Thick film power supply dropping resistor?

[bobwithatele]

Hi everyone,

I've been lurking on this very helpful site for a while, cobbling together a couple of amps, and would now love to get the benefit of your collective wisdom (and start to share my own experience).

For power supply dropping resistors, especially early on where more power capacity might be useful, any reason not to use a compact thick film resistor like this

https://uk.rs-online.com/web/p/through- ... 46259?gb=s

instead of an equivalently rated, and significantly physically bigger wirewound or ceramic resistor?

Thanks

[Raja_Kentut]

From a electrical point of view, the resistor is ok, but it's like throwing caviar into a pig trough.
As long as you make sure that the power specification is not exceeded (pay attention to the derating per ambient temperature) you can use any resistor. But the smaller the design, the higher the surface temperature for the same power, and the shorter the service life. (actually applies to every component)

[maxkracht]

I don't see why that particular resistor would be a problem, with a few caveats.

Some thick film resistors require an external heat sync to survive their stated power rating. Always read the datasheet.

Not all resistors have the same voltage rating. 350v isn't uncommon in sub 5w resistors, 500-750v is more common with higher wattage parts. We rarely drop that much voltage, but it is something to be aware of.

Just because a component is small, doesn't mean you save space. It will radiate the same amount of heat, so you need to keep things like electrolytics far enough away to avoid damage.

[bobwithatele]

Thank you, very helpful!

[bepone]

easy to bend it accidentally and make short circuit? so dangerous to use it

[maxkracht]

easy to bend it accidentally and make short circuit? so dangerous to use it

I don't see why it would bend enough to break in normal handling/operation. It's usually a relatively thick ceramic substrate, so not much different than any other resistor. I don't think these have the same issues as tiny mlccs, but I could be mistaken. If I had to guess, most likely handling/mounting problems would be where the leads attach, and that would be an intermittent/open failure, not a short.

[Stevem]

I don't understand going this route.
If you have the room and with how cheap wire wound ciramic's are you can near double the wattage ( for extreame longevity and stability) and still be under the cost of those.