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So, due to some unfortunate circumstances, I ended up blowing out a resistor on a circuit board that I have. It has color code of:

Brown Black Black Gold Black

Since the last band is black, my research says that it's a non-inductive resistor (as described here). As a result of that, however, I'm struggling to find a replacement for it. I'm still really green when it comes to basic electronics (hence the unfortunate circumstance heh....), and I would like to try to replace the resistor if possible. Is this something that can be replaced with a 10 Ω 5% tolerance resistor that doesn't have a black band on the end of it? If not, I would appreciate if anyone knows where I might be able to purchase a matching replacement resistor.

Thank you all!

Edit: for a little bit of clarity, this is on a Sonoff Basic R3 switch, and runs off of normal (US) 120 V power.

Edit 2: Pictures were requested, and I'm not sure of what exactly would be helpful, so here is a pic of the resistor itself (on another R3 unit I have that's a little less exploded heh), as we as a top-down view. The resistor is the first thing that the current flows through when entering the circuit from the entry point on the left (green box with flat-tip screws). On the PCB, it's labeled R1. Resistor Top Down

Adam V
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  • Is this an RF device? – jonk Jul 22 '21 at 18:06
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    @AdamV a more helpful thing is to know what circuit it is in, then you can determine what kind of resistor might be needed to replace it – Voltage Spike Jul 22 '21 at 18:57
  • Thanks for the comments, folks. Edited question with added detail that I hopes clarify things a bit more – Adam V Jul 22 '21 at 20:11
  • I don't think that in a "sonoff basic r3" there is a need for special resistor as you mention. – Marko Buršič Jul 22 '21 at 21:30
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    We need photos of the resistor on the location on the board at least. – DKNguyen Jul 22 '21 at 21:35
  • It is entirely possible you are not looking at a resistor, but instead an inductor. Such as: https://www.mouser.com/images/bourns/images/78F_series_DSL.jpg – Kyle B Jul 23 '21 at 05:25
  • We're just trying to gauge the circuit the resistor is being used in. I'm leaning towards "it isn't what you think it is" because I don't see why it is necessary there so that might be a normal resistor or not a resistor at all. – DKNguyen Jul 24 '21 at 01:00
  • That's OK, I appreciate your time! I added a couple of pics earlier that show both the resistor itself (or whatever it is) and a view/description of where it's at on the board. Hopefully that helps identify it? Let me know what else info I can provide to help further! Thanks again! – Adam V Jul 24 '21 at 04:13

2 Answers2

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I would guess not — if they went to the trouble and expense of putting a non-inductive resistor there in the first place, it was likely because the circuit needs it.

Finding a replacement shouldn't be that hard. Digi-key lists a number of choices when filtering to 10-ohm axial-leaded resistors with features including either "Non-Inductive" or "Non-Inductive, Non-Magnetic". All of them are 5% or better, and the in-stock ones at the moment all happen to be 1%.

hobbs
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Is this something that can be replaced with a 10 Ω 5% tolerance resistor that doesn't have a black band on the end of it?

I am betting yes. My reasoning is that a high power resistor with only 10 Ω resistance probably doesn't have many turns on it, so it's probably not 'non-inductive' but just 'low' inductance.

To test my theory I found a resistor in my junkbox that is very similar in appearance to yours, except it is 0.1 Ω and the colors are brown, black, silver, gold, black. Through the outer coating I can see 3 turns going from one end to the other, with no doubling back as would be expected with a non-inductive winding. I also bared the resistance wire close to the end caps and confirmed that it was connected to directly to them.

3 turns isn't many, but it still has inductance. Perhaps an 'inductive' version would have more turns of lower resistance wire. This might become noticeable at frequencies of several MHz.

Your device doesn't look like it is designed to operate at very high frequency, so a few extra nH of inductance probably won't affect it. I bet most similar resistors that you can buy are also 'low' inductance, even if it is not specified.

Bruce Abbott
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