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NO DC Relay Coil Collapsing Circuits

Naysayer

Well-Known Member
Mar 6, 2020
183
141
53
New York
Relays have occupied my recent free time.
After seeing how slow it is for 1 relay to control another and maybe even a 3rd relay, I had to do something.

In my online wanderings I found that in the case of NO, DC-coil relays that carry significant voltage or current, the opening is more of a priority than the closing. The tendency for contacts to micro tac-weld plus, the electro-magnetic force of the coil itself prolongs the break time. Placing a diode across the coil is the slowest method to collapse the coil’s energy field.

TE Connectivity published several Application Notes concerning relays that I found very helpful. These Notes are not product specific and address the issue of accelerating relay opening times in general terms w/ diagrams.

These Application Notes list the common methods to collapse coil fields with their release times and circuit diagrams.

The 2nd fastest method requires the addition of a Zener in-series with a diode connected Anode to Anode or K to K, across the coil.
neil, NYC
 
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If you are discussing using relays for RF switching like in a tuner or an amplifier the switching speed is not really a concern as long as you stage them properly. On bigger boxes, 5kw+, build any kinda circuit you can muster to make the output relay close before the input relay so it never hot switches.
 
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