Explanation of a small engine ignition coil.

[amdx]

Hi guys,

 I just watched this video, It seems to get a lot of praise, but, I'm
not sure it really explains the operation properly.

 It attempts to explain how a lawn mower coil produces the high voltage
for the spark plug.

 I can't explain how it works, but I don't think this nailed the
operation. I don't think he got the flux right in the larger core.

Anyone care to give their opinion?

> https://www.youtube.com/watch?v=NNlYbvDY6pI

                          Thanks, Mikek


--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

[Bill Martin]

On 7/21/21 7:59 AM, amdx wrote:
> Hi guys,
>
>  I just watched this video, It seems to get a lot of praise, but, I'm
> not sure it really explains the operation properly.
>
>  It attempts to explain how a lawn mower coil produces the high voltage
> for the spark plug.
>
>  I can't explain how it works, but I don't think this nailed the
> operation. I don't think he got the flux right in the larger core.
>
> Anyone care to give their opinion?
>
>> https://www.youtube.com/watch?v=NNlYbvDY6pI
>
>                           Thanks, Mikek
>
>

Arrgh! If you can't bedazzle with brilliance, baffle with bullshit!
Making a physics lesson out of a simple problem. Seems to me: the
trigger coil turns on the transistor switch, allowing the magnetic flux
in the main core to build up current in the primary coil. When the
trigger voltage goes away, the transistor switch opens, collapsing the
primary current and inducing the voltage spike across the secondary
coil, same as normal Kettering ignition coil in automotive systems. Only
difference is in how the magnetic flux is created, ie no battery pushing
current through the primary coil.

Bill

[amdx]

 Well that's one item missing was showing development of the primary
current through the large A core as he called it.

I had no knowledge that it had any transistors built in.

[Jeroen Belleman]

To my knowledge, there is no need for that. Magneto ignitions
existed long before transistors did. They are still common in
devices with IC engines that have no battery, such as small
motor cycles, lawn mowers, chain saws, etc. They're also used
in airplane piston engines because they are light, reliable,
and independent of other electrical systems that may fail.

Jeroen Belleman

[Lasse Langwadt Christensen]

but then they have points, no?

[Tauno Voipio]

Yes, they do, to control the spark timing.

--

-TV

[Baron]

Lasse Langwadt Christensen prodded the keyboard with:

No ! Non needed.
--
Best Regards:
Baron.

[Lasse Langwadt Christensen]

how do they then control timing and get the fast turnoff for the flyback?

[Jeroen Belleman]

Sometimes, yes, but not all do.

Jeroen Belleman

[Jeroen Belleman]

Some engines have a centrifugal gadget for rudimentary timing adjustment,
but most just have fixed timing. Simplicity is the target here. The fast
dB/dt needed to get the spark is just a matter of shaping the pole pieces.

Jeroen Belleman

[Baron]

Its all to do with the position of the magnet and coil in relation to
the ignition firing point. Some magneto systems do use points !

Have a look at some of the smaller cheaper petrol generators, no
points there, just a coil with lots and lots of turns one end
connected to the frame, the other to the spark plug.

--
Best Regards:
Baron.

[Baron]

Jeroen Belleman prodded the keyboard with:

+1
--
Best Regards:
Baron.

[Liz Tuddenham]

...and some embeded electronics to give the fast switch-off.


--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

[Liz Tuddenham]

I've never seen it done that way and I've repaired dozens of small
engines with magnetos over the years. Which engine uses that method?

[John Larkin]

And to collapse the mag field suddenly to make the HV kick.

[John Larkin]

I've seen small engines that had a mechanical snap thing that helped
speed up the field strength d/dt, for starting. Once it spun fast
enough, the rate was OK.

[Jeroen Belleman]

It's sometimes done for motorcycle engines. There is obviously no
point in doing so for engines that are supposed to always run at
about the same rpm.

Jeroen Belleman

[amdx]

Can this be done without transistors or points?

 Basically, just a magnet moving past a coil and then stepped up. (What
I always thought)

I'm still flummoxed that the coils I looked at back in the 70s had
transistors embedded in them.

[amdx]

After a couple more videos, I'm pretty sure most of what I looked at had
points and a condenser.

