Sounds similar to the one Taryl has:

That's the video that got me started down this rabbit hole in the first place. By the way, when Taryl keeps saying "fixes dead spark plugs", I think he really means "cleans fouled spark plugs"

I have an old reading lamp that used to be dimmable, but the dimming function stopped working 20+ years ago. Not long ago, I decided to give it an LED upgrade. Taking the original dimmer guts out, I saw a similar device as in that thread Ron shared. I didn't understand how it worked, so I set it aside somewhere. Maybe I'll have a closer look at it someday.

So the time interval is important after all. Makes sense. It must work across a range of firing frequencies though, as engines might run from 800 to 5000+ RPM, right? As the engine revs up the spark gets weaker? Would it be the time the switch is closed that is important, or both open and closed?

I started looking at voltage boosters, and quickly found an article from this vary website: Understanding the Operation of a Boost Converter. Right away I saw the similarities to the ignition coil circuit, but I'm also seeing differences.

If I'm understanding right, the larger the inductor, the longer it takes to create the full sized magnetic field, but don't let it go too long, or it will saturate, and bad things will happen. Also, the larger the capacitor, (capacitance wise) the longer it will take to fully charge from the inductor when the circuit is opened. A larger capacitor will be able to store more charge, so the size of the capacitor should be related to the size of the inductor.

The values I know so far are the input voltage (12V), the secondary coil winding output voltage (5kV), the permeability of the iron core (0.0063 H/m). I can measure inductance for a known number of turns, and calculate permeance for the inductor (including the air gap) and I can calculate how many turns I'll need for a desired inductance for the primary coil. (And therefore, the secondary too, I guess.)

I still need to figure out what inductance I want for each coil, the capacitor's voltage and capacitance, and how much time is needed to saturate the inductor's magnetic field and how much time is needed to fill up the capacitor with charge.

I came across some equations that might be related to this:

V=Q/C Voltage equal stored charge divided by capacitance.
C=I*D/f*ΔV Capacitance equal current times duty cycle divided by frequency times voltage ripple.
D=Vin/Vout Duty cycle equal voltage in divided by voltage out.

I'm not sure if any of these apply to what I'm doing yet.

 

The one device that I have used that actually did tend to clean spark plugs that had a carbon build up was a battery powered sandblaster. It had a very high speed DC motor that powered a small centrifugal blower that actually did blast the bottom of the plug with what looked like grit. And it did clean the ceramic insulators in the plugs.
It was very important to blow all of the grit out after cleaning the plugs. Unfortunately the abrasive material took a serious toll on the mechanism and the thing wore out. And I have not seen another one at any auto parts store locally.

 

I've been looking at both voltage boosters and old Model T buzz coils. So you guys were right about time: too much time and things overheat, too little time and not enough energy is stored up by the fields and/or capacitor. I've gotten rid of the electric motor as a switch/timer as it will likely be too slow, in favor of the buzz points like are used on the buzz coil.

I found a nice article about the principals behind an operating buzz coil:
Know your Coils - A Guide to Restoration and Adjustment of Model T Ford Ignition Coils.

I've also discovered a few goodies around the web.

Word is that the charge (Q) needed to send a spark across 1mm of air is 3.34 Coulombs.
I'm also seeing that buzz coil points operate at around 300-500 times per second, depending on who you ask. I think that speed may be a function of how much gap there is between the points when they're open?

Normal air has a resistivity of 10^16 Ω*m depending on who you ask. Apparently, it's quite variable. Across a 1mm air gap, that would be 10,000,000MΩ, so at 4kV, the current would be 0.0000000000004mA. Are these numbers correct? They seem a bit extreme to me.

Another thing is that the capacitor needs to have a high dV/dT rating that most capacitors don't meet. Greater than 550 dV/dT. This severely limits the type and capacitance of capacitors available to use. I may be able to get away with a smaller dV/dT once I know the dV part. At 300Hz, dT would be about 0.004 seconds.

The closest thing with math that I've found so far that is close to an ignition coil is a flyback boost converter in discontinuous current mode, except there is no diode or capacitor on the output side. And the output resistance comes from the spark plug air gap. I found this video which seems to describe things pretty nicely:

Though I only understand about 25% of it so far.

