MikeW wrote:

That's the type of thing I was considering
Retail energisers seem to run at about 500ma but a cars HT coil seem to
take 2amp (input)
So I was wondering what was inside the black box to conserve power.


They don't use car ignition coils, they use much smaller custom
transformers.

You can wind your own using a TV flyback secondary, but flybacks are
quite hard to get hold of these days.

--
Grunff