Question for John T :ign coils

In a set of instructions for a Mallory igntion it states to run a 2-4 ohm coil for a single plug head. Then for dual plug heads it states an ohm value of 1-2 ohms per coil [adding up to the same value as the single]. Now you have two coils at the same ohms as a single plug set-up. Would this somehow cut down the spark energy at each plug in the dual plug set-up. I have a link to the instruction sheet if it works.
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Not John, but a friend in Electricity. Yes it would. with the same approximate current flowing through 2 coils instead of one the high voltage output would be divided to each. Most systems are powerful enough to make this a moot point, but it does speak to greater plug maintenance with older leaded fuel and poor oil found in earlier machines. The limitation is point life. If the coils were wired in parallel, and of the higher Ohm rating the total resistance would be 1/2 the intended resulting in rapid point deterioration. If they were wired in series at the higher ohm rating, they would make very weak spark. Jim

A dual plug head uses two totally independent ignition system with little to no shared wiring. The idea is that if one ignition system fails, the machine will limp home on the other ignition system.
We limped into camp once up a time with a P&W 985 Wasp Junior firing mostly on one mag.

For sure on a Wasp or other Aircraft Rated engine, as it is required. But many engines use twin coils and one "switch" My Nissan PU has 2 Plugs/cyl, 2 coils, one timing sensor, and a computer delay to fire the plugs milleseconds apart. Jim

Wow, I may not be smart enough to analyze your great question. So here are my initial thinking out loud thoughts then maybe we can conclude something:

It looks to me like for the two coil set up they are using two 6 volt coils in series since a 12 volt coil is more like 3.5 ohms while a 6 volt is like half that or 1.75 (they say 1 to 2 or 2 to 4). But that's for an automotive or tractor application, but still, their values and how its wired leads me to call them a single 12 or tWo sixes in series, albeit slight different ohms values then an auto coil

That being said, an auto coil is actually wired as an autotransformer with the opposite HV tower lead connected to one of the small LV terminal and the HV is therefore between frame (or which small terminal) and the HV tower output.

On the loss spark systems like Deere Pony motors used (and I think Onan Gensets) there was a single Primary + and - while the HV (NOT autotransformer) had one end to one plug and other end to the other plug.

BUT I HAVE NO IDEA HOW THOSE COILS ARE CONFIGURED, auto transformer or no connection from HV to LV like on Deere or Onan coils that fed 2 spark plugs with a single LV Primary winding???

AS far as high voltage, a 6 volt coil can yield as high a spark as a 12 volt, its all in the current and turns ratios so two sixes in series could still produce same HV HOWEVER IF THE COILS ARE WIRES AS AN AUTO COIL AUTOTRANSFORMER the HV would be between the towers and that center series tie point AND THAT MAKES NO SENSE.

I GUESS I HAVE TO KNOW THE INTERNAL HV AND LV THE COIL WIRING BEFORE I CAAN SAY MORE?????

Like Jim was talking if the 2 HV outputs are in series each is only 1/2 of the total but I don't see that as how the system works.

Im hungry were getting ready to grill some steaks, me and a buddy are in our RV's up in Minnesota somewhere but I will check back later. Maybe yall have the answer ??? but how those coils are configured is key, are they autotransformers or open HV ended like Deere pony motor coils or what???

John T I know some things (darn few lol) but I don't know everything

Good question DR, ya got me stumped

Onan also used the lost spark system.

The old Evenrude & Johnson 2 cylinder horizontal snowmobile engines had just one set of points that fired both cylinders at the same time using 2 coils.

After I slept on it heres my final thoughts:

The 2 coils are 6 volt coils wired in series at 12 volts so each coil has its full required current and voltage so each plug gets the same energy and all that is required. Due to LV primary resistance, coil current, and LV to HV turns ratios the spark in each is about the same or near as much or the same as if it was a 12 volt coil.

The 2 coils are autotransformers same as an auto coil and NOT a loss spark coil.

Once coils HV output will be POS ground the others NEG ground and the common point in the autotransformer configuration is in the center where the 2 coils join therefore they are at opposite polarities with respect to frame ground.

This may or may not help but absent the coils internal wiring configuration this is the best I can do. I say each plug has the same spark energy as if it were a 6 volt coil on a 6 volt tractor which is the same if it were a single 12 volt coil on a 12 volt tractor.

Any thoughts?????????????

John T

I guess if it was inadequate to fire both plugs there would be alot of unhappy Mallory buyers. It seems you are familar with the ohm values of different voltage coils. I have it working fine on another bike. Some of the instructions are a bit unclear.

a lot ofthe bike systems are more concerned with not burning up the electronics, and therefore limiting the total current you can have

It is a 1949 .

dr, I have been following this with interest. It appears you are using two dual output coils with the primarys connected in series and triggered by one unilite module. If I remember, I believe the sportster orginally used one dual output coil with a single point set, a wasted spark system.

I have a question if I may: How will the coil outputs be connected? For example; will both outputs of coil number one go to the plugs in cylinder number one and the output of coil two to cylinder two? Or will you configure it as before with each coil firing a plug in each cylinder?