Author Topic: Idea to eliminate wirewound resistors inductance  (Read 1364 times)

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Offline 001Topic starter

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Idea to eliminate wirewound resistors inductance
« on: October 24, 2019, 01:48:14 pm »
Hi

Can I compensate inductance if I connect center tapered wirewound resistor as shown?
Can I use steel bolt to fit it?

Moderator note: please upload a sensible sized picture!
« Last Edit: October 24, 2019, 05:05:50 pm by Simon »
 

Offline Ysjoelfir

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Re: Idea to eliminate wirewound resistors inductance
« Reply #1 on: October 24, 2019, 03:25:06 pm »
I'm sorry but your picture is way to small. could you provide us with a bigger one so that I can see the molecular structure of the paper even better?
Also, I'm not quite sure what you mean with the steel bolt. could you explain that more precisely?
Greetings, Kai \ Ysjoelfir
 
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Offline 001Topic starter

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Re: Idea to eliminate wirewound resistors inductance
« Reply #2 on: October 24, 2019, 03:31:11 pm »
the idea is to short outer legs with wire  to parallel both windings out of phase
 

Offline james_s

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Re: Idea to eliminate wirewound resistors inductance
« Reply #3 on: October 24, 2019, 04:01:51 pm »
Don't they already make non inductive wirewound resistors that have two elements wound in opposite directions?
 
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Offline pwlps

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Re: Idea to eliminate wirewound resistors inductance
« Reply #4 on: October 24, 2019, 05:04:15 pm »
To suppress inductance you would need a perfect inductive coupling between the two halfs (the idea is to keep the total magnetic flux as small as possible). So for example it will work if the two halfs are wound on the same ferrite rod like in a transformer, otherwise if there is no ferrite the coupling will be poor unless the length of the coil is much smaller than its diameter. 
« Last Edit: October 24, 2019, 05:11:46 pm by pwlps »
 

Offline alsetalokin4017

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Re: Idea to eliminate wirewound resistors inductance
« Reply #5 on: October 24, 2019, 05:45:16 pm »
Don't they already make non inductive wirewound resistors that have two elements wound in opposite directions?

Yes.
https://en.wikipedia.org/wiki/Ayrton%E2%80%93Perry_winding

I frequently use Ohmite brand A-P wound noninductive precision resistors for current monitoring. There is usually more inductance in the wiring to it than in the resistor itself.
The easiest person to fool is yourself. -- Richard Feynman
 

Offline T3sl4co1l

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Re: Idea to eliminate wirewound resistors inductance
« Reply #6 on: October 24, 2019, 07:23:18 pm »
Yes, but only slightly.  The coupling factor between the halves of the resistor will be small, about 0.1, so the reduction compared to a pair of shorter resistors in parallel (without the adjacent arrangement) will be on par, about 10%.

Use a noninductive design.

On a related note, you can equalize it by putting an R+C in parallel, where the R's are equal and C = L / R^2.  But this shifts the current from the main resistor to the equalizing resistor at high frequency, so if you need to handle a lot of power at any frequency, yeah no...  Can be acceptable for low frequencies with rich harmonics (where the high frequency power is fairly small).

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Offline floobydust

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Re: Idea to eliminate wirewound resistors inductance
« Reply #7 on: October 24, 2019, 08:34:18 pm »
It's a messy issue as the wirewounds typically have steel end-caps and leads.
I think it's mostly air-space on a solenoid form, so none of that should saturate.
But I get weird readings with an L meter from 5-25W parts and never tracked that down.

I use plate resistors "low inductance" for audio power amp emitter resistors.
Non-inductive parts are very rare and expensive.
 


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