Brad, If you use an LED with a dropping resistor across the coil to monitor relay status, then you must use a fly-back diode. The coil of the type you're using will produce substantial EMF as power is removed and the coil field rapidly collapses. The collapsing field will produce E-I beyond the LED's maximum ratings. Failure occurs even when the LED is current-limited through a series dropping resistor.
On my remote-controlled homebrew balanced tuner, I was replacing LEDs until I discovered that the collapsing vacuum relay field was immediately burning out LEDs. Never a problem after installing 1N400X fly-back diodes. Paul, W9AC -----Original Message----- From: Topband [mailto:[email protected]] On Behalf Of Brad Denison Sent: Saturday, December 23, 2017 10:52 AM To: [email protected] Subject: Topband: Detuning Relay Flyback Diode I have a couple of 6ms 12V Kilovac relays wired up as a detuning circuit during RX. One question comes up before implementation regarding flyback diodes - would they be needed? Seeking opinions on this question. The relays are powered during TX and not powered for RX direct keyed by the radio with no sequencer. Thanks, Brad W1NT <http://w1nt.com> _________________ Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband
