Hypothetical Question

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K8MHZ said:
I beg to differ with you.

Ignition coils are DC transformers. The primary and secondary both have polarity. They can also tolerate the rated DC voltage indefinitely. Like when someone leaves the key on an older vehicle while the points are closed. ....
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Holy Faraday Batman. All these years we have been thinking transformers followed Faraday's Law and required a changing magnetic field. Now we find out that if we left the Batmobile key on, the coil will put out 10KV DC continuous. I'll call IEEE and have them start rewriting all the papers.

(Just screwing with you - I know you didn't say that)

K8 - I didn't think that interupted DC and kettering ignition systems have much to do with the discussion. But, that's okay - I'm good. And you did get the part right about how the spark happens when the points open. And your comment brings up a good point about the doorbell xfm when energized with DC could put up a good spark (on the primary side) when the circuit opens.

So, physics questions for the day.
How come there is no spark when the points close?
As for the polarity wearing out the plugs - How do waste spark systems work?​

Been maybe 40 years since I have goofed with a Kettering ignition. Good memories though. I remember my brother and I using a Lionel train transformer to drive an ignition coil and making a jacobs ladder. I'm not clear on why we didn't kill ourselves - or burn the garage down.

ice
 
K8MHZ said:
What is a waste spark system?
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The ones I've seen are on four cylinder engines. There are two double ended coils, each end connected to a spark plug. Each coil connects to two plugs in cylinders that fire 360 out (The pistons come up together, one on compression, one on exhaust) The other coil connects to the other two cylinders 180 out from the first two. The Hv spark from each coil goes through both plugs in series. The coil primaries can accept a pulse either direction.

As I understand (that's code for, "the physics eludes me") The negative going HV pulse produces a stronger spark than the positive pulse. So the trick is to pulse the coil the correct direction to put the negative pulse on the cylinder that is up on compression.

There is no distributor, just a crankshaft position sensor.

One I read about was a Ford SHO (I think) It has just one sensor. It first fires one cylinder a couple of times and if the engine doesn't catch, it switches over to the other cylinder. It keeps the timing set for which ever one fires the engine - till you shut is off.

The other one I know about is on a Lycoming IO-360. It has one fixed sensor and four magnets pressed into the ring gear. I have no idea how it picks out which one to fire - but it does - really well.

ice
 
I believe you only get the spark when the magnetic field is collapsing in the coil, or when the points open. When the points close the Flux is increasing and there would be no output until the points again open and allow the field to collapse again. Taken a step further, if you connected the 120 volt dc to the transformer there would be no output until the power was removed and then only if the primary of the transformer hadn't turned into smoke.

Bob
 
rlundsrud said:
I believe you only get the spark when the magnetic field is collapsing in the coil, or when the points open. When the points close the Flux is increasing and there would be no output until the points again open and allow the field to collapse again. ...
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That's close to my understanding (as of 50 years ago). When the points close, the magnetic field builds fairly slowly. According to Faraday, the induced voltage is porportional to the rate of change of the magnetic field. When the points open, the field collapses quickly - aided by K8's unmentioned component. Much higher voltage induced.

However this is a bit out of my area of expertice - I likely do not understand all I know on this subject.

ice
 
iceworm said:
The other one I know about is on a Lycoming IO-360. It has one fixed sensor and four magnets pressed into the ring gear. I have no idea how it picks out which one to fire - but it does - really well.

ice
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I have to disagree with you on the lycoming engine. Aircraft engines use a dual magneto system to provide redundancy, improve burn efficiency, and prevent knock. They also operate without any input from the airplanes electrical system which provides any extra level of safety as they continue to run in the event of a total electrical fsilure. They don't fire the plugs on the exhaust stroke like the waste ignition systems do.

Bob
 
rlundsrud said:
I have to disagree with you on the lycoming engine. Aircraft engines use a dual magneto system to provide redundancy, improve burn efficiency, and prevent knock. They also operate without any input from the airplanes electrical system which provides any extra level of safety as they continue to run in the event of a total electrical fsilure. They don't fire the plugs on the exhaust stroke like the waste ignition systems do.

Bob
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Oh the shame. Disagreed with twice in the same post. I'm slapping myself around the block - twice.:eek:hmy:

Bob - It's on an experimental - home built. One can do anything one wants - well, except the laws of God and Physics don't change. One still has to follow those. And, of course, the DAR has to agree it will fly.

