Hey I’m having a problem with my resistors. I purchased 3 LED clusters (http://www2.produktinfo.conrad.com/datenblaetter/125000-149999/149233-da-01-en-IR-Cluster-26mm_BL0106-15-29.pdf), and some 100 Ohm resistors, and I have 12V AC to DC adaptor which I am currently using to power them. I worked out the resistance needed, or what I thought was the resistance needed, but when I wire everything up the resistors get very hot.

LED cluster spec:
Voltage: 6V
Current: 60mA

Resistor spec:
100 ohms, 2 Watt, Metal Film

AC to DC adaptor spec:
Output Voltage: 12V
Output Current: 300mA
Output VA???: 3.6VA (whats this??)

Hope someone can help me out, as I am currently using 2 resistors per clsuter and despite this solving the problem, I’m worried I’m not getting the optimum brightness

if the led’s are not gettin hot and are well lit and its only the resistor ... then you need to go for more wattage of the resistor… same value higher wattage… i am using 100K 5W resistor for 14.2 V power supply…

The LED’s arn’t getting hot so it is the resistors, but this confuses me...every calculation I have done, both manually and using an online calculation utility has put the power dissipation at about 360 mW, and the resistors are meant to be capable of 2 W.Is this something to do with the adaptor I’m using because I can’t think of any other reason...unless Im making a mistake in all my calculations.

Another afterthought...if I wired four of the resitors I have, in a parallel ciircuit with 2 on each branch, would this solve the problem? as the overall resitance to the LED cluster would be 100 ohms (1/200 + 1/200 = 1/100). Would the power dissipation be reduced in each resistor then?

Thanks

i am not very good with the theory part of electronics but i guess the power supply you are using has a higher current rating… heating up of resistance is a normal thing if its not insanely hot and burns up. i would recommend trying higher wattage resistors first… it just might solve the problem you could try the two resistors in parallel as well cause then u’ll effectively be using a 100ohm 4 (2+2) watt resistor. ... lemme know if it works

I got my hands on a multimeter today and found that the adaptor was faulty and was supplying 20V instead of the 12 it was meant to, so everythings alright now. On a side note if I did want to combine resistors in a parallel series to obtain 100 ohms I would have needed four, two on each branch, as the current splits, and for example, if the voltage was 6V and the current 60mA, 6/0.06 = 100 ohms for the normal circuit, but if there is a parallel circuit, the current would split into 30mA for both branches, and so the resistance for each branch will need to be 6/0.03, which is 200 ohms, hence two 100 ohm resistors are needed per branch. Just something useful to know eh?

cool… thats good… m sure now u would be able to get the thing working!!! all the best