LED ight string and Voltage Detector

[Rincewindwiz]

Hi All,

I have a broken LED light string (I've two actually, one embedded in an Xmas tree and one standalone) . It seems these are wired in series so I presume that one or more LEDs are U/S. The challenge is finding the broken LED(s) and then what to do with them.

I was prpposing to simply work down the string seeing where there stopped being a voltage (and asuming the immediately prior LED was broken). But that will be tedious. The LEDs contacts are wrapped in tape so I was thinking of a non-contact voltage detector.

Are there any cheap non-contact voltage detectors that will work with LEDs? I think this string has DC as there is a PCB with 4 diodes on it (looks a bit like a recitfie) at the start of the string r and I thought non-contact voltage detectors were a bit iffy with DC?.

Assuming I can find the LED, I guess I just replace it with similar or perhaps with a simple resistor (and ignore that light). What is the correct resistance?

Thanks for an thoughts

 

[shanky887614]

most volt sticks are ac only.

 

[Pete999]

Hi All,

I have a broken LED light string (I've two actually, one embedded in an Xmas tree and one standalone) . It seems these are wired in series so I presume that one or more LEDs are U/S. The challenge is finding the broken LED(s) and then what to do with them.

I was prpposing to simply work down the string seeing where there stopped being a voltage (and asuming the immediately prior LED was broken). But that will be tedious. The LEDs contacts are wrapped in tape so I was thinking of a non-contact voltage detector.

Are there any cheap non-contact voltage detectors that will work with LEDs? I think this string has DC as there is a PCB with 4 diodes on it (looks a bit like a recitfie) at the start of the string r and I thought non-contact voltage detectors were a bit iffy with DC?.

Assuming I can find the LED, I guess I just replace it with similar or perhaps with a simple resistor (and ignore that light). What is the correct resistance?

Thanks for an thoughts

How long is a piece of string?

 

[telectrix]

not worth the effort. bin 'em and buy new.

 

[Deleted member 72666]

Have you ever heard/seen the phrase ' No user serviceable parts inside'? Heed the advice and dip into your pockets and buy a new set! Oh and Merry Christmas you tight .......lol

 

[telectrix]

if he's a yorkshireman, we've just given him a heart attack. total eclipse of the wallet.

 

[Marvo]

There's numerous configurations of fairylights, some have individual 'driver' circuits contained in each lamp some have a common driver at the beginning of the string, some are arranged with groups of lamps in series and the several groups are arranged in parallel to achieve a certain voltage at each lamp. Without breaching the insulation on the wires between the lamps or cutting them entirely I don't see how you're going to establish which lamp is the culprit then you're going to have to solder and heatshrink to repair afterwards. There could be multiple lamps faulty as well if it was surge damage.

I'm inclined to agree it's one of those jobs where you're better just replacing with a brand new item.

 

[Guest77]

How long is a piece of string?

Twice as long as it is when it is folded in half mate :biggrin:

 

[Rincewindwiz]

Clearly some of the contributors have been down the pub - lucky so -and-sos!!

I dont mind throwing away the individual string but those integrated with the tree are more expensive to replace. (c. £80 retail)

As to 'no user serviceale parts inside' - bit like "sell by dates" IMHO - Only there to get you to dispose and buy more..

Anyway, can I take it (*from the absence of replies) that there is no such thing as a cheap DC voltage detector?

 

[telectrix]

Twice as long as it is when it is folded in half mate :biggrin:

=

not quite. there's a formula:

L1 = L2(2∏Γ-s)/p

where L1 is the half length, L2 is the full length, r is the radius of the bend when you fold it in half, s is the stretchability constant for that particular type of string, and p is what i'm taking with this post.

 

[HandySparks]

You can fault find by prodding a fine needle through the insulation into the core and clipping your meter lead to it. If it's fine enough, the insulation will close up when you pull the needle out.

I would only do this if I was sure that the light string was SELV (ie separated from the mains supply).

 

[trev]

Buy another set and drape them round the tree. Then don't use the integrated ones.
Jobs a goodun

 

[telectrix]

if there's just a few out, tell visitors that some stars are eclipsed. refer them to stephen hawking.

 

[Guest77]

=

not quite. there's a formula:

L1 = L2(2∏Γ-s)/p

where L1 is the half length, L2 is the full length, r is the radius of the bend when you fold it in half, s is the stretchability constant for that particular type of string, and p is what i'm taking with this post.

. .

 

[Barry White]

led strings are usually low voltage series parralel if the full set is out i would be looking at the driver.

 

[Rincewindwiz]

THanks telectrix - its about where I thought I was going to get to. Since the greatest minds on the electricians forum cant come up with a better solution (other than the depressingly modern 'throw them away and get a new one').
Depressing really that modern technology cant do much better that we did 30 years ago.
Festive felicitations to all

 

[HandySparks]

... Since the greatest minds on the electricians forum cant come up with a better solution (other than the depressingly modern 'throw them away and get a new one')....

Didn't like my suggestion then?

 

[Rincewindwiz]

HandySparks
No - I agree with everything you said. I am just depressed that I shall have to resort to 1950s technology to fix a 2010 problem, I thought you bright sparks (no pun intended!) might have a better idea

I'd like to think the reference to Telectrix was sarcasm but actually I simply misassociated an author - not that I didn't appreciate his/her formula!

 

[efficiencyman]

I wonder if by 2050 the Chinese will come up with a fault code reader ? No it`s all a part of the big plan to make us spend more on a frequent basis. Well there goes another £50 on replacement, plus another £50 for landfill then there`s the waste carriers licence or bin men (rates) That`s not in our national benefit that add`s to our deficit.
I remember well the 1950`s 20v mes lamps, Oh they are so simple to fix ! I have only replaced a few lamps & resoldered a few screw in lampholders over the years. I have them working now, been faithful for nearly 60 years. I can`t say that for the Noma electronic controlled sets that have gone wrong the first year. Is that progress, for who ?
Having typed all this I do move with the times, have upgraded outside & in with LED fittings throughout which I highly recommend.

 

[telectrix]

nah. bring back acetylene lamps. good enough for geordie's car , so......

 

[PEG]

nah. bring back acetylene lamps. good enough for geordie's car , so......

...and how many times were you caned,for dropping carbide in the ink wells? :icon12:

 

[telectrix]

only once. second time wasa for connecting the bunsen burners to the cold water main