3 or 5 ohm coils

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Lumpy
SD900 Darmah
Posts: 327
Joined: Sun Mar 25, 2007 5:49 am

3 or 5 ohm coils

Post by Lumpy » Mon Aug 14, 2017 4:35 pm

I have stumbled across a Sachse electronic ignition system for my GTS. I note that Sachse suggest 3 ohm single output coils (bike is kick start only) for this application but else where around here I notice that 5 ohm is the weapon of choice. Little confused as I see that heat build up is said to be the issue with the 3 ohm units but I thought heat was the by-product of greater resistance?
I was going to run without ballast resistors as she is kick only.
Any thoughts?

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geodoc
750 GT
Posts: 178
Joined: Thu Jul 18, 2013 3:57 pm

Re: 3 or 5 ohm coils

Post by geodoc » Wed Aug 16, 2017 4:51 am

http://www.ohmslawcalculator.com/ohms-law-calculator

You can see plugging in 14V & 3 or 5 ohms, that with the lower resistance you get higher current (amps) / power (watts) values than with higher resistance. That must be absorbed, or a large part of it anyway, buy the coil itself and it is - mostly in the form of heat. Not a problem if the coil can live with that, but apparently Dyna coils tend toward more frequent failures at the higher current / power loadings.

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