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What is the purpose of this resistor?


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davep. 
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Posted: March20, 2017 at 5:47 PM / IP Logged Link to Post Post Reply Quote davep.
I have used this circuit on several occasions. It works. I always configure it with the capacitor and resistor values shown. I believe the resistor is to discharge the capacitor. But I have a question: The relay coils I use are 85 Ohms. Both the coil and the resistor are in parallel. Do I really need the 10K resistor as well? It seems to me that with the 82 Ohm resistance, the circuit won't even know the 10K is there too.
Thanks in advance. Both for the explanation, AND the diagrams. I've used a bunch of them as food for thought over the years and come up with some cool installs.
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astuff 
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Posted: March30, 2017 at 10:44 PM / IP Logged Link to Post Post Reply Quote astuff
Just guessing but the capacitor is there to produce a slight delay and/or reduce chatter. Resistor is not needed if relay has internal diode or resistor to take care of the coil current/voltage spike when turned off.
davep. 
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Posted: April10, 2017 at 2:58 PM / IP Logged Link to Post Post Reply Quote davep.
Thanks for the reply. The cap and resistor in this circuit are not related to "anti spike" protection.
The capacitor is there to keep the coil energized until the cap discharges, which is about 3 seconds with these values. I was asking about the purpose for the resistor that is in parallel with both the cap and the relay coil.
astuff 
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Posted: April12, 2017 at 4:59 PM / IP Logged Link to Post Post Reply Quote astuff
Why do you think that the resistor is not related to spike protection? If there is not a resistor or diode built into the relay the recommendation is to add one.
Start with page 11: http://www.autoshop101.com/forms/hweb2.pdf
the12volt 
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Posted: May08, 2017 at 8:11 AM / IP Logged Link to Post Post Reply Quote the12volt
When I started adding capacitors to relay coils in the late 70's, early 80's, I frequently had to add the resistor to eliminate the relay chatter I would get. Since then, I've always added it to play it safe.
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