Phrazemaster
Well-known member
Hey all,
I just want to make sure I'm correctly interpreting this snippet of a schematic. Specifically I'm referring to the resistors R43 and R44.
Starting with R43:
There's a voltage drop of 310-108V, which is 202V.
Using I=V/R, that means there is a current in that resistor of 202V/10000R = 0.02A, or 20mA.
That puts power rating of P=VA at P=202V *.02A = 4.1W.
Doubling that for safety, I could use an 8W+ resistor.
Do I have that right?
Same for R44:
There's a voltage drop of 365-310V, which is 55V.
Using I=V/R, that means there is a current in that resistor of 55V/1500R = 0.037A, or 37mA.
That puts power rating of P=VA at P=55V *.037A = 2.02W.
Doubling that for safety, I could use an 4W+ resistor.
I'm asking because the BOM for this project specifies 20W resistor for the 1.5K resistor R44, and a 12W resistor for 10K resistor R43. Seems way overkill, although I know higher wattage is fine.
It's easier to find resistors a bit less wattage rated, as I want to use NOS Koolohm resistors. And I just want to make sure I'm not going to fry something. I found a 9W 10K Koolohm resistor for R43 and if I have the calculations correct, it should be more than adequate.
Thanks in advance for your thoughts.
Mike
I just want to make sure I'm correctly interpreting this snippet of a schematic. Specifically I'm referring to the resistors R43 and R44.
Starting with R43:
There's a voltage drop of 310-108V, which is 202V.
Using I=V/R, that means there is a current in that resistor of 202V/10000R = 0.02A, or 20mA.
That puts power rating of P=VA at P=202V *.02A = 4.1W.
Doubling that for safety, I could use an 8W+ resistor.
Do I have that right?
Same for R44:
There's a voltage drop of 365-310V, which is 55V.
Using I=V/R, that means there is a current in that resistor of 55V/1500R = 0.037A, or 37mA.
That puts power rating of P=VA at P=55V *.037A = 2.02W.
Doubling that for safety, I could use an 4W+ resistor.
I'm asking because the BOM for this project specifies 20W resistor for the 1.5K resistor R44, and a 12W resistor for 10K resistor R43. Seems way overkill, although I know higher wattage is fine.
It's easier to find resistors a bit less wattage rated, as I want to use NOS Koolohm resistors. And I just want to make sure I'm not going to fry something. I found a 9W 10K Koolohm resistor for R43 and if I have the calculations correct, it should be more than adequate.
Thanks in advance for your thoughts.
Mike