Anyone Running MS+S with Direct coil drive?

I've got a switched 12V to the coil. Someone told me this is fine, someone else told me I should have a resistor in there. I know stock the coil got 12V directly while cranking but through a resistor while running.

I've got one of those "Blue" coils. Who knows if it actually does anything different.

Or should I just go out and spend a couple bucks on a MSD blaster coil?

Jordan

Awesome that it is running, great to hear.

As for your question re: coil voltage.
In general all coils use a reduced voltage, those that run without a ballast resistor usually have an internal resistor. The advantage of an external resistor is the ability to run a full 12V during cranking for maximum spark and then run through the resistors in the run mode.

Running a coil without a resistor will cause excessive heat, shorten the coil life, and can result in catastrophic failure of the coil (ever seen a coil explode? I have)

The specs on the coil should identify if an external ballast resistor is required or not.

Thanks Ian, that is what I was looking for. I'll see if I can google anything about the Blue I've got in there now.

Jordan

Maybe another question to ask,

What if I ran the 12V through the stock ballast resistor to the coil. So that even during start it is seeing the lower voltage? Think this would affect the starting on a car that only sees summer driving?

Jordan

Not at all. Like Ian said, some coils have an internal resistance, and many Volvos with external resistors didn't wire up a bypass during cranking anyway. You'll be fine.

Hey Matt,

I'm confused,

I'll have no problem running the 12V directly,

or

I'll have no problem running 12V through resistor, to the coil, in series, with no other 12V source. So in theory the coil is only seeing say 6V?

Jordan

What part of "you'll be fine" was confusing? LOL!

What I was saying is that lots of cars have coils hooked directly to 12v, and lots of them have an external resistor. Not very many have a resistor that gets bypassed during cranking. Aside from the K-jet 240s, i can't think of another one I've seen like that.

What Ian was saying is that some coils have higher internal resistance (3+ ohms, I think) that they limit amps drawn without help. Others have less resistance (about 1 ohm, IIRC) and need a resistor to cut down the current to survive.

Measure the resistance across the + and - terminals.

...and you call yourself a Dodge guy LOL

Many pre and early electronic ignition cars (god am I showing my age ) used a bypass coil system, (12v during cranking and 9v in run mode) Chrysler was the most famous because their resistor pack would fail on a regular basis. GM used a resistor wire system right in the harness external to the coil that I only saw 1 fail.

Matt is exactly right, if the internal resistance of the coil is too low the current draw increases, heat goes up and coil has a short life. I cannot remember the actual resistance measurments of the coils, what I can tell you is that the majority of coils use a ballast resistor, but do check your specifications.