two signal wires into one relay, safe?
Printed From: the12volt.com
Forum 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=121092
Printed Date: May 28, 2024 at 7:46 AM
Topic: two signal wires into one relay, safe?
Posted By: b1b2b3
Subject: two signal wires into one relay, safe?
Date Posted: March 31, 2010 at 4:01 AM
I have a couple of LED light strips on the front of my car, which I can turn on via a wireless module that I purchased on eBay. Now what I would like, is a 'status' LED inside of my car, so I can see if they're on whilst I'm driving (I have already been pulled over for having them on, so while I'm driving, they need to be off). I don't want to get into creating a fail safe circuit that means the LED's can't turn on when the car is on, because, well, I will want them on when the car is on sometimes..
So what I was thinking is to connect the signal input of a relay to both of the positive wires from the LED strips. Will this cause a problem when both of the LED strips are on?
The LED strips aren't connected together, I can turn one or the other on, hence my thoughts for a relay.
So basically, I have two LED strips, each turn on separately.
I want 1 status LED in the cabin telling me if either are on.
How could I safely go about this?
Thanks
Denno
Replies:
Posted By: oldspark
Date Posted: March 31, 2010 at 6:59 AM
No relay needed.
Just add a diode from switched power to each LED string (anode ends - the end away from the line around the diode body) and join the two cathode or " K" ends (nearest the line) together and run that to the +ve end of the indicator LED.
That's called a diode-OR connection - the indicator will be on whenever one or the other string is on.
Common diodes should suffice - eg, IN4004 etc (or any IN400x diode). The diode needs only carry the indicating LED's current - say 20mA. But IN4001s etc ate typically 1A or more, and rated for 50V or higher (hence ok for 12V etc).
Diodes only pass current from their Anode to Kathode which is in the direction of the " arrow" on their symbol which is like (A)-->|-(K), or IOW towards the line end - the line being the output Kathode end ion both the diode's circuit symbol and its body.
Click the Diodes link under the12Volt title above for better info.
Posted By: b1b2b3
Date Posted: March 31, 2010 at 9:52 AM
amazing feedback mate.
I'll get right on acquiring that diode.
Posted By: hotwaterwizard
Date Posted: April 03, 2010 at 11:16 PM
Why do it high tech when all you need is a lighted switch for each one. Turn the switch on the light inside of the switch goes on and so does the LED strip. KISS method my friend. (K)eep (I)t (S)imple (S)tupid ------------- John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: b1b2b3
Date Posted: April 04, 2010 at 6:29 AM
Why be a jerk? How bout you read my question before you post something next time. In it I stated that I turn them on via a wireless module, not a switch. I don't want a hard wired switch, the wireless one does me fine. I just wanted something to indicate when the lights are on.
And how are diodes high tech? It's just as simple as the switch idea. Oldspark gave good instructions as to what to do, so there isn't going to be a problem.
Nice try though....
Posted By: dualsport
Date Posted: April 04, 2010 at 4:13 PM
Just a comment, but KISS is just a commonly used acronym for the idea, and not directed towards you, just in case you misunderstood. No one calls anyone stupid around here. Not even an idiot. 
Posted By: hotwaterwizard
Date Posted: April 04, 2010 at 4:24 PM
dualsport wrote:
Just a comment, but KISS is just a commonly used acronym for the idea, and not directed towards you, just in case you misunderstood. No one calls anyone stupid around here. Not even an idiot.
That is completely right I never call anyone stupid. ------------- John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
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