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intensity setting


Mike Cole
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I've been thinking of new items for next year and had a brainfart. If I wanted to build a prop with say 10 mini bulbs on a string, could I set the intensity setting on that channel in the sequence editor to say 10%, or what ever I find is the right setting as not to blow up the string and keep it as bright as the other strings in the display, could I make it operate properly? Just a thought...........Mike

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Well, I have hundreds of extra strings now, so I won't be buying any, and my props will use 25 to 50 mini strings with a small number count, say 10 or 8 or 12 or 6.......I don't know yet. I'm cheap! I want to try and use what I have. Just trying to see if my theory is right or wrong. Maybe I will just cut a string and try it...........................

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There is a long story here, but I wont tell it. Lets just say that I had to find out something the hard way myself when I was about 8 yrs old. Grandpa just could not get it through my thick hard german head (course he was first gen here in America).

So, why dont you just do that and then come back and tell us how did it work for you. P.S. keep fire ext. near by. Just in case.

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OK.....I get the point, I think. I was looking for a discussion on the theory of what I'm trying to do, as in lowering the intensity of a channels output to power a string of cut minis. I'm not an electrical engineer, and was hoping someone here could explain if my thinking was right or wrong and why in some sort of layman terms. But, hell!, I get two LOR beta testers telling me to, buy smaller strings or build your own, and, something about a long story his grandpa told him when he was a kid, and to go try it with a fire extinguisher close buy. I'm not new here guys, and uninformative answers like this would run off a newbie. I was not looking to learn anything the hard way, as you said. I'll go figure it out ...........thanks,Mike

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Mike Cole wrote:

Well, I have hundreds of extra strings now, so I won't be buying any, and my props will use 25 to 50 mini strings with a small number count, say 10 or 8 or 12 or 6.......I don't know yet. I'm cheap! I want to try and use what I have. Just trying to see if my theory is right or wrong. Maybe I will just cut a string and try it...........................



Sorry you feel that way, Mike. Every theory has to be tested to see if it is valid.

I don't have hundreds of extra strings (I'm almost all LED) or I would be glad to chop up a string, hook it to a controller and see what happens. But first I would hook a volt meter to a controller channel, and see what different intensities produce what voltages, so that when the "chopped" string was hooked up to the controller I wouldn't be as likely to have exploding glass shards flying into my eye.

Since LOR controllers have a PWM output, I'm not sure that this would even work.

But here again, I haven't had a need to hook up my DVM to a controllers output. I only use 120 VAC and 24 and 12 VDC contollers.

I do have some some 10 count light strings from the Dollar Store that I paid 50 cents for, and I always keep some 6 and 12 volt bulbs in inventory that I get for 10 cents a pack after Christmas at Wally World.

That's why I suggested these extremely low cost options from a safety standpoint. I would never advocate nor encourage someone to proceed with a potentally dangerous activity on a public forum. (However what I do in the privacy of my own workshop I never talk about)

So from a safety standpoint, if you are modifying light strings to use a low voltage, then I would have to recommend using LOR low voltage DC controllers for this application.
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JBullard wrote:

So from a safety standpoint, if you are modifying light strings to use a low voltage, then I would have to recommend using LOR low voltage DC controllers for this application.


No disrespect to JBullard , nor to start an arguement. You can't use a DC controller on AC lights, Well, at least not to my knowledge. I think DC would burn up the AC bulbs.


Mike, Your theory sounds reasonable. Each bulb on a 100 count string(2 sections 50 bulbs each) is 2.5 volts, so depending on how many bulbs you use in your prop would be the percentage of your setting.(ie 10 bulbs * 2.5 = 25 volts divided by 120VAC will give you 20.8 or 21% for the setting on that channel) Just apply that formula to any bulb count and test it on a spare string and see if it works.
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kzaas wrote:

JBullard wrote:
So from a safety standpoint, if you are modifying light strings to use a low voltage, then I would have to recommend using LOR low voltage DC controllers for this application.

