Question about ignition coils and resistance/application

[dan filipi]

I've been chatting with a guy over at NGW about replacement coils for his 1982 1100.

The new coils he got from a trusted supplier were suppose to be direct compatible replacement but the resistance values are very different than they should be.
I'm looking for new coils because 3 of the 4 I have are cracked and I could hear a clicking from them when installed making me think spark was jumping to ground.

Has anyone had success buying coils that match the primary resistance value for all years 1100? It has to be .4 Ohm, what I'm seeing available is 2.0-5.0 Ohm.

As I have time I need to study up on why those values are so important and what could be done to change them.

 

[lew1701]

Hey Dan, after reading your post I became very curious about your problem. After reading many articles on the subject and talking to a few people I know here...I've come to the conclusion that everyone is stumped by this. The closest thing I could find was an Accel coil at .7 ohms. I can't wait to hear what you come up with.

 

[dan filipi]

Hey Dan, after reading your post I became very curious about your problem. After reading many articles on the subject and talking to a few people I know here...I've come to the conclusion that everyone is stumped by this. The closest thing I could find was an Accel coil at .7 ohms. I can't wait to hear what you come up with.

Stumped is right!

I've sent emails out to at least 2 suppliers and they can't answer it either.
I've searched other forums and find various posts asking similar questions but no definitive answers.

There must be a solution, gotta keep looking :laptop:

 

[mcgovern61]

Hey Dan, after reading your post I became very curious about your problem. After reading many articles on the subject and talking to a few people I know here...I've come to the conclusion that everyone is stumped by this. The closest thing I could find was an Accel coil at .7 ohms. I can't wait to hear what you come up with.

Stumped is right!

I've sent emails out to at least 2 suppliers and they can't answer it either.
I've searched other forums and find various posts asking similar questions but no definitive answers.

There must be a solution, gotta keep looking :laptop:

Sounds like the thread on the engine knock mystery!

 

[dan filipi]

I've found some automotive coils that have the same primary resistance value but not the dual output like we need.

From what I can gather the way a coil works, the secondary coil is totally isolated from the primary coil so the secondary resistance value shouldn't matter.

The primary resistance has to do with it's actual current requirement so with different values there could be a higher or lower current necessary to operate the coil.

In our system the coil requires (at .4 Ohms) let's say 2 amps to make the coil work. A coil with 4 Ohms resistance may require less current but a different resistor. Set up right it should work with no problem.

I'm not sure if I'm understanding this right (and I may have this backward) so don't take my word on it.

Seems like a simple coil should be an easy deal but it aint.
The main unknown variable in the whole picture is what are the spark units designed for.
I think if if these values are not right they could be fried but maybe not.

 

[joedrum]

seems i read a post somewhere about a car coil that was right for the 1100 replacement that was better than stock ....but ive never been able to find it again so it makes me question myself......are you guys saying there is no replacment coils stock or after market for the 1100 .....theres got to be somthing that will work and this would be great thing to figure out here with so many 1100 members

 

[dan filipi]

Last night I found accell and Dyna coils that should work but they wouldn't use the original wires and a pair of these coils cost about $300!
I've found a few in the range of less than $50 each. Just have to figure out how to make them compatible.

 

[WindNWing]

Guys, I hesitate to get into this thread because I can’t tell you how to replace one coil with another but I do know how a coil works.

Ignition coils are actually two coils of wire in one package that produces a step up transformer.

The step down transformer that works your door bell has a primary coil that drives a secondary coil, it transforms 120 volts down to 12 volts. In that case the primary will have 1/10 the number of coils of wire that the secondary has, the actual number of coils isn’t important just the ratio.

In the case of ignition coils the voltage is stepped way up. If the primary has 1,000 turns and the secondary has 10 turns, the output voltage would be 100 times greater than the input. 12 volts would step up to 1200 volts. The same step up could be achieved with a primary of 10,000 turns and a secondary of 100 turns but in the last example the resistance would read higher due to having more wire in the coil. The point is, a resistance reading will not tell you anything about the voltage step up.

You can certainly check the condition of a coil if you know what the resistance should be but a resistance reading will not tell you if one coil will replace another.

You are right that the two coils are not connected electrically, they induce the voltage through magnetic lines of force. An exception to that is, they may share the same ground and then you would see continuity between the two.

