Why does a coil have a polarity marked on the primary circuit? Does it matter if it is reversed?
Why does a coil have a polarity marked on the primary circuit? Does it matter if it is reversed?
THe short answer is yes according to the old ideas.
The older coils are wired as "auto-transformer" with the HT earthed direct to the body as the negative. So if it is wired backwards there is a significent reduction in the available voltage on the HT wiring side. The plugs also fire easier with the correct polarity on the side electrode. With points ignition every thing counts.
However that does not apply to later electronically driven coils as far as I know. And indeed waste spark coils fire one plug foward and the other reversed But the available voltage is now much higher than the points ignitions dreamed of.
An ignition coil consists of two windings. A primary winding , the 12vdc winding and the secondary winding, high voltage (several kilovolt) winding.
The two windings are connected together at a common point, the notional "positive" terminal.
The other end of the primary is connected to the to the notional "negative" terminal and the other end of secondary winding connected to high voltage turret.
See the diagram attached.
You will have no problem using the coil in a positive earth vehicle.
However to be technically correct always connect the +ve coil terminal the 12v ignition supply and the negative terminal of the coil and the points to -ve terminal. Reverse of what is indicated on the coil terminals in the case of +ve earth vehicles.
FWIW it probably won't make a rat's of difference if connect in reverse. It nice to consider the technicalities 'tho
A Kettering ignition coil is NOT an auto transformer. It has two separate winding neither of which are "tapped", simply connected together at a common point.
I quote from the Automotive Handbook by Bosch. 4th edition 1996
page 436 under the Ignition chapter;
"Battery-ignition systems generally enploy an ignition coil ----this coil functions as an autotransformer," ----.
---"because lower breakdown voltages are required for the negative (relative to engine ground) ignition spark, the positive terminals are generally combined on those ignition coils used with rotating distribution."
The Kettering ignition coil is not an auto transformer. I suspect the quote suffers in the translation, because the statement "functions like" it is not stated that it "is" an auto transformer. If "step up transformer" was subtituted for "auto transformer" in the above quote it would make sense.
An auto transformer has single winding. Wound in same direction on a single iron core. Auto transformers are employed to reduce/ increase voltages over a relatively small range. In most cases the step up /step down ratio is less that 100%.
An ignition coil has two separate and distinct windings this alone proves it is not a auto transformer. It also has a very voltage high step up ratio which is an unsuitable application for an auto transformer.
Here are examples of auto transformers.
Last edited by robmac; 30th April 2013 at 11:59 AM.
Well the fact that you choose to not believe it does not make it true or false However 'The Bible' of automotive technology will suffice for me. Actually it is written and published in English (and possibly other languages). Has input from the whole automotive trade. I also have some other auto electrical books from the good old days that I could dig out but why bother. I have always understood it to work as the Bible says.
Some comments that may be relevant or not, depending on your biasses.
The construction of these coils may not resemble a 'normal' electronic or electrical transformer, but that does not mean it cannot function as an autotransformer. Ditto for the step up ratio. Ditto for the actual construction of the windings.
If you redraw the circuit with one winding above the other, The HT output at the top, the + terminal as the tapping and the - terminal at the bottom, then it sure looks like an autotransformer winding diagram. EG the autotransformer diagram, stepup voltage, halfway down the Wikipedia article.
However if you choose to take a narrow look then that's your problem.
Last edited by jaahn; 30th April 2013 at 02:52 PM. Reason: trying to add diagram but failing !!
As in many cases of "religious" matters the beholders refuse to accept any discussions which are outside the bible.
Especially those who don't hold qualifications to recognize the error.
So it is pointless to discuss the matter with one of closed mind.
Just keep believing the Bosch gospel in blind faith.
One of you has been praying to the false prophet. When choosing a prophet, it's important you choose one that you believe in. Then it's just a matter of perception and reality.
'92 205 Mi16
The answers are quite clear.
I said that according to the old ideas YES
Robmac says "FWIW it probably won't make a rat's--"
Your choice as to who to pray to/with
I hope this has been helpfull for you.
From a 'religious nut' who doesn't "hold qualifications to recognize the error"
Last edited by jaahn; 30th April 2013 at 09:00 PM. Reason: corrections
you know, I reckon you could have had a brilliant career as a diplomat, Roger...
Apologies for an unkind quip.
But please do me th courtesy of considering the following difference between an auto transformer and a normal twin winding transformer.
