EE bros, is resistor neccessary for LED moonlight?

[ervine]

Hi guys,

Okay here's a foto of my tank with the moonlights on (erm.. din have tripod on me so forgive the blurry image), in any case... i wanted to know if it's essential to have a resistor connected to each LED assuming I am running the LEDs in parallel.

Also in series to the LEDs is a 12V fan, all running off a single 12V AC to DC transformer.

I didn't run the resistors coz I forgot how to put a value to them and when I tried the 500ohm ones the LEDs didn't light up... so i tried w/o any and they did.

Lastly, some of the LEDs are dimmer than the others, i've checked the connection and it seems fine, is it a problem with the LED? because the packet that I bought some of the LEDs were turquoise not blue while 1 was completely spoilt.

Thanks a bunch!

Ervine

[uyopong]

I think u need to separate DC supply for ur LED and DC fan.

I use 36 ultra bright Blue LED with 12VDC 800mA DC adapter.

Always use resistor or u risk burning ur LED.Each Ultra bright blue LED rated about 3VDC and 20mA.

For my moonlight,i connected 3 LED and 100ohm resistor in series and parallel with another 3 sets.total 9 LED with 3 100ohm resistor.

Then 1 connect another 3 sets in series similar to first set, so total 9x4=36LED which need 36x20mA=720mA.So,my 12VDC 800mA DC adapter work quite nicely with no voltage drop and every LED lights up nicely.

[ervine]

wah.. too much maths liao.. haha.. Hm... ok think i go invest in a few resistors tomorrow when I get my LEDs to replace the turqoise ones...

[supremo]

i think it's best to buy the a whole set of the LEDs from the same shop at the same time. This is because in the SLT shops they don't show how many amperes is used by the LEDs unless you could find one which comes in the original manufacturers packaging. The amperage may vary hence shows you different brigthness.

[ervine]

i think it's best to buy the a whole set of the LEDs from the same shop at the same time. This is because in the SLT shops they don't show how many amperes is used by the LEDs unless you could find one which comes in the original manufacturers packaging. The amperage may vary hence shows you different brigthness.

ah... ok so i just get another pack of super brights then

[uyopong]

SimLim Tower do sell pre assemble LED. i think 30 LED presoldered on a strip ,also with acrylic tube and can chose colours.

hassle free just get an appropriate DC adapter with correct rating and power up.

[ervine]

SimLim Tower do sell pre assemble LED. i think 30 LED presoldered on a strip ,also with acrylic tube and can chose colours.

hassle free just get an appropriate DC adapter with correct rating and power up.

yup i saw but it cost i think 18-20+ per piece... and I didn't need so many LEDs...

[gunzo]

yup i saw but it cost i think 18-20+ per piece... and I didn't need so many LEDs...

basket.. yesterday saw 2 .. today went back all taken!!!

bought the diy stick.. save $2.. hehehe

[supremo]

what's a DIY stick bro?

[gunzo]

what's a DIY stick bro?

fully done led tube is $30 .. all you need is plug in the transformer

diy stick is the same thing.. but in pieces.. you buy the parts separately ie the tube and led stick.. you need to do abit of soldering

[chrisyew]

It depends on whether you are connecting the leds in series or parallel.

Here is a very good one where you can input your supply voltage, led rated voltage and current, and the number of leds. It will calculate the resistor value for you (parallel or series).

It's best to connect the leds in parallel as if one led don't work, the rest will not be affected.

Note : Disregard the auto battery, juz take it as your standard 12DC supply.

http://www.projectx.com/Kits/LEDNotes/

[davwong]

Or try the ready made ones like those by our sponsor http://www.sgreefclub.com/forum/index.php?showtopic=29852

[erictck]

what's the value of the resistor that you are using? how many ohms?

[ervine]

shucks.. 2 LEDs blew... i think must go rethink my config liao...

[supremo]

hmmm. mine is 9 LEDs in parallel, attached 330ohms, connected to a 12v adaptor 350mA. been running for around 8 months now. no problems so far.

bro, you sure got the cathode and anode side correct?

[ervine]

hmmm. mine is 9 LEDs in parallel, attached 330ohms, connected to a 12v adaptor 350mA. been running for around 8 months now. no problems so far.

bro, you sure got the cathode and anode side correct?

330ohm per LED? yah confirm correct

[supremo]

well, like i said, i built it so many months ago and i'm not entirely sure. but the shop in SLT where I bought it from (one of the shops on the 3rd) was able to tell me exactly how many ohms to use. I think attaching an LED in parallel using 12v DC supply is soooo common that they know exactly what to sell you. It's called streetwise knowledge lah

[chrisyew]

wah.. too much maths liao.. haha.. Hm... ok think i go invest in a few resistors tomorrow when I get my LEDs to replace the turqoise ones...

If you use this page (scroll to below), you can calculate what is the required ohm of the resistor used in Parallel connection.

http://www.projectx.com/Kits/LEDNotes/

They even show you how to connect the resistor to the leds.

[supremo]

great site bro, but how do you know how much current you need for the LED?

[weileong]

great site bro, but how do you know how much current you need for the LED?

Can check the specs of the LED.

[chrisyew]

great site bro, but how do you know how much current you need for the LED?

Rating for leds like Voltage or Current is quite standard like 3V and 20mA. You may check with the seller.

[supremo]

yeah, i think you can only ask the seller cause they normally repack the LEDs hence specs is not written anymore

great, the website is really helpful. thanks for sharing bro

[little bull]

Where can i get the led buld?

[Oceandeep]

just curious... if the power supply is a constant voltage source, then if

I fix the supply to 3volt and connect without resistor. Wil the LED blow??

[Coolsky]

Guys,

If you need LED , RES or other components can buy from me just tell me the size, ohm or LED how bright. I am selling it. What colour you need just let me know. Anyone itnerested just pm me or call me at 93652833. Price will be cheaper if you get more.