bigal_scorpio
Active Member
Hi to all,
I have just built a project that uses 1W LEDs which are run from 13v or so (car) and worked out that they needed 30r to give the 240mA which they take, bear in mind that they are run through ULN2803s. This is all ok when they are running on PWM at about 50% duty when they are running in sequence but they must all be on solid whenever the car is moving so I don't break the law.
Thats when the problems start! On full the resistors quickly heat up and reach 180c in just a few minutes, where they seem to stabilise. Now I'm no expert on cooking but I know that the wife puts things in the oven at 180 and sometimes less and they always come out cooked!
The resistors in question are axial cylindrical at around 12mm length and 4.5mm in diameter. They are actually 33r as I erred on the side of caution with the current. What is the max temp they can run at? All the info on the net seems to be about the cement type and as they are a completely different construction I thought it better to ask for expert advice rather than my sons car being a fire brigade statistic.
Al
I have just built a project that uses 1W LEDs which are run from 13v or so (car) and worked out that they needed 30r to give the 240mA which they take, bear in mind that they are run through ULN2803s. This is all ok when they are running on PWM at about 50% duty when they are running in sequence but they must all be on solid whenever the car is moving so I don't break the law.
Thats when the problems start! On full the resistors quickly heat up and reach 180c in just a few minutes, where they seem to stabilise. Now I'm no expert on cooking but I know that the wife puts things in the oven at 180 and sometimes less and they always come out cooked!
The resistors in question are axial cylindrical at around 12mm length and 4.5mm in diameter. They are actually 33r as I erred on the side of caution with the current. What is the max temp they can run at? All the info on the net seems to be about the cement type and as they are a completely different construction I thought it better to ask for expert advice rather than my sons car being a fire brigade statistic.
Al