Just a trip down memory lane, just wish I could have taken all my memory
with me.  :-)

[DecadentLinux...@decadence.org]

amdx <am...@knology.net> wrote in news:sd9cnn$e1f$1...@dont-email.me:

> ķĸI can't explain how it works, but I don't think this nailed the

> operation. I don't think he got the flux right in the larger core.
>
> Anyone care to give their opinion?

It is real simple. The coil is energized at 14 Volts or thereabouts.

It generates what is refered to as a "standing field". When DC is
put on any coil, not just a car coil, a "standing field" is generated
and differs (in size) depending on the voltage applied. When one then
removes the DC energization in a very fast "sudden open switch" kind of
way (points), that field collapses back down and that mean flux lines
are crossing copper turns, and we all know what happens when that
happens. Anyway, that collapsing field has a very fast slew rate and
open circuit the coil could theoretically produce and extremely high
momentary peak voltage. Across a load, however, it produces a bit of
"work", causing the secondary to pop off at about 25k to 30k Volts for
a very small "event time" each time the points open. The time the
points are closed on a multi-headed points 'cam' is called dwell time.

So, there it is, the flux field slamming back down into the coil
produces a pretty good raw spark of a short duration at the plug.

There is actually a small peak when one energizes a coil with DC if
the feed is placed quickly as in via switch.

[DecadentLinux...@decadence.org]

Baron <ba...@linuxmaniac.net> wrote in news:sd9pvd$h47$1@dont-
email.me:

One must take the coil from full DC energization to zero in order
to create the flux collapse that generates the spak at the plug. The
coil is "always on" between 'sparks', and the points open, allowing
the field collapse to take place at a very high slew rate. That is
where the work gets done, but only for a very short duration.

[amdx]

On 7/21/2021 5:52 PM, DecadentLinux...@decadence.org wrote:
> amdx <am...@knology.net> wrote in news:sd9cnn$e1f$1...@dont-email.me:
>

>> ¶ÿI can't explain how it works, but I don't think this nailed the

  I understand how a coil generates a high voltage when the field
collapses. My first experience with that

was at about 12yrs old when I had 4 D size batteries in a paper towel
tube and I was energizing a record played motor.

Every time I removed the wire from the battery I got a shock!

Then at 16yrs old, a kid built a box with a lid, when you opened the lid

it opened a switch removing current from a coil and gave you a shock. It
was a big hit in 11th grade.

[DecadentLinux...@decadence.org]

Baron <ba...@linuxmaniac.net> wrote in news:sd9si3$5vi$2@dont-
email.me:

Nope. The spark and its timing has to be a near instananeous event
for the motor to run smoothly. I seriously doubt that there are
magneto only, coil to the plug units. I would bet that there is a
triggering device involved that opens the DC field, allowing for the
fast, high slew rate spark event and precise chronological control
thereof.

[DecadentLinux...@decadence.org]

John Larkin <jlarkin@highland_atwork_technology.com> wrote in
news:353hfgdr7876ummv5...@4ax.com:

Ding! Johnny gets it right. Good job. That collapse is the key.
errr... spark trigger.

[DecadentLinux...@decadence.org]

amdx <am...@knology.net> wrote in news:sda5p3$705$1...@dont-email.me:

> I'm still flummoxed that the coils I looked at back in the 70s had
> transistors embedded in them.
>

Diodes, ya dope. :-P

[DecadentLinux...@decadence.org]

amdx <am...@knology.net> wrote in news:sda94k$poh$1...@dont-email.me:

In 7th grade "Jr High School" my "science project" for the "science
fair" was a shock box rig with two 4 x 1/2 inch rods as the output,
and was dubbed as a lie detector... har har har...

Asked a guy how old he was, then shocked his ass and told him the
machine said he lied, and then he was barking "But I didn't lie" and
so I shocked him again.

Could never do that OSHA hazard shit these days. I'd get a SWAT
team called on me.

