I was able to purchase some LED Christmas lights at a very good price. I planned to take the lights apart. I would like to use them on the layout for streetlights, signal lights, sign lights, etc.
I have an old “ZW” Lionel transformer, 17Volt which I will be using for power.
White set –60 Rice style, 3mm
Transformer
Pri : 120v – 60Hz 0.14A
Sec : 24V-450mA Max : 10.8VA
Has attached 8-combination flasher unit
Colored Set – 20 Rice style, 3mm
4 – AA batteries
Has attached flash/no flash unit
I would appreciate any electrical help that could be provided in how to use these lights.
Thanks Doc
I'm assuming the set with 4 AA batteries is battery operated. If 20 LED's in series, that's 0.3 volts per LED. If 20 LED's in parallel, that's 6 volts per LED and if the string is in two 10 light parallel strings joined in series, that's 3 volts per LED. I'm inclined to think it's a parallel circuit with each LED getting 6 volts. Some experimenting may be in order. On the larger string, 24 volts for 60 LED's, it all depends on how it's wired. It could be series with each LED getting 0.4 volts or any combination thereof. With the 8 combination flasher in line it could be the power is going to sets of LED's, say 7 LED's per set, that would be around 3 volts per LED. I've come across some Christmas lights in the past that were wired pretty weird with very low voltage bulbs.
Dr. Frankendiesel aka Scott Running BearSpace Mouse for president!15 year veteran fire fighterCollector of Apple //e'sRunning Bear EnterprisesHistory Channel Club life member.beatus homo qui invenit sapientiam
Well there's got to be a resistor in the circuit SOMEWHERE, or the LEDs would blow, even running on batteries. if the LED is rated for, say 2.1 volts and you hook it up to a precision power supply set to 2.1 volts, the LED will still blow unless the pwoer supply is current limited to below the LED's maximum current.
As for the light strings - if you intend on using them as they are, just repalcing the battery pack with the transformer - you will need one additional component, at the very least - a bridge rectifier. The output of the Lionel transformer is AC. Hooking a single LED to AC, even with the proper resistor, is a good way to shorten the life of it - LEDs can;t handle a large reverse voltage. If you see LEDs hooked directly to DCC power - you'll see they are almost always bi-color LEDs, which are two LEDs in a single case wired back to back - thus the LED that is off only sees the voltage drop across the lit one and is safe.
A better choice to power a string of LEDs is a 1amp or less DC wall-wart. Resistors required depend on the voltage of the wall wart, but the whole thing is a lot less wasteful than using a big ZW to run maybe half an amp's worth of LEDs - each LEDs is goign to be a amximum of 20ma, and probably should be run closer to 15ma for long life - 10 such LEDs are 0.150 amp. 100 LEDs is 1.5 amps.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
topcopdocI was able to purchase some LED Christmas lights ... I planned to take the lights apart. I would like to use them on the layout for streetlights, signal lights, sign lights, etc.
Also as rringer stated the LEDs will lite only for 1/2 of the power phase of the AC current. The other 1/2 they will be acting in their role as a diode and blocking that voltage. Since some of them are coming out of a string that was intended to be used on 120VAC house current, I presume they are capable of handling the back pressure.... but that is only an assumption. Once again it depends on how the current has been limited in the entire system you are ripping them out of.
Finally, these are LEDs not light bulbs, so from an electrical perspective don't treat them as such. Light bulbs are governed by voltage, LEDs by current (hence the need for resistors).