I am building a circuit that supposedly operates at 1.8w, current being 0.20A (which I assume is 20mA) and I have calculated the resistance needs to be around 33 ohms. Since I cannot find a 2w 33ohm resistor, and I don't think it would be much trouble and cost too much to make this, I have come up with this sketch up, and I was wondering if this resistor network is capable of having a resistance value of 33 ohms, and still being able to tolerate 1.8w of power. If I calculated things right from my knowledge, total resistance would be 33.6 ohms and the wattage would be 2.5w. Here's the image: Thanks for the help, if any, I appreciate it!
isn't the formula for resistance in parallel somethin like.. 1 / ( 1/R1 + 1/R2 + 1/R3 + 1/R4 + 1/R5 ) if I use that formula in MS excel, it gives me 33.6... because I'd add all the resistors that would be in a series together, thus giving me 168 ohms x5... and then the formula in excell would be: =1/(1/A35+1/B35+1/C35+1/D35+1/E35) Where you'd enter that line of code in cell F, and then input all your R values in cells A35, B35, C35...etc.. A little trick I've learned is that if you have all the same value resistors in parallel, you just take 1 value and divide it by how many resistors are in the array. Like in my case, 5x "168 ohm resistors" (adding 100 and 68), then dividing that by 5, would give me 33.6... But besides all that, I'm just worried about the wattage. Wouldn't the wattage be like, adding all the wattages of the resistors? Since they're all going to be 1/2w, and 1/2 x 5 = 2.5, that would mean that little circuit has the power to handle 2.5w, wouldn't it?
33.6 Ohms. The power rating won't be 2.5W, since the power isn't evenly distributed between the 100R and 68R resistors. If you give us the rest of the details - i.e. how many volts this network is supposed to drop, then the power rating can be calculated.
I had changed the pic... because the first one wasn't correct... Basically, I wanted to take this fan, and have a voltage drop of 4v to reduce the amount of exhaust airflow, and prevent my case from being infested with dust. But, I have figured things out. Two of these for intake, in the bottom front of the case This one as the rear exhaust (this is the one I was going to add those resistors to, since I thought it was going to be pushing 32cfm like the first one, instead of 22cfm And I'd have this on the top for exhaust, since I'll be watercooling and this fan will cool the water in the radiator I personally think that this machine may be rather loud, but I doubt it being that the total dbA for all 4 fans is 27.1
If you pass 200mA through a 33R resistor, the heat produced is I2R, 1.32W. Voltage dropped is IR, 6.6V. Three 100R 0.5W in parallel will just do, but they'll get quite hot.