[Jasen Betts]

On 2021-07-21, amdx <am...@knology.net> wrote:

>>
> Can this be done without transistors or points?

piezo-electric maybe.
https://books.google.co.nz/books?id=OiEDAAAAMBAJ&pg=PA70&dq=Clinton+%22Spark+Pump%22&hl=en&ei=8geRTvWUIujYiALz1b3AAw&sa=X&oi=book_result&ct=result&redir_esc=y#v=onepage&q&f=false

>
>  Basically, just a magnet moving past a coil and then stepped up. (What
> I always thought)
>
> I'm still flummoxed that the coils I looked at back in the 70s had
> transistors embedded in them.

Briggs and Stratton introduced the transistorised magneto coils in 1982
as "Magnetron ignition" before that they had points driven either by the
crank or the camshaft. (sometimes the points were hidden behind the flywheel)

Video showing different briggs and stratton magentto coil assemblies:

https://www.youtube.com/watch?v=KvBx4Mh1Lvw


--
Jasen.

[Joe Gwinn]

That was the clue I needed. Patent US4270508 is what the OP's video
showed. A related but more complex version is US4188930.
Non-transistor background is in US3527266. Inventor is John D. Santi.

Get pdfs by entering these numbers (with the US) into Google Patents.

Joe Gwinn

[Baron]

Liz Tuddenham prodded the keyboard with:

No ! Liz. Its all done with magnets. No electronics needed. The
magneto is a simple many years old system of generating a high
voltage. Try holding the ends of a coil wound on a ferrous former
and waving a magnet over the core !

The original telephone system used a magneto to ring the bell at the
other end of the line. Or how about the Avo wind up "Megger" used for
insulation testing.

All these devices used a coil of wire and a magnet to generate high
voltages. The secret with ignition systems is where the magnet and
coil is in relation to the position of the engine piston.

--
Best Regards:
Baron.

[Baron]

DecadentLinux...@decadence.org prodded the keyboard with:

> amdx <am...@knology.net> wrote in news:sd9cnn$e1f$1...@dont-email.me:
>

>> ś˙I can't explain how it works, but I don't think this nailed

Your description is right for a "Kettering Ignition System", but not
for magneto systems.

--
Best Regards:
Baron.

[whit3rd]

On Thursday, July 22, 2021 at 12:40:11 PM UTC-7, Baron wrote:
> Liz Tuddenham prodded the keyboard with:
> > Baron <ba...@linuxmaniac.net> wrote:

> >> Have a look at some of the smaller cheaper petrol generators, no
> >> points there, just a coil with lots and lots of turns one end
> >> connected to the frame, the other to the spark plug.

> > ...and some embeded electronics to give the fast switch-off.

> No ! Liz. Its all done with magnets. No electronics needed.....

> All these devices used a coil of wire and a magnet to generate high
> voltages. The secret with ignition systems is where the magnet and
> coil is in relation to the position of the engine piston.

There's actually one nonlinear electronic device in all those systems,
that deserves mention: the gap in the spark plug. Spark gaps
are crude, primitive, and very robust technology that we all
ignore. The platinum-plug tech is THAT good, we can ignore it.

[Liz Tuddenham]

Those produce sinusoidal(ish) voltage waveforms; a spark-ignition system
requires an accurately-timed pulse. In the case of a magneto, this is
generated by shorting an auxiliary low-voltage winding to 'slug' the
change of magnetic flux in the iron core while the magnets move to
another position. When the short is removed, the flux flips over to the
new value and generates a fast pulse in the high-voltage winding.

Because the induced voltage is proportional to the rate of change of
flux (as well as the number of turns), a much higher voltage is produced
than if the flux change were allowed to follow the relatively-slowly
changing field due to movement of the magnets.

Some early magnetos incorporated a mechanical mechanism which had a
spring coupling between the armature and the shaft. At cranking speed,
a pawl held the armature stationary while the engine rotated and the
spring was tensioned, then suddenly released it to give the armature a
flip. There were still make-and-break points to give the rapid flux
change, but the faster mechanical movement at (hand) cranking speed made
for more reliable starting. The armature reverted to continuous
rotation once the engine reached idling speed.

Some very slow speed engines (portable agricultural engines) used a
system whereby the magneto shaft was spring loaded to a central position
and not directly coupled to the engine rotation. A projection on one of
the valve rods caught in a lever on the magneto shaft and pulled it away
from the central position against the tension of the spring. At a point
corresponding to top-dead-centre, the projection disengaged and allowed
the magneto shaft to flip back under spring tension, thereby generating
a high voltage pulse. The magneto armature performed several cycles of
oscillation before coming to rest, ready to be wound up again.

