Talk:Ignition system

Please use decent references

The references were removed before because they are blogs or do not support the claim. Supplying many poor quality references does not improve the source for a claim. Books that cannot be found in WorldCat or books whose focus is incidental are also inappropriate.

The purpose of the capacitor is to limit dv/dt across the switch contacts while they open. That's in Ott, cited above. The voltage must be kept below about 10 V (V_A) to prevent an arc occurring while the contacts separate at microscopic distances. Consider 10 V across a distance of 1 micrometer is a field of 10 MV/m. Furthermore, the voltage must be held to less than 300 V while the contacts are separated at the minimum of Paschen's law. If the voltage is too high, then the air breaks down, there's a glow discharge that allows some current to flow, that current then increases into a low-voltage arc discharge. The arc discharge would limit the primary voltage to a small value; the secondary voltage would also be limited by the transformer action. The simple way to achieve that goal is to have 300 V * N exceed the spark plug breakdown voltage.

Now, the addition of capacitor also happens to cause a resonance, but that is not a design goal in the automobile ignition system. A resonance is exploited in exotic induction coils, but that is not the case here. That is also mentioned in the above discussion. That resonance is prevalent if there is no spark (that's what the Harvard lab notes talk about; also phaco fig. 8). In functioning ignition systems, the resonances that are seen are due to leakage inductance. (phaco p. 15.) The resonances are on top of the magnetizing inductance; phaco points out that the resonance never interrupts the spark current. (phaco p. 15.) The resonance is not a design goal; it is not a design goal.

The article's statement ("As a result of this resonance the duration of the spark is sustained and so implements a good flame front in the air/fuel mixture") is unsourced and just wrong. The spark is maintained by the magnetizing inductance; the linear decay of is clearly visible during the later portions of the spark in phaco figure 9, middle trace, spark current from E to F. If the "resonance" is sustaining the spark, then why is the spark still going when the resonance has decayed away?

Glrx (talk) 18:12, 24 October 2016 (UTC)

You are the only person who seems determined that resonance has nothing to do with it. As such you are also keen to dismiss two references that discuss the subject as 'incidental' plus others that specifically mention the point (though large numbers of references saying the same thing are pointless). The resonance angle is too well referenced, to be ignored. The fact that you cannot find the books does not preclude them. WP:AGF says that you have to accept them, especially as they appear to specifically discuss the subject. I cannot locate them either (but they seem to be old books, so this may be why), but in the absence of any indications to the contrary, I have to accept them. 148.252.128.92 (talk) 16:33, 28 October 2016 (UTC)

STOP PRESS: Although my local library does not have copies of either book, they have just phoned me to say that they have located a copy of the Williamson book and are getting it for me (so at least it exists). 148.252.128.92 (talk) 16:47, 28 October 2016 (UTC)

@Glrx: Thank you for your patience during these prolonged and sometimes repetitive discussions. If nobody is able to satisfy the WP:BURDEN of providing citations that directly support the disputed material, I support its removal. Burninthruthesky (talk) 16:29, 31 October 2016 (UTC)

Rejecting a citation because you have not seen it is a violation of WP:SOURCEACCESS in the Verifiablity policy. The AGF policy does require that if one editor asserts that an offline source supports a fact, we must all accept it unless we hve seen it with our own eyes. Editors might agree that there are multiple other sources that contradict the offline source, but those other sources would have to be cited by you. If you have nothing to contradict Williamson and the Emerson citations, then you don't have any reason to reject it, and WP:BURDEN has been met. You can't tag a source as "fails verification" if you haven't seen it yourself.

Besides citing additional sources, if you can't find the two books in your local library, go to Wikipedia:WikiProject Resource Exchange/Resource Request and reuest another editor find it and check it for you, or ask their advice on tracking the book down. There's lots of assistance for settling something like this. --Dennis Bratland (talk) 17:18, 31 October 2016 (UTC)

@Dennis Bratland: Have you read and understood the material above? There are citations that contradict the claim.

See this delta whose before contains a cite about the single purpose of the capacitor and whose after is the vague claim about resonance.

