12V coils in series

Hi all.
I've done a search and there's alot of info but to me it is all over the place and nothing clear cut in any one post IMHO. So here goes

A combat i recently purchased has a MK3 Boyer with 12V coils The wire that runs between the coils is wired neg on one coil to the posi post on the other coil.
1] Is this what they call wired in series?
2] If using 12V coils should they be wired in parallel?
3] I assume parallel is + to +

Thanks Brett

For two coils 12V in parallel, 6V in series. Your 12V coils looks to be in series and need to be wired parallel or swapped for 6V coils, so the boyer black wire goes to both -ve coil terminals and the red connects to earth and both +ve terminals.

dart6 said:

A combat i recently purchased has a MK3 Boyer with 12V coils The wire that runs between the coils is wired neg on one coil to the posi post on the other coil.
1] Is this what they call wired in series?

Click to expand...

Yes.

dart6 said:

2] If using 12V coils should they be wired in parallel?

Click to expand...

No. Do not connect 12V coils in parallel when using a Boyer (and some other types of EI).

dart6 said:

2] If using 12V coils should they be wired in parallel?

Click to expand...

L.A.B. said:

No. Do not connect 12V coils in parallel when using a Boyer (and some other types of EI).

Click to expand...

The only way to use two 12v coils in parallel is to use a diode in the drive line of each coil. However this still is an undesirable configuration.
A combat would have originally had 2-6v coils. Makes you wonder why the coils got swapped?

My 1970 Fastback originally had two 12v coils and no ballast resistor running with points. I fitted a Boyer and used the two 12v coils wired as per the Boyer diagram i.e.. in series no problem (still no ballast resistor) years later I changed the coils to 6volt, no big difference.

From 1971 on, stock Norton Commando ignition using points would have two 6 volt coils run in parallel, and a ballast resistor. (1968 - 1970 didn't use a ballast resistor). Boyer tells you to run the two 6 volt coils in series, no ballast resistor.

Most late 60's/early 70's Triumph twins use two 12 volt coils run in parallel, no ballast resistor. Boyer tells you to run the two 12 volt coils in series. They also say that in some high compression installations, you may need to swap the 12 volt coils for 6 volt coils. Problem is that in some installations, two 12 volt coils in series can overload the Boyer black box, leading to erratic running.

If your Norton is running fine with two 12 volt coils in series, there is no need to change it.

Stephen Hill

Stephen Hill said:

From 1971 on, stock Norton Commando ignition using points would have two 6 volt coils run in parallel, and a ballast resistor.

Click to expand...

The coils are physically mounted in parallel but:
I will advise everyone to disregard the "run in parallel" claim since they NEVER run at the same time in the normal points configuration, they are duty cycle alternating @ 45% each coil. The ballast is running @ 90% total for both cylinders/coils.
For those who did not spend 6 years in college and 40+ years in technical industry as I did, I also taught college level for 7 years.
Correct terminology counts when scoring a test paper or when wiring equipment. I did both :mrgreen:
If you want to see... come by for one of the tech sessions:
http://nneno.org/events-calendar

Stephen Hill said:

Most late 60's/early 70's Triumph twins use two 12 volt coils run in parallel, no ballast resistor. Boyer tells you to run the two 12 volt coils in series. They also say that in some high compression installations, you may need to swap the 12 volt coils for 6 volt coils. Problem is that in some installations, two 12 volt coils in series can overload the Boyer black box, leading to erratic running.

If your Norton is running fine with two 12 volt coils in series, there is no need to change it.

Click to expand...

I'm not sure two 12V coils in series will "overload" the Boyer box (I'd think that would be more likely if the 12V coils were connected in parallel?) but with two 12V coils connected in series they will be sharing the available voltage so there's a loss of spark energy with 12V coils although it's adequate for many British bike applications.

Here is how Brandsen describes the effect of coil resistance:

"A wrong type of ignition coil with a very low primary resistance (under 2 to 3 ohms) will draw a very high current and produce a large volt drop across the wiring. All these will keep turning the ignition on and off, generating a chain of sparks."

