Re: [CAD_CAM_EDM_DRO] Getting Parallel port to run relay

Tom Hubin wrote:

>The coil does not actually generate a high voltage spike when the
>circuit is opened. The coil tries to continue the current at the value
>just before the circuit opened. Think of rushing water when you close
>the dam gate. The water has momentum and will break down the gate if
>there is any serious speed and volume involved.
>
>

When a voltage is applied to a coil the coil will resist the flow of the
current, putting the power into a magnetic field, until the coil is
saturated, at which point the coil stops resisting the current flow
(this is inductive reactance). When the voltage is removed the magnetic
field begins to collapse. Of course a moving magnetic field generates
an EMF, in this case opposite to the one that formed it. The voltage
that forms will drive current backwards out of the coil, if there is a
circuit the current will flow, if not the voltage will continue to
build. A snubber diode across the coil will allow the current to flow,
avoiding the voltage spike. Of course the diode has to be able to
handle the stored power.

CS