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Re: DC resonant charging



Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 07:39 PM 2/11/2007, Tesla list wrote:
Original poster: Ed Phillips <evp@xxxxxxxxxxx>

Hi,

I am thinking of building a small DC resonant charging TC. As there
are no 15 kV NSTs available in this country, I need to look for
another source of HV.

How many mA of filtered DC could I expect to get from a standard 12 V
car ignition coil? Target DC voltage is 15 kV.

Any help is appreciated very much.

Bye             Herwig "

   Based on experience here I doubt if you'll get as much as a milliamp.


I'd agree... you might get a "bit" more...

Here's the scoop... the typical car coil is designed to have the current be about 5A when the points open, and take on the order of a millisecond or so to get there. (6000 RPM=100 rev/second, 8 cylinder 4 stroke engine = 400 sparks/second 2.5 milliseconds per spark). Standard Kettering ignitions on a v-8 ran a dwell angle of about 30 degrees (out of either 90 or 45 degrees, I'm not sure which), which is roughly consistent.

The current waveform would then be a ramp lasting about a millisecond to a peak of 5A (so average current is 2.5A), with an overall duty factor of, say, 50%. So the average current through the coil is about 1-2 Amps... and this sets the amount of heating (because of the IR losses in the coil).

Now.. 1 Amp on the primary of a 100:1 transformer means you get 0.01 amps (10 mA) on the secondary.