The references that I have used cite to the purpose of the capacitor. The break arc must be suppressed; that is a French invention; Taylor states the purpose. Ott discusses contact arcing in both the resistive and inductive cases. Ott discusses a hybrid contact breakdown model the combines both short-arc and gas breakdown. He draws a graph that shows the breakdown characteristic as a function of contact separation distance from submicron to mm distances. He then redraws the x-axis to be time (integrate contact opening speed to get contact separation). He then describes using a capacitor to prevent short arc breakdown. The switch, before it opened, was feeding a constant current (I) through an inductor. Putting a capacitor across the switch limits the rate the voltage can rise (dV/dt) to the current divided by the capacitance (I/C). Use a large enough capacitance, and the contact voltage will stay below the breakdown portion of the curve.

Under normal operating conditions, that's all that the capacitor needs to do. Nothing is said about resonance. There can be another purpose of the capacitor: limiting the peak voltage across the contacts if the spark plugs are disconnected. In that scenario, one notices that the energy stored in the magnetizing inductance (0.5 L I²) will be shifted to the capacitance (0.5 C V²). Consequently, choose C to be large enough to store at least all the inductor's energy at the maximum desired V; conservation of energy does the rest. The issue is not resonance: there's no compelling reason to choose a particular resonant frequency. It's just recognizing that the inductor and capacitor will transfer energy back and forth. And it is irrelevant to the normal operation of the ignition system because the spark plugs must breakdown before reaching that maximum voltage -- otherwise they will never fire.

Leakage inductance introduces a much more subtle issue. The worldphaco source is good on that point but would be impenetrable to most readers.

Both Williamson and Emerson were cited without specifying publishers or dates. There were direct requests for that information. That is not a SOURCEACCESS issue but rather a source identification issue. I don't care about an isbn; I have plenty of books that don't have an isbn. Williamson is quoted, but the quotation shows Williamson does not understand what is going on. Williamson claims the energy "discharges into the condenser"; the energy is discharged into the spark gap. Emerson's quotation only states a resonant circuit is formed. Nobody disputes there's a resonant circuit. Hobbyist can see an L and a C and conclude there's a resonant circuit. The issue is what is the purpose of the capacitor. The reliable sources do not say it is to form a resonant circuit. It's to prevent an arc on the primary side so the spark will happen on the secondary side.

Glrx (talk) 18:50, 31 October 2016 (UTC)

Have it your way. There are easier ways to resolve this kind of content dispute, and resources are available to help you. You should not say a source fails verification based only on a short quote. If you haven't seen the book, you don't know. I've learned to not use quotes at all in my citations; without the complete context, quotes merely fuel debate rather than put it to rest. --Dennis Bratland (talk) 19:27, 31 October 2016 (UTC)

The AGF policy requires no such thing. Direct quotations of the relevant sources were duly volunteered in accordance with WP:VER. On that basis, the {{Fails verification}} tag in the article is absolutely correct. Burninthruthesky (talk) 10:22, 1 November 2016 (UTC)

What are you on about? The sources given directly discuss the resonance. Thus the 'failed verification' is not appropriate given that it has been verified (see next para).

I picked up the Williamson reference from my library this morning. The quoted passage appears om page 55 (not 54) in this copy, but it is the third edition so may have moved in a revision. This third edition was published in 1953 and appears to be a college text book written for the days when people actually repaired the electrical parts in your car rather than just swapped the entire assembly for a new one.

It is lost in the article history who originally wrote the paragraph, but given the discussion and that the paragraph is not attempting to document the modus operandi, has anyone considered some compromise wording? Since the resonance is double referenced, It can be mentioned along with what it does (cited by Williamson and one other ref). The point about sustaining the spark is unreferenced and can be deleted until a reference is found. The point about minimising arcing at the contact breaker is mentioned in Williamson, so I have added that as a cite, but deleted the one point not mentioned. 185.69.145.139 (talk) 17:01, 2 November 2016 (UTC)

Who is the publisher for Williamson? I want to be able to find it in WorldCat or similar index. The publisher suggests the stature of the work. Something published by Cambridge University Press / McGraw-Hill / John Wiley carries more weight than Haynes / Howard W. Sams.

