Large Scale Central

Electricity question, missing something....Christmas lights.

General Discussion
#1

Okay, I’m putting people in my passenger cars and lighting the interiors. Great. (Pictures eventually.) I wanted to use regular warm Christmas tree bulb lights, the little ones. Not going to work apparently, so I’m going with warm led lights hooked up to a box with a switch, cheap on ebay.

My question is this: how come you plug in 110 volts coming from the wall and it brightly lights up hundreds of warm Christmas lights, amounting to a fraction of a volt per light, YET when I hook up just five lights to a nine-volt battery, almost two volts per light, the light is very dim, not bright enough to light up a passenger coach that’s for sure. It makes no sense. It takes four or five volts just to brightly light one Christmas tree light; I’d have to have a battery for almost every light in the coach to make them bright enough, which is not happening. I thought I had a great answer for using all those extra Christmas lights and the battery boxes I bought cheap.

Something’s not computing here.

#2

That is because there are not hundreds of LEDs in one series string, but multiple sets of “strings” of LEDs in series.

(read here, scroll down to the part “string construction” http://www.ciphersbyritter.com/RADELECT/LITES/LEDLITES.HTM )

So, typically 110v is applied to about 30 leds ( 110v divide by 30 is 3.66 volts )

So, the 110v LEDs are arranged in multiple strings of 30, and then those strings are in parallel, each string getting 110v.

There is nothing magic about the LEDs used.

On 9 volts, dividing by 3 gives 3 volts each, below the typical 3.6 volts, and they should be dim. Some LEDs will work on much reduced voltage, so results vary.

9 volts is not a great choice, you would be better off using a lithium battery which is about perfect for a LED and wire your LEDs in parallel.

Basically your difficulty here is you are not considering parallel connections and you have selected a voltage that is not optimal for putting LEDs in series.

Greg

#3

The Christmas lights I tried to use are regular incandescent lights, not LED lights. They’re the lights that come on green strings usually and you plug them into the wall and you get hundreds glowing brightly. That’s what I don’t understand here. Why won’t more than one or two, cut out of the string of lights, glow brightly on a nine-volt battery?

#4

Sorry, same information is valid in terms of theory… if they are the small incandescents… a combination of series and parallel.

Also, they draw more current, which will probably tax a 9v faster. (you never stated LED or incandescent)

Are these the miniature ones that are about 1/8" in diameter and 5/8" long? By the way there are SEVERAL different voltages used, so this becomes more of an issue of finding out what voltage they need. (I have seen 2v, 2.5v and 3v miniature bulbs)

It would be easiest to just put one on an adjustable power supply and turn the voltage up on ONE bulb until it is of the same brightness as when plugged in, then you can determine the voltage of the bulbs you have.

But! the current draw is so much higher I think this will not be a good solution for battery power.

I’d get the LED ones they are cheap and then will take less wattage from your battery, i.e. run longer.

Greg

#5

I guess I’ll never understand why 450 bulbs can run for weeks on 110 volts and five bulbs can’t run for an hour but dimly on nine volts. Oh well; the leds with batteries and switches are on their way from Dallas! Nine bucks for ten strips.

#6

OK, taking the assumption you really want to understand… I might be boring the others on this thread…

You have put several parts into your question, so let me split them apart to help reduce the confusion.

On “run for weeks”… clearly the power to your house is infinite in time, will continue forever, and a 9v battery is limited in the power it can produce. Also in terms of energy stored (watts) it’s about 2 AAA cells… you trade voltage for capacitity.

So the length of time it can run is separate from running dimly on a different voltage.

Now you mention 5 bulbs are dim on a 9v battery.

Run time:

I mentioned the voltage of these bulbs, they are typically 2.5 volts each… so when you put 5 in series, you need 5 times 2.5 volts which is 12.5 volts… but you only have 9 volts, and a battery that cannout put out that voltage for long at a heavy load. So the time comparison between being plugged into your house and running on a battery has nothing to do with brightness.

Brightness:

So you are giving each lamp 1.8 volts when they are designed to work at 2.5 volts… it makes complete sense they are dim… will your car operate if your battery is likewise at 72% lower voltage (8.64 volts)? NO it won’t, and your interior lights will be dim.

I hope this helps explain…

If you want to use these bulbs at 9 volts, then you need to try 4 bulbs but they will be somewhat dim, and if you try 3, then they will probably be bright right before they burn out. Bottom line, your 9v battery and the 2.5 volt incandescent bulbs are a poor match for many reasons, some of which I have stated here.

Greg

#7

I see the time factor, that makes sense of course. And I see the problem if each bulb needs 2.5 volts, and you’ve described my experiment exactly.

But if each bulb takes 2.5 volts, why doesn’t it take 1,125 volts to run three Christmas strings of 150 bulbs each? Hell, even an electric dryer needs only 220 volts.

