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Explain coil resistance to me.

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lingeringstin...
Trackday Trickster



Joined: 01 May 2014
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PostPosted: 02:22 - 10 Sep 2017    Post subject: Explain coil resistance to me. Reply with quote
I've got a twin cylinder engine with a 360 crank. Both pistons up and down at the same time, alternate firing. It's got an AC feed off the alternator to the CDI box which feeds the coils. What I want to know is whether there's any difference running the two coils in series or parallel. The engine fires up and runs either way, but is there any reason why one way is better than the other?
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temeluchus
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Joined: 01 Oct 2008
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PostPosted: 04:51 - 10 Sep 2017    Post subject: Re: Explain coil resistance to me. Reply with quote
lingeringstink wrote:
I've got a twin cylinder engine with a 360 crank. Both pistons up and down at the same time, alternate firing. It's got an AC feed off the alternator to the CDI box which feeds the coils. What I want to know is whether there's any difference running the two coils in series or parallel. The engine fires up and runs either way, but is there any reason why one way is better than the other?


If the standard is series, putting them in parallel will reduce the primary resistance and draw a fair bit more current through the igniter.
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Pete.
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Joined: 22 Aug 2006
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PostPosted: 07:09 - 10 Sep 2017    Post subject: Re: Explain coil resistance to me. Reply with quote
temeluchus wrote:
lingeringstink wrote:
I've got a twin cylinder engine with a 360 crank. Both pistons up and down at the same time, alternate firing. It's got an AC feed off the alternator to the CDI box which feeds the coils. What I want to know is whether there's any difference running the two coils in series or parallel. The engine fires up and runs either way, but is there any reason why one way is better than the other?


If the standard is series, putting them in parallel will reduce the primary resistance and draw a fair bit more current through the igniter.


It'll also cause the coils to run at double the voltage, using double the current. They'll get hot and die pretty quickly most likely.
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Robby
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Joined: 16 May 2002
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PostPosted: 21:27 - 10 Sep 2017    Post subject: Reply with quote
Are you sure about the alternate firing? The standard setup would be to trigger the spark at the crank and use wasted spark ignition.
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Pete.
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PostPosted: 21:42 - 10 Sep 2017    Post subject: Reply with quote
Not many bikes taking the trigger off the camshaft. CB100/125 single is one I recall, can't bring to mind any others.
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132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy
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lingeringstin...
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PostPosted: 23:31 - 10 Sep 2017    Post subject: Reply with quote
Robby wrote:
Are you sure about the alternate firing? The standard setup would be to trigger the spark at the crank and use wasted spark ignition.


Yeah, it's both pistons up and down at the same time but one is on the exhaust stroke while one is on the combustion and there is a wasted spark, and it's triggered off a coil in the alternator which is on the end of the crank. I like that because it's the best setup for single carb.
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Pete.
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PostPosted: 23:40 - 10 Sep 2017    Post subject: Reply with quote
Why do you need two coils then? A single coil with twin outputs would suffice and it's still wasted spark.
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132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy
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lingeringstin...
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PostPosted: 02:10 - 12 Sep 2017    Post subject: Reply with quote
Pete. wrote:
Why do you need two coils then? A single coil with twin outputs would suffice and it's still wasted spark.



Ah, well you see I've got an assortment of random coils to use. At the moment I'm using a Yamaha Banshee 350 coil which is twin lead but I don't know how old and knackered it is. I've also got a pair of brand new Chinese CA250 coils which I suspect are common fodder on a lot of Honda clones of all sizes. But having never used Chinese coils I'm not wanting to rely upon them yet. I've also got a coil off a 50cc thing that looks pretty much just like a Chinese 250 coil in a different casing.

But the best spark I've had so far was from a couple of old car coils I rigged up just to see what would happen. Great spark but they're quite big coils and hard to locate somewhere, so at the moment I'm using the old twin lead Yamaha coil until I can rig something else up.

Anyway, I've got assorted coils and spark and the engine runs so I'm not that bothered.
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