The said:
How about some numbers? What inductances are you measuring
and at what frequency? Which resistors gave which numbers?
Big question, but I'll try to give some short answers.
Most power resistors are wirewound types. Exceptions
are wire-strip resistors with values below 0.3 ohms,
carbon-composition resistors, some metal oxide types,
and ceramic-composition resistors (rare). I eliminate
common film types, etc, from this list, because they
cannot handle high pulse-power or surge levels.
Unless they use a special winding technique, such as
Aryton-Perry, wirewound resistors have high inductances
compared to composition types, and typically become
inductive above 5-15MHz (1 to 5W parts with values
above 20 ohms) or above 0.5 to 5MHz (for values from
1 to 20 ohms). For example, standard 3-ohm wirewound
resistors I measured became inductive as low as 430kHz
(1.17uH for an Ohmite 10-watt part) to 2MHz (275nH for
an IRC 3-watt AS-2 part).
A 5-watt Sprague KoolOhm part measured 48nH, or about
10MHz, which is 5 to 20x better than those others. A
2-watt 3 ohm carbon is 2-3x better yet, about 20MHz.
A straight wire, bent and fixed in the same position
as the 2W carbon, had nearly the same inductance, 14nH.
Well, I am finding some low-inductance parts, even in my
own inventory. For example, DigiKey stocks Yageo's low-
cost RSF metal-oxide series, but only in the 1 and 2-W
sizes (Yageo makes them from 1/2W to 5W). In contrast,
the KoolOhm resistors went to 10 and 20W or thereabouts.
The cool thing about KoolOhm was that they were low-cost
standard high-power parts, yet you got low-inductance
Aryton-Perry windings, or the equivalent.