The original ignition was a single drive, dual magneto. The other accessory case hole has the oil pump for the prop governor. The original mag was traded for a single drive, impulse coupled, single mag. That is now the backup. The primary ignition is now an aftermarket crank triggered electronic.

ice
 
iceworm said:
Even the big cross country DC 500kV lines use this principle. At the terminal, the DC drives an oscillator (probably called an inverter or converter - can't use the word "oscillator" when the transistors are bigger than a hockey puck). But they use 60hz. Then they send the current through a transformer to get to useable voltage levels.
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Most of the larger HVDC systems use SCRs (thyristors).
A converter at the sending end rectifies the AC utility supply to get the DC. At the receiving end the DC is inverted back to AC using a mains line-commutated inverter. Much like a regenerative (four quadrant) DC drive.
And the power frequency can be that which is used in the region - sending or receiving.
We, UK, have a few interconnectors to continental Europe. They are 50Hz both ends.
But there's one between two islands in Japan which is 50Hz one end and 60Hz at the other.
 
iceworm said:
Oh the shame. Disagreed with twice in the same post. I'm slapping myself around the block - twice.:eek:hmy:

Bob - It's on an experimental - home built. One can do anything one wants - well, except the laws of God and Physics don't change. One still has to follow those. And, of course, the DAR has to agree it will fly.

The original ignition was a single drive, dual magneto. The other accessory case hole has the oil pump for the prop governor. The original mag was traded for a single drive, impulse coupled, single mag. That is now the backup. The primary ignition is now an aftermarket crank triggered electronic.

ice
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Sorry I wasn't trying to DIS on you, (get it, DIS as in distributorless ignition system). I was just pointing out that the standard IO-360 wasn't a waste ignition system. I didn't mean to offend a fellow pilot.

Bob
 
rlundsrud said:
Sorry I wasn't trying to DIS on you, (get it, DIS as in distributorless ignition system). I was just pointing out that the standard IO-360 wasn't a waste ignition system. I didn't mean to offend a fellow pilot.

Bob
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Ah ... no.. I would not have got it - Still, good pun.

I'm fine - never was offended.

So, a pilot joke:
The two most dangerous words one can hear in the cockpit? ...... "Watch this":eek:

And if one is on the ground it's, "Hold my beer and watch this.":blink:

ice
 
120VDC

120VDC

mike_kilroy said:
Where would you get 120v DC?
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I had a 120VDC telemetry system on a surface water treatment plant.
It was used to readout tank levels back to the main control panel.
 
Harley used to make ignition systems that 'fired into a dead hole'. That meant one set of points for two cylinders and no distributor. You couldn't get the plug wires on wrong, either.

We used to have a 2 stroke 175 cc 2 cylinder Steyer-Daimler-Puch that only had one set of breakers for two cylinders. Both cylinders shared a single combustion chamber and acted like a single cylinder, but looked like a regular single cylinder with two exhaust pipes and only one spark plug.
 
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K8MHZ said:
...
Take a car coil, a 12 volt battery, a spark plug and a plug wire. Bond the threaded part of the plug to the case of the coil. Connect the positive lead of the battery to the + terminal of the coil. Touch the negative lead of the battery to the - terminal of the coil for a fraction of a second and then take it off. A spark will occur. About 10kV or more.
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I learned that theory testing transformer winding continuity with a flash light continuity tester. When you take the leads off, if you are still touching the winding leads
the single output pulse from the collapsing field can bite.
 
don_resqcapt19 said:
I learned that theory testing transformer winding continuity with a flash light continuity tester. When you take the leads off, if you are still touching the winding leads
the single output pulse from the collapsing field can bite.
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You can get that effect even with the low current of an analog ohmmeter. :)
 
Harley used to make ignition systems that 'fired into a dead hole'.

The old JD440 2 cyl engine with points/coil will run that way. Found that out one day when I was operating in heavy brush and the dizzy cap got knocked off, kept on running, never did find the rotor but the spark was HV enough to arc between center post and cyl leads. Only found the cap was off and rotor missing when I shut down and tried to restart.

What is very interesting in some of these threads is gaining an appreciation for how may miscomprehensions there are on how electrical 'stuff' works. Lots of accurate info but interspersed with some wild and crazy misconceptions about how 'stuff' works.
 
K8MHZ said:
One day while working at my auto electrical shop, I got nailed by the ignition on a 1980 Citation. I had been nailed many times, but this was like getting hit by a truck.
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Anyone who has engaged in shade tree mechanics on older cars has probably learned the hard way not to lean on a car with a running engine with your crotchal area in contact with the fender, and reach in and pull off a spark plug wire with your bare hand. It's like getting hit with TWO hammers several times in rapid succession. Most have done it, and most have done it only once.
 
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