Hi Guys I have a very limited knowledge of electronics but understand the basics
I have a question about those new LED Christmas lights. I know that an LED does not take very much current or voltage 2-3 volts. How is it that they can plug those things into 110v. The reason I ask is my Daughter wants to dress up as a Christmas tree for a party. Is there any way to rewire a string of say 25 led's and run them off a battery pack from a drill. My husband has several of them at 9 volt or 12 volt or a 18 volt Thanks Nikki
Those LEDs are in series. A string of 70 LEDs would require close to
150v. When you figure that 110v AC is merely a measurement of RMS and not peak, adjust the value for peak volt to about 155v peak, it is just enough to drive all the LEDs without burning them out or requiring resistor.
Do keep in mind that all LEDS absolutely must have the same facing polarity. All LED must connect anode to cathode of next LED, anode to cathode of next LED, etc. If one LED is in reverse, none of them will light up.
If you use smaller LED, it has lower voltage and you will need more to light them. If you use big LEDs, they may have higher voltage requirement. Check the specs before comitting to buy x LEDs.
LEDs are more than just lower electric bills, they are also safer. Bulbs don't shatter like regular bulb so no exposed wiring or sharp glass. Also little heat so little fire hazard as well. Finally with proper care, those LEDs would outlast the wires they are mounted on!!!
As for the battery pack, a 9 v will probably work with 4 or 5 in series. 12v can do 5-6, and 18 should be able to handle about 8 or 9.
When you hear the toilet flush, and hear the words "uh oh", it\'s already
too late. - by anonymous Mother in Austin, TX
There are several examples of connecting a few LEDs to various batteries. For example, you can hook 4 red LEDs in series and add a 270 ohm resistor to connect to a 12 volt battery. Connect another 4 leds plus resistor for a total of 8, etc.
Only if each has its own series dropping resistor, which shouldn't be too hard. But, as has been mentioned, you can put strings of 2 or 3 or 4 (or whatever, depending on the voltage) LEDs in series with one dropping resistor for the set.
LEDs don't cooperate well in parallel - one will hog the current, and you'll get a cascade failure.
Thanks guys I tried the leds in parallel about 25 of them and only a couple of them came on. I ended up using the mini lights with a 4 volt 6.5 a/h that should last a little while but not as long if it were the led's Thanks for your help Nikki