 

Why is generating a spark so very important?? The shunt resistance is what dampens a spark, taking energy away fro the spark heat that ignites the fuel/air mix. A simple push button and spark coil can produce a spark.

 

@rebelrider.mike,

Take a look to these links,
may be some information in them will helpful for you:

https://forum.allaboutcircuits.com/threads/600v-dc-from-12v-dc-source.179704/post-1646715

https://forum.allaboutcircuits.com/...for-ignition-coil-project.191664/post-1796069

 

Ok, I think I've wrapped my brain around this a little more.

You have wound transformers before, and you have the correct formula, but this is not a transformer, it is an inductor with two winding. Subtle, some would say pedantic, difference. A transformer transfers energy from primary to secondary: it stores (in theory) no energy. An inductor stores energy for one part of the cycle (points closed) then releases it through to the spark plug. The energy is stored in the air gap. In an ignition coil, it might not be obvious where the air gap actually is, but it goes all the way from one end of the core back to the other end.

The magic seems to happen when the points open, and the magnetic field in the iron core collapses. This sends voltage in both directions, that is, backwards through the primary coil (flyback), and forwards through the secondary coil. The current will prefer the easiest path, which would be split between the primary, making a spark across the points, and the secondary, making a spark across the spark plug. Each spark would get about half the power(?) making the sparks relatively weak.

Except there's a capacitor on the primary side that slows things down by... doing its magic capacitor thing.

The capacitor absorbs the coil current initially as the points open, slowing down the voltage rise, so by the time the voltage increases to the sparking voltage, the points are too far open to create an arc.

So that makes the majority of current head through the secondary instead. Then the primary and secondary coils both produce a voltage dependent on the energy stored in the magnetic field rather than relative to each other.

You all have been telling me this the whole time, but I think I've only just now got it. At least I really hope so. I'm also intrigued by the possibility of simulating an ignition coil in LT-spice. I'm terrible at using that program, but maybe I'll take a crack at it.

I've drawn a couple diagrams of my interpretation of how the buzz coil, and distributor type ignition coils work:





These are of course, based on diagrams I found online, but I've tried to understand why each part and wire goes where, rather than just making copies.

I'm curious as to why there are two secondary coils on the buzz coil. I've heard they're connected in series, so effectively, they act like a single coil. Was it just easier to manufacture that way?

I've bought a few materials, and hopefully I'll be doing some practical tinkering over the next few days.

 

Except there's a capacitor on the primary side that slows things down by... doing its magic capacitor thing.
So that makes the majority of current head through the secondary instead.

With the proper size capacitor essentially all the current/energy goes to the spark through the secondary.

Then the primary and secondary coils both produce a voltage dependent on the energy stored in the magnetic field rather than relative to each other.

But the primary and secondary voltages are related by the turns ratio, which is typically 100:1 for the old single ignition coils.
So if you have 20kvolts on across the spark gap, for example, you would have 200V across the point gap.

 

Why does your 2nd dwg show the HV traversing through the distributor.?
A modern coil has isolated secondary BTW.
Also BTW the second illustration is all wrong
Coil common!!! ??

(Condenser! I mean capacitor should be across the points}

 

Why does your 2nd dwg show the HV traversing through the distributor.?

Because in the old single-coil system it does.

Coil common!!! ??

Through the points!!!

 

One reason I use the modern waste spark versions now for projects , I prefer the LV-HV isolation!

 

As far as I can see, the second drawing is wired like the ones I've seen around the internet. Both drawings have a capacitor across the points.

I got my iron rods today. I went to measure inductance with some wire wrapped around it, but my super cheap gadget keeps auto-sensing it as a resistor. I've ordered an LCR meter that I'll be able to set specifically for L. Should be here Friday.

My curiosity was piqued a few posts ago with the idea of simulating this stuff in LTspice. I'm actually quite terrible at using that program, so I decided to start with a simple boost converter. Here's what I've got so far:

 

Here's what I've got so far:

Always use actual device models (such as for the diode) in LTspice, as sometimes the generic ones give flaky results.

