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need to time delay a relay


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overdriv 
Member - Posts: 11
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Joined: February 19, 2007
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Posted: February 19, 2007 at 8:02 PM / IP Logged  
I have a relay on my electric fuel pump that also turns on another relay for my Ignition box. The power to the coil on the first relay is from the ignition switch but runs through an oil pressure switch. If oil pressure should drop below 7 psi, I think, it will drop my fuel pump relay which in turn will drop the ignition. What I'd like to do is have a 3-5 second delay in the fuel pump relay.
Does anyone know if I can get a time delay relay for automotive use, 12V?      Or can someone suggest a way to incorporate a resistor and capacitor that would delay the drop of the relay 3-5 seconds.
Thanks
hotwaterwizard 
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Posted: February 19, 2007 at 9:28 PM / IP Logged  
need to time delay a relay -- posted image.
John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
overdriv 
Member - Posts: 11
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Posted: February 19, 2007 at 9:41 PM / IP Logged  
Thanks John, I'll give it a try. How durable would you think that circuit be? This wiring is under the rear of the bed on my hot rod S10 ext. cab V8.
hotwaterwizard 
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Posted: February 19, 2007 at 9:48 PM / IP Logged  
Put it in a Plastic Key box if you like.
John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
hotwaterwizard 
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Posted: February 19, 2007 at 9:54 PM / IP Logged  

Here is another circuit.

need to time delay a relay -- posted image.

John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
overdriv 
Member - Posts: 11
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Posted: February 19, 2007 at 9:55 PM / IP Logged  
Would it matter if the wire coming off "E" terminal of the transistor is about 10' long? Acc power comes from the fuse block, I could implement that circuit under the dash if the long run would not matter??
Thanks.
overdriv 
Member - Posts: 11
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Joined: February 19, 2007
Location: United States
Posted: February 19, 2007 at 10:05 PM / IP Logged  
hotwaterwizard wrote:

Here is another circuit.

need to time delay a relay -- posted image.

In the second example, the resistor, which is not specified, is what controls the length of the time delay?? How about the first example, what controls the delay time, only the size of the cap?
Thanks again!
hotwaterwizard 
Silver - Posts: 1,350
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Posted: February 19, 2007 at 10:06 PM / IP Logged  

need to time delay a relay -- posted image.

Wouldn't matter.

John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
overdriv 
Member - Posts: 11
Member spacespace
Joined: February 19, 2007
Location: United States
Posted: February 19, 2007 at 10:08 PM / IP Logged  
Pardon my ignorance, but what program do you guys use to draw those great looking diagrams?
hotwaterwizard 
Silver - Posts: 1,350
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Posted: February 19, 2007 at 10:14 PM / IP Logged  

I use Paint

need to time delay a relay -- posted image.

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