You state that the book is about auto repair. "An engineer's guide to vehicle electrical systems" implies a reference work about designing electrical systems. A book about repairing such systems is much different: an auto repair guide must know how to fix systems but need not know the details about how they work. The quotation shows that Williamson is either careless in his explanation or confused.

If this "resonance" is important, there must be some reference that explains why the resonance is important. Thank you for deleting the sentences about the resonance sustaining the spark and implementing a good flame front because it failed your verification. But where is the design rationale behind the resonance?

Where do you see a compromise? Do a capacitor and an inductor form a resonant circuit? Yes. Is that the purpose of the capacitor across the points? No. Furthermore, which capacitance and inductance are we talking about? The secondary has a lot of stray capacitance: EF's worldphaco ref says 50 pF; refer that to the primary and it becomes 85² × 50 pF = -0.3 μF -- which is comparable to the 0.22 μF capacitor that is across the points. Also, which inductance are we talking about? If there's no spark, then the magnetizing inductance dominates; if there is a spark, it essentially shorts out the magnetizing inductance and leakage inductances are more prevalent. See worldphaco around page 11, "expected resonances"; one resonance is 2 kHz; another is 7 kHz. Does Williamson address leakage inductance?

The paragraph you edited is full of technical nonsense. WP cannot rely on sources such as MGAguru's personal website. I do not see Williamson as a reliable source for the design of ignition systems; the given quotation indicts his reliability.

I've provided sourced content that disagrees with the WP text. Taylor-Jones is old but reliable; T-J built a 250 kV induction coil back in the day, so he should know a thing or two about using inductors and transformers to generate sparks. Ott is a recognized source on contacts, Ott comes from Bell Telephone Labs, and the publisher is John Wiley.

This subject is not simple.

Glrx (talk) 19:31, 2 November 2016 (UTC)

That was partly my point for the way I CEed the section. Williamson and Emerson and others all mention the fact that the coil and 'condenser' (capacitor) are in parallel and thus form a parallel resonant circuit. Thus the point is cited (and indeed true) and can be included in the article. There is a cite already in the article for a claim about energy repeatedly being transferred to the secondary until exhausted that has been there for some time (so that stayed). But if the source is unreliable (you suggest it is WP:SELFPUBLISHed), then delete the claim and allow someone else to find a source.

For the two works (and many other sources) even to mention the resonance implies that it is important. However, Williamson does not expand the overall effect it has on the circuit operation and only leaves the implication (I have no idea what Emerson says beyond the quote). Therefore without any references as to that effect, the claim about sustaining the spark and extending its duration has to go unless a supporting reference can be found.

Unfortunately, having no further need for Williamson, I returned it to the library and failed to note who the publisher was before I did so. As I said: the book was clearly aimed at motor engineers perhaps a cut above your average garage mechanic. It did have quite a bit of technical detail on how the more complex parts of a vehicle's electrical system (battery, dynamo, starter motor, charging regulator etc. etc.) actually worked but without going into the sort of theory that a proper electrical engineering textbook might. It looked as though it was written by a lecturer on the subject as a course text book.

The library informed me that the only place they have found Emerson is the copy that is in the British Library, which they (or anyone else) are unable to borrow. Going there is just impracticable and I don't have the time.

The compromise was including all that was cited and removing that which was not. A capacitor and a coil in parallel (including capacitance and inductance elsewhere in the circuit but appears in the primary circuit) unconditionally forms a resonant circuit. This would remain true even if you were to find a way of totally 100% damping the oscillation somehow (not possible in practice). The resonant part of the circuit must still produce some resonance as there has to be something present for the damping to damp. If the oscillation were totally eliminated, the damping would have no effect allowing some oscillation to occur.

As I see it: the contention here is if this resonance is important to the operation of this specific circuit? This is what is not adequately supported by reference. Opinion seems divided. You seem to believe it doesn't, others seem to think it does. I have no idea, but it does somehow seem logical. A cite either way is required. Yoy state that you have provided such a cite. Where? What cite have you provided that specifically states that resonance has no part to play in the operation of the circuit? 148.252.129.151 (talk) 14:45, 8 November 2016 (UTC)

Thanks for the comments.