6V Lucas coils draw 1.7-1.9 ohms, 12V 3.3-3.8 ohms
So two 6 volt coils in series would draw about 3.6 ohms, and two 12 volt coils would draw about 7 ohms, right?

In which case, I don't understand why two 12 volt coils in series would lead to a low voltage situation. Seems like two 6 volt coils would be more likely to create this problem. Thoughts?

Stephen Hill

Stephen Hill said:

Here is how Brandsen describes the effect of coil resistance:

"A wrong type of ignition coil with a very low primary resistance (under 2 to 3 ohms) will draw a very high current and produce a large volt drop across the wiring. All these will keep turning the ignition on and off, generating a chain of sparks."

6V Lucas coils draw 1.7-1.9 ohms, 12V 3.3-3.8 ohms
So two 6 volt coils in series would draw about 3.6 ohms, and two 12 volt coils would draw about 7 ohms, right?

Click to expand...

"Draw" = current = Amps. Ohms = resistance.

Stephen Hill said:

In which case, I don't understand why two 12 volt coils in series would lead to a low voltage situation.

Click to expand...

Two 12V coils in series won't because the total resistance will be around 7 Ohms as stated, and two 6V coils will be about 3.6 Ohms but that's not what they are saying, they are saying the wrong type of ignition coil i.e. one coil or one dual coil with a low primary resistance of less than 3 Ohms as it says in the instruction sheets "A single dual output coil can be used as long as its primary resistance is more than 3 ohms."

Just throwing my two cents in here, and I could be off base on this. I think that two 12 volt coils, in series, in a 12 volt system do not receive enough voltage to operate at full power. My thinking is if you replace the coils with light bulbs in a similar fashion you can see the problem. In a 12 volt system, if two 12 volt bulbs are wired in series they would be dim, but two 6 volt bulbs in series would be bright. So two 12 volt coils in series are only operating with 1/2 the required volts needed in a wasted spark system such as a Boyer.
Two 12 volt coils in series might also try to draw more power from the Boyer box and this could also be why Boyer doesn't recommend using them. IMHO

Pete

Deets55 said:

Just throwing my two cents in here, and I could be off base on this. I think that two 12 volt coils, in series, in a 12 volt system do not receive enough voltage to operate at full power. My thinking is if you replace the coils with light bulbs in a similar fashion you can see the problem. In a 12 volt system, if two 12 volt bulbs are wired in series they would be dim, but two 6 volt bulbs in series would be bright. So two 12 volt coils in series are only operating with 1/2 the required volts needed in a wasted spark system such as a Boyer.
Two 12 volt coils in series might also try to draw more power from the Boyer box and this could also be why Boyer doesn't recommend using them. IMHO

Click to expand...

But, the total resistance of two 12V coils in series is higher than two 6V coils.

Boyer recommends 6V coils because of what you said in your first paragraph that two 12V coils in series produce less spark energy than two 6V coils.

Okay, cool discussion. Now let's apply all this theoretical analysis. Who can explain why in some installations, using a Boyer ignition, no ballast resistor, two 12 volt coils WIRED in series, the bike will run fine. And then sometimes it won't? And installing two 6 volt coils WIRED in series, everything works again.
It seems like some electrical values in the first 12 volt coil scenario are marginal but functional, But with minor changes, the ignition system suffers.

What is going on here?

Stephen Hill

Stephen Hill said:

Okay, cool discussion. Now let's apply all this theoretical analysis. Who can explain why in some installations, using a Boyer ignition, no ballast resistor, two 12 volt coils WIRED in series, the bike will run fine. And then sometimes it won't? And installing two 6 volt coils WIRED in series, everything works again.
It seems like some electrical values in the first 12 volt coil scenario are marginal but functional, But with minor changes, the ignition system suffers.

What is going on here?

Stephen Hill

Click to expand...

Well, as LAB said, two 12 volt coils in series produce less spark energy. Therefore, in some engines where everything else is cock on, and perhaps low compression, this will be fine. But in another engine that is not in such good fettle, and / or is high compression, those weak sparks will show up as poor running.

