Artist seeks electrical advice

Hi, I have limited experience with electrical wiring and am getting into something complicated. I want to use a 4-channel controller to create chasing lights in a sign. I've done that much before successfully. The problem is I want to use 4 sets of string lights (35 "pearl" lights per string) that are wired in series, and I only need to have anywhere between 4 and 9 lit lights per string. The remainder are "extra" and I would like to shorten each string accordingly, so I'm not hiding a bunch of hot lights within the body of the sign. I do not know the wattage of each bulb, but they definitely have the right look, so I'd like to use them.

I've been told I can't shorten the strings because it will cause the remaining lights to overheat and burn out. I am wondering if I can solve my problem by using a resistor on each string to compensate for missing lights. If so, how do I do that math to figure out what strength resistor I need for each string? I don't really understand volts, watts, ohm, etc., so any advice would be greatly appreciated.

Thank you, Heidi Cody

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Reply to
artfrogger
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The resistors would dissipate the same power as the bunch of hot lights. So they would need a way of getting rid of the heat, say with a heatsink and fan, or they would get as hot as the lights..

Calculating their value just needs the voltage of the supply and the wattage of the existing 35 lamps and how many lamps you want to have in your string.

The math is relatively simple. But there may be an easier way.

You have 35 lamps to a full string. So each one has V/35 volts across it (where V is your supply voltage). Each lamp will be a V/35 volts lamp.

However, if you swap the lamps with ones rated for V/4 volts, you can run the string with only 4 lamps.

'Frinstance lets say your supply voltage is 210V. Then the 35 string has lamps rated at 210/35 = 6 volts.

Now lets say you can get some 12 volt lamps - you could have a string of just 18 of those.

With 24 volt lamps, you could have a string of just 9 lamps..

With 48 volt lamps, you could have a string of just 5 lamps..

And so on.

So it may be worth looking to see what voltage lamps you have and what voltage lamps you could get..

Reply to
Palindr☻me

Thanks, that's very helpful. I thought that might be the case with the math. And that makes sense with the resistors getting hot, but I think

4 hot resistors would be easier to handle than 4 clumps of 20-25 hot lights and wires. Unfortunately the look of the lights has been hard to match. They're miniature yellow frosted globe lights, about 1/2"d. And they don't screw in, so they'll be hard to replace. The trick will defininely be finding identical looking lights in different voltages. But I will look. Thanks again. Heidi
Reply to
artfrogger

you do need to understand that each "hot resistor" will have the equivalent heat of the 20-25 lights that you are removing.

Reply to
no_one

I suggest you use a transformer to lower your voltage. The most common place to get a transformer would be Radio Shack, although there are many electronic supply houses that could supply one. You need to divide you mains supply voltage by the number of bulbs you have, this will give you the voltage per bulb.

Ex. 125v / 35bulbs = 3.5 volts per bulb

Next multiply the number of bulbs(in your string) times the volts per bulb.

Ex. 7 bulbs x 3.5 volts per bulb = 24.5 volts needed to drive string.

You could purchase a transformer with a 24 volt output and all would be fine.

However you said "I only need to have anywhere between

4 and 9 lit lights per string". If each string doesn't have the same number of bulbs, then the above solution will not work. But you could pick a tranformer based on the string with the maximum number of bulbs, then put the proper resistor in the other strings to lower the voltage. This resistor would not need to be as large as the one required if you were running from 120v. Another solution would be to use a transformer of the same voltage as each bulb, in my Ex. that would be 3.5 v, then the bulbs would need to be put in parallel. Feel free to ask for more info. Mike
Reply to
amdx

This does presume that the "4-channel controller", powering the lamps, is compatable with a transformer as its load. It may not be - it may be outputting DC or full/half wave rectified mains. Unlikely, but possible. I think that you need to be asking Heidi for more info before giving more yourself.

If it were an ac output, a simple rectifier would allow the lamp count to be reduced substantially (about half). A triac light dimmer would do the job for any number of lamps - but would need attention paid to fusing.

The resistors and changing the lamps for ones with a different voltage rating will work for every sort of controller I can think of..

I would have been loathe to suggest the triac lamp dimmer, even if the supply was going to be compatable. I can see a race as to which self destructs first, the controller, the dimmer, a lamp, or the fuse...all it needs is for the controller to be inadvertently set high, not low, and the power switched on.

Reply to
Palindr☻me

Paint the lights you don't want to use black.

sQuick..

Reply to
sQuick

Wow, thanks everyone. I clearly in the deep end, but hopefully I can find my way out. The controller has 4 channels, each of which says 300W and there is a toggle switch that says AC line and I can switch back and forth between 110v and 220v. Each light string says 125V1A on the plug. String 1 has 8 exposed lights; string 2 has 9 lights; 3 has 5 lights; 4 has 7 lights. The form is a concentric 1/2 circle of lights with 6 "rings", thus the crazy numbers.

Stupid question: when I plug it into a regular US outlet, is it 110V?

Thanks--ther is so much information since I last checked that I am going to reread it and try to get my head around the new info.

Heidi

I really appreciate all the advie sQuick wrote:

Reply to
artfrogger

Yes, I do. These are just crappy Christmas lights, and what I know I don't want is bulbs touching the wires. Thank you though.

Reply to
artfrogger

yes US power will be 110V from a normal house outlet.

