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Thread: LED Conversion Help Please

  1. #11
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    Default Re: LED Conversion Help Please

    This is what I am considering. I have to test all 40 canes to see if they are all working correctly. I found 15-20 light strings online but at $5-$8 a piece that isnt something Im willing to do prior.

    Last year I bought a whole carton of 50 strand LEDs from Walmart for .74 each. Too bad they are multicolored.

    If I can swing the AMPs then I will use the incans this year and swap out for next year.

    Quote Originally Posted by Wolfie View Post
    The only option is to run them on DC which involves a DC power supply. Since you expressed interest in sequencing them as AC strands, then going with LED strings is the way to go.

    Strips would look different than the led strands would in the canes. By going with the strands you maintain what they look like now with a slight nod to old school look.

    There are ways to shorten led strings. However, you need the strings to start with and this may not be the best time to be shopping for them. Stuff is bing put out for halloween and is going to be premium priced. After Christmas (late Dec/early Jan) you can pick up strings of lights at Walmart, Lowes, Home Depot, etc that are extremely cheap. I would do a count and see how many incans are in the canes now and do some shopping (not buying) over christmas for led strings that are similar in count and length. If you can find ones of similar count and length, the you won't have to cut and shorten them saving quite a bit of headache and time. You may want to roll with the incans this year and buy up the cheap LED strands after christmas and then do the conversions over winter for next year. Could save you quite a bit of money and give you something to work on in the bleak winter months.

  2. #12
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    Default Re: LED Conversion Help Please

    Sounds like a good plan

    Maybe if amps is an issue, just put a few canes out that you can afford the power to run and put the whole schebang out next year.

  3. #13
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    Default Re: LED Conversion Help Please

    Hi, how many incans are in each cane at the moment? It looks like about 40 & @ 3.2V for white leds that would be 128V or one section of a string.
    How long is the cane?
    Are you goning to use 40 channels for them or group them (5's 8 channels - 10's 4 channels)? If so how many in a group?

  4. #14
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    Default Re: LED Conversion Help Please

    A few years back... A lot of folks would upgrade them using sections of clear rope light. LED rope light is kinda expensive, especially if you had to buy a rectifier for each cane. Or, you could build your own rectifiers.

    -Craig

  5. #15
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    Default Re: LED Conversion Help Please

    I am going to test them to see what the amp pull will be.

    As far as how many channels I will run on these I am unsure. I have a total of 32 channels at the moment. I may not use all 40 this first year.

    Quote Originally Posted by Barnabybear View Post
    Hi, how many incans are in each cane at the moment? It looks like about 40 & @ 3.2V for white leds that would be 128V or one section of a string.
    How long is the cane?
    Are you goning to use 40 channels for them or group them (5's 8 channels - 10's 4 channels)? If so how many in a group?

  6. #16
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    Default Re: LED Conversion Help Please

    First of all - great find! I always wonder why I can't be so lucky.

    If these candy canes are similar to the (Walmart) canes I have, then they have 20 bulbs in each string/cane. Your picture looks like it has more lights so this may or may not help you. Depending on the actual white LED you use (they can vary 2.9v-3.4 v), you can put 20 white LEDs in that string (paying strict attention to polarity) AND add a 2,000 ohm 2 Watt resistor, you should be OK. If you want to use 25 LEDs, just use a 1.5K 1W resistor. I just did this type of conversion to some incan snowflakes.

    If you had them available, you could take a 50 ct white HALF-WAVE LED string and cut it into it's two 'segments'. Look in the middle of the string where there are only TWO wires twisted together. You can cut there and add a female vampire on the one, and a male vampire on the other - and you will wave two shorter stings - adding the female end is optional but make sure you cover the exposed wires with double0wall heat-shrink tubing. Now you can remove the old incan string and insert a 25 ct LED string into each cane. You might have to stuff them a bit - the canes typically have 2"-3" spacing while the LEDs have 4".

    ***This splitting option ONLY applies to HALF-WAVE strings. Full-wave stings can be split but it is much more work.***


    I have also re-bulbed the Walmart 50 ct multi LEDs into solids (I've done almost 100 strings this way). You do have to modify resistor in the strings:
    * green and blue strings should change to 1.5K ohm 1W (or 2W for more safety).
    * However, you can leave the 2.6K resistor in the blob and they are still bright enough. Or you could remove 4 LEDs (21 ct) for full brightness.

    * red and yellow strings need a 3K ohm 1W resistor. Alternatively you can add 4 LEDs in each string (29ct) and leave the original 2.6K ohm resistor.

    One LED more or less in any string will not cause harm or excessive dimness.


