3 second delay
Printed From: the12volt.comForum 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=126803
Printed Date: April 29, 2024 at 8:32 AM
Topic: 3 second delay
Posted By: neo_1975
Subject: 3 second delay
Date Posted: March 31, 2011 at 8:48 PM
I assume I need this to do a 3 second delay. I thought I would try a 4.7uf cap and 1k resistor. It wouldnt even trigger the relay. I i remove the cap and resistor, the relay energizes. Sooo...I am wrong with the cap and resistor. Anyone know what radio shack parts i need for 3 second delay? Thanks for the help
-Neo
-Neo
Replies:
Posted By: oldspark
Date Posted: April 01, 2011 at 4:42 AM
The simplest is six-folding the cap value - ie, to change from 1/2sec to 3 secs means 6x 1kuF = 6mF => 6.8mF or 6,800 uF - say 10,000uF.
The problem is that the resistor forms a voltage divider with the relay (coil's resistance), so that has a limited range of values.
But the resistance value will change with the relay. The original diagram assumes a Bosch type automotive relay of (say) 60-200 Ohms.
The other problem (IMO!) is that being of small resistance value, the capacitor need to be large/ (IE - smaller resistance = higher current = bigger cap to store the required charge (time).)
Except maybe for small relays (coil resistances of 1,000 Ohms or higher), I prefer to use buffers - ie, transistors or FETs. Then small caps and small current resistors (high-Ohmage resistors) can be used and timing is usually independent of the relay... eg:
(from brunningsoftware.co.uk - specifically 2 minute on circuit... (down the page).
The problem is that the resistor forms a voltage divider with the relay (coil's resistance), so that has a limited range of values.
But the resistance value will change with the relay. The original diagram assumes a Bosch type automotive relay of (say) 60-200 Ohms.
The other problem (IMO!) is that being of small resistance value, the capacitor need to be large/ (IE - smaller resistance = higher current = bigger cap to store the required charge (time).)
Except maybe for small relays (coil resistances of 1,000 Ohms or higher), I prefer to use buffers - ie, transistors or FETs. Then small caps and small current resistors (high-Ohmage resistors) can be used and timing is usually independent of the relay... eg:
(from brunningsoftware.co.uk - specifically 2 minute on circuit... (down the page).
Posted By: hotwaterwizard
Date Posted: April 06, 2011 at 1:13 AM
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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !