Hi there...This my first post and I hope someone can answer my query. I have good electrical knowledge but my experience on electronics is limited.

My query is this:

I have a 12vdc LED, one leg is fed from a 12vdc positive supply.
The output to switch the other leg is 12vdc positive that changes to 0v to switch the LED on.

I have tried using a standard 12vdc automotive N/O relay but I believe this is causing problems with the electronic source that is changing the polarity in order to switch the LED via the relay.

Can any of you "Guru's" offer any advice or circuit details on how I can achieve it,

Thanks

 

While I believe I know what you're describing I can't be certain. Many times we think we know what the OP is asking but it turns out to be something entirely different. This is why a schematic is vital. To paraphrase our Sgt.Wookie "Schematics are the language which we speak". Please sketch a schematic and use the "Manage Attachments" button to post it.

 

one leg is fed from a 12vdc positive supply.
the other leg ... changes to 0v to switch the LED on.

If this is a 12 V LED then you don't need a relay, just connect the LED between the two legs.

If the LED doesn't light, turn it around as it is connected backwards. If it still doesn't light perhaps this isn't a 12V LED and it is now a bad LED.

 

If this is a 12 V LED then you don't need a relay, just connect the LED between the two legs.

If the LED doesn't light, turn it around as it is connected backwards. If it still doesn't light perhaps this isn't a 12V LED and it is now a bad LED.

Hi...thanks for your reply. I was concerned about applying 12vdc+ to both legs but you have re-assured me and I will give it a go.

Perhaps I did not explain too clearly and I apologise for my lack of electronic circuitry knowledge. I was bought up in the age of relays, contactors, transformers and induction motors, the word "Electronics" did not exist.

The wire that gives the negative input to the LED which turns it on comes from an electronic unit that I do not have the details of other than the function summary which states that it changes from a 12v positive to 12v negative to activate and illuminate the warning lamp (LED). I am therefore unable to provide a detailed circuit diagram as I do not have access to the info.

Give me a 440Vac three phase 200amp control with thick cables and heavy contactors and I am at home !!!

Many thanks

 

Are you certain that this is a 12V LED? This implies that it's a hybrid, which means that this is not a single component but rather an LED packaged with a limiting resistor or other solid state current limiting device. If it's a bare bones LED and you hook it up to 12V you will blow its brains out.

 

Please post a link to the LED and the relay product . This will eliminate guess work.

 

The LED is from www.rscomponents.com item no.204-079.
The Relay is a standard auto relay normally open, 12vdc operating votage rated at 20 amps.
I am using the same LED's straight from a 12vdc supply and they are working perfectly...none have exploded !!
Tell you what....I would rather work on high voltage stuff any day...these electronics are a pain in the ass !!

 

It has the built-in resistor as expected.
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0204079#header

 

...I was bought up in the age of relays, contactors, transformers and induction motors, the word "Electronics" did not exist...

The first issue of "Electronics Magazine" dated from 1930, and the term had clearly been coined well before then.

Were you really an adult in the 1920s?

 

Tell you what....I would rather work on high voltage stuff any day...these electronics are a pain in the ass !!

Ha, this is basic stuff and whether it's 120V, 240V, 480V or 30KV, it doesn't change the laws that govern electron flow.

 

Looks very much like I have dropped into a forum of "Geeks" who, instead of putting sensible replies.....Apart from ErnieM, are intent on just showcasing their "Expertise" and expecting everyone to have the same knowledge as themselves.
I asked a simple question and got a load of "Mumbo Jumbo" and interrogation regarding circuits, component details etc.
Sorry guys, but this is not how I envisaged the forum to be.

I'm off !!...............

 

Looks very much like I have dropped into a forum of "Geeks" who, instead of putting sensible replies.....Apart from ErnieM, are intent on just showcasing their "Expertise" and expecting everyone to have the same knowledge as themselves.
I asked a simple question and got a load of "Mumbo Jumbo" and interrogation regarding circuits, component details etc.
Sorry guys, but this is not how I envisaged the forum to be.

I'm off !!...............

Your statements here are synonymous with being invited to someone's pool party and ******* in it! Your first post was not specific enough to give you an intelligent answer. We didn't know if you had a LED or, as it turns out, a LED packaged with a limiting resistor. Ernie took your information at face value but not without a (CYA) caveat.

If this is a 12 V LED then you don't need a relay, just connect the LED between the two legs.

You took his information and ran with it. You had only a 50-50 chance of lucking out because this was prior to you posting the link to your LED, which clearly shows a LED with an integral Resistor package, making this a 12V indicator.

I and many other members will not take an OP's statements at face value because we've learned that they aren't always accurate. This is why I asked for a link to your LED. I find it unfathomable how you can denigrate us for merely trying to protect you from damaging your LED..... or worse.

For the record.. All those great technological advances, that surround your everyday life, were brought to you by Geeks.

 

Looks very much like I have dropped into a forum of "Geeks" who, instead of putting sensible replies.....Apart from ErnieM, are intent on just showcasing their "Expertise" and expecting everyone to have the same knowledge as themselves.
I asked a simple question and got a load of "Mumbo Jumbo" and interrogation regarding circuits, component details etc.
Sorry guys, but this is not how I envisaged the forum to be.

I'm off !!...............

Well, my comment was somewhat flippant, and I don't mind apologising for that if it upset you. Perhaps I was being a geek to have challenged your assertion that you are older than electronics, but I am no spring chicken myself, and I started playing with electronics well before my voice broke.

The questions about circuit and component details were however quite reasonable. You have come asking for advice on a subject which you are not familiar with, so you can hardly be surprised to have overlooked some details in your original enquiry. The point about the 12V or otherwise LED was a particularly good one: many novices destroy the standard types of LEDs by connecting them to unsuitable voltage supplies.

 

I asked a simple question.

I still don't know what the simple question was.

 

The question was obviously not simple to the OP, or he would not have brought it here. I am sorry, though, that my sarcasm may have contributed to his reaction.

Had he stayed about, there might have been some useful points to have been checked out, such as whether whatever is driving the LED has enough current capacity to do so reliably, and whether the two 12V levels are necessarily identical.

Depending on his answer to these further "interrogations" we might have come to a view about the need or otherwise for using a driver transistor, and / or reverse protection diodes.

It is better not to (spit) into a well that you may later wish to drink from.

 

I will not miss him.