    I have found that these multi strings have twice as many red and yellow bulbs as they do green and blue. So, if you take apart 6 multi strings, you can make 2 reds, 2 yellows, but only 1 green and 1 blue 50ct strings. Your entire carton has 30 boxes, so this would yield you 10 red strings. Each individual string box has 1 red and 1 yellow spare LEDs which you could use to make a string, but this would only give you one 25ct red segment and one 25 ct yellow segment. This is not enough to convert all of your canes even if you put reds in some and yellows in others.

    You could just insert the multi string and see how it looks. Don't forget that you can cut each 50ct string into two 25ct segments as described above.

    Let me know you need any help in trying to do what I have suggested.

    Jimboha
    Springville, Utah

  7. #17
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    Default Re: LED Conversion Help Please

    Resurrecting an old thread here...

    I too have been considering doing the same thing. I have a bunch of those Walmart candy canes I would like to convert to LED, as well as some other props. I want to convert instead of replace for reasons such as: odd number of bulbs, colored wires, and or already mounted in/on something. As an electrical engineer, this does not seem too difficult. I haven't tried it yet, but when I get around to it I will keep you posted.

    As I see it: First count the number of bulbs. Multiply that times the forward voltage of the LEDs, typically 2.7-2.9v for red, yellow, orange, typically 3.0-3.2 for blue, green, purple, white.
    Once you know the total voltage of the LEDs, subtract that from the peak voltage from your mains, around 170 volts for the U.S. (120v RMS) or 340 for Europe (240v RMS).
    Divide the voltage difference by the desired current. Most LEDs have a max of 20ma. Using a little less, say 15ma will cause very little reduction in brightness and a greatly increased life. This calculation will tell you what size resistor you need. It should be rated for at least 1-2 watts.
    Splice into the string, and add the calculated resistor and a 1N4004 diode in series.
    Pull out the lights one by one. Unbend the leads of the incandescent bulb and remove it, insert an LED and bend the leads over and trim them. Pay attention to polarity!! Normal premade LED strings have sockets that are keyed in some way so they only insert in one direction. With incandescent strings, the sockets are typically non-polarized and can be inserted either way ** so you need to pay careful attention to how you reinsert them and make sure the polarity of the LEDs all line up. (** I've seen some recently made incandescent strings that have polarized sockets, probably so they can use the same sockets and wiring to manufacture either type)
    If you use the right value of resistor, and get the diode and all the LEDs all in the same direction, it should work just fine.

    Example 1: Convert a string of 20 incandescent bulbs in a green candy cane to green LEDs with a forward voltage of 3.1 volts.
    20 X 3.1 = 62 volts for the LEDs. 120v RMS line voltage = 170 volts peak, minus 62 volts, means you need a 108 volt drop.
    108 volts divided by .015 (15ma) is 6800. So you need a 6.8K or larger, 1 watt resistor (and the aforementioned 1N4004 diode).
    Example 2: Same thing for a red candy cane:
    20 red leds @ 2.8v = 56v. 170 - 56 = 114v. 114v .015A = 7.6KΩ

    Do any of you other electrical engineers see a flaw in my logic?
    Last edited by DrWizard; 03-03-2019 at 12:25 PM. Reason: correct typos, misspellings
    Wizlights.com

  8. #18
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    Default Re: LED Conversion Help Please

    No real issue in your logic, maybe one of your assumptions. I have never been able to figure out the actual resistance in the way you outline - it's been much faster to just be pragmatic about it. For example, for my (half-wave) LED strings with 25 LEDs in each segment (note: 2 25-ct segments in a 50 LED string), I have found R = 1500 Ohms to give similar 15ma readings when TESTED with ammeter.

    I have found it easier to START with a known resistance for a given string (as the manufacturer calculated), and adjust that resistance up or down based on the voltage drop difference I am introducing. This works for adding or subtracting LEDs or even for changing colors.

    With this logic, in your case, for 20 LEDs, I would expect 1500 Ohm + [5 *(3.1v/0.015A)] = 1500 + 5(207)=1500 + 1033 =2533 ohms. I would use 2.5K or 2.6K.

    I have never seen the extra 1N4004 or other diodes. If used, I would expect the voltage drop due to it to be negligible in this calculation.

    "Assumption" : I think the difference in resistance is due to the clipped-A/C average voltage/current calculation. Your calculation determines the resistance at max voltage, which only occurs a small part of the time. Considering other parts of the A/C sine wave, forward conduction will only occur when the ("positive") A/C voltage is upwards of of 20*3.1 = 62 volts. in your model, you would actually see pulses 60 times per second from 0ma to 15ma, lasting for only (just making a crude guess) 1/3 of each positive half of the cycle. My calculus is really rusty, but if you summed and averaged that, you would see far less than 15ma on average particularly since the max your determine will only be 15ma)

    Remember that LEDs can withstand much higher forward currents when pulsed. The shorter the pulse duration, the higher the current can be during that pulse - within reason. And in our case, they are pulsed 60 times per second, but only in the one half of the cycle, and then only when the voltage exceeds the total forward voltage drop of all the LEDs in the string (segment).