Look, I suspect I’m missing some basic bit of understanding about electricity, but I’m not sure what. Maybe somehow the 110 volts is steady throughout the whole 450 bulb string and doesn’t dissapate with each bulb? Maybe you’re using 450 times more electricity than you would with one bulb? (And the electric light company charges you more.)

If that’s true, then there must be something in the light string you can’t see that prevents any of the bulbs from getting the full 110 volts, because they would burn up otherwise. And it doesn’t matter is you have 150 or 600 bulbs running in that case.

I think I better stick to painting portraits.

#8

Ahh, refer to my previous posts, the typical set of bulbs in series to work with 110v is around 35… that will give around 2.5 to 3 volts per bulb… let’s call this group of 35 bulbs a “string”… a "string of 35 bulbs wired in series… To have more bulbs, you put strings in parallel… that means each string still gets 110v…

If you look carefully at your entire set of strings of bulbs you don’t see 2 wires, but 3 for a lot of the length… so you have strings of 35 in series, and wire those strings in parallel to 110v…

Take your string of lights out and look at how many wires there are… you will be surprised.

Greg

p.s. I think this was explained in the links I provided, but maybe you did not read them fully…

#9

Greg Elmassian said:

p.s. I think this was explained in the links I provided, but maybe you did not read them fully…

Seems to be the general consensus around here.

#10

And if you use a rechargeable 9 volt battery, you get less than 9 volts, but more constant voltage.

Alkaline batteries start at about 9.45 volts and drop down to 7 volts after being used awhile (read depends on the load/current draw).

Perhaps a candle could be better.(http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-surprised.gif)

#11

And most rechargeable 9v are actually 8.4 NiCad or NiMih, but why confuse the issue?

I was working hard to give John explanations to his questions.

#12

Greg Elmassian said:

…

Take your string of lights out and look at how many wires there are… you will be surprised.

…

Well, actually, Greg, you be dead right, son, dead right, and now it makes sense. There aren’t 150 bulbs needing 350 or so volts; there seem to be three separate sections of about 50 bulbs each all three sections with their own separate access to 110 volts, and now that explains why when I cut out some test bulbs in the first “section” the other two still lit up, to my big surprise at the time, when I plugged the string back into the wall outlet.

So there you go. As soon as my warm leds get here from Texas, and I get them all arranged in a coach, I’ll get some pictures up. I’m really very pleased with what I’m doing with a bunch of random Bachmann old-time passenger cars, very nice I think.

#13

Maybe I missed it but in this conversation was the difference between a series and a parallel circuit ever discussed?

If not here is a good explanation.

https://www.youtube.com/watch?v=x2EuYqj_0Uk

#14

Thanks, Marty, that was the best explanation of series/parallel construction. I got the increase in amps at the very end and the bigger draw and it all clicked.

#15

Oh yeah, here it is…I learn by seeing!

#16

Rick Marty said:

Maybe I missed it but in this conversation was the difference between a series and a parallel circuit ever discussed?

If not here is a good explanation.

https://www.youtube.com/watch?v=x2EuYqj_0Uk

that video - and some more it lead to - really helped.

thanks for that.

now there is only one christmas-chain mistery left.

i understood - and do use - common returns. (very helpfull, to save cables)

if i got more than one circuits, i can bundle all negative (or all positive) cables into one. needing as many cables as circuits plus one. (instead of two cables per circuit.)

fine…

then i look at an old fashioned christmas chain and see:

one plug

three cables

and THREE sections (strings?/circuits?)

using common wire = as many cables as circuits plus one

so how can they make three strings with only three wires???

#17

that is the definition of parallel… in the terms I used before, the bulbs in series are called a string.

make up your strings to match your voltage…

Connect as many strings in parallel as you wish (although you may run into too much current being drawn if you are trying a 9v battery)

Greg

#18

using common wire = as many cables as circuits plus one

so how can they make three strings with only three wires???

3 wires, hot, neutral and the string. Or to (incorrectly) use DC terms, positive, negative and the string.

#19

so, other than the limits of the wire, you can continue the 3 wire setup, 30 or so lights at a time, forever…

Not sure this is helping the OP, maybe we can be told the goal, like 9v batteries with “X” number of LEDs… If it was me, I would use AAA batteries, and try LEDs at 3 volts, no regulator and see if they are bright enough.

9v batteries are very expensive for the power you get (watt hours)

Greg

#20

This has all been very helpful. I thought I knew what I was doing, it didn’t work, I couldn’t figure out why, you guys illuminated, or as you will see below, “iluaminated,” me, in “everydirection” and now I understand how all this works. I couldn’t stand not understanding, if you know what I mean. And aside from the fact that I will never look at Christmas lights the same way again, all this will help me with buildings and other lighting on the layout. But for the coach cars that initiated my interest, I’ve decided to go with these little devils (nine bucks for ten of 'em) from Dallas by way of China, and they come with “Baterryies”: