[RFI] LED Christmas Light RFI -> LED lead corrosion
garyk9gs at wi.rr.com
Mon Dec 2 21:38:28 EST 2013
And if you haven't checked out Jeff's website it is well worth it. GREAT
On 12/2/2013 7:43 PM, Jeff Blaine wrote:
> Gary is on the money, you could say.
> Those little generic T5 LEDs have a manufacturer's side cost basis in
> the 1-2 cents range. And the price competition is murderous. The
> hang-up to cost reduction is the packing materials cost - not the
> actual LED chip cost.
> -----Original Message----- From: Gary K9GS
> Sent: Tuesday, December 03, 2013 10:17 AM
> To: rfi at contesting.com
> Subject: Re: [RFI] LED Christmas Light RFI -> LED lead corrosion
> Welcome to the world of low-cost consumer electronics. I would imagine
> the LEDs used in Christmas lights are about the cheapest ones
> available. I just did a quick check. A 60 LED string of lights can be
> bought at Target for $7. That works out to ~$0.12 per LED.
> The low cost consumer LEDs used in these types of products are likely
> using steel in the leads to save cost. That's why they are so cheap.
> One other possibility is if the leads were gold plated. You cannot
> electroplate gold directly on to copper. You have to use an
> intermediate metal on the copper and then plate the gold on to the
> intermediate metal. Typically, the intermediate metal is nickel which
> IS slightly magnetic. But I highly doubt that's what we're talking
> about here :)
> Remember, these types of LEDs with leads are designed to be indicators.
> They're not designed for lighting applications like you'd find in high
> performance lighting applications. Those types of LEDs are usually
> surface mount parts and are MUCH brighter. But for illuminating things
> like meters in amplifiers what you're using are perfect.
> On 12/1/2013 9:58 PM, Kim Elmore wrote:
>> Now THIS is interesting. Up until now, I have used the classic series
>> strings and have always suspected that corrosion occurred during
>> storage. Yet, I could never find much evidence of corrosion because
>> the lamp leads are copper and the socket material is brass.
>> I recently replaced incandescent lamps in my amplifier meters with
>> white LEDs. As I was cleaning up, I noticed to my astonishment that
>> the clipped parts of the LED leads are magnetic. I remembered
>> thinking that whatever they were, they sure were surprisingly tough
>> to cut... If the leads are some sort of ferrous material (likely mild
>> steel) that has been copper plated and then tinned to make soldering
>> easier, the corrosion you see is easily explained.
>> It's also interesing that they depend on the (poor) PIV ratings of
>> the LED series string for string AC operation. If this is how they
>> manage the LED strings, then these will be very RF quiet though they
>> may not last long as outdoor lights if this is the common
>> construction practice.
>> Kim N5OP
>> On 12/1/2013 6:30 PM, John DeGood wrote:
>>> My father-in-law WA3GNU has 3 strings of LED holiday lights at his QTH.
>>> They consist of 60 LEDs per string: each string is divided into 2
>>> with each half consisting of 30 LEDs in series with 3 x 735 ohm
>>> resistors (sealed in heatshrink tubing) connected directly across the
>>> 120 VAC line and protected by a pair of fuses in the plug. Given this
>>> circuit topology, I would not expect RFI problems and WA3GNU has not
>>> noticed any.
>>> When we took them down last year they were all working, but all 6
>>> of the 3 strings were dark when we attempted to return them to a third
>>> season of service this week. Troubleshooting, I discovered that
>>> approximately 25% of the LED lamps had suffered corrosion failure in
>>> which one lead was broken due to corrosion. Many of the remaining LEDs
>>> with both leads still intact showed obvious evidence of serious
>>> corrosion in progress.
>>> These LED lamp strings are constructed identically to miniature
>>> incandescent holiday lamp strings, with the LED leads simply inserted
>>> through a pair of holes in a small keyed plastic base and then bent
>>> against opposite sides of the plastic base to serve as the contacts.
>>> plastic base is then inserted into a keyed plastic socket such that the
>>> LED leads press against a pair of flat contacts which appear to be made
>>> of brass or a similar metal.
>>> I hypothesize the corrosion resulted from the combined effects of
>>> moisture, dissimilar metals (LED leads vs. socket contacts), and DC
>>> current (the series LED string acts as a rectifier). A few of the LED
>>> lamps showed no evidence of corrosion: I hypothesize they might by
>>> chance have been positioned such that they did not get wet. Thus, this
>>> corrosion failure mode might not occur in a dry indoor environment.
>>> John NU3E
>>> On 12/1/2013 3:51 PM, Kim Elmore wrote:
>>>> Does anyone have experience with RFI from LED Christmas lights? Are
>>>> some better than others? All bad? No problems?
>>>> Kim N5OP
>>>> "People that make music together cannot be enemies, at least as
>>>> long as the music lasts." -- Paul Hindemith
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