    For your red LEDs, I found that 3K is good for 25 at 1.9v Vd. For 20 LEDs, I would (again) add 5(1.9/0.015) or 5*127 = 630 ohm, for a total of 3K + 630 = 3.7K. For your 2.8v reds, this would be different, but I do not think 7.6K would be right - they would be very dim. 3K + 5*(2.8/0.015)= 3.9K.

    This is according to my experience.

    Jimboha
    Springville, Utah

  9. #19
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    Default Re: LED Conversion Help Please

    FYI a 7.5K resistor running at 15ma would dissipate 1.7w.

    No matter what you do, doing this type of replacement will flicker a bit (Due to the late turn on at 62 volts). However, you can reduce the flicker a bit by putting in a full wave bridge rectifier in each string. The set up as described (single diode inline) will only conduct current for one half of the AC cycle. Every thing will be off for the other half. That means you lose half of your possible light energy AND you get larger 'dark' time.

    WARNING: If you do put an LED in backwards, It will take most of the line voltage and fry pretty quickly. Be very careful.


    2019 - Just moved into a new home (yet another change of plans). Will be dim but not dark. Too much to do at the new place to leave time for a show.
    https://www.youtube.com/channel/UCyX...ttrsZNARkUce0Q

  10. #20
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    Default Re: LED Conversion Help Please

    Quote Originally Posted by MartinMueller2003 View Post
    FYI a 7.5K resistor running at 15ma would dissipate 1.7w.
    That's for DC, and for full-duty A/C. In the example above, for half-wave, the LEDs only conduct at most one half of the A/C cycle, and then again only part of that cycle due to forward voltage requirement of the string. The actual power is a little more complicated to calculate. But to be safest, by all means, use this simple power calculation P = i^2R (in amps and ohms, returns watts) - this will give you plenty margin of safety, especially if you double that value as is often done.

    Quote Originally Posted by MartinMueller2003 View Post
    No matter what you do, doing this type of replacement will flicker a bit (Due to the late turn on at 62 volts). However, you can reduce the flicker a bit by putting in a full wave bridge rectifier in each string. The set up as described (single diode inline) will only conduct current for one half of the AC cycle. Every thing will be off for the other half. That means you lose half of your possible light energy AND you get larger 'dark' time.
    Yes, ALL half-wave line-voltage strings will flicker. Just how visible the flicker is will depend on a few factors, the biggest of which is the actual observer. For US A/C, the LEDs will flicker off and on 60 times per second, well within the visible/noticeable range (50Hz-75Hz). Some people are very sensitive, others will not see anything. The flicker will be even more evident in peripheral vision (ie. out of the side of your eye).

    Since we can't change the observer, we could consider changing the frequency, but we are stuck with 60 Hz from the power company (in the US). The only other option is to convert to full-wave which changes the effective doubles the frequency to 120Hz, well above the visible range (and 100Hz for others, still high enough). This also produces more light as Martin said. This is which full-wave LEDs look better and are preferred.

    Notice that this changes the power dissipation issue in the resistor (and in the LEDs)! The portion of time in each cycle when the voltage is high enough to conduct remains the same, but instead of conducting once per A/C cycle, it will happen twice. This doubles the power dissipated - not the simple P = i^2R as calculated above, but the actual power which, as I already said, is harder to calculate. Thus, if you are converting an existing half-wave LED string to full-wave, you will essentially be doubling the amount of power dissipated in the stock resistor. You should probably put in a larger power-rated resistor. And since the LEDs are conducting more often, they might overheat over time and reduce their lifetime. Thus a slightly larger resistance value might be a good idea.

    But if you are building your own string and you use the simple power formula, your 1.5W resistor for 7.5K and 15ma will still be suitable.

    Quote Originally Posted by MartinMueller2003 View Post
    WARNING: If you do put an LED in backwards, It will take most of the line voltage and fry pretty quickly. Be very careful.
    While this maybe true, I have put individual LEDs in backwards by accident numerous times. I have only had a few ever burn out that way. They only see a part of that full voltage for short periods. It does depend somewhat on the quality of the LEDs themselves.

    However, when working with such strings involving line voltage, you should always be careful! Very careful!!

    Jimboha
    Springville, Utah

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