" In an auto transformer portions of the same winding act as both the primary and secondary." "An auto transformer has single winding." These conditions need to met without making any external connections to the transformer windings.
I will concede that an ignition coil is connected (ie a common point of both primary & secondary) to become a kind of auto transformer.
But because a coil is manufactured with two separate windings, in different locations on the iron core by definition it not an auto transformer, just a plain double wound transformer. With windings connected together.
I still believe the passage from Bosch Bible is far from literal English.
I was not being intentionally anal, but when I went to school there was a clear and district engineering reason why an ignition coil in not an auto transformer. I felt it was appropriate to point that out.
If have any friends who are electrical engineers please ask them to confirm or refute my claim.
Frankly I'm happy to drop the matter completely rather have further discussions .
Last edited by robmac; 1st May 2013 at 10:17 AM.
My father found the 2cv coil was hooked up backwards.... so either I plugged the wiring on backward (or the coil 180degrees out), or it was wired backwards from the factory. It appeared to make bugger all difference when put right
'85 Series II CX2500 GTi Turbo I
'63 ID19 http://www.aussiefrogs.com/forum/showthread.php?t=90325
'72 DS21 ie 5spd pallas (last looked at ... about 15years ago)
'78 GS1220 pallas
'92 Range Rover Classic ... 5spd manual.
Yay ... No Slugomatics
'07 Poogoe 407 HDi 6spd manual
seemed to recall from the distant past that it was important to get the coil the right way round, why..... ? When all else fails, read the book
So, according to Messrs Dales & Thiessen, "Automotive electronics & engine performance", way back in 1984.....
"An ignition coil is a pulse transformer that steps up the low voltage from the battery or generator to a voltage high enough to ionise (electrically charge) the spark plug gap and ignite the air/fuel mixture in the cylinder. A typical coil is made up of a primary winding consisting of a few hundred turns of relatively large wire and a secondary winding consisting of many thousand turns of very small wire. These windings are insulated and assembled over a soft, iron core and are enclosed by a soft iron shell. This assembly is inserted into a one-piece steel or die cast aluminium coil case, which is filled with oil and hermetically sealed by a coil cap made of moulded insulating material The cap contains the primary and secondary high voltage terminals.
Ignition coils are hermetically sealed to prevent the entrance of moisture, which would cause coil failure. During manufacture, the coil case is filled with oil at a high temperature. As the oil temperature decreases to more nearly match the temperature of the surrounding air, the oil contracts to occupy less volume, thus allowing room for expansion when the coil heats up during normal operation. The oil acts as an insulator to prevent high voltage arc-over within the coil.
Some coil designs are not encased in a metal housing. Instead of being filled with oil, this type is potted in plastic and has external laminations much like a transformer. The coil has the usual two primary connections (labelled + and —) and one secondary connection which has a male terminal similar to the distributor cap terminals. This coil has a very low primary resistance and is used without a ballast resistor. A "current control" circuit was added to the ignition module which eliminated the need for ballast resistors.
The ignition coil is connected in series between the resistor and distributor assemblies. The function of the coil is to induce in its secondary windings the voltage required to cause a spark at the spark plug gap. The primary terminal posts of the coil are marked BAT. and DIST. or positive (battery) and negative (distributor), + or —. This ensures correct plug polarity (centre electrode negative). Negative plug polarity requires less voltage to jump the spark plug gap. Electricity will jump from the hot centre electrode to the cooler ground electrode more easily than it will the opposite way. If primary ignition wires are incorrectly hooked up to the coil, the coil will have reverse polarity, resulting in poor performance and a high-speed miss.
Secondary Voltage Requirements:
Voltage in the coil secondary increases until the voltage at the spark plug becomes so high that the plug gap breaks down and is ionised, and part of the secondary energy is dissipated in the form of an arc which ignites the air/fuel mixture.
The voltage required to fire a spark plug depends on many factors such as engine compression ratio, engine speeds, fuel mixture ratios, spark plug temperatures, the width and shape of spark plug gaps, and many other factors. Actual voltage produced by the secondary system is determined by the requirement of the spark plug.
Used plugs may require as much as 5000 volts more to fire than new plugs, due to the increase in plug gap and the rounding of the centre electrode that occurs with usage. Cleaning the plug, filing the electrodes flat, and readjusting the gap will lower the voltage requirement to approximately that of a new plug, as long as the plug is not otherwise defective.
