momentary latching circuit?

Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=98760
Printed Date: June 24, 2025 at 3:24 PM

Topic: momentary latching circuit?

Posted By: stridey
Subject: momentary latching circuit?
Date Posted: November 08, 2007 at 5:45 AM

I need to create a circuit that wil latch a relay for 1/2- 1 second or so. The trigger is a simple on/off switch.

The important thing is that the second circuit stays on for a short time, but switches off. re-setting itself. I am hoping to use capacitors and relays, but cant seem to work out a clever method.

Thanks!

Replies:

Posted By: dualsport
Date Posted: November 09, 2007 at 12:53 AM

You can use something like this- for a half to one second pulse use a smaller cap like 1 uF, or a smaller resistance than the 1M. Just change the values to change the amount of time the relay stays on.

It'll trigger when you close your switch to 12V, and reset when you bring the input back down to ground. If you just use an on/off switch you'll need to put a resistor on the input to ground, to discharge the cap after you open the switch, otherwise it won't reset for the next pulse.

Posted By: hotwaterwizard
Date Posted: December 05, 2007 at 5:30 PM

https://www.the12volt.com/relays/page5.asp

Constant to Momentary Output
The capacitor allows the coil of the relay to be energized until the capacitor stores a charge, thus de-energizing the coil. The resistor bleeds off the charge of the capacitor when positive voltage is removed from the other side of the coil. You can increase the output time by simply changing the value of the capacitor. This one will give you about a 1/2 second output.

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !