On 10/25/2014 08:54 AM, Arfa Daily wrote:



Think of it as an RC snubber without the C. The capacitance will be
whatever the coil and wiring supply.

Cheers

Phil Hobbs


Don't you think that's starting to get a bit complicated Phil ? I would
have thought that the amount of C in the coil and associated wiring was
comparatively small - even given a car wiring loom. I reckon that its
just a simple damping load across the L to encourage it not to 'ring' so
fiercely as the field collapses ??

Arfa

The reason you care about the ringing is primarily insulation
degradation due to the peak voltage. If the parallel resistor is six
times the coil resistance, the peak voltage kick will be close to six
times the drive voltage of the relay (because the coil current wants to
be constant).

That's how RC snubbers work, except that since they don't represent a DC
load, you can use lower value resistors (with a tradeoff in switching
speed, of course). The speed of the ringing is set mostly by the
capacitance of the winding, unless the snubber resistor is very small.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net