The maximum voltage requirement occurs at acceleration at low speeds. A "missing" condition is usually first noticed under these conditions, where the voltage requirement first exceeds the maximum available voltage. The margin of voltage which can be produced above that required to fire the spark plugs represents the electrical reserve built into the ignition system.
Since electrons flow more readily from a hot surface than a cold one, the spark gap ionises more readily from the centre electrode, which, is the hottest part of the spark plug. Thus, a spark plug with a negative polarity at the centre electrode requires much less voltage to fire than one with a positive polarity at the centre electrode.
The coil is wound to provide a negative polarity voltage at the spark plug centre electrode when it is properly connected, regardless of battery ground polarity."
Also seem to recall, that incorrect connections showed up on the 'scope as an inverted pattern and that the primary connection "+" & "-" markings are not to be trusted - particularly in days of yore when we had both +ve and -ve earthed cars around and the markings may have been arranged to suit a particular vehicle.
Thanks for that apology. Not really necessary but appreciated never the less.
I would say that my initial reply was a bit sloppy technically as I wrote it from memory (suspect), and even a bit muddled. However the answer, yes, is correct as this was believed correct in pre-electronic ignition days. As Bob pointed out also, from his text book.
I accept that an ignition coil is not like any autotransformer. Perhaps it only acts like one because of the unique manner of its operation. The coil "fires" only on switching off the current. At that point it dumps the stored magnetic energy into the HT winding. It does not work like a conventional transformer on a regular waveform input. The turns ratio is only about 100/1, so in normal terms it would only generate say 1400V. We know that it gives more than 10x-15x this voltage !
I am happy to let it rest too.
Just consulted one of my library of automotive books, "Electricity for Motor Mechanics" (primarily designed as a textbook for apprentice motor mechanics) Tis written and prepared for publication by The New Zealand Technical Correspondence Institute. second edition published 1971, and at that "target level" seems to practically cover the subject.
But then if you can understand all the references above, my intepretation of Chapter 5 of this book (ignition systems) might just add to the puzzle, though I find it very handy and practical reference to refresh ones aging/fading knowledge on the subject.
Amazin how many people can describe the same things, but with slightly different emphasis..
After some reflection on the reversed coil polarity scenario.
If the coil connections are reversed the only difference is that the primary winding of the coil will be in series with the secondary, ie the +ve end of the HT secondary will return to +ve via the primary winding.
Since the primary winding resistance is a few ohms compared to several thousand ohms for the secondary the voltage drop across the additional, in series, primary winding will negligible. The not so nice factor is that the 12volt primary may a higher than rated voltage applied. But modern coils are oil filled and well insulated.
I'm tipping it will make no practical difference at all.
The caveat is we are talking Kettering ignition, not electronic systems.
My car has each of the two bosch '008 igniters running two single ended coils wired together.
I'm not bright enough with electrickery to work out what thats all about, but everything I read on the net says dont wire it like that, without me understanding why not and what to expect.
I'd be keen to hear what you guys think of the setup
Yes I was talking about double ended coils firing one plug foward and the other reverse. This is because the spark flow goes 'out' one end and returns 'back' through the other to complete the electrical circuit, as must happen for current to flow
What I understand you to be saying about your setup is; you have two 008 ignitors and each one is firing two single ended coils. Total of 4 coils for your 4 cyl engine. So the ignitors have to switch the current for two coils each time they fire. Correct
I would think that the current draw for the two coils would be higher than the 008 would be normally rated for. This means they may run much hotter than designed for. Depends on the coils used also. The older points type coils are higher impedance('resistance') so draw less current. The electronic types are lower impedance so they draw more current for a better spark. Some 'performance' coils draw even more, for even more spark.
If it works ok then who's to question it I guess the matching of components is important in electrickery so the smoke does not come out Double ended coils are considered the normal in your case and so may be a better bet. The web is certainly a good source of solutions to mix an match car problems. But sometimes fashions rule more than thinking
Whether it works (and keeps on working) depends on the primary resistance of the coils. If they're a relatively less modern coil with a primary resistance of say 0.8Ω, then all might be well. The nett resistance would be 0.4Ω. But two high current modern coils of say 0.4Ω in parallel, would be effectively 0.2Ω and push the current beyond the limits of the '008 ignitor.
I wire the LS1/LS2 coils in parallel for wasted spark applications, but they have internal ignitors. Thus I'm not wiring the primary side of coils in parallel.
'92 205 Mi16
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