I have asked this before i know???

[Anonymous]

Im looking in my haynes manual and the resistances for the coils are shown as 3 to 5 ohms on the primary side and 31 to 33 ohms on the secondary side. This does not seem as though it is correct because the secondaty voltage only has a multiplication factor of about 6. Can any one explain this is it a mistake in the book and if not whats the scoop??

[Anonymous]

The two sides to the coil do not relate directly - that is, you can't just multiply the voltages by the variation in coil resistance to get the spark voltage.

The primary side gets a kick of 12 volts from the system and induces a voltage in the secondary somewhere between 10,000 and 40,000, depending on the coil efficiency and design. Average is prob 15,00 to 20,000.

The difference in the induced voltage is independent of the coil resistance, it is dependent on the number of turns in each coil and the efficiency of the former upon which the coils are wound.

The resistance in each coil is set to give optimum rise and fall rate in the voltage across each coil. It is that rise and fall, the variation of voltage, that actually transfers the charge from one side to the other. The resistance of the coil, therefore, has more to do with the ignition timing than with the induced voltage.

On the primary side the resistance is also within a range that the igniter prefers. It's just wire wound around silicon steel plates but there is a lot going on in there. If I could remember more of my almost three years of electrical engineering back in the dim dark past I could tell you more. Perhaps I will come back when my memory is sparked up.

Kim

[Jay B]

Yeah what he said.

[Anonymous]

ok then the coil windings are the key which i knew was how the voltage was boosted. But I always seemed to remember that the resistance in old auto coils that i had tested seemed to be proportional to the ratio of the low voltave to the high voltage. Thanks for the reply.

[Redman]

Like said before, the proprotion of the voltages is more related to the proportion of the number of turns (loops of the coil) of the primary winding to the secondary winding. The resistance of each winding is more related to the length of the wire and type of wire in that coil as measured with the direct current (steady/constant) that is produced by the meter. Whereas when the bike is running: the ignitions spark (secondary voltage) is produced by CHANGING the current in the primary. So the resistance test with the meter is just to see if the coil is not completly open (wire broke, infinite resistance) or if there is some bad connection inside (way too high resistance) or if some of the turns of the winding are shorted to each other (way too low of resistance). So, the scoop is no real relationship between the porportion of the resistances to the proportin of the voltages.

[Anonymous]

on my yamaha the schematic shows a common minus and then 2 diferent readings for the primary side and the secondary side . So some coils must have a common connection. As far as the resistance not having any direct relationship to the voltage boost i can see that.

[Anonymous]

Yeah what he said.

JB
Look at the schematics that you sent me and you will see thecomon conection to the 2 windings. This schematic shows the same type of setup to my Yammy even though my yammy is a double fire coil and the schematic you sent me is a single fire
AS I AM TYPING THIS I WENT OUT TO THE GAREGE FOR A SECOND LOOK AT THE SCHEMATIC. SMART ME WAS LOOKING AT I DON'T KNOW WHAT. I guess only single fire coils will have a common wire to both the primary and secondary windings.

I place a lot of faith in a schematic as a guide and i guess i just got mixed up. Well thanks for the persistance in all the explanations.
Maybe one too many driveway drops. :? :?

[Anonymous]

The coils will have a common connection on one side because both sides of the coil have to be earthed to the frame. Every component on the bike has that feature but the schematic does not show the connections close together on the page so you miss seeing it.

Kim