Cutting LED lights Confusion

[B-Rock]

So, I have been doing research on this forum and the Planet Christmas forum, and I am more confused now that I was before I started the search. Can someone please let me know, in layman's terms, whether I can cut full wave LED strings in half or not?

I have the full wave 70-count LED lights from http://www.holiday-lights-express.com. These lights have, from what I can tell, 3 module diodes (?) on the string. There is one by each plug (male and female) and one in the middle.

I have read that once you cut LED light strings each half will become half wave, affecting the brightness. I have also seen that if I cut them, one one half will work, and other will not. I have seen where folks will add diodes to the strings to make them work. My head is spinning...

I am absolutely confused to whether I can do this or not, but I do have a need for a half string. I don't have an issue with purchasing a smaller string, but why do that if I don't have to.

I apologize in advance if this causes duplicate posts on the forum.

[Guest wbottomley]

Why ruin a string of LED's when you can purchase a smaller set. It's pretty simple to me.

[Steven]

B-Rock wrote:

Can someone please let me know, in layman's terms, whether I can cut full wave LED strings in half or not?

The answer, in layman's terms, is: "It depends on the way the string is wired."

The reason you have not been able to get an answer is the technology is relatively new, and as is the case with any new technology, the manufactures have found about a dozen different ways to construct the light strings.

One example of "No, you can't" is where the plug and socket both have 3 wires, which is common with the GE brands.

A good technique to determine if you can cut a string in half is to go down the string looking for a place where you could make a cut that only cuts 2 wires. If so, then the first half of the string will most likely still work after the cut.

Depending on the string, the 2nd half will probably also still work, but it may have been full-wave before and now is half-wave. This may still be satisfactory. A friend purchased a bunch of strings where the rectifier failed, making the string dark. He simply removed the rectifier, making it a half-wave string, and it still looked good in his display.

[B-Rock]

Steven wrote:

B-Rock wrote:

Can someone please let me know, in layman's terms, whether I can cut full wave LED strings in half or not?

The answer, in layman's terms, is: "It depends on the way the string is wired."

The reason you have not been able to get an answer is the technology is relatively new, and as is the case with any new technology, the manufactures have found about a dozen different ways to construct the light strings.

One example of "No, you can't" is where the plug and socket both have 3 wires, which is common with the GE brands.

A good technique to determine if you can cut a string in half is to go down the string looking for a place where you could make a cut that only cuts 2 wires. If so, then the first half of the string will most likely still work after the cut.

Depending on the string, the 2nd half will probably also still work, but it may have been full-wave before and now is half-wave. This may still be satisfactory. A friend purchased a bunch of strings where the rectifier failed, making the string dark. He simply removed the rectifier, making it a half-wave string, and it still looked good in his display.

Thanks for the reply. I actually emailed the owner of holiday-lights-express and he didn't know for sure. I guess I will just have to sacrifice a string to see if it works. Because it has rectifiers at each plug and one in the middle I am hoping it works. The only worry I have is the rectifier in the middle, it has 3 wires in and out of it.

[rstately]

If that does not work out for you,
Here is a place you can buy full wave short strings. I've bought them here and am happy with them.

http://www.christmas-leds.com/category.aspx?categoryID=284

[grump010]

I just finished cutting string with the 3 rectifiers in them and only one half will work. You will need a rectifier on either end in order for them to work full wave. I cut about 6 string, I will make a couple of string out of the remains at a later date.

Cheers
Daryl B.

[B-Rock]

grump010 wrote:

I just finished cutting string with the 3 rectifiers in them and only one half will work. You will need a rectifier on either end in order for them to work full wave. I cut about 6 string, I will make a couple of string out of the remains at a later date.

Cheers
Daryl B.

Thanks Daryl, that is what I suspected when I saw the 3 wires in and out of the middle rectifier.

Of course when my wife heard I was going to cut lights she decided for me that I would just double up the strings. Problem is that I have to do that around the entire house to look right. Oh well, more work for me.

Thanks everyone for your responses.
Brock

[Steven]

B-Rock wrote:

The only worry I have is the rectifier in the middle, it has 3 wires in and out of it.

If you have a "blob" in the middle that has 3 wires in, and 3 wires out, and there are no other wires that go "around" this "blob", then there are likely 4 diodes in that blob, wired like this crudely-drawn picture.

If this is the case, then to separate the halves, you would either have to cut the blob apart (nearly impossible!) or make your own with 2 diodes (like 1N4003 200V 1A general purpose, about $0.05 each).

At this point, it's all about how much is your time worth, if you would like some "free" electronics education along with your Christmas light display, and if the DIY sense of satisfaction saying: "I built it myself!" is worth it.


Attached files

[thevikester]

Steven wrote:

B-Rock wrote:

The only worry I have is the rectifier in the middle, it has 3 wires in and out of it.

If you have a "blob" in the middle that has 3 wires in, and 3 wires out, and there are no other wires that go "around" this "blob", then there are likely 4 diodes in that blob, wired like this crudely-drawn picture.

If this is the case, then to separate the halves, you would either have to cut the blob apart (nearly impossible!) or make your own with 2 diodes (like 1N4003 200V 1A general purpose, about $0.05 each).

At this point, it's all about how much is your time worth, if you would like some "free" electronics education along with your Christmas light display, and if the DIY sense of satisfaction saying: "I built it myself!" is worth it.

If you cut just before the blob as you put it...would both halves be in operable, or just the second half?

[Steven]

thevikester wrote:

If you cut just before the blob as you put it...would both halves be in operable, or just the second half?

The second half would still work (assuming you connect the power plug to the correct 2 wires), but the first half will not.

The way that wiring works is the blob on one end sends positive current down the string of LEDs, and the blob on the other end sends negative current. The other two wires carry the AC power from one end to the other.