Once again I am about to put my ignorance of electronics on display. I purchased a set of LED street lights which I am going to use as platform lights at one of my depots. These lights came with some good instructions and used a couple terms I was unfamiliar with, Anode and Cathode. In the past, using grain-of-wheat incandescent lights, I would daisy chain them to a single power source but it appears I can't do that with these LEDs.
It says to place a 1000 ohm resistor (included) between the 12V power source Anode and the Anode (red wire) on the light. The Cathode (black wire) connects to the Cathode on the power source. If I want to connect several lights to the same power source (and I do), I should use a distribution block, connecting all the Anodes on the lights to the Anode on the power source with the 1000 ohm resistor between them. All the Cathodes from the lights will be connected to the Cathode on the power source.
My question is how do I determine which is the Anode and which is the Cathode on my power source or does it matter?
I stirred up too much subsequent confusion to leave the original post in place to potentially confuse others.
The anode and cathode polarity differs between a galvanic cell producing power and an electroplating (or electrolytic) one being driven against its natural potential. A good reason, perhaps, to avoid using anode and cathode for wiring conventions!
OvermodThe purpose of the resistor is as a voltage drop. LEDs can be highly intolerant of 'too much voltage' (it turns them into evocatively-named DEDs by releasing the magic smoke impregnated in their construction... ) One resistor ('in series') will work for any real length of string; as you get more and more LEDs you may be able to reduce the resistor value if they don't come on to desired brightness.
Actually, the purpose of the resistor is to limit the current.
OvermodWhat they appear to be saying is to connect all the LEDs together in parallel, using the junction blocks (and a fairly large amount of wire) and then put a 1000-ohm resistor -- I'd recommend at least 1/4W power dissipation capacity just to be safe -- in series between the junction block and the 'black' power terminal. That effectively puts 1000 ohms resistance in any path through the parallel array...
No, you need a resistor between the junction block and each LED. The resistor is going to limit the current to (12 - voltage drop of LED) / 1000. If you only have one resistor, that current will be spread across all of the LEDs, making them much dimmer if they light at all.
OvermodOne resistor ('in series') will work for any real length of string; as you get more and more LEDs you may be able to reduce the resistor value if they don't come on to desired brightness.
Nope, When wiring LEDs in series you do only use one resistor but when working with low voltages you are severely limited in the number of LEDs you can wire in a single series. You have to allow for the total voltage drop of the LEDs. For example, with a 12 volt supply and LEDs with a 2.2v drop, you could wire five in series. A sixth LED would give a total voltage drop of 13.2, greater than the supply voltage. While you might actually get a way with 6, there's virtually no chance of lighting 7 or more in a single series.
OvermodTreat anode and cathode as - and + for DC. Don't let the fancy terms worry you. DC electricity follows the conventions for a galvanic cell operating as a voltage source.
Actually, anode is generally (+) and the cathode is (-).
John,
The lights have been prewired for you using red for (+) and black for (-), which is a pretty common DC wiring scheme. Just wire it to your power source in that manner with the needed resistors.
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
Nobody answered my question. Does it matter which terminal of my power source goes to the Anode and which one goes to the Cathode?
John-NYBW Nobody answered my question. Does it matter which terminal of my power source goes to the Anode and which one goes to the Cathode?
tstage anode is generally (+) and the cathode is (-).
Is your power supply not marked? If not you'll need to test with a miltimeter, or you could just hook them up and if they don't work swap them, negative voltages generally don't damage LEDs unless exposed for a long time or a very high negative voltage.
CSX Robert John-NYBW Nobody answered my question. Does it matter which terminal of my power source goes to the Anode and which one goes to the Cathode? tstage anode is generally (+) and the cathode is (-). Is your power supply not marked? If not you'll need to test with a miltimeter, or you could just hook them up and if they don't work swap them, negative voltages generally don't damage LEDs unless exposed for a long time or a very high negative voltage.
I intended to use a 40 year old MRC power pack. I was going to use the 12V DC terminals and no, the terminals are not marked + or -. I'll check them with the Multi-Meter before hooking them up.
tstageActually, anode is generally (+) and the cathode is (-).
That used to be taught in school, but if it isn't any longer, it's not the OP's fault that he doesn't know. A sad commentary on our education system.
A brief exposure to the wrong polarity won't damage the LED's, they just won't light. A brief exposure to too much voltage will let the magic pop out of the LED's and they will never light.
Having a multimeter is a refreshing change in a conversation about power or polarity, That will work too.
As I edited this about 6 times, I'm not sure the English skills stuck.
Henry
COB Potomac & Northern
Shenandoah Valley
BigDaddy tstage Actually, anode is generally (+) and the cathode is (-). That used to be taught in school, but if it isn't any longer, it's not the OP's fault that he doesn't know. A sad commentary on our education system.
tstage Actually, anode is generally (+) and the cathode is (-).
I graduated from high school in 1969. So when was this being taught.
John-NYBWI graduated from high school in 1969. So when was this being taught.
I graduated in 1956 and it was taught then.
Joe
I don't recall when I learned it, but to remember it I think of Canadian National or CN for cathode negative and A&P, the supermarket AP, for anode positive.
To bring some sense of closure to this mess that I helped bring about, here is a discussion of anode and cathode with respect to diode components that answers his question for diodes.
https://www.dummies.com/article/technology/electronics/general-electronics/electronics-components-diodes-180014
To answer John's question: a LED is a diode: it passes current wired one way, and blocks it the other way. So it only lights when current goes through it the 'correct' way.
The devices are sensitive to overvoltage, so start low when testing. I used a 'coin cell' years ago.
Something I was taught many (too many) years ago. I guess it helps to be a cat lover.
Cations are positive thus they are attracted to the - cathode.