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I need a big resistor to dump reactive energy to. But I need it 'fast' since otherwise the input TVS will overload. The situation: parasitic inductance of wiring makes the whole circuit substantially a huge boost converter and for cost reasons I can't put there a leveling capacitor. For reference, nominal 12V in and I see peaks of 90V. So at the moment the plan is to use the equivalent of a braking resistor and dump the excess (there is a whole water tank to sink, so power dissipation is not an issue).

A good and cheap part would be something like this http://www.arcolresistors.com/resistors/hs25-aluminium-housed-resistor/ they make both inductive and non-inductive parts but, of course, the non-inductive ones are made on paper only these days.

Do you have any experience on the typical inductance of such a wound inductor? even just as a magnitude order, like, about 100nH or 1µH or whatever.

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  • \$\begingroup\$ For the inductance of that resistor, measure it. For this as an XY problem, what are the specifications for your dump resistor? You could probably make something non-inductively wound quickly, assuming it's a one-off. What's the continuous power rating? What's the single event energy rating? What's the tolerance? What's the maximum inductance? All those are computable for a bulk resistor made with wire. \$\endgroup\$
    – Neil_UK
    Mar 23, 2022 at 8:52
  • \$\begingroup\$ your question needs rewriting so somebody downvoted it .I think that you could tart it up so it might get an answer, \$\endgroup\$
    – Autistic
    Mar 23, 2022 at 9:50
  • \$\begingroup\$ Try searching for non-inductive resistors. Sellers of those may have some comparison information. \$\endgroup\$
    – user80875
    Mar 23, 2022 at 11:51
  • \$\begingroup\$ I did some simulation so it's not terribly critical if it's somewhat inductive (like 1 or 2µH)… however I've seen no datasheet stating some value so I hoped someone had experience. Guess I'll buy some and measure them \$\endgroup\$ Mar 24, 2022 at 9:30
  • \$\begingroup\$ Please provide a schematic, operating conditions, etc. It takes a LOT of inductance to exceed the energy rating of a TVS, even at high currents. \$\endgroup\$ Feb 2, 2023 at 12:12

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I was asking myself the same question, so I measured some 100 watt power resistors similar to the ones linked in the question with an LCR meter. Here are the results:

  • 22R Arcol HS100: 5.9 µH
  • 10R Tyco HSC100: 0.6 µH
  • 4R7 Arcol HS100: 1.9 µH
  • 1R0 Tyco HSC100: 0.15 µH

There are significant inductance differences between the power resistors. Based on this very limited set of measurements you can guess that lower resistance also means lower inductance for a specific power resistor series. But if a couple of µH series inductance matter in your application, you will have to measure the inductance of the power resistor to be sure.

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  • \$\begingroup\$ The arcol parts are without dubt of the wound type! the tyco have probably some special winding method to reduce the inductance. thanks \$\endgroup\$ Feb 2, 2023 at 12:10
  • \$\begingroup\$ Thanks for these measurements, Lars. Have you estimated the contribution of the leads in those measurements? As these resistors are fairly large, the leads will surely have a considerable loop inductance (1e-7 .. 1e-6 H), regardless of the internal winding geometry of the resistive wire. In other terms: Do you see the possibility that your figures are dominated by lead inductance and that component inductance is actually much lower? \$\endgroup\$
    – tobalt
    Mar 16 at 7:35
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    \$\begingroup\$ @tobalt The resistors all have the same package size and the measurements were done in the same way. LCR meter with short measurement leads (~10cm) was used. However, I'm not sure if I removed this measurement offset or not. So there could be a 100 nH offset in all measurement, but I don't think it matters much. \$\endgroup\$ Mar 16 at 8:59
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Myself and others have used Caddock resistors for for dummy loads. They are have pretty good low inductance loads up to about 200 MHz. https://www.qsl.net/in3otd/ham_radio/dummy_loads/Caddock_MP9100.html

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