Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

USB Powered LED Kitchen Lights - Please help!

Status
Not open for further replies.

itsallgood

Member level 2
Joined
Mar 15, 2002
Messages
48
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
329
Hi guys,

I'm wanting to add plinth kitchen lights to my kitchen...

a0bhow.jpg


My idea is to just use some 5mm white/bright LED's that i have:

Code:
Forward voltage: 3.2 - 3.4V DC
Forward Current: 20mA
Luminous intensity: 12000 - 16000 mcd
View Angle: 25 Degree
Lens Color: Water Clear
Life rating: 100,000 hours

and run them from a USB cable powered by a spare apple iphone charger plug... (as it takes the full UK voltage down to a nice 5v)

xrneq.jpg



By just snipping off the iphone connector - and attaching wires to power the LED's.


Apart from this idea - I don't know how to do it :(

I don't know about resistors, or how many LEDs could be run from a 5v charger, or if my idea is even SAFE!!! 8-O


Thanks for any help with my project - i want to get started, but thought i better ask the experts first :)

Many thanks.
 

I think an ipone charger is rated at 5V 1 Amp That will supply current to 50 LEDs. Use a 120 ohm resitor in series with every LED
 
A 120 ohm resistor might make them a little dim, only giving them about 15mA.

I would use an 82 ohm, 1% resistor which will give them about their rated 20mA.

Connect one leg of an LED to a resistor, then the power goes to the other side of that resistor (thus, the resistor is in series with the LED) and to the other LED leg. Remember that the LED must be connected the right way around - the long leg goes to positive.

Regarding using the iphone plug - if it is rated for 1A then, as klystron says, you could power up to 50 LED's from that (1A/20mA = 50) BUT...

The charger plug might get hot if run at its full-rated current all the time. In normal use (charging an iphone) it would not be, so it depends how well it is built. If you go for the full amount, keep an eye on the plug and see if it seems to be getting uncomfortably hot. If it does, it probably won't live long. Then again, it might be just fine. Worst case, if it gets too hot, buy another 5V supply rated 2 or 3A for a couple of quid from your favourite auction site.
 
I think an ipone charger is rated at 5V 1 Amp That will supply current to 50 LEDs. Use a 120 ohm resitor in series with every LED

WOW! What a great fast - reply! Thanks klystron :)

50 LEDS thats amazing! - The sets sold on ebay only have 10.


So just to check - does this look right?

k02i46.png



And i will get the resisitors ordered. Does the wire i use make any difference?

Thanks again. :)



FoxyRick -- you replied while i was writing my reply :) Thank you also.

I would like my LEDS to be as bright as possible - so the 82 ohm resistors would be better. Does my picture show the right way to wire it up if i use the 82 ohms?


I am a bit worried about the plug getting hot now - Is using a USB plug not the best idea? I was hopeing the low voltage of the plug would make it safe to stay on hours with no problems. How could i cut the risk of the plug getting hot? Maybe only connect 20 LEDS???

Thanks again all.
 
Last edited:

No, that circuit is wrong. You need to do this - click it to make it bigger:

led.jpg

Each led needs a series resistor to limit its current, then each [LED/resistor] group needs connecting in parallel across the supply lines, like sleepers on a railway track. Just keep adding as many as you want.

I would guess that 20 LED's would be fine (if the charger is 1A - check it - it should say somewhere on it)

I really don;t know if you would get away with 50 - like I say it depends how well the charger is built to handle 1A all the time.
 

Wrong!

All of one side of the LEDs, lets say the cathode end for simplicity are connected together and to the negative supply. The other end of each LED is wired to its own 82 Ohm resistor and he other ends of all those resistors are joined together and connected to the positive supply. In other words, each LED/Resistor combination is wired in parallel and across the supply. Be careful to connect them the right way around, LEDs only light up in one polarity and are easily damaged in the other.

Brian.
 
  • Like
Reactions: ve1arn

    ve1arn

    Points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top