No disrespect to JBullard , nor to start an arguement. You can't use a DC controller on AC lights, Well, at least not to my knowledge. I think DC would burn up the AC bulbs.

What is an AC light?

Sorry to disagree with you, but an incadescent light bulb doesn't care it if it's AC or DC.

Pull a bulb from a 35/70 (3.5 volts) count string of incadescent lights. Remove the lens cover from a two cell flashlight (3 volts). Swap the bulbs. It works.
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JBullard wrote:

What is an AC light?

Sorry to disagree with you, but an incadescent light bulb doesn't care it if it's AC or DC.

Pull a bulb from a 35/70 (3.5 volts) count string of incadescent lights. Remove the lens cover from a two cell flashlight (3 volts). Swap the bulbs. It works.

You make a good point, I don't know if you own a Lightkeeper Pro, but on that is a light tester. I do test my so called AC lights with it and it is powered by batteries.

I stand corrected, Sorry about that JBullard.
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Ok, just get a little tired of the "what will happen if I cut down a string of lights"? Be it ican or LED. And then there are a few on here that push the "Think outside of the box". Well it gets a little bit much and I get a wee bit snippy. At least you are not talking to me about 6 months ago.

Ok, PWM means pulse width modulated. So all I am doing is changing the width of the pulse, not the amplitude of that pulse. on icans, this will limit the time that the filiment has to heat up. Which can be as little as ruby red to white hot. Which will dictate how much light it will put out. So, now the question is this. Taking a string of 100 which is two 50s. And cutting down to 10 bulbs is a circuit that would as pointed out be best powered by a 25VAC circuit. But LOR controller is still pumping out 125 VAC (or there abouts). So, will only pulsing for10% of the time of a normal sine-wave. Will this not over heat the filament to the point of melting? Now if LEDs lamps I would think that they would come up to melt down in a very short period of time and will pop them for sure. With icans, there is a chance they will survive. So long as you keep the intensity down real low.

And so, what is your problem with my suggestion of keeping a fire ext. near by? I have built a few things that I almost need one. Esp the time I put an electrolytic cap. in backwards. You have seen what happens when you do that? Almost pee-ed on myself.

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I disagree with you Max-Paul. And I just proved it to my self by measuring the output of one of my controllers. At 40% Intensity it was only putting out 46.5VAC at 75% it putting out 94VAC. The circuit works like this, it turns on the triac at sinewave zero crossover then at the intensity setting, it turns off the triac and the output sinewave returns zero. If the intensity is set to 40% then the sinewave will only rise 40% giving you only 40% amplitude thus 46VAC.


As you said you are changing the pulse width which in turn is changing the sinewave rise time and amplitude. Just picture a sinewave and think about it.

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Kzaas,

Ok, can see what you are getting at, sort of. What happens once you past the 50% point. I mean from zero to 180 degrees would be 0% to 100% right? This is strictly talking about the positive phase and what happens on the positive phase would be mirrored on the negative half of the sine wave right?

So max voltage would be passed out of the Traic when you get to 50% setting. But to realize the max energy, you would need to pass all of the positive half of the sine wave.

Wondering, what did you measure this with? a VOM or DVM will read the average voltage. While an O'Scope will read the peak or p2p volages. And I will promise you this. A LED will sense peak and pop if it is over its PIV value.

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The two biggest issues I have with this idea are:

1) Inrush current.. Even if the RMS voltage is 25% of 110 VAC, your sine wave peak is 170V on 110VAC, and at 75% of the way through the half wave where LOR is likely firing for 25%, there may still be 100V present. So your inrush current may be much higher with 100V into 10 cold bulbs, instead of worst case for a normal string of 170V into 50 cold bulbs. No telling if the bulbs will reliably handle it.

