12V coils in series

When I bought my commando, it was very hard to start and keep running. I was young and clueless back then.... Now, I'm no longer young... 8)

Anyway, My commando's original set up when I got it was Points, and two 12 volt coils wired in parallel WITH a balast resistor. No wonder it ran so poorly back then. I really didn't know that my ignition system could be vastly improved. As the years went by, I did enough reading about commandos to switch out the 12 volt coils for 6's in series, and then get rid of the points for the analog boyer... the bike got better with every upgrade.

todays version of that same bike is a boyer microdigital, 12 volt dyna dual lead coil, and numerous extra grounds to make sure I have a strong spark. Today's version starts up easily, and runs solidly.

I struggled to make my bike reliable back when I got it around 1978, but really didn't know enough to succeed in my task. I really wanted to ride the commando around back then when everyone else was riding japanese bikes.... but it took a long time for me to learn the things I needed to do. My bike has benefitted greatly from that learning to get it to the point where it's pretty well sorted out, and a very reliable rider, but not so much a beauty queen... :lol:

*One of the great things about this site is that you don't have to understand all the physics to benefit from the advise of those people who do.

The standard wiring on a points Commando is not really two coils in parallel. As Dyno Dave says it is effectively two separate ignition systems. the coils don't come into contact with each other electrically apart from sharing a common earth.

gripper said:

The standard wiring on a points Commando is not really two coils in parallel. As Dyno Dave says it is effectively two separate ignition systems. the coils don't come into contact with each other electrically apart from sharing a common earth.

Click to expand...

Thank you. That's it in a nutshell. I didn't really get that when I first read Dave's post.
So any postulation about the resistance of two 12V coils wired in parallel doesn't count for anything here.

What does count is the total resistance when wiring the coils in series, and the 12V coils will offer twice the resistance of of 6V coils.

Without digging up the instruction sheet for the analogue Boyer that I installed some time in the early nineties, I recall them recommending 6V coils in series, but saying that 12V coils in series could be used " as long as they are in good condition." After reading through this thread I would say that other engine factors are also important.

My 1970 bike had 12V coils so I used them. Unfortunately, at the same time I swapped to a single carb. setup using an old Amal 932 I had lying around, and the bike was effectively unused for some years. It was doomed to failure.

I now have a Pazon surefire with a twin outlet coil supplied by Pazon, and a new Amal 932 carb. The bike gets used now - sort of.

MFB said:

gripper said:

The standard wiring on a points Commando is not really two coils in parallel. As Dyno Dave says it is effectively two separate ignition systems. the coils don't come into contact with each other electrically apart from sharing a common earth.

Click to expand...

Thank you. That's it in a nutshell. I didn't really get that when I first read Dave's post.
So any postulation about the resistance of two 12V coils wired in parallel doesn't count for anything here.

What does count is the total resistance when wiring the coils in series, and the 12V coils will offer twice the resistance of of 6V coils.

Without digging up the instruction sheet for the analogue Boyer that I installed some time in the early nineties, I recall them recommending 6V coils in series, but saying that 12V coils in series could be used " as long as they are in good condition." After reading through this thread I would say that other engine factors are also important.

My 1970 bike had 12V coils so I used them. Unfortunately, at the same time I swapped to a single carb. setup using an old Amal 932 I had lying around, and the bike was effectively unused for some years. It was doomed to failure.

I now have a Pazon surefire with a twin outlet coil supplied by Pazon, and a new Amal 932 carb. The bike gets used now - sort of.

Click to expand...

Just remember that when using points and 6 volt coils that there is a ballast resistor in the loop. That does two things, it prevents the 6 volt coil from burning out. It also reduces the voltage across the points to help them last longer. I personally think this was why 6 volt coils are used, to help with point(s) life. When you make the jump to 12 volt coils I am pretty sure the ballast gets tossed.

Pete

it

The earlier question was why does it run fine sometimes with the 12v in series?
I want to submit my Layman's answer to the experts for review.
The 12v series has more draw than the a single phase can produce at low RPM.
Thus drawing on the battery. So performance is battery related and depending on load, lights etc
Makes for inconsistent operation.

MichaelB said:

The earlier question was why does it run fine sometimes with the 12v in series?
I want to submit my Layman's answer to the experts for review.
The 12v series has more draw than the a single phase can produce at low RPM.
Thus drawing on the battery. So performance is battery related and depending on load, lights etc
Makes for inconsistent operation.

Click to expand...

With two coils connected in series, their resistance is doubled so less draw than two 6V coils.

http://www.britcycle.com/Products/331/331_series.htm

NOTES: Coil Requirements - Boyer Electronic Ignition Kits work best with less than six ohms total resistance on the primary side of the coils. Since the coils are wired in series, the resistance is the total of all the resistance in all the ignition coils in the system. Stock 12 Volt coils have 3.5 ohms of resistance each, so a twin cylinder bike with two coils has a total resistance of seven ohms, and a three cylinder bike has a total resistance of 10.5 ohms; both more than the limit of the Boyer kits. The modification is to install 6 Volt ignition coils, which have a resistance of approximately 1.7 ohms each, so that the total resistance in a twin is 3.4 ohms, and in a triple is 5.1 ohms, both within the allowed impedance range. Only the ignition system is involved, nothing else needs to be changed. Since single cylinder bikes have one coil (3.5 ohms) they do not require a new coil. Later Norton Commandos have six-volt coils with a ballast resistor so the coils are kept and the ballast resistor removed.

Click to expand...

Deets55 said:

Just remember that when using points and 6 volt coils that there is a ballast resistor in the loop. That does two things, it prevents the 6 volt coil from burning out. It also reduces the voltage across the points to help them last longer. I personally think this was why 6 volt coils are used, to help with point(s) life. When you make the jump to 12 volt coils I am pretty sure the ballast gets tossed.

Pete

Click to expand...

If it's just about increasing the resistance in order to increase the life of the points and coils, then why didn't they simply stick with the 12 volt coils without a ballast resistor?

I'll answer that.

While I can't explain the electrical machinations as to how it works, I believe they changed to 6 volt coils plus ballast resistor to enable the coils to work well if the battery voltage was low.

My explanation for the 6V conversion is for the then impending (doomed) starter. for 1971
The 1971 coil would have had, like in 1975, a ballast bypass for hot starting. The failed 71 starter mod did not make the 6V system unusable...so it stayed.

I'm an electrical retard , but if what I learnt recently while looking for coils for my land rover is there is know such thing as 6 . 12 & 24 VOLT COILS, the only thing that changes is the ohm rating.

I'm now erecting the flack deflector and waiting to be roasted alive for the above comment

splatt said:

what I learnt recently while looking for coils for my land rover is there is know such thing as 6 . 12 & 24 VOLT COILS, the only thing that changes is the ohm rating.

Click to expand...

Yes, that is true.

Being an electrical dummy, I find it helpful to use the analogy of electricity flowing through a conductor being similar to water flowing through a pipe.
Whereby voltage = pressure, and current = volume flow.

Resistance is similar to the friction loss in the pipe, so a the smaller the bore and the longer the length of pipe means greater total resistance.

Higher resistance will restrict the flow (current) but not lower the pressure (voltage).

Lower resistance will allow greater current flow, but at the risk of causing pressure (voltage) drop.

Taken to the extreme, very high resistance would cause flow to cease, which would not be conducive to the operation of the system.

There are subtle differences however:
Low resistance /high current in wires can cause heating of the wires and high drain on the battery.
If a wire is cut, resistance goes high (insulated by air), so flow ceases.
You know what happens if a pipe is cut.