04-05-2017, 12:58 AM
Rob, I think you are missing the point that Jeffrey has made.
Forget the data sheet and use simple formulae such as Ohms Law.
The current through the resistor will determine the voltage drop across it. Multiply the two together to find the power dissipated in the resistor. If it exceeds 7 watts, it won't be suitable for your purpose!
You should find that if the voltage drop across a 300R resistor is 45.825V, the current through it is 152.75mA and the power dissipated is 6.99976875W.
This is rather academic as it assumes a ±0% resistor tolerance and you should derate these figures in practice but the important thing here is that no way does the voltage drop approach 200V!
The 200V figure is the maximum for any value in the W22 series - the voltage drop will increase for resistors with higher values but must not exceed that limiting figure. These limits apply to various resistor types - I produced a table once for lower power resistors to illustrate this, but I haven't got it on this PC. If I can locate it, I'll post it here.
Forget the data sheet and use simple formulae such as Ohms Law.
The current through the resistor will determine the voltage drop across it. Multiply the two together to find the power dissipated in the resistor. If it exceeds 7 watts, it won't be suitable for your purpose!
You should find that if the voltage drop across a 300R resistor is 45.825V, the current through it is 152.75mA and the power dissipated is 6.99976875W.
This is rather academic as it assumes a ±0% resistor tolerance and you should derate these figures in practice but the important thing here is that no way does the voltage drop approach 200V!
The 200V figure is the maximum for any value in the W22 series - the voltage drop will increase for resistors with higher values but must not exceed that limiting figure. These limits apply to various resistor types - I produced a table once for lower power resistors to illustrate this, but I haven't got it on this PC. If I can locate it, I'll post it here.