2) On an unmodified string, those 3A fuses are there for a reason. Often when enough lights fail in a string, the remaining bulbs will reach a point where they start failing in cascade. The fuse is there to prevent the wire in the string from burning up next when the cascade event happens. If you are cutting 100 count strings down into 10 count strings, are you going to be sure you have those fuses in all your cut down strings? Using 10 light strings, cascade events are much more likely to happen. Then add the extra stress of beating up on the string with 100V inrush on a 25V string, and I think cascade events are very likely. I've used 22 gauge wire as a very nice fire starter on 12V. I would imagine it works even better on 25V..

I think it is a bad idea to start with, and an extra bad idea if any shortcuts are taken on fuse protection. But if you do decide to try it at home, please take some video of it all. And I'd strongly suggest keeping a fire extinguisher handy, except for the fact that the video could be much more interesting without it. :shock:

Now I will say that the DC power supply and controller idea is pretty good. You should be able to find 24VDC power supplies pretty easily, and you can fuse each of your inlet banks at 3A, to protect from cascade events, but you do take out all or half a controller when it happens.

But, I do have some strings of 20 made from cut down 100's, running on a DC controller, and 48VDC power supply. I've run those for 2 years with no issues so far. Well, maybe one. You don't want to take a LKP anywhere near a string that is powered by a DC card. I used a 20W power resistor of an appropriate size in series with the connectors I am using, to be able to plug one of these strings into 110V for testing/LKP use.. In hind sight, I probably should have used a sting of 30 lights as my ballast resistor.

But, you can buy a lot of 10 or 20 light strings for the price of a DC card...

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Thanks KLB,

I spend way to much time working on PWM DC motor controllers. So, the voltage out is always the same. But the amount of power available changes with the width of the pulse.
Got to remember to address my answers accordingly. Also unlike some of you, I am so new to this sequencing stuff that I just do not have money or controllers to have one laying around and not in use. So, during the season all of my hardware in out in the yard. Heck I am working on a fix for those strings that Paul sold last year. Fellow asked me to hammer it before sending it back to him. Well it is not going to happen till next week when I start pulling in my controllers.

Again thanks for jumping in with your information.

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Max-Paul wrote:

Heck I am working on a fix for those strings that Paul sold last year. Fellow asked me to hammer it before sending it back to him. Well it is not going to happen till next week when I start pulling in my controllers.


Off topic alert:

Those strings were sold in 2008, not last year. In 2008, most of us cut off both ends of those strings (that contained the problem capacitor). Then added bridge rectifiers and dropping resistors to be able to use them for the 2008 display season, They were replaced free of charge in 2009. Have two years on the replacement strings with no problems.

Back to topic.
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OK you are all making good arguements, But think about it, yes I measured with a DVM, the same DVM that I measure with to ensure that I have 120VAC input. If I take a 100 bulb string (whether its LED or incandesant) feed it 100% intensity, you still get all those inrush's and P2P that you are speaking of. So now if I decrease to 40% intensity, my inrush's and P2P will follow. So if the bulbs can handle at 100% with 100 Bulbs divided by 2 sections then why couldn't it handle it 21% for 10 bulbs. The bulbs would actually be receiving 2.5 volts.

It all engineered the same, just different voltage levels.


I'm not saying to cut up a bunch of lights and put them in place. Cut up a test set and run it for quite a few hours before proceeding. And as KLB pointed out "Ensure you have a fused plug".

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Here is one place I know my stuff. A VOM like an old simpson or the cheap-o radio shack mechanical meter has the problem that physically the needle does not move fast enough to give you a true measurement of peak voltage. And depending on how good of a DVM you have (sample time) will effect the value of the measurement. To get a true reading of voltage applied across a load that is being feed from a PWM output, an O'scope is required. Now Ican lamps can handle peak or should I say P2P voltage and dampen it due to ramp up time of a heated wire. But an LED does not have this ramp up time and over voltage becomes more critical. This is the point I have been trying to make, but my tongue got wrapped around my eye tooth and I could not see what I was trying to say till now.

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