As far as I know, that was the only system that did not use points or a
transistor to give the required sharp change of magnetism.

> All these devices used a coil of wire and a magnet to generate high
> voltages. The secret with ignition systems is where the magnet and
> coil is in relation to the position of the engine piston.

If it was that simple, why did nearly every spark-ignition engine
manufacturer use points, condenser and a double winding on the coil or
magneto throughout the 70 year period before transistors were available?

[Chris Jones]

You can't see the electronics, because the pot it inside the
encapsulation of the coil. Don't believe me if you don't want to. Look
here at the picture titled "evolution of the ignition armature":

https://www.briggsandstratton.com/eu/en_gb/support/faqs/browse/ignition-system-theory-and-testing.html

I also have an old magneto from before when transistors were invented,
and it has points (a mechanical switch) to perform the function that
nowadays is performed by semiconductors.

[Fred Bloggs]

That's the gist of it. The magnetic field from the flywheel magnets doesn't induce a voltage in the primary coil, mainly because it is a short. It does induce a current that produces a magnetic field in the core to oppose the flywheel magnetic field. The magnetic circuit should be close to zero flux when the primary circuit is opened. The action of opening the primary results in an impulse magnetic field being applied to the core unopposed- it takes current to oppose the magnetic field and this only occurs when the induced voltage in the secondary winding strikes an arc. The magnetic circuit properties, the secondary turns and the arc voltage of the fuel/air mixture in the spark gap all go into determining the duration of the spark. According to B&S, the arc voltage for the fuel/air gap is about half again greater than would be required to jump the corresponding air gap. This is accounted for in that little spark tester they sell. The same principles apply to all magnetos, electronic or points. The spark has to be synced to top dead center of the piston stroke- simplistically, there are various reasons for adding a lead angle or even a variable lead adapted to RPM.

>
> Because the induced voltage is proportional to the rate of change of
> flux (as well as the number of turns), a much higher voltage is produced
> than if the flux change were allowed to follow the relatively-slowly
> changing field due to movement of the magnets.
>
> Some early magnetos incorporated a mechanical mechanism which had a
> spring coupling between the armature and the shaft. At cranking speed,
> a pawl held the armature stationary while the engine rotated and the
> spring was tensioned, then suddenly released it to give the armature a
> flip. There were still make-and-break points to give the rapid flux
> change, but the faster mechanical movement at (hand) cranking speed made
> for more reliable starting. The armature reverted to continuous
> rotation once the engine reached idling speed.
>
> Some very slow speed engines (portable agricultural engines) used a
> system whereby the magneto shaft was spring loaded to a central position
> and not directly coupled to the engine rotation. A projection on one of
> the valve rods caught in a lever on the magneto shaft and pulled it away
> from the central position against the tension of the spring. At a point
> corresponding to top-dead-centre, the projection disengaged and allowed
> the magneto shaft to flip back under spring tension, thereby generating
> a high voltage pulse. The magneto armature performed several cycles of
> oscillation before coming to rest, ready to be wound up again.

Sounds like something Volkswagen would do.

[Baron]

Chris Jones prodded the keyboard with:

The first part of this link describes exactly how a magnet + coil
ignition system works.

https://www.briggsandstratton.com/eu/en_gb/support/faqs/browse/ignition-system-theory-and-testing.html

quote "When you start your lawn mower or small engine, you turn the
flywheel and its magnets pass the coil (or armature). This creates a
spark. The ignition system coordinates the timing so that the spark
will ignite the air-fuel mixture in the combustion chamber just as it
reaches maximum compression in each engine cycle- thus, maximising
the engine’s power.

Once the engine is running, the flywheel keeps rotating, the magnets
keep passing the coil and the spark plug keep firing based on a
specific timing." unquote.

Absolutely no mention of points, diodes or transistors !

> I also have an old magneto from before when transistors were
> invented, and it has points (a mechanical switch) to perform the
> function that nowadays is performed by semiconductors.

--
Best Regards:
Baron.

