One point that I stumbled over is that adding a simple snubbing diode across
a relay coil increases the relay hold time. The current flow through the
diode when the supply voltage is removed goes through the relay coil,
countering the spring force that is returning the relay to the normal
state.
In a hot switching application, you may need the full spring force to pull
the contacts apart quickly, or tack welds are created.
If hold time or relay contact life reduction due to slow drop out while
switching current are a factor, a slightly more complex snubber consisting
of a zener diode in series with the diode might be appropriate. The zener
voltage value is derived from the protection needs of the switching device.
See http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3264.pdf and
http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3311.pdf for the
details.
Dick, K6KR
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