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

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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.
Click to expand...
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.
Click to expand...
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?
Click to expand...

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
Click to expand...
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.
Click to expand...
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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