Can 6 volts coils be used in place of 12 volt coils ?

Fast Eddie

Fast Eddie

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A mate with 12v coils and points suspects a dud coil. Can he try with 6 volt coils to test the dud coil hypothesis?

Any down sides to running 6 volt coils in a 12 volt system ?
 
Without a ballast resistor, a 6V coil in a 12V points system will draw more current than is desirable. Likely to overheat the coil, might burn the points. Could overtax a marginal charging system.
 
Two 6 volt coils can be run in place of a 12 volt coil, if connected in series in a wasted spark set-up. I use a double-ended 12 volt coil off a Honda.
 
Triton Thrasher said:
Without a ballast resistor, a 6V coil in a 12V points system will draw more current than is desirable. Likely to overheat the coil, might burn the points. Could overtax a marginal charging system.
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Ok, thanks.

Don’t wanna do any of that!

He just wants to see if it’s starts and runs.
 
Measure the ohms of the 6 V coil, and put a resister of equal value in series with the coil.

Use a resister of at least 1 Watt. Will work for a start up test.

Slick
 
I suggest that you swap the coils and see if the plugs rat-out the a bad coil.

Before you do that remove the primary wires. With a good multmeter the coils should show equal ohm readings, give or take less than, less than. 3 ohms. Check both primary terminals to see if either shows continuity to the coil case, technically if you have an internal short either terminal will tell you. You will also see a difference when you do the resistance check across the 2 terminals.


Best
 
Fast Eddie said:
Ok, thanks.

Don’t wanna do any of that!

He just wants to see if it’s starts and runs.
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It'll be fine just to try
I accidentally ran my BSA b 44 for a while with a 6v coil until i realised the coil was getting really hot
 
Fast Eddie said:
Can he try with 6 volt coils to test the dud coil hypothesis?
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Possibly with two 6V coils connected in series with one coil HT going to one plug and the other 6V coil HT earthed/grounded would work as a 'test' with one of the two 12V coils connected to the other cylinder.
 
baz said:
It'll be fine just to try
I accidentally ran my BSA b 44 for a while with a 6v coil until i realised the coil was getting really hot
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It worked fine and runs a treat. He now has new 12v coils coming.
 
Fast Eddie said:
It worked fine and runs a treat. He now has new 12v coils coming.
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Yep the weird thing was I bought a rolling chassis that was complete bar the engine
Everything on it was 12v
The bulbs the hooter the dead battery etc
I fitted the b44 engine and it was ok until I started doing longer runs on it by which I mean 30 -40 miles and it started playing up
Whilst poking around I touched the coil it was really hot
I let it cool and rode back
When I removed it it was 6v !!!
Of course I don't know the history of the bike
 
Other than burning up eventually, he higher spark voltage is nice :)
Not 100% true but double the designed input voltage = double the output voltage.
 
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