Soldering iron is giving off usable power - Page 1
Forum section: electronics / beginners

author: BigBrother
author_rank: Regular Contributor
timestamp: January 13, 2013, 06:12:50 pm
content: I tried to solder some Cree MX6 LEDs just now and I noticed that a couple of them lit up, oh so faintly. They are on an MCPCB (Metal Core PCB).The soldering iron in question is an M-Line Mark V from Micro-Measurements.

author: SeanB
author_rank: Super Contributor
timestamp: January 13, 2013, 06:30:34 pm
content: Soldering iron tip is not connected to ground properly.

author: dog80
author_rank: Regular Contributor
timestamp: January 13, 2013, 06:57:02 pm
content: Was the PCB powered or plugged in while you soldered it?Since the tip of the solder iron is ground referenced you might complete a path to ground by touching it to the LED.

author: BigBrother
author_rank: Regular Contributor
timestamp: January 13, 2013, 07:35:47 pm
content: Quote from: dog80 on January 13, 2013, 06:57:02 pmNo, in fact it was on my plastic-lined desk.Quote from: SeanB on January 13, 2013, 06:30:34 pmHow do I ground it? it uses a 2-pin connector to the base.

author: IanB
author_rank: Super Contributor
timestamp: January 13, 2013, 08:02:24 pm
content: Quote from: BigBrother on January 13, 2013, 07:35:47 pmIn that case it's probably best not to use the iron for any sensitive electronic work. Irons suitable for electronics will be marked "ESD safe" in the product literature and will have a three pin mains plug with ground connected to all exposed metal parts.

author: David_AVD
author_rank: Super Contributor
timestamp: January 13, 2013, 09:22:33 pm
content: I'd guess that his soldering iron is properly grounded. I've seen exactly the same thing happen when hand soldering 5050 RGB LEDs with a Hakko 936 iron.I suspect that the stray field from the 240VAC running under my bench coupled via me (holding one side of LED) and returned via the grounded tip.It only takes microamps to make the LED glow and if the room lighting is low enough you'll see it.

author: Psi
author_rank: Super Contributor
timestamp: January 13, 2013, 11:53:32 pm
content: I've seen leds glow with one leg connected to an oscillating MCU pin and the other leg floating in air with no connection what-so-ever.The only thing i could think of was some sort of radio receiver effect.(Like a crystal radio set using only the energy from the radio waves.)Perhaps the LED leg just so happened to be the right length to pick up something.

author: amyk
author_rank: Super Contributor
timestamp: January 14, 2013, 06:11:26 am
content: Quote from: Psi on January 13, 2013, 11:53:32 pmSounds more like it's transmitting, actually.

author: Psi
author_rank: Super Contributor
timestamp: January 14, 2013, 06:53:55 am
content: Quote from: amyk on January 14, 2013, 06:11:26 amInteresting, yeah. That didnt occur to me but makes more sense.

author: BigBrother
author_rank: Regular Contributor
timestamp: January 14, 2013, 11:16:18 am
content: what's the final say? Will the soldering iron hurt the LEDs in some way and can this damage other electronics?

author: David_AVD
author_rank: Super Contributor
timestamp: January 14, 2013, 11:44:55 am
content: No apparent damage to any of the countless LEDs I've soldered and seen this effect on.The solder iron is not "giving off usable power". It's just completing a circuit.Linger to marvel at the mysterious light then move onto the next component I say.

author: Ketturi
author_rank: Regular Contributor
timestamp: January 14, 2013, 12:45:34 pm
content: Ive noticed this too with white smd leds. Often if iron is grounded but you aren't and vice versa, there is floating AC current around, which is often half of local line voltage. Currents are minimalistic and are caused from devices that have capacitors between line and ground (for meeting emi standard or so). Even very small potential differences from longer ground wires can cause leds to light up. White leds have often lowest current threshold to light up partially, and can be powered actually with RF power from wlan antenna connectors or leaking microwave oven etc. if leads are long enough to make antenna.This leakage current can also ruin some smd leds and active parts, so using ground wristband connected to near soldering irons ground point is good move. (ESD also!)

author: Praxis
author_rank: Contributor
timestamp: January 15, 2013, 11:03:35 am
content: Quote from: Psi on January 13, 2013, 11:53:32 pmI had an LED connected to ground in a breadboard battery-powered circuit and it'd light up when I touched the other leg with my finger. I figured it had to be some kinda RF pickup being rectified by the diode. I made sure I was electrically insulated against any kinda direct conduction.