You won't find references saying that "resonance has no part to play". That's not how relationships are described. Just like you won't find a reference that says elephants do not get to vote in US elections. You should be able to find references that say what the purpose of a component is. I don't want a reference that simply says the "sky is blue" (there is a resonance); I want a reference that describes the sky is blue due to short wavelength (e.g., blue) light being scattered and long wavelength (e.g., red) light not being scattered.

Here's my ref that got deleted:

Under the Rayleigh theory, "the only use of the primary condensor is to check the formation of an arc at the interrupter". (Taylor-Jones 1921, p. 17) (emphasis added)

• Taylor-Jones, E. (1921). The Theory of the Induction Coil. Pitman & Sons. {{cite book}}: Invalid |ref=harv (help)

Taylor-Jones does not say the purpose (or the secondary purpose) of the capacitor in the Rayleigh is to form a resonance. Taylor-Jones does explain that the capacitor is a disadvantage in the Rayleigh theory. Lord Rayleigh got a much better spark when he did not use the capacitor but rather used a rifle bullet to interrupt the primary current (create a large physical gap and blow out any arc while you're at it). Rayleigh and others understood that the energy storage characteristics of inductors and capacitors will set a maximum voltage, but there is no preference for choosing a particular resonant frequency (other than lower capacitance allows higher voltages for the same energy). If you cannot use rifle bullets, then you must use a capacitor. Furthermore, Taylor-Jones knows to discuss when resonance is important because he has a much more exotic induction coil theory that resonates the primary to 3 times the secondary resonance to achieve an in-phase voltage addition at the secondary (Taylor-Jones 1921, p. 38); T-J shows how to exploit resonance to maximize output voltage. (That is not a concern in an automobile ignition system; it is not seeking a world record spark.)

Ott describes the purpose of the capacitor is to keep the voltage across the contacts below their breakdown voltage. "if a discrete capacitor is placed in parallel with [the contacts], the peak voltage and the initial rate of rise of contact voltage can be reduced to the point where no arcing occurs." (Ott pp. 184-185.) The capacitor is not going for a resonance but rather reducing the rate the voltage rises across the contacts and the maximum voltage. The purpose is not to create resonance but rather to suppress arcing.

Ott also describes that once an arc starts, it is a lot harder to stop it. A DC arc can be stopped by reducing the voltage below the arcing voltage (about 12 to 18 volts) or the current below the minimum current (about 400 mA to 700 mA but possibly 40 mA). (Ott p. 176.) That's will be difficult to do with a magnetizing inductance fluxed to 4 A.

Glrx (talk) 19:11, 8 November 2016 (UTC)

We have already established that Taylor-Jones is an unreliable source. That he does not mention resonance proves nothing. That many sources do must mean it is important otherwise, why would they bother? This has been discussed to death and I see no point in just repeating the points that you are reluctant to accept. I have not read your attempted technical explanations they are unreferenced (read: snow job). --Elektrik Fanne 14:07, 11 November 2016 (UTC)

• Note. Elektrik Fanne has been blocked indefinitely as a sockpuppet. Glrx (talk) 20:24, 17 December 2016 (UTC)

Merge proposal

It has been proposed to merge Ignition switch into this article (Ignition system).

• Oppose. Ignition system deals with igniting the fuel-air mixture in the cylinder. The ignition switch (aka starter switch) has other duties such as powering all electrical accessories and temporarily engaging the solenoid/starter. Glrx (talk) 19:52, 5 November 2016 (UTC)

Model T

This article needs a lot of work. I started fixing some stuff in one section, but then realized the material was incorrectly covered in the previous section. The Model T magneto is an alternator in today's terminology. The Model T didn't need to use rectifiers to make DC (which could recharge a storage battery) because the voltage peaks were synchronized for powering the induction coils. Glrx (talk) 18:33, 28 August 2017 (UTC)