Coil Selection.

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Josh Cox

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LAB, forgive me if I have already asked this question.... :D

Presently have the Boyer MK111 with two 12 volt coils, thinking of dual output single, thoughts ?.

Two 6 volt in series versus two 12 Volt in series ?.

Why put two 12 volt in series ?, if one coil stops working, so will the other, whereas if they are in parallel, yes more current, but the loss of a coil will not have you pushing the bike home......
 
Josh Cox said:
LAB, forgive me if I have already asked this question.... :D

Presently have the Boyer MK111 with two 12 volt coils, thinking of dual output single, thoughts ?.

Two 6 volt in series versus two 12 Volt in series ?.

Why put two 12 volt in series ?, if one coil stops working, so will the other, whereas if they are in parallel, yes more current, but the loss of a coil will not have you pushing the bike home......
Click to expand...
Dyna coil "DC71" 5ohm
 
Josh Cox said:
LAB, forgive me if I have already asked this question.... :D

Presently have the Boyer MK111 with two 12 volt coils, thinking of dual output single, thoughts ?.

Two 6 volt in series versus two 12 Volt in series ?.

Why put two 12 volt in series ?, if one coil stops working, so will the other, whereas if they are in parallel, yes more current, but the loss of a coil will not have you pushing the bike home......
Click to expand...

Electronic ignitions don't work with the coils in parallel, if you try it on a bench, you will have sparks on both, but they are weak and unable to jump the gap at higher pressures. That's just how it is.

Jean
 
Josh Cox said:
Why put two 12 volt in series ?,
Click to expand...

Why indeed. Two 12V coils in series isn't really a good thing as the spark energy will be less than two 6V coils in series.


Josh Cox said:
if one coil stops working, so will the other
Click to expand...


Not necessarily, the fault would have to be in the primary winding of one coil for it to affect both.


Josh Cox said:
whereas if they are in parallel, yes more current, but the loss of a coil will not have you pushing the bike home......
Click to expand...


You may still have to push the bike home? If the coil current exceeds 5 amps it will eventually blow the Boyer box!

As far as I'm aware Boyer do not recommend that coils are wired in parallel-either 12V or 6V.
 
I have measured the old 12 volt coils, 4.4 ohms each.

In parallel they would exceed Boyers recommended current, in series, without a condensor cap I guess they must be quite adequate.

Still throwing them in the bin and replacing them with new technology.
 
I have measured the old 12 volt coils, 4.4 ohms each.

In parallel they would exceed Boyers recommended current, in series, without a condensor cap I guess they must be quite adequate.
Click to expand...

In series, they will produce much reduced spark. 8.8 ohms combined.

Still throwing them in the bin and replacing them with new technology.
Click to expand...

Others have chimed in with suggestions - I'll add one more: TriSpark 6V coils. They look, smell and taste just like Lucas but with better spark output.
 
I have a Triumph TR6C running two PVL 12V coils with a Boyer MkIII ignition and it seems to work fine. Boyer recommends two 6V coils and total resistance 3 to 4.5 ohms. The 12V coils seem to work fine in some applications and not in others. On my Commando, I run a 5 ohm Dyna dual-fire coil. Works great.
 
Two 12 volt coils in parallel will not work. The inductance of the coils is what is important especially with electronic ignition. The inductance does not change with the same formula as resistance when you put them in parallel and it will easily cause damage to the module.
Two 6 volt coild in series works fine or one 12 volt coil will make a similar output. Jim
 
Reply from Boyer:

Q-Hello,

I presently have a Norton Commando which has Boyer MK111 fitted, why are the two 12 volts ignition coils on this system wired in series ?.

The bike is 12 volt. ( I understand the increased resistance of two in series )

In series, if one coil open circuits, then no ignition at all, in parallel you would still be able to ride home......

Thanks

Joshua Cox
Cairns Australia

A-Hi Joshua,

No with two in parallel the energy from one coil will flow into the other that is not under compression conditions, also the system will draw to much current.

Regards,
Tech Dept

Boyer Bransden Electronics Ltd
Frindsbury House
Cox Street
Detling
Maidstone
Kent
ME14 3HE

Last Question, will two 6 volt in series compared to two 12 volt in series make the bike easier to start ?.
 
Last Question, will two 6 volt in series compared to two 12 volt in series make the bike easier to start ?.

Absolutely, It is a wonder it runs at all with 2-12 volt coils in series. Jim
 
I hope I did it correctly. Installed a Tri-spark in my '73 750. Wired it up per instructions to the stock Lucas coils. Didn't occur to me to look to see if there were ballast resistors but I assumed there were and that I'd leave em there. I saw something in the part number on the coils that suggested 6 volt so I went ahead.


Hundreds of trouble free miles but now I'm worried. Did 6 volt coils come on my bike? How can I tell, how do I know definitively?
 
I believe you only need a ballast resistor if you are using a single 6 volt coil in a 12 volt system.

If you have two 6 volt coils in series, that does not require a ballast resistor.
 
xbacksideslider said:
I hope I did it correctly. Installed a Tri-spark in my '73 750. Wired it up per instructions to the stock Lucas coils. Didn't occur to me to look to see if there were ballast resistors but I assumed there were and that I'd leave em there. I saw something in the part number on the coils that suggested 6 volt so I went ahead.


Hundreds of trouble free miles but now I'm worried. Did 6 volt coils come on my bike? How can I tell, how do I know definitively?
Click to expand...


With a tri-spark the two six volt coils will be wired in series and will act like one 12 volt coil. No worries and no ballast resistors needed. Jim
 
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