windings. The spark is directed to a specific plug by the position of the rotor in the "cap", exactly as it is directed to the correct plug in a battery-type ignition system. A magneto is timed in much the same way as a POINT TYPE battery powered ignition system is timed, to make it fire with the correct amount of ignition "lead".

Edited July 3, 2012 by Ace-Garageguy

[Ace-Garageguy]

What is a "dizzy" and how does it work ?

An older distributor does two things. 1) It tells the coil when to fire and 2) it directs the resultant spark to the correct spark plug. (Many later-model distributors ONLY direct the spark to the correct plug and have no role in establishing ignition timing).

It knows when to tell the coil to fire because it has a sensor of some type, either points, a magnetic device, or an optical device, that senses the position of the distributor shaft in relation to the crankshaft (and cam). This is called "ignition timing". It can be varied by manually twisting the distributor body during tuning, or automatically by mechanical or vacuum "advance" mechanisms while the engine is running.

A little wire running from the distributor to the coil carries a signal that makes the coil "fire" (resulting from a collapsing magnetic field inside the coil), and the resultant secondary current, the "spark", is directed back to the distributor by the one BIG wire in the center, and sent to the correct spark plug by the "rotor", which turns with the distributor shaft and aims the "spark" at the correct BIG wire going out.

This is an oversimplification, and I've used some terms loosely, but that's how it all works in a nutshell.