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[Frank]

Well it seems we are now talking in a unified voice, but perhaps Count Johnny can enlighten us as to the reason behind his initial query which has occupied my mind over the weekend?

[Scalyback]

Coils and how they work.

Ignition coils have two coils in them. the amount of turns of wire on the coils, determine the change (if any) between current (amps, milliamps) and voltage.

Few things to know,

coils (and transformers) only work with changing or fluctuating voltage like alternating current (AC), or with Direct current (DC) IF It is being switch ed on and off. (Like bullet points opening and closing)
Ratio of turns on coils equals ratio of input/output voltages.

Power going into your coils from battery and points, we call primary winding.(well, I going to for this explanation.)
Power going between coils and spark plug, we call secondary winding.

Here is a hypo-pathetical coil... 12 volt systems.

If it had 10 windings on the primary (points) coil and 10 windings on the spark plug coil, and you put 12 volts across it, you would get 12 volts out (not enough for a spark, but keep reading)

If it had 10 windings on the primary, and only 1 on the secondary, you would get 1.2 volts, but also ten times the current in amps. (Think of mig welding)

If it had 10 windings on the primary, and 100 on the secondary, the secondary is ten times bigger so then you get 120 volts!

Ditto 10, Ditto 1000, Ditto 1200 volts

SO, For the 1 to 150 ratio as JTL said above,

ditto 10, ditto 1500, output, which is 12 volts times 150, giving 1800 volts. Not enough yet...

as long as the ratio of turns is the same, the number of turns can be changed to get more or less current flowing, therefore taking from above post,

30 turns on battery and points coil, 4500 turns on secondary to spark plug, gives you... 1800 volts again, as it is still 12 volts times coil ratio of 150

SPARK PLUGS NEED 10,000 to 20,000 volts to work well, This is why It not nice to put a finger there

We will say 12,000 volts for ease. That is 1000 times larger than the 12 volts we are putting in, therefore, the number of windings (Turns) on the secondary coil needs to 1000 times the number of turns on the primary.

ditto 10 turns, ditto 10,000 turns, gives 12,000 volts, because difference in coils (10,000 / 10 =1000) times input voltage (12V) 12 * 1000 = 12,000 volts.


(Why, oh why did I start this? my bloody head is going round now!)

Search for this post in future, I never repeating it.

Wailyback

[Scalyback]

where me spaces go???


Coils and how they work.



Ignition coils have two coils in them. the amount of turns of wire on the coils, determine the change (if any) between current (amps, milliamps) and voltage.



Few things to know,



coils (and transformers) only work with changing or fluctuating voltage like alternating current (AC), or with Direct current (DC) IF It is being switch ed on and off. (Like bullet points opening and closing)

Ratio of turns on coils equals ratio of input/output voltages.



Power going into your coils from battery and points, we call primary winding.(well, I going to for this explanation.)

Power going between coils and spark plug, we call secondary winding.



Here is a hypo-pathetical coil... 12 volt systems.



If it had 10 windings on the primary (points) coil and 10 windings on the spark plug coil, and you put 12 volts across it, you would get 12 volts out (not enough for a spark, but keep reading)



If it had 10 windings on the primary, and only 1 on the secondary, you would get 1.2 volts, but also ten times the current in amps. (Think of mig welding)



If it had 10 windings on the primary, and 100 on the secondary, the secondary is ten times bigger so then you get 120 volts!



Ditto 10, Ditto 1000, Ditto 1200 volts



SO, For the 1 to 150 ratio as JTL said above,



ditto 10, ditto 1500, output, which is 12 volts times 150, giving 1800 volts. Not enough yet...



as long as the ratio of turns is the same, the number of turns can be changed to get more or less current flowing, therefore taking from above post,



30 turns on battery and points coil, 4500 turns on secondary to spark plug, gives you... 1800 volts again, as it is still 12 volts times coil ratio of 150



SPARK PLUGS NEED 10,000 to 20,000 volts to work well, This is why It not nice to put a finger there



We will say 12,000 volts for ease. That is 1000 times larger than the 12 volts we are putting in, therefore, the number of windings (Turns) on the secondary coil needs to 1000 times the number of turns on the primary.



ditto 10 turns, ditto 10,000 turns, gives 12,000 volts, because difference in coils (10,000 / 10 =1000) times input voltage (12V) 12 * 1000 = 12,000 volts.




(Why, oh why did I start this? my bloody head is going round now!)


Search for this post in future, I never

[JTL]

Scalyback... Thanks for coil lesson #1 (hope you are ready for a little more). So, to understand the physics of a coil to be able to pick the right coil for the Bullet is essential as a first step. As I understand it. When this thread has reached its end I will make a print for the workshop tech archive. Until then I have a question regarding the impedance ratio between primary and secondary coil... Let's say the primary is 3,5 ohm and the secondary is 8500 ohm. What does this tell me about the ratio between the windings of the two coils? And how to determine which primary coil impedance is the optimal for a Bullet in the first place? Some coils have 0,7 ohm, some have 3,5 and others have values in between. Usually the primary coil impedance is mentioned in relation to the type of ignition. How does this connect?... My goal for this inquery is to get a coil with a hot and very strong spark for my Bullet, but without damaging the electrics (my rev counter blew up with the aftermarket coil).. all the best Jacob

[Dennis C]

JTL, There are basically only two mainstream 12v coil types used on motorcycles the higher resistance primary coil type you list are for traditional points ignition type the primary resistance is carefully chosen to give a good spark whilst not putting too much load on the points which would give short points life as the main but not the only adverse side effect, Boyer, Pazon, etc, also use this type.

