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Can someone explain resistance.....

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gavbriggs
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Joined: 11 Jun 2013
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PostPosted: 05:42 - 07 May 2014    Post subject: Can someone explain resistance..... Reply with quote

....in the context of:

If I have a 4 pot enging with two coils, one does 1&4 th other does 2&3.as per the k4 bandit 1200(and many more I suspect)

Each has coils with a handbook value of 3ohms across the primary side(can't remember the secondary) could a coil of lower resistance be used? The replacement coils check out as per thier particular specs, I don't want to mention what coils they are yet as this could sway opinion.

Main thing is can it damage anything? My mind is thinking that the lower resistance would make the electrics work less therefore giving a stronger spark? My conscience is telling me that suzuki used these coils for a reason and to stop being stupid trying to fix shit that ain't broke.

I so know of the stick coil conversion but I haven't tried it or got any to do it yet.
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jjdugen
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PostPosted: 06:47 - 07 May 2014    Post subject: Reply with quote

Coils primaries come in two flavours, low resistance, circa 3 Ohms and high resistance, circa 5+Ohms.
Lower Ohms were used on points type ignition, the mechanical switch is not particularly affected by coil resistance but using a high Ohm coil would increase the current needed to energize the primary winding and leads to arcing at the points contacts.
Electronic ignition uses transistors or Mosfets as the switch. too low a primary resistance will lead to more current passing through the device that can lead to overheating and even failure of the device.
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gavbriggs
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PostPosted: 08:04 - 07 May 2014    Post subject: Reply with quote

So using a coil with a lower resistance isn't a good idea. Or could a 2 ohm resistor be put in to make 2.7(for these particular coils) wouldn't help?

Just trying to get a nice strong spark and a cheap backup if my coils go down and wondered if a set from a car(free) would do the job reliably!!
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davebike
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PostPosted: 08:45 - 07 May 2014    Post subject: Reply with quote

I think your out of your depth
Coils are NOT a simple DC device with pure Resistance

You need to consider Impedance i.e. Ac resistance !

I would seriously sick to the correct coils
Drawing too much power / sinking too much power to earth via the ignition module's output stage could blow it

Yes it may work but if it doesn't it will cost lots

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Islander
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Joined: 05 Aug 2012
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PostPosted: 12:27 - 07 May 2014    Post subject: Reply with quote

jjdugen wrote:
Coils primaries come in two flavours, low resistance, circa 3 Ohms and high resistance, circa 5+Ohms.
Lower Ohms were used on points type ignition, the mechanical switch is not particularly affected by coil resistance but using a high Ohm coil would increase the current needed to energize the primary winding and leads to arcing at the points contacts.
Electronic ignition uses transistors or Mosfets as the switch. too low a primary resistance will lead to more current passing through the device that can lead to overheating and even failure of the device.


Eh?

Using a higher resistance decreases the current drawn not the other way around. You've said the opposite in the first part of your post and then corrected it in the second.

Also, as pointed out, inductance is a major factor here. You're looking at rate of change of current through a coil over a variable cycle. Mosfets are used because they're fast and minimise the amount of time that that change of current occurs across, hence reducing overall dissipation in the device.

OP if your switching device (CDI or management unit) is rated for a particular coil then use that coil - unless the manufacturers say otherwise. It's a dynamic system with complex impedance matching - adding passive resistance isn't the answer either. DC resistance checks are just there to give you a pass/fail with a simple ohmmeter.
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