LED Christmas Lights Troubleshooting

[levittownnick]

Last year I purchased several long strings of these LED lights thinking that LED's should have a longer life than incandescent bulbs.Bad Thinking.

I have a Greenlee Voltage Detector that I purchased several years ago to help isolate open filaments in series strings of decorative lights but that doesn't work with the LED strings. I'm only guessing but it don't work with the LED's because they only draws current on 1/2 cycle leaving full voltage on the other 1/2 cycle so that the Voltage Detector thinks all the lamps are open.

The question is: Without removing each of the LED's 1 at a time and checking the socket, is there a reasonable troubleshooting method?

A side question, I see a small module in each string that looks like it has 12 resistors. Are these just to limit current (or are these not resistors)?

Thanks,
Nick

 

[levittownnick]

I have tried the internet and found some additional information. Some information is good, some outright dangerous and much just a waste of time.
1st. I want to confess that above I had speculated that the proximity type voltage detectors don't work with the LED's is not an accurate statement on my part. While the type I have may or may not work, separating the wires and then applying the tester may give some results, also if the detector does not detect the voltage on an individual LED, try reversing the plug on the string and see if that helps.
2nd. It was pointed out to me that many LED's have the leads made of a metal that may rust thru and break if they are exposed to moisture. This was true for the sets that I have.
3rd. The sets that I have are 50 foot long and are made up of multiple strings each with 50 LED's. I found it easier to just take the string that isn't working and remove the LED's one at a time checking for a broken/missing lead.
4th. I asked if the inline module were just a resistor bank, the answer is yes because LED's are not like filament bulbs, as the voltage increases the LED's draw current at an exponential rate and will self destruct is there is no other means of limiting the current.
5th. a statement that is absolutely wrong and leads to dangerous, even life threatening conclusions: "Everyone knows that electricity takes the path of least resistance". If it were true (AND IT IS NOT TRUE) there could be no parallel circuits, A Generating Station/Utility Company could only supply one load/customer (The load/customer with the least resistance). What is more accurate is that Electricity will supply all the resistive paths in proportion to there resistance/impedance (A path with 10 times the resistance will draw 1/10 of the current as a path of the lowest resistance etc.).

Thanks,
Nick

 

[dingbat]

5th. a statement that is absolutely wrong and leads to dangerous, even life threatening conclusions: "Everyone knows that electricity takes the path of least resistance". If it were true (AND IT IS NOT TRUE) there could be no parallel circuits, A Generating Station/Utility Company could only supply one load/customer (The load/customer with the least resistance). What is more accurate is that Electricity will supply all the resistive paths in proportion to there resistance/impedance (A path with 10 times the resistance will draw 1/10 of the current as a path of the lowest resistance etc.).

Your talking in circles...it’s true electricity does take the path of least resistance.

Your “more” accurate statements says so.....
Grass isn’t green ...it’s a mixture of blue and yellow

the power company can only supply all houses as long as supply mets or exceeds demand.

 

[gm280]

When one goes out they all go out... I like that Christmas song!

Some of what you say is correct, but not all. The LEDs are directional and do need current limiting or they will light, but only for a few milliseconds. Think flashbulb!

So they install dropping, or current limiting resistors in series with each LED. And that is there so each LED is its own circuit, parallel with the other current limited LEDs. Otherwise, "When one goes out they all go out" rings true.

You can use a Battery type light tester IF you install a limiting resistor in that tester. If the tester uses a 9 volt battery, you could use a simple 1K ohm resister and it will work just fine. Then you can remove and test each LED out of the line. But remember, if the LED doesn't light, reverse it before discarding it as bad. Because they are directional as you already know. And as far as testing the strings, I'd have to see them to figure out how they are strung together to come up with a viable option for testing. Could be some are Seried while others are Paralleled. And your low voltage tester will not light a sting whatsoever. It would take a lot higher current limited voltage to do that. How much higher, that depends on how they are strung together... JMHO

 

[levittownnick]

5th. a statement that is absolutely wrong and leads to dangerous, even life threatening conclusions: "Everyone knows that electricity takes the path of least resistance". If it were true (AND IT IS NOT TRUE) there could be no parallel circuits, A Generating Station/Utility Company could only supply one load/customer (The load/customer with the least resistance). What is more accurate is that Electricity will supply all the resistive paths in proportion to there resistance/impedance (A path with 10 times the resistance will draw 1/10 of the current as a path of the lowest resistance etc.).

Your talking in circles...it’s true electricity does take the path of least resistance.

Your “more” accurate statements says so.....
Grass isn’t green ...it’s a mixture of blue and yellow

the power company can only supply all houses as long as supply mets or exceeds demand.

