This has very little to do with the original discussion of points,
condensers, and spark, so if you're tired of coils and transformers, delete
now.
At 07:28 PM 8/18/98 -0500, ccrobins wrote:>
> .... I suppose I'll be forced to go crack a textbook, now. ....
>
>Harlan Jillson wrote:
>> .... don't forget that the coil "primary" and "secondary" are both part
of the same windings, being an autotransformer, and that does change the
math a little....
Save your effort Charlie, I already did the book worm chore, just to be
sure my memory was still good. There is a decent description of an
autotransformer in Colliers Encyclopedia.
An autotransformer is basically one continuous winding with a center tap,
so you only have three electrical connections rather than four. The length
of winding between the center tap and one end is shared by the input and
output circuits. In short, it makes for less material for construction
because the input and output are sharing the core and windings, and it
boosts efficiency a bit because not all of the current has to be
"transformed". If anyone wants a more complete description of exactly how
it works, go look it up, because I don't feel like re-writing the book here.
Autotransformers are generally used for small step-up or step-down ratios,
like 2:1 or 4:3, where the input and output currents are not too much
different and can comfortably be accomotated with the same wire for the
windings. Also, as this ratio aproaches 1:1 the amount of current actually
going through the winding is less, and it starts looking like two
through-connect wires.
Im not sure the single spark ignition coil truly qualifies as an
autotransformer, because the step-up ratio is so high, at least 100:1 or
higher, and the primary winding is constructed of heavier gauge wire to
carry the larger current. What makes it look like an autotransformer is
the fact that the two windings have one end connected in common so they
will have the same potential (voltage) at that point (like the common end
connection on a center tap transformer) and only have three leads to the
outside world.
Now I'm sort of speculating on the next statement, but I think that the
waste spark ignition coil (dual spark output) is not an autotransformer,
because it has four external leads and no need to have the windings
connected at any point internally. If it is an autotransformer, it's just
a matter of efficiency, and one of the input leads will be common with one
of the output leads, easy to check with an ohm meter.
Now if anyone else wants to continue this thresd, you have my blessing, but
I'm out of it, already took my best guess here.
Baeney Gaylord
1958 MGA with an attitude
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