Relay Dropping Resistor Needed?

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darioism

Member - Posts: 3

Joined: May 08, 2006

Location: United States

Posted: May 17, 2006 at 8:30 PM / IP Logged

I will be installing a pair of running lights into my 1993 240sx which use 1156 bulbs. I will power them using a relay (fused of course) controlled by a switch installed in the dash. My question was whether the relay would need a dropping resistor to keep it from burning up, or can it stay closed for a long time? I would have the 85/86 side directly connected to my ignition from the fuse panel, with the switch in between.

With all the current that a car battery puts out, I feel that a little coil in the relay will be no match. When testing at home with a 12V source, the relay coil does heat up. If needed, would I run the resistor in parallel or series, and how big would the resistor need to be? Thanks.

Relay Dropping Resistor Needed? - Last Post -- posted image.

(The loop I am concerned about is hilighted in blue.)

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ff-mike

Copper - Posts: 199

Joined: November 15, 2004

Location: United States

Posted: May 19, 2006 at 9:07 AM / IP Logged

If this is a typical 'bosch' 12v relay, you can run it continuously without a resistor.

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darioism

Member - Posts: 3

Joined: May 08, 2006

Location: United States

Posted: May 19, 2006 at 4:31 PM / IP Logged

Thanks Mike. It's a "Potter & Brumfield" automotive relay, so I assume it's almost the same thing.

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hotwaterwizard

Silver - Posts: 1,350

Joined: December 11, 2003

Location: California, United States

Posted: June 20, 2006 at 12:21 AM / IP Logged

First off the Diagram is wrong. You have all grounds and no + wires. The relay just shorts out the bulbs. Second the relay is going to get hot and a resistor will just make it get hotter because more resistance just makes more heat. And if you put it across the coil then it will drop the voltaqge too low to activate the relay. If you are concerned about the heat just add a small fan.

Relay Dropping Resistor Needed? - Last Post -- posted image.

John DeRosa (Hotwaterwizard)

Stockton California

When in doubt, try it out !

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darioism

Member - Posts: 3

Joined: May 08, 2006

Location: United States

Posted: June 20, 2006 at 4:37 AM / IP Logged

Yeah, I had realized that the diagram was wrong, but I guess everyone got the idea. Turns out that those relays are made to be on constantly, like any relay used to power headlights, air conditioning, fuel pump, etc. I installed it all and it works great. Since I put the switch on the ignition circuit, I don't even have to worry about turning off the lights. Also, with my remote starter, it looks awesome to watch the car start itself from a distance.

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Relay Dropping Resistor Needed?

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