Re: Ignition Coil Experience

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Hi Mike,

The peak current going into the ignition coil primary will be considerably
higher than 100's of milliamperes when the series capacitor/dimmer circuit
is used. When the Triac fires, the series capacitor may be charged with up
to TWICE the peak line voltage, and this energy is then suddenly "dumped"
into the primary each time the TRIAC fires. Assuming a low impedance source
(the incoming mains), the peak current can be many 10's of amperes, limited
mainly by the series inductance and resistance of the ignition coil and ESR
of the capacitor. The average power can also be significant. For example,
in another post where an ignition coil was being used on a 240 Volt circuit
using a 20 uF cap, the maximum bang size can be as high as 4.8 Joules, and
the average power being transferred to the coil approached 500-600 watts
(50-60 Hz)...

Best regards,

-- Bert -- 
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "Mike Veldman by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <vmike-at-email.ceat.okstate.edu>
> 
> I've done some work with automotive ignition coils, for their origional
> intended purpose and some others.  The numbers I'll use here are close
> approximates since it's been awhile.  In normal applications the coils
> primary current is in the 3 to 4 amp range at 6 to 9 volts, the secondary
> current under those conditions is divided by about a thousand.
> 
> A capacitor used in a series AC circuit will limit the current to approx.
> 20ma/MFD.  So, a 5uf is about 100ma to the coil primary and about a
> microamp out of the secondary.
> 
> I've used automotive coils in a number of applications for which they were
> not designed, successfully, but always at low current.  I do, however have
> one that will put out a measured 35ma secondary current at 20kv.  It
> consists of a 600 watt dimmer driving a bank of 660vac oil filled run
> capacitors (forgotten the total mfd) into a GM HEI coil suspended in a
> gallon of transformer oil (gallon paint can), used to flare off hard to
> ignite gasses from a grass gassifier project.  I was using ignition
> transformers, but their survivability rate was poor, this one has never
> failed.
> 
> For a tesla supply however, a NST is a lot easier.
> mike
> "I tried to contain myself, but I escaped"