Power LED polarity

[_helio_]

Please, can someone indicate to me the anode and cathode of this LED?

**broken link removed**

Thanks

 

[Hero999]

Ask the seller?

 

[_helio_]

Yes, the easiest and fastest way, so the best one. But, how about a rule of the thumb to identify the anode (or cathode) in all LEDS?
Thanks

 

[KMoffett]

Take a look at the eBay ad pictures. The CAD drawing shows a + on one of the tabs.


.....Never mind!.... When I enlarged the image it's a hole. The pixels on my monitor made it look exactly like a "+".

Ken

 

[_helio_]

Thanks to your keen view, I can see the positive now

My expensive LED will be handled with care.

Thanks again

 

[Hero999]

I can't see a positive sign anywhere or is it just me?

I hope you know that you can't connect this LED directly to 12V, you need a constant current driver.

 

[KMoffett]

hero999,

Re my post:
".....Never mind!.... When I enlarged the image it's a hole. The pixels on my monitor made it look exactly like a "+". "

Ken

 

[audioguru]

Don't buy a cheap Chinese no-name-brand LED at a high price. It doesn't even have a datasheet. It might not work.

 

[Mike_2545]

Don't buy a cheap Chinese no-name-brand LED at a high price. It doesn't even have a datasheet. It might not work.

Its one or the other

 

[Hero999]

Not necessarily so, it could be a cheap LED from China, resold for a high price.

 

[HarveyH42]

10W High Power LED>>Shenzhen Caijing Electronics Co., Ltd>>

 

[_helio_]

thanks for the clue, I've just noticed that my super chinese power supply, digital readout, current controlled (price $70), doesn't control the current

with LEDs the history is different: I often see that the most innovative LEDs appear first on ebay, and after some months they are sold by retailers of the big brands

 

[_helio_]

KMoffett,
the LED works very well thanks to your suggestion

there are not '+' on the drawing, but there is a further hole on the photo, and this terminal presents a dent too

I've considered this the anode (and I was right), then applied 12 V, AND NO LIGHT

I've reversed the supply and applied power just for a second, and still no light

then I've again reversed the supply and increased smoothly the voltage: the first dim was at 14V, the full light at 18V; the current was 0.7 A

 

[_helio_]

Hero,
when I have to do with a LED of unknown polarity I gently increase the voltage by starting at 1 V and keeping track of the current

I confess, if no light appears I reverse the polarity just for a fraction of time, but I'd like a rule to individuate the polarity

I've noticed that if I read the voltage between the anode and the cathode it is ≈ 70 mV, and that if I reverse the polarity the voltage is ≈ 15 mV: can this constitute a rule?

 

[blueroomelectronics]

Nice 100W LED, 3.2A
**broken link removed**

 

[Hero999]

Hero,
when I have to do with a LED of unknown polarity I gently increase the voltage by starting at 1 V and keeping track of the current

I confess, if no light appears I reverse the polarity just for a fraction of time, but I'd like a rule to individuate the polarity

I've noticed that if I read the voltage between the anode and the cathode it is ≈ 70 mV, and that if I reverse the polarity the voltage is ≈ 15 mV: can this constitute a rule?

The LED is really three banks of three series LEDs connected in parallel. This means that the maximum reverse voltage will probably be 15V.

Just connect the LED to a 15V supply in series with a 47R resistor.

 

[mneary]

Shine a bright light on the diode. It will generate a small voltage in the same polarity as it needs to be connected. (The anode will show the positive voltage.)

A white or blue LED needs a very bright light containing blue or ultraviolet wavelengths (e.g. sunshine or fluorescent) and it will generate a few millivolts and a few microamps.

 

[audioguru]

If you can't read the Chinese datasheet then you don't have a clue what they sell.
Maybe they don't know what they sell.

 

[_helio_]

mneary, a splendid idea

 

[_helio_]

The LED is really three banks of three series LEDs connected in parallel. This means that the maximum reverse voltage will probably be 15V.

Just connect the LED to a 15V supply in series with a 47R resistor.

Hero, the maximum voltage I've applied is 22 V, without damages (current 0.7-0.8 A); at 15 V this LED only starts to glow

sure about the need of resistors? strangely, I've tried the LED from 1 to 22 V by increasing gradually the voltage without current limiters, and it never showed signs of extra current nor of overheating