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Re: [TCML] auto coil HV supply

Hi Doug,

The problem is that every time your dimmer TRIAC or SCR fires, the series capacitor and induction coil primaries generate a high-current, oscillatory voltage transient that appears across your AC mains. It's inherent in the operation of this circuit. The larger the series capacitor, the higher the transient currents and the greater the risk of damage to other devices on the same circuit.

Under worst case conditions, the series capacitor will be charged to the previous peak line voltage when the dimmer fires. For 120 volt mains, if the dimmer fires at a mains voltage peak (170 volts), the fully charged series capacitor dumps an ADDITIONAL 170 volts through your ignition coil primaries. A portion of this 340 volt transient appears across the mains, potentially wreaking havoc to other devices connected to the same circuit.

Depending on the primary inductance of your ignition coils, a comparatively high frequency oscillatory current (500 - 2 kHz) with peak current of 10-30 amps will flow through the mains wires. If there is significant inductance or resistance in the supply path between your breaker box and driver circuit, these repetitive transients can damage sensitive electronic equipment on the same circuit. Powering the driver from a line protector outlet strip may even cause catastrophic failure of its internal transient suppressors.

One "brute-force" fix might be to connect a higher-value motor-run capacitor across the mains at your ignition coil driver. The mains shunt capacitor will help to bypass the higher-frequency currents, thereby reducing voltage transients seen by other devices across the AC mains. I'd recommend using a mains capacitor that is at least 2 - 3X the size of your existing capacitor to tame the "nasties" originating from your driver.

Bert Hickman
Stoneridge Engineering, LLC
World's source for "Captured Lightning" Lichtenberg Figure sculptures,
magnetically "shrunken" coins, and scarce/out of print technical books

doug wrote:
Hi Ed; Thank you for your reply and thanks also to Dave and Miles for
your replies. What I have is a dual ignition coil, dimmer switch and
24uf/370v motor run Cap setup and this thing is really "HOT'! I didn't
realize how "HOT' until I powered a 12 inch lightning screen with a 5
inch center plate on it. I had used the HV supply with a Jacobs ladder
and other stuff with no problems. When I powered the lightning screen
with it, which is really just a lop-sided Capacitor, it really back
fired! took out a fluorescent ballast on the same circuit and fried the
mains outlet it was plugged into! Luckily the mains outlet was remote
from the wall outlet, like an outlet box with a cord which was plugged
to the wall.
I tried to find something on [Corcoms] as some suggested but could
nothing. What I was hoping was that someone could supply me with a
diagram with component values, that I could build, on the order of the
terry filter.
Thank you all; Doug

-----Original Message----- From: Ed
Sent: Thursday, December 31, 2015 10:15 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] auto coil HV supply

What kind of coil driver circuit are you thinking of?  Some will glitch
the line and some won't.  With the capacitor discharge light
dimmer/thyristor approach a normal EMI line filter can raise the
impedance at the coil end so much that the peak current is limited and
sparks are cut way down.

On 12/31/2015 12:07 PM, doug wrote:
Hello; Can any one advise me on some kind of filter or device I can
build or buy that will stop any HV spikes from an automobile ignition
coil high voltage supply from backing into the mains?
Doug J
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