The lower resistance type are mostly used on bikes designed with electronic ignition and electric start the Japanese developed these to mainly overcome voltage drop when using electric starters and the coil voltage is increased when the starter is in use and then drops back to a lower voltage when the engine is running, these should not be used with the aformentioned points etc system.

Early car systems used a version of this, a balance resistor and 6v coils were fitted the resistor was bypassed when the starter was operated allowing the full battery voltage to reach the coil, when the starter was released the resistor was then back in circuit dropping the voltage back to the normal coil operating voltage.

[Scalyback]

It is about now that the worms have found their own can opener, and are on a do it yourself job.



Coil quality



The thicker the wire in the coil, the better it can conduct electricity.



The primary wire might only have 15 to 20 turns, but is usually much thicker that the secondary.

this is because of the second so far untouched point of curret





that stuff that comes in mA and A (amps)



as seen the voltage rises with the number of turns in the secondary, but (ohms law) the current in amps drops in direct proportion to the voltage rise.



This is how MIG electric welders work. you put 240 V ac into 1000 turn primary, but the secondary is only 10 turns of very thick wire or usually strip metal.



from last lesson, the voltage drops 100 times to 2.4 volts BUT the current increases 100 times from say 10 amps to about 1000. this is enough to bend any wire coat hanger, and also explains why you do not get a shock for touching both terminals, as the skin resists voltage to about 50-60 V when dry.



SO....we need a minimum amount of current in the secondary or there will not be enough electricity to jump the spark gap with a nice big spark.



we need a nice big spark at say 12,000 volts and just a few mA (milliamps) so the primary winding (battery points) will have to be thicker wire to carry enough current so that the secondary coil (spark plug) will still work with a current 1000 times smaller than the input, while the voltage comes out 1000 times bigger.



Physical size

area taken by 10 turns of relatively thick wire, plus area taken by 10,000 turns of 'thickness of a hair' or less wire,
plus thing to wind them on and external can.



power taken



this is where we go look at the old trusty ammeter! YES, we know it already.


during starting, when the ammeter flicks to the left, the the points just closed and power is flowing through the primary winding. Kick a little further, and the ammeter centers. the points just opened, producing a spark and cutting power to the coil. The ammeter shows you exactly what is happening.



We get to immediatly before TDC and the ammeter centres, ie the ignition fires.



The ammeters are not that accurate for measuring current, but they give a good indication. WHEN the meter goes to the left, try to decipher from the ammeter's scale, how many amps the coil is using. If enough of us do that, then we will know the value of current taken for a good coil.



I am wildly assuming about 3 amps, so with Ohms law, we are looking at 12 divide by 3 = 4 ohms resistance for the primary, which is close to impedance on a DC switched on and off (points) circuit. Impedance gets more wild with AC circuits operating at 50 cycles per second (Hz)



There are other factors, when running your bike electrics will be around 14V, but just means juicier spark.



For those of you with 6 Volts



your turns ratio is usually doubled.



whereas 12V into 10 turns will give 12,000 volt coming out of 10000 turns,


6V into 10 turns will give 12,000 volt coming out of 20,000 turns.


ALSO



6V into 5 turns will give 12,000 volt coming out of 10,000 turns.





RIGHT... I supposed to be up at eight to take Thunderbolt from Switzerland to France. Many Kilometers and about 2 celcius with possible snow. I have a feeling I will be getting a lift, and will have to collect my poor bike next month!

[Alan R]

------------- and nobody has mentioned the part played by the capacitor ( Urban name of Condenser)in all this !!......Question}--- How many coils does the magnetic field collapse over ??....Answer}--- 2 ..a back EMF is created within the Primary which energizes the Capacitor..and creates another magnetic field around BOTH coils...Upon reaching saturation the capacitor switches off....this collapses the field around BOTH coils and creates a back EMF within the Primary which energises the capacitor........ etc, etc, etc......This happens at a frequency of 1,000's of times a second and from this we get that sharp "CRACK" sound and BLUE colour spark at the plug.....Unfortunately we cannot get perpetual motion ( electrically) and the sequence dies off as each cycle consumes energy in order for it to take place...........The closing of the points then short-circuits this and energises the coil direct from the battery via earth...all ready to start the sequence all over again....The HT coil is electrically designed to match the circuit it's in, such that it is at a peak of Flux saturation just when the points are opened........The reference to a Ballast Resistor}--My 1975 Honda GL 1000 Gold Wing has such a system built in.....The Bedford HA vans on the Royal Mail had it as well.........The coils were special 10 Volt items because the Ballast resistor, when TAKEN OUT OF the circuit by the ignition switch during start sequence, would allow 12 Volts to be placed over this 10 Volt coil, thus giving a boosted spark......After starting, the ignition switch would now have the Ballast Resistor RUNNING IN CIRCUIT, thus supplying 10 Volts across a 10 Volt coil............The down side is obvious ie}-- that Ballast Resistor could (and would) start to partially break down....with poor running, back-firing etc.....I took mine out of the wiring loom, joined the two wires together and fitted normal, 12 Volt coils.......

[Alan R]

PS--------- forgot to mention the a TEMP INCREASE will also increase the Resistance of a conductor.....The reverse of this being the SUPER-CONDUCTOR.....Have a look at this }------- http://ffden-2.phys.uaf.edu/113.web.stu ... hat_is.htm -----------

[Scalyback]

You mean that little spark quench capacitor across the points?



Or there is another capacitor somewhere?

[Scalyback]

Who was it that asked in the first place ???




Bet you're sorry now!