# Do high power through hole resistors need a heat sink

I'm using the following resistor: click. To be precise, the MCKNP05SJ050KAA9 found here. From what I've been able to determine, my device is the MCKNP 500-S, measuring in with a length of 17.5 mm and diameter of 6.5 mm.

Now, I'm wondering whether it is first of all possible, and second of all needed to put a heat sink on though-hole power resistors.

At first I had found SMD Power resistors, though the only ones that could dissipate the required 4.5 W was a 35W. This one did have a metal plate on top for a heat sink. But for Through-hole components, I haven't got a clue.

Typically power resistors are designed to operate without a heatsink (or have one built-in). If the manufacturer recommended use of a heatsink, it would be covered in the datasheet.

That said, they can get quite hot, so care should be taken to keep temperature-sensitive components away from a power resistor that is dissipating a lot of heat. Additionally you may want to ensure that the resistor is mounted with an air gap below it as well (not touching the PCB) to promote air circulation on all sides.

A surface mount power resistor with a pad for heatsink may require a copper pour/heatsink or a physical heat sink of some kind attached (see the datasheet for the component in question).

Typical power resistor

Power resistor that incorporates a heatsink

• Then I guess there isn't one needed. As for the air circulation, since they are through-hole I guess care should be taken in soldering, but this shouldn't form an issue for the PCB design. Thanks! – jdepypere Jan 28 '14 at 18:30
• The part you linked is a 5W wirewound power resistor, so it will be similar to the "typical" picture I linked. Power resistors (no matter the wattage) can get quite hot when doing their job, so be cautious. When I salvage parts from commercial boards, I frequently see such resistors mounted with a bit of extra lead length to elevate them from the PCB somewhat. Keep in mind (based on the chart on datasheet page 2) that at the full 5W, the resistor can reach 150°C over ambient. – JYelton Jan 28 '14 at 18:36
• Your second picture shows a resistor with an aluminum case, but in iorder to handle its maximum rated power, it does indeed need to be bolted to an external heatsink. – Dave Tweed Jan 28 '14 at 19:37
• @Dave That's true; some of them have heatsink fins but lack mounting holes. I just grabbed [stole] an image from the web; but obviously it goes without saying to check the component datasheet. :) – JYelton Jan 28 '14 at 19:41