 

[lew1701]

Guys, I hesitate to get into this thread because I can’t tell you how to replace one coil with another but I do know how a coil works.

Ignition coils are actually two coils of wire in one package that produces a step up transformer.

The step down transformer that works your door bell has a primary coil that drives a secondary coil, it transforms 120 volts down to 12 volts. In that case the primary will have 1/10 the number of coils of wire that the secondary has, the actual number of coils isn’t important just the ratio.

In the case of ignition coils the voltage is stepped way up. If the primary has 1,000 turns and the secondary has 10 turns, the output voltage would be 100 times greater than the input. 12 volts would step up to 1200 volts. The same step up could be achieved with a primary of 10,000 turns and a secondary of 100 turns but in the last example the resistance would read higher due to having more wire in the coil. The point is, a resistance reading will not tell you anything about the voltage step up.

You can certainly check the condition of a coil if you know what the resistance should be but a resistance reading will not tell you if one coil will replace another.

You are right that the two coils are not connected electrically, they induce the voltage through magnetic lines of force. An exception to that is, they may share the same ground and then you would see continuity between the two.

Ok, I think I'm understanding this: so for example if you have a known input voltage to the coil, 12 volts in this case, and you have a certain required voltage output for the bike to operately properly...am I correct in assuming that any coil meeting the required input/output rating will work? (disregarding configuration, size and mounting requirements)

 

[thewhiterhino]

Guys, I hesitate to get into this thread because I can’t tell you how to replace one coil with another but I do know how a coil works.

Ignition coils are actually two coils of wire in one package that produces a step up transformer.

The step down transformer that works your door bell has a primary coil that drives a secondary coil, it transforms 120 volts down to 12 volts. In that case the primary will have 1/10 the number of coils of wire that the secondary has, the actual number of coils isn’t important just the ratio.

In the case of ignition coils the voltage is stepped way up. If the primary has 1,000 turns and the secondary has 10 turns, the output voltage would be 100 times greater than the input. 12 volts would step up to 1200 volts. The same step up could be achieved with a primary of 10,000 turns and a secondary of 100 turns but in the last example the resistance would read higher due to having more wire in the coil. The point is, a resistance reading will not tell you anything about the voltage step up.

You can certainly check the condition of a coil if you know what the resistance should be but a resistance reading will not tell you if one coil will replace another.

You are right that the two coils are not connected electrically, they induce the voltage through magnetic lines of force. An exception to that is, they may share the same ground and then you would see continuity between the two.

Ok, I think I'm understanding this: so for example if you have a known input voltage to the coil, 12 volts in this case, and you have a certain required voltage output for the bike to operately properly...am I correct in assuming that any coil meeting the required input/output rating will work? (disregarding configuration, size and mounting requirements)

In simple terms that should be correct. The primary loading could interfere with the device that creates the pulse if electronic, but usually not.
Some older car could run on 6 volts and during the starting process have 12 volts applied for a spark boost during the starting process. If 12 volts is used all the time the coil will fail in time. I will look at the applied voltage when I change my wires and check the voltage during starting and running for an answer to that.
With the newer ignition systems I believe they have 12 volts all the time and a much higher output voltage which allows running a wider spark plug gap and creating a much more potent spark. As expected more spark is better.

 

[dan filipi]

Guys, I hesitate to get into this thread because I can’t tell you how to replace one coil with another but I do know how a coil works.

All input on a subject is welcome to help sort out a question or problem.

I know how a coil works but your explaining it again has helped to sort it out some in my head.

 

[WindNWing]

The new coils he got from a trusted supplier were suppose to be direct compatible replacement but the resistance values are very different than they should be.

My thinking is, the fact that the resistance of the replacement coils don't match the resistance of the stock coils may have no bearing on whether or not they can replace the original coils.

Beyond taking the suppliers word that they will perform electrically the same, I have no idea how you would tell.

 

[kirkwilson]

Isn't the number of turns in the primary compared to the secondary what determines the curremt in the secondary, not the voltage? And the voltage in the secondary is dependent on both the current and the resistance of the secondary? So the higher the resistance of the secondary the higher the voltage output will be given an equal ratio of turns ( primary to secondary)?

