# Re: Danger, and I don't understand why.

```Hi Antonio and All,

At first, I did not think the secondary could sustain the current long
enough to store this energy for any real length of time.  Typically, such
loop currents would be damped very quickly once the power is removed.

However, some math does tell a different story.  If my secondary is 3711
Henries and the resistance is 2373 ohms (my best measurements)  Then the
time constant (L/R) is:

3711/2373 = 1.56 sec

Five time constants = 7.82 seconds

Since just a "little" current being interrupted can kick to a high
voltage, the secondary of a sorted neon could probably hold a good jolt for

Also consider the energy stored in the transformer.  If it is a 60mA
transformer and you happen to catch it at the peak current of 85mA.  Then
the energy stored per leg is 0.5 x L x I^2.  It this case, 0.5 x 3711 x
.085^2 = 13.4 joules!!  Given both legs, the neon can store almost six
times the energy the primary cap can!  So the neon by not only be able to
shock you but easily kill you too!!!  Dangerous indeed....

Cheers,

Terry

At 11:03 AM 8/14/99 -0700, Antonio wrote:
>
>Shorted inductors store energy as well as capacitors in open circuit.
>If the input connection of the transformer is opened when there is a
>significant current in the transformer windings, the secondary current
>will first increase somewhat, as the energy stored in the primary
>winding
>is transferred to the secondary winding, and then will decay
>exponentially
>with a time constant L/R, where L is the inductance of the secondary
>and R its resistance. This may leave significant current circulating
>for a few seconds, and if the short is opened, the large inductance
>of the secondary will force the current to continue, increasing
>the voltage at the terminals as necessary for a spark.
>
>Antonio Carlos M. de Queiroz
>

```

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