Sorry dingbat but I respectfully disagree with you unless your saying that the statement means that in addition to all the other resistive paths, electricity takes the path of least resistance also. If that is not true, I will need someone to explain to me how parallel circuits work. I do have a technical error in one of my statements, the current is in Inverse proportion to the resistive path, ie. the more the resistance the smaller the current (The less the resistance the greater the current).

Nick

 

[levittownnick]

When one goes out they all go out... I like that Christmas song!

Some of what you say is correct, but not all. The LEDs are directional and do need current limiting or they will light, but only for a few milliseconds. Think flashbulb!

So they install dropping, or current limiting resistors in series with each LED. And that is there so each LED is its own circuit, parallel with the other current limited LEDs. Otherwise, "When one goes out they all go out" rings true.

You can use a Battery type light tester IF you install a limiting resistor in that tester. If the tester uses a 9 volt battery, you could use a simple 1K ohm resister and it will work just fine. Then you can remove and test each LED out of the line. But remember, if the LED doesn't light, reverse it before discarding it as bad. Because they are directional as you already know. And as far as testing the strings, I'd have to see them to figure out how they are strung together to come up with a viable option for testing. Could be some are Seried while others are Paralleled. And your low voltage tester will not light a sting whatsoever. It would take a lot higher current limited voltage to do that. How much higher, that depends on how they are strung together... JMHO

Yes, individual LED's are directional (polarized) and unlike incandescent bulbs do need some type of current limiting device or they will mimic a flash bulb. The most common method (but not the only method) is with a series resistor. Most decorative LED light strings are in series and use a resistor or resistor network to limit the current and protect the LED's. A single resistor in series with the LED string will protect the entire series string, It is not necessary to have individual resistors for each LED. There are other configurations of LED strings but the will still require a resistor or some type of current limiting. For example a string of LED's could consist of pairs of LED's that are configured Back to Back in series with with other Back to Back LED's. The advantage would be that both halves of the AC Sin Wave would be used (non polar) but requires 2 times the power and LED's but would be brighter and other colors could be made.

Nick

 

[DouglasW]

Electricity only uses the path of least resistance in accordance with Ohms law. In other words, the current in each parallel path is inversely proportional to it's resistance. The path of least resistance does not necessarily get all the current.

Unfortunately a long string of series-connected loads (like LED's) cannot be easily troubleshot for opens without measuring each node in the circuit.

As for any increased reliability of LED's over incandescent bulbs, that depends entirely on the quality of the parts, which is low in products like these.

 

[levittownnick]

Electricity only uses the path of least resistance in accordance with Ohms law. In other words, the current in each parallel path is inversely proportional to it's resistance. The path of least resistance does not necessarily get all the current.

Unfortunately a long string of series-connected loads (like LED's) cannot be easily troubleshot for opens without measuring each node in the circuit.

As for any increased reliability of LED's over incandescent bulbs, that depends entirely on the quality of the parts, which is low in products like these.

Sorry DouglasW, but I strongly disagree with you. Ohm's Law states I=E/R where I is the current in Amperes, E is the Voltage and R is the Resistance in Ohms. It don't talk about parallel Paths or the Path of Least Resistance. If there is a Voltage across a "Path" of a certain Resistance, The current in that Path will be defined by that formula. If there is more than 1 Path, Each Path will be defined by that formula. The total current will be the Sum of the currents in the total number of paths that the Voltage is applied to. It should e noted that if the source of that voltage can't supply that total Current the source voltage will drop to supply the Current that the source can supply. (That can also be calculated but I don't care to do that now.) What remains here is when calculating the current in each path that the actual Voltage that is impressed on the resistance after all voltage drops be used in the calculation. Notice that the term "Path of least resistance" is absent from any calculation.

Regards,
Nick

 

[DouglasW]

Sorry DouglasW, but I strongly disagree with you. Ohm's Law states I=E/R where I is the current in Amperes, E is the Voltage and R is the Resistance in Ohms. It don't talk about parallel Paths or the Path of Least Resistance. If there is a Voltage across a "Path" of a certain Resistance, The current in that Path will be defined by that formula. If there is more than 1 Path, Each Path will be defined by that formula. The total current will be the Sum of the currents in the total number of paths that the Voltage is applied to. It should e noted that if the source of that voltage can't supply that total Current the source voltage will drop to supply the Current that the source can supply. (That can also be calculated but I don't care to do that now.) What remains here is when calculating the current in each path that the actual Voltage that is impressed on the resistance after all voltage drops be used in the calculation. Notice that the term "Path of least resistance" is absent from any calculation.

Regards,
Nick

Haha. Now Nick please do not argue with an EE of over 45 years. I am saying the same thing and you are strongly disagreeing ;-)