Jesus stop. What your saying makes no sense at all. Parallel and Series is how batteries are wired not how coils "connect electrically"
It's how
any electrical components (including resistors, which is all our "coils" really are from an electrical perspective) are wired, not just batteries.
A parallel coil is when you wrap a single coil with 2 strands or more of wire
Electrically, there is really no difference between this, what you're calling a "parallel coil" (try not to be too jealous of my mad MS-Paint skillz; I'm just illustrating a point, not a textbook):
... and this, which is "two coils wired in parallel":
...both are a "parallel" circuit, and the total resistance is found by the formula:
R
t = 1 / ((1/R
1) + (1/R
2) + (1/R
3) + [...] + (1/R
n))
...where R
t is the total resistance, and R
1-R
n are the individual resistances of each coil/resistor in the circuit. In the (most common, for our purposes) case of two, identical coils, this can be simplified to:
R
t = R
i/2
...where again, R
t is the total resistance, and R
i is the individual resistance of each of the two (identical) coils. I'm pretty sure that in the post I replied to, when Unsneaky said "you need to make 1 parallel coil .4 ohms when you make them dual it will cut to .2 ohms", they were talking about the second type: "
you need to make 1 parallel coil .4 ohms when you make them dual it will cut to .2 ohms" == "
you need to make each individual coil in the circuit at .4 ohms so that when you wire them in parallel, it will total .2 ohms."
Now on the other hand, a
series dual coil (or, "two coils wired in series") is a different animal entirely, and would look something a bit more like this:
...and in this case, finding the total resistance would simply be a matter of adding up all the individual resistances in the series:
R
t = R
1 + R
2 + R
3 + [...] + R
n