Re: auto ignition coil: why autotransformer?

George <_g_bnotreallymyaddresseccles@xxxxxxxxxxx> wrote in
news:a3p5j2510bu7md5fqcseuborf9ljkq8e56@xxxxxxx:

I want to use an old automotive ignition coil to generate a spark. I'm
puzzled that the (HV) secondary is connected to the primary. (I guess I
knew this, but I never gave it much thought before.) So, the spark
return current has to go through the battery and the harness:

________+12__________________
| | |
| | |
Batt PRI SEC
| | |
| | | (HV lead to distributor)
| | |
| POINTS SP PLUGS
| | |
|_____Gnd_____|_____________|


It seems it would make more sense to have an isolated secondary, with
one side connected to the coil's case. Then, the spark return current
could just go through the block back to the coil:

________+12____ _______
| | | |
| | | |
Batt PRI | SEC
| | | |
| | | | (HV lead to distributor)
| | | |
| POINTS | SP PLUGS
| | | |
|_____Gnd_____|_______|_____|
(block)

I must be missing something?

Thanks,
George


yes you are. The spark return is through the block since it is at ground
potential and so is one side of the coil....


spark
o
|
c
c sec
c
12v- |
c
c pri
c
|
gnd

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