Electronics - advice on circuits and LEDs

dbov22

dbov22

dbov22

Associate
Joined
27 Jan 2011
Posts
262
Location
Washington
Hello, haven't posted for ages but still read a good few times a week.

I recently got some entusiasm to start making an LED light panel.

I have done some research on internet and youtube but am confused by different pieces of advice.

I used a DC transformer from a garden light set which has the following info stamped on it.

INPUT 220 - 240V ~50Hz 5W 0.002A
OUTPUT: 12V COS (CIRCLE WITH LINE THROUGH SYMBOL) = 0.98
MAX 5W MIN 0.2W 0.8A 250V

Right, now maybe wrong here and don't fully understand the theory behind all of this (working on it) but I bought some LED's from Ebay which were 0.022A.... I worked out I could put 40 in my makeshift panel, I wired them all up in what I beleived to be correct way and then plugged into a small 3V watch battery - they all worked, then wired up to mains - they all worked.

I dont get how they work on a 3V battery and also with 9V mains. Also, I placed no resistors in the circuit but should I have done and why?

Could I put more LED's in the circuit or less and what would happen?

Thanks guys!!

Dan
 
No doubt I will have done something wrong, the LED's have been on for 4 hours now without any sign of dimming, blowing out etc, I will draw a circuit diagram and take a pic of what i've done - give me 12 hours, lol...Bed time!

zzz zzz zzz
 
here are the pics - all i'll say is, I know cardboard is not the best for a curcuit board - I just wanted to make sure everything worked!

Please don't judge, just advise - I am not a pro and have little knowledge but want to learn!

20120827134551.jpg
By squeekybean at 2012-08-27[/IMG]

20120826165132.jpg

By squeekybean at 2012-08-27

20120826165210.jpg

By squeekybean at 2012-08-27
 
there are no resistors at all, as a youtube video advised me that if you put the correct amount of LED's in the circuit with the transformer then no resistors are needed?!
 
the LED's are all completely even in brightness, and all very bright so I'm not sure how?

What would be the best method to wire up 40 LED's also where would each resistor have to go and which resistor. I keep being told different things by different people.

hmm (scratches head).

Dan
 
Thanks for the encouragement Tim.

right - the rating on my transformer says 0.8A - am I correct in thinking that if each LED is 0.022A I can fit (0.8 divided by 0.022) 36.36 LED's in my circuit and if I have more then the LED's will be dimmer and if I use less then the LED's will need resistors or am I way off the mark?

In this circuit (new photo) where should the resistors Bitslice mentioned go - at which letter? also is there a better way of wiring up this circuit? layout wise etc?
201208271743401.jpg
By squeekybean at 2012-08-27[/IMG]
 
Right, I have re-read bitslice post and this is starting to make sense...I think what has been confusing is the fact that I have had bad advice from people claiming to know what they're talking about...a good friend of mine said it would need a startup capacitor!

Currently doing more research and starting from the beginning!

Thanks mate, 1 for not just ****ging me off and 2 for your patience dealing with my apparent lack of any understanding. Lol

Dan
 
Well, the saga continues - there doesn't actually seem to be any solid advice on this subject...

I found a much bigger transformer which is 24V in the shed, it doesn't say what Watts it is though (confused)

Anyway can someone maybe just tell me how to make the following, maybe a quick drawing of the 20 panel (i'll make x2) and the 10 panel (i'll make x3).

Ideally all from the original transformer in the 8th post, or this new one..

201208281751171.jpg
By squeekybean at 2012-08-28[/IMG]

20120828171820.jpg
By squeekybean at 2012-08-28[/IMG]

or

20120828171854.jpg

By squeekybean at 2012-08-28
 
The LED's i'm using are white -3.4-3.7 Vf, 0.020 A. I am not interested in using the AC adaptor - seems like too much fuss. There's a DC adaptor on ebay which is 12V, 5A and 60w.

That will certainly power my 70 LED's, just got to work out which resistors to put where
 
Thanks, I really appreciate the effort, I'll get to it. Can you clarify one thing though. In my original method of wiring the LEDs this is wrong and I should be wiring them like yours where literally the LEDs are joined to each other rather than me joining all the annodes together then all the cathodes together...
 
But say I'm just using 3 LEDs for example and a resistor (forget ANY calculations or volts etc). Would it be wire from +ve to LED, join other leg of LED to another LED then repeat the to resistor then from other end of resistor to -ve of power source?
 
Well, just been into Maplins to get some matrix board and resistors - the resistors were a fortune and one of the assistants asked if I wanted some help - the entire staff did not know that there was a difference between series and parallel and anyway...long story short they didn't have a clue.

One thing they were all CERTAIN of (hmm) was that the transformer I originally used is a AC transformer and NOT and DC. I measured the voltage coming from the transformer and it was 13.64....apparently this is a give away sign it's AC and also the fact it has the following symbol on it:

____
- - -

back to square one dudes
 
Yeah, I googled it and I knew I was right but when 7 "electronics assistant experts" in Maplin tell you you're wrong you believe it!

I put my multimeter on the number 20 in the top left corner V section. No idea where it's meant to go.

Multimeter.jpg
 
I think I'm starting to get somewhere now. Tealc can you help with this one please, no matter where I place the multimeter in the circuit it always comes up around 3.4V on average, this is with a 3x 1.5v cells together as well as my 12v transformer.

I don't understand why it would do this.

Also, am I correct in thinking that if I keep the LEDs in parallel (I know this isn't the best way to do it) I'm saying If... Then my 40 LEDs x 3.7v (each LED) x 0.02 (amps per led) = 2.96watts. My power supply is rated 5w so this should be ok?

But if wired in series this would obviously be different and closer to overloading the transformer?

I have also just been to buy a cheap LED torch, it has nine white LEDs. There are no resistors anywhere and it is powered by 3x 1.5v batteries. So this is overpowering the LEDs by at the most 1.1V? So at the worst this will just reduce the life of the torch?
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom