Heat dissip. series vs. parallel
in [Design]
|
Prev: Compound feedback topologies
Next: ARM sample code
From: Kevin Roberts on 1 Apr 2010 06:54 I need to fit 20 Ohms worth of power resistor as a dummy load in a confined space. In practice, is there any difference in terms of heat disspation between using two 10R in series or two 40R in parallel? Voltage is 12V giving about 7W dissipation. I would be using 25W rated resistors just to be sure. Thank you, Kevin Roberts
From: David Eather on 1 Apr 2010 06:20 On 1/04/2010 8:54 PM, Kevin Roberts wrote: > I need to fit 20 Ohms worth of power resistor as a dummy load in a > confined space. In practice, is there any difference in terms of heat > disspation between using two 10R in series or two 40R in parallel? > > Voltage is 12V giving about 7W dissipation. I would be using 25W rated > resistors just to be sure. > > Thank you, > > Kevin Roberts no difference
From: Bitrex on 1 Apr 2010 06:27 Kevin Roberts wrote: > I need to fit 20 Ohms worth of power resistor as a dummy load in a > confined space. In practice, is there any difference in terms of heat > disspation between using two 10R in series or two 40R in parallel? > > Voltage is 12V giving about 7W dissipation. I would be using 25W rated > resistors just to be sure. > > Thank you, > > Kevin Roberts Each resistor is dissipating 3.6 watts - the only thing I can think of is maybe if you used smaller resistors the space wouldn't be so confined? :)
From: Martin Brown on 1 Apr 2010 07:32 Kevin Roberts wrote: > I need to fit 20 Ohms worth of power resistor as a dummy load in a > confined space. In practice, is there any difference in terms of heat > disspation between using two 10R in series or two 40R in parallel? > > Voltage is 12V giving about 7W dissipation. I would be using 25W rated > resistors just to be sure. Two 40R in parallel will cost more - not an E12 value (39R is). A failure in either one of a series pair will go open circuit. 20R is 20R for power dissipation but physical layout could matter in a confined space. Heatsinking might be helpful to keep it cool. Regards, Martin Brown
From: ehsjr on 1 Apr 2010 12:57
Kevin Roberts wrote: > I need to fit 20 Ohms worth of power resistor as a dummy load in a > confined space. In practice, is there any difference in terms of heat > disspation between using two 10R in series or two 40R in parallel? > > Voltage is 12V giving about 7W dissipation. I would be using 25W rated > resistors just to be sure. > > Thank you, > > Kevin Roberts You're stuffing 50 watts of dissipation capability in there where you need only about 15. I guess if you have room and cost doesn't matter, it's a case of "why not use a bigger wattage". Series or parallel doesn't matter. Depending on layout, you could get some advantage by physically locating the "hot spots" (where the resistors are installed) to minimize heating of nearby components. That's about the only reason to use multiple resistors in this case, where your budget and space allows selection of a 25W resistor to dissipate ~ 7 watts. Maybe 4 5W 5 ohm resistors would serve you better? Ed |