Possibly,
Magnetic fields collapsing and capacitors discharging.

It seems much energy can be stored in this
way and is used by physics peoples to power
very brief as well as very powerful experiments.
It possibly is the release of stored energy on shutdown.

We had these Hula dancers ( motor generators)
to power our transmitters and they would be stopped (shut down) by
sinking their power into a special resistor bank.
If you did not do this it may take tens of minutes instead of
one to stop them.
Sort of like an undamped pendulum.


-----Original Message----- 
From: Richard Schneider
Sent: Friday, January 07, 2011 5:47 PM
To: psnlist@..............
Subject: Re: Engine Start/Shutdown Noise Spikes From Automobile


Geoff,

That all makes sense, but what is the explanation for shutting down the engine and seeing a similar in amplitude spike occur at that 
very instant?  At that point, the starter is not involved.
It appears to point to the alternator field collapsing on shutdown. BTW, the start-up spike and the shut-down spike's have opposite 
polarities.


On Fri, Jan 7, 2011 at 7:38 AM, Geoffrey  wrote:
When you first start an AUTO like 50 or more amps
might flow through the starter motor creating a large
circuit for an electro magnet ??

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