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12vDC Two Trigger Relay

Harperrn

Dec 17, 2022
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Dec 17, 2022
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Hello!
I’m working on a n automotive project where I want to use two input triggers for relays to power one common output. In this example, I would like to use the interior lights circuit as a trigger so my new lights come on with the dome light timer. I would also like to incorporate a switch to allow the lights to power when I want as the other trigger.

I believe I need to use two 12v relays, one with each trigger wired in and common output to the light I want to turn on. Will this work? Also, how can I prevent from doubling the output if both are triggered at the same time? Will it still only be 12v or will it increase the voltage when both are on?

Any help is appreciated thank you!
 

AnalogKid

Jun 10, 2015
2,925
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Jun 10, 2015
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First, consider replacing "trigger" with "control signal". "Trigger" has specific meanings in electronics, and I don't think they apply here.

If I'm reading your post correctly, you need only one relay. The two control signals are:

1. +12 V from the dome light circuit.
and
2. +12 V from the vehicle battery (or ignition circuits) through a switch.

First question - the source of the +12 V for the switch. If it is the battery, then the load can be powered even when the key is removed from the ignition switch. This is either a good or bad thing, completely up to you.

Second question - the load. What is the relay switching? Voltage? Current? Power? Resistance? any little bit of information helps. This determines the size of the relay needed, and that determines the components controlling the relay.

Before any answers, my guess is a 10 amp automotive relay fed by two diodes. One diode goes to the dome light circuit, and the other goes through a simple SPST switch to a +12 V source. The load is wired directly to the battery through the relay contacts.

ak
 

Harperrn

Dec 17, 2022
2
Joined
Dec 17, 2022
Messages
2
Ak,
Thank you for the info. The load is 12v 2A simple led light strip. So in this case you are using the diodes to prevent the dome lights from coming on when the switch is ON? This was the hurdle I was trying to overcome… to prevent the dome lights from coming on when the switch power is on.

With these specs, what type of diode should I look for?

RH
 

AnalogKid

Jun 10, 2015
2,925
Joined
Jun 10, 2015
Messages
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The relay is switching the load, and the diodes are steering only the relay coil current. A low cost 1 A rectifier such as a 1N4004 should be fine.

ak
 
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