"Ian Jackson" wrote in message
...
In message 49f90619.961412546@localhost, Don Pearce
writes


But isn't that a series of splats, rather then a continuous arc? I
know how my boiler behaves when it is firing up, and it is "tick tick
tick, whoomph".

No. Unless I'm completely mistaken, it's a continuous arc - well,
probably a 50 or 100Hz arc. I think the plug's driven by the mains
(stepped up). Both sparkplug boilers were like that.
--

If it's anything like my boiler then the sparkplug is simply connected to
the high voltage (around 2kV) secondary of a mains transformer. This
transformer is energised as soon as the blower motor starts, though the oil
tap is not turned until around 15 seconds later. The transformer is switched
off as soon as light from the flame is detected by a light-dependant
resistor or, if no light is detected within 30 sec, the whole system trips
out until it is manually reset.

David.