what's the function of resistor wire on coil ?

installing pertronix ignition , and was just wondering why the coil needs a resistor wire ? is it to protect the points from frying out ?

Re: what's the function of resistor wire on coil ?

The resistor wire reduces the voltage to the coil and keeps the points from burning up so fast.

Re: what's the function of resistor wire on coil ?

excellent ! can't decide to get a regular coil or just throw 12 volts directly to the igniter.

Re: what's the function of resistor wire on coil ?

A little more information for you. As Don mentioned, the resistor rerduces the voltage to the coil...sort of.

The reason the resistor is there is to prevent the coil from overheating when the ignition is on and the engine is not, and at low rpms. It does this by limiting the current flow through the coil.

The coil has very little resistance, but quite a bit of primary inductance. Without the resistance, when the points close, the current in the inductor would ramp up linearly to a very high value, causing the coil to overheat. With the resistor, as the current ramps up the resistor drops some of the voltage...the result is an logarithmic curve, which has a maximum current value no matter how long the points are closed.

Why bother explaining this? It may change the type of coil you decide to use. The lower inductance, the quicker the coil current comes up, which favours high rpm spark energy (flamethrower etc), at the expense of low rpm energy.

A standard coil has comparably larger inductance which favours lower rpm use. Given we use lower rpms mostly (Under 5k) I feel the stock coil is better for the application.

The electronic ignitions tend to have internal current limiting, and therefore don't need an external resistor. This is ideal as the increase in current through the coil primary is as fast as possible, but the current is also limited to prevent coil overheating.

C

Re: what's the function of resistor wire on coil ?

When I did my Ignitor II I changed out the coil to a Flamethrower II so I could eliminate the resistance wire.

Re: what's the function of resistor wire on coil ?

What makes this a little confusing sometimes, is that some coils have the resistance built in. So, you don't have a resistor and a coil, just a coil, but the resistor is still there, it's just hiding!


Regardless, 'resistance type' meaning resitor and coil, or resitor/coil combo do not need a current limiting device, and a 'flamethrower' coil only type does need one.

So, if you're going without a resistor, the right question to ask is does the ignitor have a current limiter built in?


Chay

Re: what's the function of resistor wire on coil ?

I got the Pertronix 1 system. I "hot-wired" the positive red cable directly to battery+ and the negative to coil - . Wow, what a difference in starting. The boat started in 2 rev's. A lot better than points system.

I found a positive lead on the starter solenoid that is only hot in "run" position and I think that's where I can hook up the + from the igniter.

Re: what's the function of resistor wire on coil ?

CaptainMak said:

I got the Pertronix 1 system. I "hot-wired" the positive red cable directly to battery+ and the negative to coil - . Wow, what a difference in starting. The boat started in 2 rev's. A lot better than points system.

I found a positive lead on the starter solenoid that is only hot in "run" position and I think that's where I can hook up the + from the igniter.

Click to expand...

Nope, you will burn up that coil unless it says on the side of it "internal resistor" If it says "Use External Resisitor" you`ll fry the coil.
There is no hot lead on the solenoid "hot in run position". The small lug gets its power from the key on "start" and the other small lug supplies 12v to the coil only in "start"position.

Re: what's the function of resistor wire on coil ?

hmm, I'll test it again, but I am pretty sure it was hot only when the key was is the "on" position (one click clockwise)