Coil voltage

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RedEvo

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May 23, 2009
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Hi,

Another dumb question I'm afraid ;)

I decided to replace the coils on my 72 Combat. Not knowing any better I ordered 2 new 12V coils from RGM as it's a 12V battery......

On looking at the current coils I see they are 6V coils?

The bikes got Boyer Micro MkIII and standard switch gear at the moment.

Are the 12V coils OK to use?

cheers

d
 
Cheers - I'll hold off then. To continue the dumb questions why does a 12V system use 6V coils?

cheers

d
 
Norton used 6 volt coils with a ballast resistor on the Commando supposedly to get a hotter spark. As some of the electrical gurus on this forum can explain, ignition coils aren't really 6V or 12V by nature since they are essentially step-up transformers.
 
To use the 12V coils you would have to put them in parallel as opposed to the series arrangement with the 6V ones. The problem then is the primary resistance (the resistance across the +/- terminals) will be reduced and be possibly too low for the boyer which will have a resistance range it will operate with.
I say possible, as I don't know what your coil resistance is or what the Boyer will work with.

I had a friend who was into tuning engines who reckoned the 2 x 6V coils was quite clever but it was a bit beyond me.
 
Supposedly, the 6V coils were used to allow starting with a nearly flat battery, as the coils only need 6 volts for full spark. Boyers require a full strength battery to provide a decent spark, so the original thought behind the 6V coils is moot if you run a Boyer.
 
RedEvo said:
The bikes got Boyer Micro MkIII and standard switch gear at the moment.

Are the 12V coils OK to use?
Click to expand...


Boyer do say in their instructions that 12V coils (in series) can be used "With this system two 12 volt coils can be used as long as they are in good order"
http://www.boyerbransden.com/pdf/KIT000 ... 00017_.pdf
But for engines that have a reasonably high compression ratio, it wouldn't really be advisable to fit two 12V coils.
 
Rich_j said:
To use the 12V coils you would have to put them in parallel as opposed to the series arrangement with the 6V ones. The problem then is the primary resistance (the resistance across the +/- terminals) will be reduced and be possibly too low for the boyer which will have a resistance range it will operate with.
I say possible, as I don't know what your coil resistance is or what the Boyer will work with.

I had a friend who was into tuning engines who reckoned the 2 x 6V coils was quite clever but it was a bit beyond me.
Click to expand...

12 volt coils in parallel will not work with an electronic ignition, the oscillating circuit will not go to a very high value giving a weak spark, same goes for point ignition, paralleled coils will not work. If you are going to use a 12 volt coil, the best way is to use a coil with dual outputs and make sure it has a high enough primary resistance (around 5 ohms) or the Boyer will have a heart attack.

Jean
 
Just noticed the Boyer website says.....

"Refit timing cover. With this system two 12 volt coils can be used as long as they are in good order The
standard 6 volt coils do short out to the metal case, check for damage by the mounting clamps. A single dual
output coil can be used as long as its primary resistance is more than 3 ohms. This should be mounted on the
frame in a manner that will take the heat from the centre core."

Thoughts?

d
 
RedEvo said:
Just noticed the Boyer website says.....

"Refit timing cover. With this system two 12 volt coils can be used as long as they are in good order The
standard 6 volt coils do short out to the metal case, check for damage by the mounting clamps. A single dual
output coil can be used as long as its primary resistance is more than 3 ohms. This should be mounted on the
frame in a manner that will take the heat from the centre core."

Thoughts?
Click to expand...

If the coil clamps are too tight then the coil cases can be crushed, which can allow the coil windings to short to earth (as the coils and clamps bolt directly to the frame) I wasn't aware this affected 6V coils any more than 12V coils? Just make sure the clamps don't crush the coils. Some members have fitted a dual output 12V Harley type coil with some good results, but as the instructions say, the coil primary resistance must be over 3 Ohms.

Or there's the new high power Tri-Spark coils?
 
I'm running two huge 12 volt coils. They were good on the Boyer and better yet on the Tri Spark. Others have told me they have run 12 volt coils on the Boyers, perhaps it's not as efficient? I had to drop my resistor to get a good big blue spark, I think the 12 volt coils like closer to 12 volts.
 
Cookie said:
I'm running two huge 12 volt coils. They were good on the Boyer and better yet on the Tri Spark. Others have told me they have run 12 volt coils on the Boyers, perhaps it's not as efficient? I had to drop my resistor to get a good big blue spark, I think the 12 volt coils like closer to 12 volts.
Click to expand...

If they are car coils, they were probably meant to be used with ballast just like the Norton coils. At any rate, the primary resistance is probably low enough to produce a big fat spark on a car and when you use two in series on a Norton, he spark is most likely good enough.

Jean
 
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