LED lighting question

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#1
Alright guys, after much searching on the internet that has only confused me further, I need some opinions on how to light our airport. The airport is in 2 sections, with about 15 or so LED's per section. My goal is to have a batter pack (using AA batteries) and a switch to turn them on and off. Now my question is, what is the best way to light them? Should I wire in a series or parallel? My original thought was to power them in parallel using 1 1.5v AA battery (the max voltage on the 3mm LED is 2.2V, so 2 AA would blow it). I wasnt sure how long the battery like that would last however. They also come with resistors for use with 12 volt systems. Any help would be greatly appreciated. http://www.ebay.com/itm/260767377511?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

These are the exact LED's I have.
 

bigB

Active Member
#2
Alright guys, after much searching on the internet that has only confused me further, I need some opinions on how to light our airport. The airport is in 2 sections, with about 15 or so LED's per section. My goal is to have a batter pack (using AA batteries) and a switch to turn them on and off. Now my question is, what is the best way to light them? Should I wire in a series or parallel? My original thought was to power them in parallel using 1 1.5v AA battery (the max voltage on the 3mm LED is 2.2V, so 2 AA would blow it). I wasnt sure how long the battery like that would last however. They also come with resistors for use with 12 volt systems. Any help would be greatly appreciated. http://www.ebay.com/itm/260767377511?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

These are the exact LED's I have.
You could go to radio shack and get one of those 3v/6v/12v AC powerpacks and build yourself a self-contained system for it. Just an idea.
 

Rico

BN Modeller
#3
I wire my bulbs in series to dim them down, don't think that works for LED's tho.
I'd go with parallel and a resister.
Now the batteries are another matter.
Putting them in series or parallel changes the amperage but not the volts.
If I'm wrong let me know.
 

Larry

Long Winded Old Fart
#4
I use the resisitors on all of mine & power them w/a small train transformer.
I just run a small 18ga. set of Buss wires for the lights in the area that I am powering. I do all of my lights in sections because the layout is so big, that way I don't get to many lights on one transformer. Today I'm going to change a lot of the smaller transformers over to Computer Power Supplies that I have. Batteries is not the way to go. Those batteries will not last very long. You need to solder the resistors to the lights & solder the wires to the Buss wires.
If you go to my Blog under my signature there's a section explaining all of the lighting I do on my layout.:)
 
#6
Series does change the voltage of the bulb need, parallel doesn't. For a 12 volt transformer, you can run 8 1.5 volt bulbs, 4 3 volt bulbs in series. In parallel, you can run 12 volt bulbs until you exceed the mA capacity of the transformer. I just asked an electrician and that is what he said. You will need to add up the mA of each bulb and that will limit you, whether in series or parallel, if it is larger than the mA output of the transformer. I'm planning on doing a string of building lights and have the same question. I found a 12V DC trans 1000 mA so I should be able to do a heck of a lot of 30 mA 12 volt bulbs (my guess is 30) in parallel. In series, it would be smaller voltage bulbs with multiple strings as each would max out at 8 bulbs if they were 1.5 volts. Stay away from batteries as you probably have a bunch of the "wall wart" style ones laying around from things that quit working. Edit: I hope this is correct but so far it seems logical and matches my minimal research!
 
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#7
Shoot howdy! Just reread the specs on what you have and I see 2 volts per bulb so with a 12 volt power supply, you can series 6, and then parallel another 6 in series from the supply, and then parallel another 6 in series from the supply, etc. At 20mA per bulb, you should be able to power 20 with a 400mA wall wart (cell phone , rechargeable flashlight, dust buster, or whatever charger). You will have multiple LOOPS back to the supply. This is cool stuff and I need to know what you come up with, keep me posted as I love this wiring thing as it seems like a way to beat the system!
 
#8
Huh, I never thought about the loop idea. And the only reason I wanted batteries is that the airport is far away from any outlets, and out in the middle of the layout by itself. But i will just have to play around with it and find out what works. Ill let ya know what I do.
 
#9
Ok I decided to do a bit of experimenting today, just to see if my original idea would work. The LED's wont light up with one double A (kinda figured that since the min stated is 1.9) so I decided to see what would happen if they were connected in a parallel series with 2 double A's. They seem to be working just fine. Im timing them to see how long they last (currently an hour.) If I can get 5 hours or so out of them I will be happy, since the lights wont be on that long for a time, and since the airport is in the middle of the layout, the lack of a cord to an outlet would be nice. The resistor is 620 ohm, and it appears to be doing just fine (for any of you electrical savy people out there, would this be enough, to much, not enough?) After a quick calculation, it looks like it is around 4.83mA (3volts/620 ohm's, X1000) well below the 15-20, so this should be good. If I am wrong or dont know what Im talking about please let me know lol. But, I shall see how this goes.
 
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UPBigBoy

J&A Paint Shops
#10
If you are running off the 2 batteries shown in the picture, remove the resistor as it is not needed. In fact it is putting a draw on the batteries but you aren't getting anything from this draw - no light.
 
#11
Every LED has a resistor, but If I put it up to the battery without, it turns red, then goes really dim then burns out (the LED's are only rated for 2.1 volts)
 
#12
...After a quick calculation, it looks like it is around 4.83mA (3volts/620 ohm's, X1000) well below the 15-20, so this should be good. If I am wrong or dont know what Im talking about please let me know lol. But, I shall see how this goes.
The current draw would be much lower. You have to take in to account the voltage drop of the LED: (3 - 2) / 620 = 0.0016 amps = 1.6 ma. Those look to be pretty bright even at 1.6 ma. Goes to show that you generally do not need to drive LED's anywhere near their maximum rated current.
 
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#13
Shoot howdy! Just reread the specs on what you have and I see 2 volts per bulb so with a 12 volt power supply, you can series 6, and then parallel another 6 in series from the supply, and then parallel another 6 in series from the supply, etc. At 20mA per bulb, you should be able to power 20 with a 400mA wall wart (cell phone , rechargeable flashlight, dust buster, or whatever charger). You will have multiple LOOPS back to the supply. This is cool stuff and I need to know what you come up with, keep me posted as I love this wiring thing as it seems like a way to beat the system!
Instead of using enough LED's in series to drop the full voltage, I feel it is better to use fewer and still use a resistor, for example, with a 12 volt power supply and 2 volt LED's I would use 5 LED's in series with the correct resistor to get the current I wanted. It is true that the resistor will be burning off "wasted" energy in the form of heat, but since LED's are current controlled devices instead of voltage controlled devices, you will get more consistent and more predictable results this way.

When powering LED's in series, you do not add the current of each LED. For example, if you have five LED's in series operating at 20 ma, the current draw of the whole circuit is 20 ma. You do add the currents of parallel circuits, so if you have 5 circuits in parallel, and each circuit has 5 LED's in series running at 20 ma, the total draw of the circuit is 5 * 20 = 100 ma.
 
#14
Ah yes thank you, I forgot about the voltage drop. They are still going strong after 6 hours, so I think this setup will work just fine for me. Now when we do the city lights, streetposts, etc, we will use the 12 volt power packs and plug it in.
 
#15
If you are running off the 2 batteries shown in the picture, remove the resistor as it is not needed. In fact it is putting a draw on the batteries but you aren't getting anything from this draw - no light.
No, a current limiting resistor on every LED is required for reliability.
A resistor is series with an LED does not draw additional current, in fact it is just the opposite, the resistor decreases the current draw from the battery. The current through a resistor/LED is calculated as (using Ohm's law):

I = (V battery - V led_forward_drop) / R
 



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