Reply to
no_one

With a shortened string and resistance to make up for it: String 1 needs 97 ohms at 100 watts String 2 needs 93 ohms at 100 watts String 3 needs 107 ohms at 110 watts String 4 needs 111 ohms at 115 watts

That will produce about 100 watts extra heat per string - way too much. The wattage makes that solution impractical, so a different solution is called for.

With 2 18 VAC 2 amp center tapped transformers, #7843 from

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at $4.63 each,

4 relays and some resistors you can build what you need. You will make assemblies of 4 bulbs in series. String 1 (8 bulbs) is made from 2 assemblies in parallel. String 2 (9 bulbs) is made the same way, and an additional bulb is switched in with a relay. String 3 (5 bulbs) uses 1 assembly with an additional bulb switched in via a relay. String 4 is one assembly. The diagram is shown below. +----------------------+ | | | 9VAC(T2) | | | | 18V(T1)-+----------+ +--------+ +---+--------+ | | | | | | [R1] [R2] [R3] [R4] [R5] [R6] | | | | | | |
Reply to
ehsjr

Look, I am going to make a guess that the output to you lights is plain mains ac - and the controller merely switches the supply on and off to each string.

Now, any competent engineer/technician, seeing the controller, could confirm this in a few minutes or less - or you could take the risk and work on the basis it is. If wrong, this could mean going out and buying a new controller. If right, this gives you a simple solution - using low cost lamp dimmers that you can find anywhere.

If you want to take the risk - just buy a dimmer and an inline mains-rated 1A fuse and receptacle (I assume that such things are available in the US) and wire them in series with a full string of lights and see if the dimmer works. You could even wire it in place of one of the lamps.

If it does, put it to minimum, shorten the string by a few lamps and see if the dimmer lets you brighten them to normal intensity.

If it does, then you have a working solution to each of your string of lights - just add a dimmer and inline fuse to each shortened string and turn up each dimmer to the right level.

Now, if you turn the dimmer up too far - it will blow the lamps or the fuse or the controller. I hope the fuse, but am still guessing on the nature of the controller and the wattage of the lamps.

This is a risky suggestion - I have only a little idea of what the controller does and am making a whole load of assumptions that I shouldn't.. An engineer/technician with the controller in his sticky fingers could tell in a few minutes whether what I am proposing will be ok or not. So you could wander into the electrical dept of your local uni, with controller, and see if a lab tech would give it a once over for the price of a beer or two. Or just try it and see.

Me, I'd give it a go! But not if the controller cost too much to risk.

Reply to
Palindr☻me

Thank you! I will probably try Sue's solution first, because it sounds like you are guessing correctly and I can manage it on my own. And Ed thanks for taking the time to diagram that out and tell me where to buy components. It's a bit too advanced for me but I might be able to find someone who can help me do it. I'll keep everyone posted. It'll happen this week hopefully. I will post a picture of this piece tonight if I can, although I'm not going to get this problem solved today.

Heidi

Reply to
artfrogger

a small bucking transformer on the output of each chase zone may well be reliable and cost effective.

Reply to
TimPerry

Thanks Tim,

What's a bucking transformer -- can I get it at any electronics place? I will look into that too, although I have the fuse and receptacle and dimmer to try first.

I couldn't figure out how to post a picture to this site, but here's the link:

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Reply to
artfrogger

Very impressive!

You will probably find that, if a dimmer doesn't do it - a simple bucking transformer won't either...

Basically it is a transformer that sits in series with a supply and is wired so as to produce a lower voltage on its output side than in its input side - hence "bucking" the input compared to a "boost" vesion - which has a higher voltage on the output side than the input side.

With a bit of electronics, the bucking transformer almost certainly could do the job, irrespective of the controller - but it will get kinda complicated, especially the electronics bits.

Fingers crossed for the dimmer...

Reply to
Palindr☻me

Do you have 3 seperate circuits consisting of 6 lights, 8 lights, and 10 lights ? If this is the case and the voltage required for each bulb is a 3.5v, then you could purchase 3 transformers one with a secondary voltage of 21v, one with a 28v secondary, and one with a 35v secondary. These exact voltages may not be found but you could get close then equalize the bulb brightness by adding series resistors. If you decide to go this way then we can start talking about current ratings for the transformers.. Have you figuired out what the single bulb voltage is?

Mike

Reply to
amdx

I am stuck prepping for a class I teach tomorrow evening today and tomorrow. If I find time I will go ask at the place that has the bulbs tomorrow, see if they can tell me something. But it's right that the mains is 110-120 AC and that there are 35 bulbs on each wire. There are

4 circuits in the current set up so there is no "gap" in the chase. If I put it to 3 there will be an unwanted pause...I think. Anyway I would much rather be tinkering on the sign but it has to wait till Wednesday. I'll check back in when I know something. Thanks, Heidi
Reply to
artfrogger

Now *that's* neat!

Ed

Reply to
ehsjr

Great News: The dimmer works! It must pay to take the path of least resistance. How's that for an electrical joke? Thank you Sue!

Also, thanks EVERYONE for all your advice and enthusiasm. I still have to figure why all the lights are not working correctly with the chaser, but that could be solved by the dimmer or it could be that there's a bad connection. I'll be working on that today. Also I will be working with red leds in the headband (that's a first too), and then a fog machine that blows "smoke signals" will be installed behind the whole thing, ideally. So, I will update that link as this piece progresses. FYI it is the Land O' Lakes Headdress in front of the Nature Valley Granola Bar graphic. Best, Heidi

Reply to
artfrogger

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