wire wound power resistors

[Bradselph]

after ordering my neon transformers i started shopping around for a proper protection circuit for them and have had one question arise and it comes to the power resistors used in the terry filter

seems the aluminum cased ones are everywhere yet the the long tube type ones are not.

would there be any reason to choose one over the other?

i thought about a series connection of say 4 25watt 250ohm aluminum housed resistor to equal 1kohm and it extend the length to help with possibility of a flash over.

does that sound plausible?

[T3sl4co1l]

Note that they only achieve their rating when heatsinked, similar to transistors.  They don't have much temp rating (similar plastic filling), and not much overload capacity.  The failure mode is: the plastic melts, decomposes, and pops out like a cork gun, taking some of the element with it.  The element and case may end up open or shorted.

Whereas, the enameled ones are only slightly higher priced (at the usual mainstream distributors, anyway), don't need heatsinks, and can survive glowing red for hours if heavily overloaded.

That said, these are unfairly well rated, for some reason:
https://www.mouser.com/ProductDetail/TE-Connectivity-CGS/THS501K0J?qs=sGAEpiMZZMtbXrIkmrvidHzXe9tGSbePVnWBZTYpuxU%3D
20W without heatsink, 275°C(!) maximum operating.  Also have the best pulse ratings, though only in lower values (under 10 ohms).

But others even within the same family are not so lucky. Look at that THS25 derating curve, yikes!  Always RTFDS!

Compare with:
https://www.mouser.com/ProductDetail/Vishay-Dale/AVT05006E500R0KE?qs=sGAEpiMZZMtbXrIkmrvidAl35n5xACJLdSQS8JyFBDol8cr0PzbUvg%3D%3D
Derated linearly up to 350C ambient; it'll probably handle even more than that, but it may crack, especially if it's overloaded rapidly.  Element tends to fail open, unless, like... some wire bits fall onto nearby mounting hardware, or something.

At high voltages, you might not want to use the end mounting metal clips?  Or you can but mount them in turn on an insulated platform.  Or use ceramic or fiberglass hardware to mount them.  YMMV.

Tim

[Bradselph]

Thank you

I noticed that the price difference wasn’t to bad that’s what brought up the question

I’ll definitely invest a few more dollars in just to get the better reliability’ as I have a bad habit of pushing things to the limit and then over it thinking it might handle it 😬