Also use the "Label Net" command to give the nodes of interest a name (e.g. Input, Output, etc.) as a plot labeled V(n001) doesn't tell us what's being plotted.

 

Actually, like shown in post #26, the high voltage returns thru the battery positive. The reason for that strange scheme has to do with the coil production process. Wind the coils, insert the core, then solder the leads to the posts. THEN insert it in the case, fill with the oil, and either crimp closed or press on the retainer and weld it. Grounding any windings to the case would add cost.

 

@rebelrider.mike

The primary winding of an ignition coil will typically contain 150 to 300 turns of wire;
the secondary winding will typically contain 15,000 to 30,000 turns of wire,
or around 100 times more than the primary winding.

 

There you have the picture of why there is no "ground" connection to the housing of the coil!

 

That and buzz coil housings are wood, and modern coil housings are plastic, aren't they? Only the distributor type housings are metal. I saw a couple of YouTubers get surprised when they cut open the can and found that a bunch of oil came out! I would have been surprised too, but it makes sense. Big transformers are kept under oil too for the same reasons.

While I wait for the LCR meter, I may play around with the electromagnetic properties of the coil. Its got 70 turns on it, so it should make an ok electromagnet. Maybe I'll get some real numbers I can play around with.

I had to google both how to do net labeling and how to find a non-generic diode in LTspice. But I got it figured. Here is the latest boost converter simulation:

 

I saw a couple of YouTubers get surprised when they cut open the can and found that a bunch of oil came out! I would have been surprised too, but it makes sense. Big transformers are kept under oil too for the same reasons.

Also some induction motors run oil-filled, e.g. my basement sump pump for one!

 

Oil filling for both cooling and insulation makes the most sense. It will not crack from temperature cycling or vibration, and it is much simpler to do an adequate fill with oil. I did see a tar filled (and failed) ignition coil once, back in about 1955, I think. It also had a plastic case( might have been bakelite.) I am not sure that I have ever seen a failed oil filled ignition spark coil. I suppose it could happen, though.
I am thinking that the change to multiple coils was a cost reduction to get rid of the rotary distributor. Consider that dragster engines still use distributors, though. Evidently performance is more important than cost reduction for some applications.

 

the change to multiple coils was a cost reduction to get rid of the rotary distributor.

Yes, getting rid of the mechanical distributor along with its shaft and gears, as well as the long spark plug wires is likely a significant cost savings.

Consider that dragster engines still use distributors, though. Evidently performance is more important than cost reduction for some applications.

I think that's simply because dragster engines are old V8 designs that have distributors.
I don't see any reason a distributor would give better performance than individual coils for each plug or plug pair, and some reasons that it would be worse, but it's apparently adequate for dragster engine operation.

 

OK, a lot of comments made and not a single one asked just what the tester is supposed to prove about the plug under test. It will not measure leakage, it will not display breakdown voltage to arc and it certainly will not tell the condition of the series resistor in the core of the ceramic insulator.
A quite useful test of spark plugs can be done with the plugs still installed in the engine. The device to do the test may be as simple as a good VOM (Volts& Ohms Meter)You will need to disconnect the high voltage cable and clip the red meter lead to the connection on top of the spark plug. THEN you will need to connect the other meter lead to a solid connection to the engine block. Set the meter to the highest working resistance range, it should show an open circuit. A plug that is "bad" will show resistance, possibly several kilohms, maybe more. THAT tells you that it is not firing correctly. Now you need to check the resistance of the wire to the spark plug. For cars with distributors that is a two step check. With the ohm meter lead still connected to the engine block, check the resistance to the end of the lead that was on the spark plug. It should read open. If not, then there is a leakage path in the distributor cap. Then unplug the other end from the distributor cap, and connect the other meter clip to that end. The resistance should be just a few ohms if the wires are not resistor types, or several kilohms if they are resistor wires/

Yes, thanks for stating that, I wonder what exactly can be measured that lets us detect a difference between a working and a failed or failing, spark plug.

I'd imagine knowing the voltage that is necessary to make it spark would be helpful as well as any leakage/resistance as that voltage rises.