10mm LED Bulbs - Page 1
Forum section: electronics / beginners

author: justintime2001
author_rank: Newbie
timestamp: October 05, 2015, 05:54:25 pm
content: I am trying to replace 2 flashing LED's in a bait boat. I wanted to replace them with constant LED's but they blow as soon as connected. I have managed to fit 2 new flashing LED's but these dont flash as such they stay on but sort of swap from dim to brighter rather than actually flash. Can anyone please advise or point me in the right direction? They are 12 volt LED's and the boat runs on a 12V 10Ah battery.

author: LA7SJA
author_rank: Regular Contributor
timestamp: October 05, 2015, 07:20:31 pm
content: You must connect a current limiting resistor in series with the LED, use a value of 4700 Ohm (bright) to 10000 Ohm (dim). This shuld give the LED 25 to 1mA with most LED's. The "flashing" LED's have build in electronics for 12V suply.Johan-Fredrik

author: justintime2001
author_rank: Newbie
timestamp: October 05, 2015, 08:21:43 pm
content: Thank you Johan,Does this mean a resistor before each LED or one for all of them? Could the lack of resistor be why constant LED's are blowing? Thank you.image attached

author: tec5c
author_rank: Frequent Contributor
timestamp: October 05, 2015, 08:57:17 pm
content: If that is how you initially wired them (without the resistors) then you replaced them in backwards. The longer leg is (almost always) the positive leg.Flip them around and connect them up with the resistors (like the diagram shows) and you should be fine.

author: justintime2001
author_rank: Newbie
timestamp: October 05, 2015, 09:17:02 pm
content: Brilliant, thank you.

author: mariush
author_rank: Super Contributor
timestamp: October 05, 2015, 09:44:26 pm
content: As an observation, if you connec several leds in series like you show in the picture, you only need ONE resistor at one end of the chain to limit the current going through all the leds.The current going through the leds can be determined using the formula Current (in amps) = ( Battery Voltage - number of leds x forward voltage of one led ) / Resistor value in ohms

author: tec5c
author_rank: Frequent Contributor
timestamp: October 05, 2015, 10:08:52 pm
content: My mistake, I was in a hurry.I initially thought that the diagram showed the LEDs connected in parallel. On second look, what mariush suggested is a more suitable approach.

author: justintime2001
author_rank: Newbie
timestamp: October 06, 2015, 12:46:57 am
content: Thanks guys. The boat actually appears to be wired like the diagram below, but possibly without all the resistors. Hope it makes sense?

author: mariush
author_rank: Super Contributor
timestamp: October 06, 2015, 02:05:50 am
content: No, that's really not right.Go here :http://www.falstad.com/circuit/then click on File > Import from text and paste the following (make sure you select all, watch the scroll bar):Code:$ 1 5.0E-6 10.20027730826997 50 5.0 43v 112 352 224 352 0 0 40.0 -12.0 0.0 0.0 0.5162 128 64 208 64 1 2.1024259 1.0 0.0 0.0162 240 64 320 64 1 2.1024259 1.0 0.0 0.0162 384 64 464 64 1 2.1024259 1.0 0.0 0.0162 512 64 592 64 1 2.1024259 1.0 0.0 0.0r 96 192 176 192 0 100.0r 272 192 352 192 0 100.0r 480 144 576 144 0 100.0r 624 144 704 144 0 100.0w 224 352 208 64 0w 128 64 176 192 0w 96 192 112 352 0w 240 64 272 192 0w 384 64 480 144 0w 512 64 624 144 0w 224 352 416 352 0w 416 352 320 64 0w 352 192 352 240 0w 352 240 176 192 0w 112 352 112 400 0w 112 400 736 400 0w 736 400 704 144 0w 592 64 608 352 0w 608 352 416 352 0w 624 144 576 144 0w 464 64 416 352 0w 480 144 352 192 0o 1 64 0 35 2.5 0.2 0 -1o 2 64 0 35 5.0 0.0125 1 -1o 3 64 0 35 5.0 0.1 2 -1o 4 64 0 35 5.0 0.2 3 -1It will simulate the circuit your drew in the picture, only the components are arranged in a much uglier way. You can move mouse over the oscilloscope drawings at the bottom to see how much current goes through each led.Basically some leds receive more current because they get energy through two resistors and one of the led will barely light up or won't light at all according to your schematic.

author: justintime2001
author_rank: Newbie
timestamp: October 06, 2015, 10:44:15 am
content: Thank you mariush, It is how the boat is wired up at present. It's like a ring main in the uk. I will rewire the whole thing I think just how you guys have said.

author: justintime2001
author_rank: Newbie
timestamp: October 07, 2015, 12:52:23 pm
content: Hi Guys,I just wanted to let you know that I have rewired the boats lighting following your guidance and it has worked a treat.It may be simple to the experts but for me it was an achievement, so a big thank you for your help.All the best, Ian.