0805 LED Current

[glowlamp]

I've soldered some 0.1mm enamel wire leads to a few 0805 size SMD leds.

They are white and rated the same as a standard white led - around 3.2 volts and around 20-25ma max current.

They work as expected, although above 9ma they start to get quite hot. At 13ma, touching them on my lip they feel quite toasty.

Is this to be expected as they are attached to 0.1mm wire instead of to the larger mass of a PCB ?

An advice appreciated.

 

[Pommie]

I tend to use these on pcbs at around 1mA as they are surprisingly bright at this current. At 20mA they will be heated by about 75mW so I would expect them to get very hot. Why not run one to destruction as a test.

Mike.

 

[dknguyen]

They will run cooler on a PCB, especially if you make the pads real big and/or one connects to a plane.

 

[gophert]

I've soldered some 0.1mm enamel wire leads to a few 0805 size SMD leds.

They are white and rated the same as a standard white led - around 3.2 volts and around 20-25ma max current.

They work as expected, although above 9ma they start to get quite hot. At 13ma, touching them on my lip they feel quite toasty.

Is this to be expected as they are attached to 0.1mm wire instead of to the larger mass of a PCB ?

An advice appreciated.

Yes, 0.1mm wire is like a bundle of 4 human hairs so, not much heat transfer to the rest of the world.
However, most LEDs can handle temps up to 85°C - way hotter than the threshold of your "hot lips" test.

 

[dknguyen]

Yes, 0.1mm wire is like a bundle of 4 human hairs so, not much heat transfer to the rest of the world.
However, most LEDs can handle temps up to 85°C - way hotter than the threshold of your "hot lips" test.

Oh man. You touch your lips to it? lol. I'd never do that due to leaded solders and I'd rather have burnt fingers than burnt lips. Are your fingers heavily callused or something?

 

[ronsimpson]

due to leaded solders

After 50 years of holding part in my mouth I can't remember what lead does to your brain cells.

My fingers can insulate to about 50 volts (can't feel a thing) and can survive 110 for a short time. My lips feel 9 volts! I do not put anything in my mouth that has power on it! When you are dead from current in your mouth, lead poisoning will not effect you much.

 

[gophert]

At 13ma, touching them on my lip they feel quite toasty.

Oh man. You touch your lips to it? lol. I'd never do that due to leaded solders and I'd rather have burnt fingers than burnt lips. Are your fingers heavily callused or something?

"Hot lips" is not my test, it was the OP's test. I use my infrared vision to determine temperature.
(And, just for the record, I can also see well into the UV.)

 

[dknguyen]

"Hot lips" is not my test, it was the OP's test. I use my infrared vision to determine temperature.
(And, just for the record, I can also see well into the UV.)

Well I have an oscilloscope between my thumb and index finger and can smell lines of flux.

 

[gophert]

Well I have an oscilloscope between my thumb and index finger and can smell lines of flux.

I believe the oscilloscope story but the ability to snort lines of "flux" does not make you a superhero - rock stars have been doing that for years.

 

[glowlamp]

Many thanks for the replies. I thought I might have an off spec batch of 0805 leds.

I have an 800g reel of this "Soldex C1.00" SWG 40 enamelled wire which I am using with the LEDs. It has a matt red finish which looks okay in my little lamps.

I've tried using the "non-tarnish" 0.1mm silver plated copper "craft" wire, but it's just not reliable.

However, what I really want is some certified electrically sound clear coated 0.1mm silver coloured wire. I don't want insulation which will add significantly to the diameter of the wire.

Does anyone know if such a product exists ?

Thanks.

 

[dknguyen]

"Clear-coated, silver coloured wire"?

So you're looking for tin or silver-plated wire that has a thin clear insulation so the silvery colour shows through? I don't think you'll find any since functionally, it's a bit redundant. Unless there exists magnet wire that is silver-plated for some reasons.

 

[glowlamp]

Well it turned out that the silver "non-tarnish" 0.1mm craft wire was working fine. I had just failed to properly tin the other ends for the power.
The wires are twisted together tightly, no shorts. Looks good