 

[dan filipi]

The new coils he got from a trusted supplier were suppose to be direct compatible replacement but the resistance values are very different than they should be.

My thinking is, the fact that the resistance of the replacement coils don't match the resistance of the stock coils may have no bearing on whether or not they can replace the original coils.

Beyond taking the suppliers word that they will perform electrically the same, I have no idea how you would tell.

Interesting.

I found this on the Accell site:

WARNING: Use of coils with too low an impedance (resistance) will damage the motorcycles ignition system. We do not have a complete list of applications, so if your motorcycle has an electronic (breakerless) ignition, you should determine the correct set of coils by performing one of the following two simple tests. Keep in mind that the higher impedance coils are by far the most popular and will not damage your ignition system if they are the wrong choice.


That's kind of a contradiction because they state also they are not responsible for coil or ignition damage but it does seem to say the higher (2.5 ohm) coil is ok to use on our lower (.4 ohm ) system.

Anyway,
I have a second complete ignition system so I might see if I can find a dual tower coil this weekend and do some tests even if the coil has a higher impedance.

 

[kirkwilson]

I take that all back- think of voltage as electric pressure and current as electric flow- voltage is what causes the arc across the spark plug gap and as long as the coil is rated a high enough voltage output the resistance doesn't matter- I think....I don't know... Nevermind...

 

[dan filipi]

I take that all back- think of voltage as electric pressure and current as electric flow- voltage is what causes the arc across the spark plug gap and as long as the coil is rated a high enough voltage output the resistance doesn't matter- I think....I don't know... Nevermind...

LOL, yeah I'm trying to get my head around how the resistance comes into play here, then second why the ballast resister is needed and why is it on the ground side of the primary and not the positive.

 

[WindNWing]

Dan,
Notice that they said impedance and then resistance was in parentheses. Impedance is the resistance to current flow in a coil during operation. This depends on a lot of things that are engineered into the coil so impedance isn’t what we normally think of as true resistance.

If you put an ohm meter on a coil, you are only reading the true resistance of that amount of wire and it wouldn’t make any difference if it was a straight piece of wire or that same length of wire wound into a coil with 1,000 turns. The straight wire would have no impedance but the coil of 1,000 turns would and that impedance would add to the true resistance of the wire during operation.

Kirk,
Voltage and current are always locked together. If a coil steps the voltage up 10 fold in the secondary, the current will decrease in the secondary 10 fold. You are also correct, what we are looking for is a high voltage (pressure) to jump the plug gap and produce that blue arc that eventually lets us get that wind in our faces.

 

[joedrum]

i have no time right now to join in on this ....but i do know that if you stumbble on a setup that works and produces better spark there is lots to be gained over stock setup .....i think your looking for somthing that will produce better spark than stock ....wont damage the electronics....and operates without a ballist resistor...this would cover all bases of a huge improvement .....windnwing your insite is very plain to understand and very helpful to me ....an explanes all the gains i got on my 1000 ....witch i got in egnorance to true knowledge....

 

[dan filipi]

Dan,

Voltage and current are always locked together. If a coil steps the voltage up 10 fold in the secondary, the current will decrease in the secondary 10 fold.

I'm not sure I understand this.

Presumably the secondary voltage could be increased any amount, 10k , 20k, even 100k volts depending on the number of turns of wire in the coil. It seems to me the primary coil would also have to have a different number of turns in relation to the secondary turns in order to produce that increased voltage.
Would this not require an increased primary current?

Ultimately what I'm after is to get the hottest spark possible with the stock wire and plug cap set at an affordable price.

 

[WindNWing]

Dan,


I'm not sure I understand this.

Presumably the secondary voltage could be increased any amount, 10k , 20k, even 100k volts depending on the number of turns of wire in the coil. It seems to me the primary coil would also have to have a different number of turns in relation to the secondary turns in order to produce that increased voltage.
Would this not require an increased primary current?

Dan,

It looks like you DO understand. If the number of turns in the output coil increase in relationship to the input coil, the output voltage will increases and the current driving the input coil must also increase.

I’m afraid I still can’t give any advice on what coil set would be equivalent to the stock coils and also give an increase in output voltage or even that it would be advantageous. I tend to not second guess the professional engineers that designed the system.