ENERGY AMPLIFICATION

[synchro1]

Here's Imtotob's circuit schematic.

[Farmhand]

What about this:

>>  Stepped-up high voltage from not so high turns ratio.

An experimenter is interested in determining the approximate turns ratio of an automobile ignition coil. He impresses a small audio frequency sinewave on the primary terminals and uses an oscilloscope to measure the induced voltage in the secondary. As a result of this measurement technique, it is found that the voltage step-up is approximately 100. This does not appear reasonable because 100 times the 12 V of the automobile battery falls far short of the 15 000-30 000 V needed for firing spark plugs. What is the nature of the discrepancy? Although not commonly referred to as a 'flyback' transformer, the ignition coil develops its high secondary voltage in a similar manner to the flyback transformer in a television set. In both instances, the primary winding requires a waveform with a very high rate of voltage or current change. Such a waveform induces a high voltage counter EMF in the primary and it is this induced voltage which is stepped-up further in the secondary. Thus in an automobile ignition system, the abrupt cut-off of the applied 12 V induces a counter EMF in the primary with a peak amplitude of about 250-300 V. When this purposely-produced 'transient' is multiplied by a 100 to 1 step-up turns ratio, one obtains the 25 kV or so needed for reliable firing of the plugs. << - from Practical Transformer Handbook.

Hi Qwert, all ignition coils are not created equal, some have resistors in them, ignition coils are DC pulse transformers and do operate like a flyback but the transformation rate is higher than 1:100 I think, typically an ignition coils primary has a 240 to 500 nF capacitor, one end of the secondary is connected to either the ground or positive of the primary which makes it a circuit ground connected 1/4 wave device if at resonance. The primary capacitor allows a much greater delivery of energy to the primary and the primary voltage is more like 14 volts,  yes because of the use of a sine wave excitation the transformation ratio test is flawed. During the off time of the primary the magnetic field discharge would cause a steep rise in voltage. Ignition coils are similar to flybacks as they use a DC pulse input but they also employ capacitor across the primary.

Try an experiment to see the difference in voltage produced with a 50% DC pulse with and without the capacitor. Or even with AC sine wave excitation.

When the stored energy in the primary is discharged the resulting emf is forward and not counter, it is in the same direction as the applied emf. The counter emf is only present to oppose the charging of the coil and the discharging of the coil, counter emf is always opposing the emf and the discharge from a coil is forward emf.

The counter emf does nothing to induce voltage in the secondary. If the coil discharge was counter emf what would it be countering ? Counter emf only exists when there is emf to counter. the instant the applied emf is stopped the counter emf ceases to exist then when the coil discharges it produces emf which is then opposed by counter emf . A coil cannot discharge counter emf, it makes no sense.

Cheers

[Magluvin]

Hi Qwert, all ignition coils are not created equal, some have resistors in them, ignition coils are DC pulse transformers and do operate like a flyback but the transformation rate is higher than 1:100 I think, typically an ignition coils primary has a 240 to 500 nF capacitor, one end of the secondary is connected to either the ground or positive of the primary which makes it a circuit ground connected 1/4 wave device if at resonance. The primary capacitor allows a much greater delivery of energy to the primary and the primary voltage is more like 14 volts,  yes because of the use of a sine wave excitation the transformation ratio test is flawed. During the off time of the primary the magnetic field discharge would cause a steep rise in voltage. Ignition coils are similar to flybacks as they use a DC pulse input but they also employ capacitor across the primary.

Try an experiment to see the difference in voltage produced with a 50% DC pulse with and without the capacitor. Or even with AC sine wave excitation.

When the stored energy in the primary is discharged the resulting emf is forward and not counter, it is in the same direction as the applied emf. The counter emf is only present to oppose the charging of the coil and the discharging of the coil, counter emf is always opposing the emf and the discharge from a coil is forward emf.

The counter emf does nothing to induce voltage in the secondary. If the coil discharge was counter emf what would it be countering ? Counter emf only exists when there is emf to counter. the instant the applied emf is stopped the counter emf ceases to exist then when the coil discharges it produces emf which is then opposed by counter emf . A coil cannot discharge counter emf, it makes no sense.

Cheers

If we are talking about a standard points ignition, the cap is not really 'across' the primary.

12v from batt to the + of the coil primary
12- from batt to points(switch)
Other side of points switch to - of coil primary
Cap is connected across switch.

When the points are closed, the cap is shorted by the switch and not a working part of the circuit. The closed period is longer than the open period

When the switch opens, the coil field collapses (in both primary and HV coil) inducing currents in the coils

If the cap were not there, a lot of the collapse energy will be lost in a spark across the switch and no more activity, thus small spark on the output.

With the cap(empty from being shorted), the primary collapse will charge the cap(no spark at switch as the cap provides an alternate path), and then oscillation. Thus big long spark on the output.

When you carefully observe the output spark of a setup with and without the cap across the switch, without the cap, you will see 1 thin short spark. With the cap. big long, multiple sparks.  Like multi strands of wire in a bundle, compared to just 1 strand. Its actually visible. Try with sunglasses or some dark filter. Its not just ionization that makes the spark so thick, its multiple sparks that are not traveling the same path as the previous one. It all happens so fast it is like it is all happening at once. But each of the multiple spark strands happens with each phase of operation over time.

So in reallity, a standard ign system is a multiple spark ign of sorts. An MSD actually discharges a cap multiple times to the primary. No oscillation there, but the MSD produces high power in each of the multiple sparks during the timing period, where the standard IGN with oscillation gradually dies out from the initial start of the oscillation.

Mags

[Magluvin]

Oh, forgot, the oscillations of the cap and coil when the points are opened, go through the battery also, as it is part of the series circuit inline with the cap and coil. Not that it means anything, but is a fact.

Mags

[Farmhand]

Well maybe on your car coil it is but all the ones i have seen and bought and used the condenser is directly across the primary coil right on the top of the ignition coil and bolted to it's low voltage terminals.  There is also one in the distributor. It is there to absorb the spikes, depending on how the ignition is wired depends on how the condenser is placed. The object of it is to absorb the spikes and stop arcing in the points but when used in experiments if it is placed directly across the primary the coils performance is improved.

Some ignition coils have the LV end of the secondary connected to the primary positive and some have it connected to the primary negative, some cars can also have a positive ground from what I've been told. And some a negative ground.

http://au.answers.yahoo.com/question/index?qid=20080803011923AAKIebG

In this distributor here the condenser in the distributor can be seen poking out from behind the right side of the rotor..

http://www.ebay.com.au/itm/holden-253-308-distributor-/300826423233?pt=AU_Car_Parts_Accessories&hash=item460aa6efc1#ht_500wt_1414

..

Cheers