That's my thoughts at least.

Stephen Hill said:

Okay, cool discussion. Now let's apply all this theoretical analysis. Who can explain why in some installations, using a Boyer ignition, no ballast resistor, two 12 volt coils WIRED in series, the bike will run fine. And then sometimes it won't? And installing two 6 volt coils WIRED in series, everything works again.
It seems like some electrical values in the first 12 volt coil scenario are marginal but functional, But with minor changes, the ignition system suffers.

What is going on here?

Click to expand...

Engine compression appears to be a major factor as higher compression needs more voltage for the spark to reliably jump the plug gap, as it says in the Pazon instructions;
http://www.pazon.com/files/PDF/PA2.pdf

"For low compression ratio engines (less than 9:1), two 12 volt coils connected in series can be used, but we strongly recommend running with two 6 volt coils connected in series or one 12 volt dual output coil with a primary resistance of 3 to 4.5 ohms."

Click to expand...

I seem to remember Boyer saying similar at one time.

Edit: Yes, the older Boyer instructions used to include the following information:

For low compression engines two 12 volt coils in series are satisfactory, but for racing and high compression engines two 6 volt coils in series or one 12 volt double ended coil with a primary resistance of 3 to 4.5 ohms will give the best results.

Click to expand...

L.A.B. said:

Engine compression appears to be a major factor as higher compression needs more voltage for the spark to reliably jump the plug gap, as it says in the Pazon instructions;
http://www.pazon.com/files/PDF/PA2.pdf

"For low compression ratio engines (less than 9:1), two 12 volt coils connected in series can be used, but we strongly recommend running with two 6 volt coils connected in series or one 12 volt dual output coil with a primary resistance of 3 to 4.5 ohms."

Click to expand...

I seem to remember Boyer saying similar at one time.

Edit: Yes, the older Boyer instructions used to include the following information:

For low compression engines two 12 volt coils in series are satisfactory, but for racing and high compression engines two 6 volt coils in series or one 12 volt double ended coil with a primary resistance of 3 to 4.5 ohms will give the best results.

Click to expand...

Click to expand...

Air is an insulator and the more air there is the more voltage required to create the plasma stream. Add gasoline which is also an insulator and the voltage requirement for plasma goes up. Once you have plasma ( called spark for us gearheads) you get the combustion.
All these manufacturers use the term resistance for the coils yet in reality it is inductance measured in henries (The henry (symbol H) is the SI derived unit of electrical inductance). The real difficulty is when you use Direct Current language to try and describe an AC alternating current action of physics. After all this is NOT electronics it's physics.
Do most or any of you know that a proper coil usually makes 2-3 sparks rather than one for each firing cycle. If you run 2 -12v coils in series you may degrade to only 1 sparking of the plug and on ocassion it may not sufficient to ignite. It can all depend on how open the throttle is or how cold and dense and humid the air is.
All of this may look great with a plug laying on the head in open air, but in the chamber the test really begins.
I'm only a master electronic technician, high voltage technician, electromagnetic technician, mechanical designer and fabricator and hobby gearhead and play at amature physics. So please don't expect to much thanks.

I did some research 10 years ago on coils on my distributor machine:
http://atlanticgreen.com/coils.htm
Followed up by some magneto research ...oh sorry Off topic.... commandos don't have those
send my post to the scrap heap...."other nortons"

I use a double ended 12 volt coil , probably from a Honda CB750. However my comp.ratio is standard for an 850.

Electricity in an ignition system amazes me.

In the Navy avaiation ground support electrical shop, we had a test rig for spark plugs; screw the set of plugs into the rig, hook up the leads of the distributor being tested, with it's coil, connect a shop air hose to the box, then turn on the rig.

You'd peer through each window and expect to see a nice steady arc at each plug. Any intermittency would be easy visible, indicating a bad plug. Sometimes even a very nicely cleaned plug that sparked just fine in open air on the APU cart would be DEAD on the test rig.

two 3 ohm resistance coils in series equals 6 ohms. two 3 ohm coils in parallel equals 1.5 ohms