[Lasse Langwadt Christensen]

next paragraph:

Types of Ignition Systems:

Solid-state systems: the more modern option, these systems use a tiny transistor in the coil or armature to close the electrical circuit that travels through the spark plug lead to the spark plug(s).

Breaker point systems: used on engines made before 1980, these systems use a mechanical switch instead of a transistor to close the electrical circuit used to produce a spark.

[amdx]

Exactly what I was ready to post!

*Types of Ignition Systems*

* Solid-state systems: the more modern option, these systems use a

tiny transistor in the coil or armature to close the electrical
circuit that travels through the spark plug lead to the spark plug(s).

* Breaker point systems: used on engines made before 1980, these

systems use a mechanical switch instead of a transistor to close the
electrical circuit used to produce a spark.

Repair Small Engine Ignition System by Briggs and Stratton

[Liz Tuddenham]

Fred Bloggs <bloggs.fred...@gmail.com> wrote:

> On Friday, July 23, 2021 at 5:05:26 AM UTC-4, Liz Tuddenham wrote:

[...]

> >In the case of a magneto, this is
> > generated by shorting an auxiliary low-voltage winding to 'slug' the
> > change of magnetic flux in the iron core while the magnets move to
> > another position. When the short is removed, the flux flips over to the
> > new value and generates a fast pulse in the high-voltage winding.

> That's the gist of it. The magnetic field from the flywheel magnets
>doesn't induce a voltage in the primary coil, mainly because it is a
>short. It does induce a current that produces a magnetic field in the
>core to oppose the flywheel magnetic field. The magnetic circuit should
>be close to zero flux when the primary circuit is opened. The action of
>opening the primary results in an impulse magnetic field being applied
>to the core unopposed- it takes current to oppose the magnetic field
>and this only occurs when the induced voltage in the secondary winding
>strikes an arc.

The purpose of the condenser (capacitor) across the contacts is to allow
the primary current to continue flowing as the points separate. The
voltage builds up across the capacitor at a slightly slower rate than
the breakdown voltage of the points increases as they pull apart, so the
energy of the coil isn't dissipated in arcing across the points. Before
the primary voltage can reach the breakdown limit of the capacitor, the
secondary voltage will have risen to the voltage needed to fire the
sparking plug.


I recently had the secondary winding on the magneto of an industrial
Honda engine break down. When I stripped off the secondary I found that
arcing had tunnelled through several layers of insulation and there was
no chance of saving it. The engine was so old that no spares were
available but the associated equipment was quite valuable and the engine
itself was hardly used, so I looked for a way of repairing it.

My local garage donated a secondhand 12v ignition coil off a scrap BMC
Mini, which I fitted on the outside of the engine with its primary wired
across the primary of the magneto, which was still in good condition.
It gave a spark which wasn't quite as vigorous as I remember the
original spark had been, but was adequate to run the machine.

The slightly weak spark makes the starting mixture more critical, but
last weekend we ran it continuously for several hours with a reasonable
load and it was quite satisfactory. I've found a smaller 6v coil at a
car boot sale and will be trying that to see if it is a better match and
gives easier starting.

[John Doe]

The group idiot "Always Wrong" bragging about shocking people
in 7th grade...

--
DecadentLinux...@decadence.org wrote:

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> From: DecadentLinux...@decadence.org
> Newsgroups: sci.electronics.design
> Subject: Re: Explanation of a small engine ignition coil.
> Date: Wed, 21 Jul 2021 23:21:17 -0000 (UTC)
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>
> amdx <am...@knology.net> wrote in news:sda94k$poh$1...@dont-email.me:
>
>> On 7/21/2021 5:52 PM, DecadentLinux...@decadence.org
>> wrote:
>>> amdx <am...@knology.net> wrote in news:sd9cnn$e1f$1...@dont-email.me:
>>>

>>>> 락푭I can't explain how it works, but I don't think this

[DecadentLinux...@decadence.org]

l...@poppyrecords.invalid.invalid (Liz Tuddenham) wrote in
news:1pcrjha.gs395sbp3lc4N%l...@poppyrecords.invalid.invalid:

Everything Liz said is 100% accurate.

Jedi inflection: "The engineering knowledge is good in this
one..."


