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Coil resistance

Posted: Tue May 02, 2017 3:34 am
by torp68
Hi guys

Recently acquired a new top coil from dbelectrical on eBay.
http://www.ebay.com/itm/NEW-IGNITION-CO ... N7&vxp=mtr" onclick="window.open(this.href);return false;

The maintenance manual for the RD500 gives the following values for coil resistance:
Primary Coil Resistance: 0.67 Ohm +/- 20% at 20 degr C
Secondary Coil Resistance: 12 kiloohm +/- 20% at 20 degr C

I tested an original one, and found the values were within the limits above.

The aftermarket coil has the following resistance:
Primary Resistance: 3.2 ohm
Secondary Resistance: 15,6 kiloohm

This means both values are outside what the manual calls for. Is this going to affect the ignition and running of the bike? If so; how?
Everything else on the bike is to original spec., std ignition etc.

Re: Coil resistance

Posted: Tue May 02, 2017 5:41 am
by phildu31
Hi.
Resistance is a measure done with direct current.
It is an easy way to get sure that your coil is not cut off.
Normal operation of a coil is with pulses which are a series of alternate currents.
In this case, the equivalent of resistance is impedance which is not easily measurable.

So don't attach too much importance to the resistance if your values are off limits.

Re: Coil resistance

Posted: Tue May 02, 2017 8:14 am
by Rick Lance
You have purchased a coil designed for an inductive ignition system that expects 3.2 ohms of resistance to work properly. Your RZ has a Capacitive Discharge ignition which runs with very little resistance (0.5 ohm). This is why tachometers from 4stroke bikes will not function with your RZ. The coil is incorrect for your application. It may run anyway but would not be optimum or even a good idea. You may want to give these aftermarket coils a try. I have used them without excellent results.

http://www.ebay.com/itm/V-Twin-32-9342- ... xQ&vxp=mtr

Re: Coil resistance

Posted: Tue May 02, 2017 8:17 am
by two-stroke-brit
Rick Lance wrote:You have purchased a coil designed for an inductive ignition system that expects 3.2 ohms of resistance to work properly. Your RZ has a Capacitive Discharge ignition which runs with very little resistance (0.5 ohm). This is why tachometers from 4stroke bikes will not function with your RZ. The coil is incorrect for your application. It may run anyway but would not be optimum or even a good idea. You may want to give these aftermarket coils a try. I have used them without excellent results.

http://www.ebay.com/itm/V-Twin-32-9342- ... xQ&vxp=mtr
hey Rick,would it work on a 350 as well ?.
thanks mark

Re: Coil resistance

Posted: Wed May 03, 2017 3:24 am
by torp68
Ok, Rick! Thanks for your advice!! Another item for the return bin then...... :mad:
I guess using the Dyna coil requires a new bracket, so I´ll see if I can find a used item till summers past and it´s back in the garage again!
Again, thanks!!

Oyvind

Re: Coil resistance

Posted: Wed May 03, 2017 8:04 am
by Rick Lance
two-stroke-brit wrote:
Rick Lance wrote:You have purchased a coil designed for an inductive ignition system that expects 3.2 ohms of resistance to work properly. Your RZ has a Capacitive Discharge ignition which runs with very little resistance (0.5 ohm). This is why tachometers from 4stroke bikes will not function with your RZ. The coil is incorrect for your application. It may run anyway but would not be optimum or even a good idea. You may want to give these aftermarket coils a try. I have used them without excellent results.

http://www.ebay.com/itm/V-Twin-32-9342- ... xQ&vxp=mtr
hey Rick,would it work on a 350 as well ?.
thanks mark
Any bike equipped with CDI including your RZ350 would be a good home for this coil. They are sold individually on eBay.