ORIGINAL: OldRookie
I wasn't quite getting the voltage I wanted. I tried the 4 10 ohm 1 watt resistors in series and got pretty good results. The next thing I tried is putting two sets of 10 ohm 1 watt resistors in parallel, and then put the two parallel resistor sets in series. What type of load does this put on the system compared to the 4 10 ohm 1 watt resistors in series? I don't know the formulas for series and parallel circuits.
Greg
hey there, I got your PM, so here it goes.
The formula for TDP is voltage squared over resistance, so it's 5.15^2 or 26.5/resistance. For series you add all the resistance together to put it on the bottom, and for parallel, you do two different equations and then add them together
so in your case four 10Ω resistors rated at 1w each, will give you a total resistance of 4 x 10Ω or 40Ω then 26.5 / 40Ω = 0.66w TDP between all 4 resistors, so if you divide that 4 ways, then it is 0.165w per resistor, or about a 16.5% load, which is a good range to keep them running cool.
In the second case you would really up the amount of power draw. Two 10Ω resistors in series will give you a total of 10Ω + 10Ω = 20Ω then you take 26.5 / 20Ω = 1.33w per two resistors, or 0.66w per resistor, or about 66% of the capacity on a 1w resistor, so that puppy is gona get hot. Then when you add the second set in there, you'll get a total TDP of 2.65w, and 0.66w per 1w resistor.
so the first one you'll get 0.66w load on the 5v rail and the second example you'll get 4 times that at 2.65w load on the 5v rail. The temp diff in the resistors between the two is going to be very different. I'll bet in the second example you'll be getting close to 180F or 200F for each resistor, especially without a heat sink.
Hopefully that answers your q