Yes... very accurate.

Especially the "If it were that simple..." part.

All the transistorized versions give is a solid state version of a
set of points. A high slew rate (read quick) voltage snap which
induces the same in the step up transformer referred to as a coil.
The transistorized versions are fast enough to trigger directly into
the coil, whereas a point version was "ON" with a standing DC field
placed on the coil and then released by the points "OPENING" Zap!

Back in the CB radio days it was very hard to fully shield a car's
ignition system using hard conductor plug wires. "Fooly Shielded" was
more like it. Ham and CB enthusiasts tried to suppress it in many
ways. Magnetic pulses tend to prove that it penetrates entire
planets so all we can do is attenuate or provide an alternate path
and thereby receive viable attenuation on the 'protected side' of
your work.

[Jasen Betts]

absense of proof is not prood of absense.

--
Jasen.

[DecadentLinux...@decadence.org]

Baron <ba...@linuxmaniac.net> wrote in news:sdeplr$tvu$1@dont-
email.me:

> Absolutely no mention of points, diodes or transistors !

"The ignition system" is what it "mentions".

Nice job of overlooking that.

It says that "it" coordinates the timing of the spark..."

So what do you think that coordinator is? The relatively slow
approach of a magneto magnet ring passing a magneto pick up coil?
Or maybe there are points in that "ignition system" it mentioned.

Remember that a spark is a very fast event and that the sinusoidal
energy 'waveform' presented by the magnet of the magneto generates
the needed energy, but not the needed "trigger event".



As to the operation of a magneto ignition here is a quote:

"As the magnet moves with respect to the coil, the magnetic flux
linkage of the coil changes. This induces an EMF in the coil, which
in turn causes a current to flow. One or more times per revolution,
just as the magnet pole moves away from the coil and the magnetic
flux begins to decrease, a cam opens the contact breaker (called “the
points” in reference to the two points of a circuit breaker) and
interrupts the current. This causes the electromagnetic field in the
primary coil to collapse rapidly. As the field collapses rapidly
there is a large voltage induced (as described by Faraday's Law)
across the primary coil."

[Chris Jones]

As I said, don't believe me if you don't want to. Have fun!

[Les Cargill]

Liz Tuddenham wrote:
<snip>

>
> If it was that simple, why did nearly every spark-ignition engine
> manufacturer use points, condenser and a double winding on the coil or
> magneto throughout the 70 year period before transistors were available?
>

Coil/condenser/points for engines that varied in speed ( up to and
including variable spark timing dependent on RPM - mechanical/vaccuum
advance ) .

Magnetos for cases where the goal was more like constant RPM -
lawnmowers, aircraft.

Magnetos came first. The distributor systems add a lot of part count so
there needed to be very competitive environments to allow for that, like
the auto industry. There are Youtube videos of people assembling
engines, and things get real quiet when they put the distributor in.

That's a very low-resolution answer but it should describe the basic app
space.

--
Les Cargill

[ke...@kjwdesigns.com]

On Sunday, 25 July 2021 at 08:48:19 UTC-7, Les Cargill wrote:
...

> Magnetos for cases where the goal was more like constant RPM -
> lawnmowers, aircraft.
>
> Magnetos came first. The distributor systems add a lot of part count so

...
Actually Hot-tube and trembler coil ignition came first.

The Ford Model T used a trembler coil with an untimed spark until 1927.

Neither of those methods timed when the ignition occurred so engine efficiency was limited.

Magneto ignition was developed about the start of the 20th century with the modern Kettering ignition system a few years later.

The big advantage of the magneto was that it didn't need a battery so has been traditionally used on small engines or vehicles without any other electrical system (eg lawn mowers, motor scooters, motor bikes) or in aircraft where very high reliability is required (typically they will have two magnetos to provide redundancy as well).

kw

[amdx]

 I'd like to see an example, because I don't think just a magnet
passing a coil is enough to do the job.

Mikek

[Liz Tuddenham]

Les Cargill <lcar...@gmail.com> wrote:

[...]

> Magnetos came first. The distributor systems add a lot of part count so
> there needed to be very competitive environments to allow for that, like
> the auto industry.

Magnetos had points and a condenser too, they just didn't need a battery
supply.