/sci/ - Science & Math

>>5433324
> easiest way to step down the voltage
buy a wall wart from radio shack

>>5433333
I'm sorry but I don't understand your answer. To be fair I am from Denmark so my English is not perfect. What kind of device is a "wall wart"? Is it some sort of resistor ?

>>5433345
generic ac adapter for electronics, bulky black plugin

also, http://led.linear1.org/led.wiz

>>5433333
Holy quints

>>5433374
>http://led.linear1.org/led.wiz
very nice but can you help answer my questions please. I need something like a 117 volt resistor to block most of the volts before entering the array of three LEDs

>>5433380
https://en.wikipedia.org/wiki/AC_adapter

>>5433383
but i have three numerically listed questions that have yet to be addressed in my original post. please assist it the recalling of the question thank you

>>5433324
1: get a step down transformer
2) max
3, series = add the voltage, leave the current

>>5433388
ahh thank you, i like

>a 117 volt resistor to block most of the volts
>step down transformer

running LEDs from a voltage source

it hurts

>>5433534
> norton and thevenin
> their powers combine

okay so i think I needs 3.8+3.8+3.8=11.4 volts. So he should get a step down converted from 120VAC to 12VDC then add in a 20mA/.6V = 33 OHM resistor.

Can some one make a bill of materials for the items to get at radio shack store? the guy there did not know

ALso what wire do i use? I have been using test leads what is better? copper wiring?

>>5434264
If it's in parallel, voltage stays constant

>>5434272
You don't want to put LEDs in parallel.

>>5434277
exactly if you put LEDS in parallel often one will get greedy and take more amperage and burn out.

I am putting three in parallel. they are all the same type and take 3.8 volts at 20mA each. Can anyone help me with a bill of materials?

>>5434277
this. You don't wanna put LEDS in parallel one will suck out more amps and burn out. I am putting three in series.

Can anyone help out with a bill of materials? this seems like it should be a easy project

>>5433324
Not to get too technical, but if you put the LED's in series, the input voltage has to increase. LED's aren't voltage devices like a regular light bulb, they require a current. The voltage across the LED's will change very little as you vary the current. Normally you'd want to use a transformer to "knock" the 120V down to something less, like 12V. A resistor for use on 12V would be 600 ohms at 0.25 watts. With 120V the resistor would be 6000 ohms at 2.4 watts. The 0.25 watt resistor would run cooler and be cheaper, plus the transformer would isolate the dangerous mains voltage.
Try this website:
http://ledcalculator.net/

120*sqrt(2) =~ 170

170 - 3*3.5 = 159.5

159.5/0.02 = 7975

Get an 8kOhm resistor

>>5434433
>>5434437
okay so i need a 8 ohm resistor (radio shack) and a 120VAC to 12VDC. THe 12VDC will go to the 8 Ohm resistor to lower the voltage to the perfect 11.4 V. Won't 11.4 volts burn out the first LED as it is only designed to take 3.8 max?

>>5434455
no, you won't need a transformer if you use a 8kOhm resistor. But it's pretty inefficient because you have to burn 159.5V*0.02A =~ 3.2W peak power and your resistor has to be able to handle this. Notice that only one half wave will be usable without rectifiers.

If you use a transformer that goes down to 12VDC you only need a 12V-3*3.8V=0.6V => 0.6V/0.02A = 30Ohm resistor.

>bill of materials

what bill? you need a 12V power supply (the smallest 'wall wart' you can get) and a 33 ohm resistor with a power of (20mA)^2*33Ω=almost nothing. I would buy ten of them because the smallest power supplies are usually unregulated and so you can wire some resistors in series to arrive at 20mA. And a cheap multimeter would be a good idea.

Okay! The way a diode works is not like a light bulb. A light bulb is a resistive device; a diode is like a switch. Once the breakdown voltage is achieved, it will conduct all the current it can, just like a bare wire. You need a resistor in series to clamp the current.
1. Step down the voltage with a transformer or better yet a power supply like a wall wart.
2. put a resistor in series with the diode
3. look up diode model on wiki to calculate values

>look up diode model

better rtf data sheet

>>5434506
so the "breakdown" voltage in this case is 11.4 with 3 LEDS. using 7 1.5 C cell batteries in series should deliver a nice glow from all three batteries?