Date: Fri, 14 Jun 1996 09:02:50 +0100 (BST)
From: Philip Pick
On Fri 14 Jun, MikeTnyc@aol.com wrote:
> In a message dated 96-06-13 19:45:13 EDT, you write:
>
> >With a RITA the amplifier can be damaged if the plug is not grounded.
The
> >manufacturers recommend that you not exceed a 5mm air gap, so that
you can
> >ensure the spark can jump to ground.
> >
>
> What I've often wondered is how SOON it has to be grounded, i.e.,
could I
> whip one plug wire off a running engine and ground it immediately,
will this
> cause no harm, or do I have to stop the engine, ground the plug wire,
then
> restart the engine? I have a Boyer, but I'm assuming Boyer and RITA
are
> similar in their need for grounding.
>
> Mike Taglieri
> Raul -- '72 Commando Interstate
Ground the lead before starting. The damage is caused by the back EMF generated.
Quick lesson about coils. Power feed to the primary winding builds up a magnetic field. When the points (or amplifier in the case of an electronic system) open to stop this power supply the field decays. As it decays it generated high voltage in the secondary coil. This winding is connected the HT lead to the plug...hey presto... a spark. However this decaying magnetic field also generates a voltage (EMF) in the primary winding that generated the field in the first place. Whoops.
In a points system this is the voltage that causes a spark at the points, and the capacitor is there to absorb. Cleverly the capacitor charges from this voltage and then as the field continues to decay discharges back into the primary, speeding the collapse of the magnetic field. Result, better spark. Note this is why a system with a failed capacitor will run, but very badly.
Back to the point ;-) The electronic amplifiers are switches, to switch off the primary current. They do not take kindly to being subjected to excess back EMF. If the HT lead in not grounded (with or without a gap) the back EMF generated in the primary is far higher than if the HT lead is grounded. Ergo possible damage.
Having said all the above the amplifiers will take a lot of this abuse but for the want of a simple operation why risk it?
--
Philip Pick, Triple Cycles, 228 Henley Road Ilford Essex IG1 2TW England
Telephone +44 181 478 4807 Fax +44 181 478 4807