Quote:
|
Originally Posted by OutToLunch;342035I would play it safe and assume that there will be some type of enclosure involved here so that the resistor itself will be creating the ambient temperature, which would be well over 70C. |
- It doesn't matter whether you use a 3W resistor or a 6W resistor, providing the power actually dissipated is the same, the temperature rise inside the case will be the same.
- The case ambient temperature shouldn't exceed 70°C as it could burn the user. If you think it's going to get that hot then add ventilation holes.
Quote:
|
A resistor running continuously at 120C would have a very high probability of damaging the FR4 board material.
|
I don't know about that. It depends on the board material, cheap paper composite board might be damaged but I can't see more expensive fibreglass board being damaged - always read the datasheet.
Another thing you can do is leave a gap between the PCB and resistor so it doesn't heat the board too much.
Quote:
Originally Posted by Nigel Goodwin  I didn't say it 'melts it' - it 'destroys it' - it's common where resistors are under specified like you're suggesting, the soldered joint, the PCB, and the wire of the component are all ruined making repairs difficult.
I don't know what happens chemically, but the copper of the board, and the wire itself become impossible to solder to, and the old solder becomes crystalline.
Just do the job properly, apply sensible design considerations, and build a circuit that's made to last. |
As above, leaving a gap between the PCB and the resistor will help to minimise this effect as the temperature at the soldered junction will be much lower.
30th August 2008, 01:31 AM
Similar Threads 
Linear Mode
