Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: F4TCT on August 05, 2013, 11:30:10 AM

Title: LED's
Post by: F4TCT on August 05, 2013, 11:30:10 AM

Can anyone suggest where to buy some either 3mm or 5mm clear ultra bright L.E.D's from please? They must be 12v type.

Title: Re: LED's
Post by: john44 on August 05, 2013, 11:40:44 AM
Hi Dan,
have you tried component shop?

Title: Re: LED's
Post by: F4TCT on August 05, 2013, 11:43:12 AM
I have John, they don't seem to have 12v ones.

I used them for my tug and cant remember where i got them from. maplins dont seem to have any 12v clear, but they do have coloured.
Title: Re: LED's
Post by: mrturbo553 on August 05, 2013, 12:21:11 PM
Dan do a search on flea babble 370690323037 use this item number
Check his other items or try model accessories Crewe ?
Over and out biggles !!!
Title: Re: LED's
Post by: montessa315 on August 05, 2013, 06:36:43 PM
3mm clear 12v led's, but not ultra bright.

Title: Re: LED's
Post by: Netleyned on August 05, 2013, 06:54:15 PM
LEDs will run OK on 12v with the right resistors.
Component Shop will advise.

Title: Re: LED's
Post by: irishcarguy on August 06, 2013, 01:49:05 AM
Hi Dan I got a large supply off fleabay both 3 & 5 MM with the resistors already wired they were dirt cheap too, look under LEDS, I think even the postage was free.led-world2007 is the fleabay company, 50 for $7.62. Hope this helps, Mick B.
Title: Re: LED's
Post by: F4TCT on August 06, 2013, 11:07:18 AM
rapid want about 35 including postage for 25 leds - dont think so like...

I'll just resister them myself using the component shop. Might work in my favour thinking about it anyway,

thanks for the replies.

Title: Re: LED's
Post by: plug on August 06, 2013, 10:33:35 PM
Normaly get mine from here reliable seller and they come with resistors, worth a look
regards Jack.
Title: Re: LED's
Post by: Gerardy on August 19, 2013, 02:21:38 AM
Maybe you can try   :P
Title: Re: LED's
Post by: MLT44 on October 31, 2013, 09:58:08 PM
Hi I use led on my tug lighting, if you have a word with the lads at Components, they will tell you witch resisters, and they will give you a colour code chart for the resisters
Title: Re: LED's
Post by: StuartL on November 11, 2013, 11:08:14 AM
The resistor you need for the LED is relatively simple maths.  You need to know the current draw and voltage of the LED.  If you don't have this available assume 1.6v and 20mA (0.02A) and work from there.

If powering the LED from 12v you need to drop the voltage by (12v - 1.6v) = 10.4v at 20mA.

Ohms law says that V = IR, or R = V / I.  Resistance you need is therefore 10.4 / 0.02, or 520 Ohms.  Lots of people just use the readily available 470 Ohm resistor and accept that they're going to shorten the life of the LED a bit.

The same maths works with multiple LEDs.  If putting LEDs in parallel they each need their own resistor (i.e. 520 ohm each).  If putting LEDs in series you can power them all from one resistor.  The current remains the same but the voltage will change...

Four LEDs, each at 1.6v, would be 6.4v.  Voltage drop across the resistor would be (12v - 6.4v) = 5.6v.

The resistor can be calculated as:

R = V / I, so R = 5.6 / 0.02 = 280 ohms.

Note that you must have a resistor, even if you have enough LEDs to meet your battery voltage.  The resistor serves to drop the supply voltage if the LEDs try to draw more current, thereby self-regulating the current through the LED and avoiding the LED blowing up.
Title: Re: LED's
Post by: MLT44 on November 11, 2013, 02:17:43 PM
Hi. If you phone components they will tell witch res to use for 12v, the res are about 25pence each, and the res are pence each, they sell all the colours and sizes.
             Hope this is helpful. I buy mine in tens Dave
Title: Re: LED's
Post by: MLT44 on November 11, 2013, 02:25:01 PM
Hi I made a mistake the leds are 20 pence the res are pennyes. Sorry senior moment.
Title: Re: LED's
Post by: More Coffee on December 10, 2013, 07:55:24 PM
led calculator.... ( (
don't forget..
for a single Led on 12v supply with a proper resistor you may require 1/2watt resistors .. versus the 1/4 .
I know for a fact a 1/4 watt 470ohm resistor will get seriously hot supplying a ultra bright led on a 12v supply..
If your running a 12v pb  battery keep in mind the battery is considered dead ..If memory serves me correct 11.6 volt..
so your calculations should be based on 13v-13.6volt.. this also give you some overhead with the resistor. ..its not detrimental but the extra volt or two can stress the led and shorten its life..
The reason I mention this ..I often put a DC wallwart on my system to power the lights when company come's or just because I want to ..without going around re-installing the Battery for just a few hours..
Unless its a switched mode power supply chance's are the DC wall wart rated at 12v will often test upwards to 15v.. something to consider.