G'day Guys,
A question of power rating.
I have a resistor of 820R
Passing 0.017A
Dropping 13.94Vdc
I make this a power output of 0.237W.
This resistor is dropping voltage from the 37Vdc main supply rail to a 24vdc relay coil so the power will be continuous during operation.
I've tried deciphering the derating curves but predicting the temperature rise inside the amp chassis and the temperature rise of the resistor itself is beyond my understanding.
So. As a rule of thumb, am I safe to run a 1w carbon film resistor at 1/4 of its 1w rating continuously?
Assuming of course, that the temperature inside the chassis doesn't get obscene, which it shouldn't since this is a class AB amp.
A question of power rating.
I have a resistor of 820R
Passing 0.017A
Dropping 13.94Vdc
I make this a power output of 0.237W.
This resistor is dropping voltage from the 37Vdc main supply rail to a 24vdc relay coil so the power will be continuous during operation.
I've tried deciphering the derating curves but predicting the temperature rise inside the amp chassis and the temperature rise of the resistor itself is beyond my understanding.
So. As a rule of thumb, am I safe to run a 1w carbon film resistor at 1/4 of its 1w rating continuously?
Assuming of course, that the temperature inside the chassis doesn't get obscene, which it shouldn't since this is a class AB amp.
Well, you should not front much problem since you are 4x to 5x the nominal dissipation.
If it was me, I would go for a 2W resistor, and barka !
For a plate resistor of 100K with a 1.2mA current (think a basic ECC83) you have a 0.15W dissipation. Fender used 0.5W carbon comp and the amp lasted for years. When I replace those resistor, I put 1W carbon film for a better quietness and a lifetime duration...
For a cathode resistor with 100mA and 390R, you have 3.9W. I use then 50W chassis resistor, but a 20W wirewound tubular or ceramic would be correct (temperature at circa 50°C on surface).
So my usual marging is 5x to 10x grosso-modo...
T
If it was me, I would go for a 2W resistor, and barka !
For a plate resistor of 100K with a 1.2mA current (think a basic ECC83) you have a 0.15W dissipation. Fender used 0.5W carbon comp and the amp lasted for years. When I replace those resistor, I put 1W carbon film for a better quietness and a lifetime duration...
For a cathode resistor with 100mA and 390R, you have 3.9W. I use then 50W chassis resistor, but a 20W wirewound tubular or ceramic would be correct (temperature at circa 50°C on surface).
So my usual marging is 5x to 10x grosso-modo...
T