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Zero ohm resistors.

Discussion in 'Off-Topic Members Lounge' started by HarryA, Jun 19, 2018.

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  1. HarryA

    HarryA

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    Jan 22, 2017
    Hello from Penn's woods.

    You are thinking why would anyone want a 0 ohm resistor. Why not use a piece of wire?
    Yes; but how do you insert a wire? With an expense machine. So if you have a machine
    to insert resistors you can use a 0 ohm resistors for jumper wires!

    How much current can you put through a 0 ohm resistor?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    A zero ohm resistor had the same form factor as any other resistor. Since resistors are common, there are no problems getting them automatically populated on boards. It makes sense to house a link in the same package.

    Zero ohm resistors can be used to provide a link for the purpose you'd use a link :) .For example, they could be used to set factory options on a board, or as a method to ease the routing in a printed circuit board.

    Meet zero ohm resistors are part of the normal resistor series and have a power dissipation limit. This doesn't help you calculate the current though. Typically you wouldn't use them in a high current path. The datasheets may give some guidance.
     
  3. Kabelsalat

    Kabelsalat

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    Jul 5, 2011
    I find it hard to get a precise voltage divider out of zero ohms resistors . . .
     
  4. davenn

    davenn Moderator

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    hahaha indeed :p:D
     
  5. shrtrnd

    shrtrnd

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    i remember this argument some years ago here.
    I repair a lot of Hewlett Packard (vintage now) test and measurement equipment.
    HP LOVED to use these components.
    The argument went that they're just used as jumpers, probably due to ease of automatic insertion in PCBs.
    My input (for which I was ravaged), was that I often see them between the output of one board in a unit, to the input of another board in the instrument. Frequently finding them blown, I speculated that they were put there as known-value fuses. I just fix the instruments, I didn't design them.
    MY EXPERIENCE in HP gear still leads me to believe that while they are jumpers, they're also some protection between the boards in the instrument. Rather than just allowing excessive current to flow from one damaged board to the next one in the circuit, the zero ohm resistor opens; as opposed to using a jumper wire that won't open, allowing the excessive current to damage the next board in the circuit.
    Go ahead and beat me up over this again.
    I find plenty of instruments that have automatically inserted actual jumper wires. You don't require some expensive
    machine to insert them, the jumpers come on reels just like the components.
    I don't know the current they're supposed to handle, I just know I find plenty of blown zero ohm resistors.
    I've got several reels of actual jumper wires for automatic insertion, as well as reels of zero ohm resistors.
     
  6. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Zero ohm resistors are standard sized to allow use in the same placement machinery as ordinary components. By using a wire link you have to have a specific 'arm' to place those links and also, in many cases, thru-holes don't exist to put them into anyway. In high density boards a thru-hole is a wasted space! (well, one that carries a 'link' anyway).

    Board design is such that the use of them is minimal and your suggestion that they are used a fusible links doesn't fit (exactly) as they could simply be places where tests are made before being 'linked' to other sections.

    If the links were fitted on POWER lines between boards I might concur however you seem to imply that they are fitted on 'all' links of a connection whereby data lines would be part of it and imho NEVER a cause of shorts that would 'save' any connected circuitry. Anyway, if they wanted to 'fuse' such links they can use...... fuses! These also exist in SMD form.
     
  7. kellys_eye

    kellys_eye

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    Here's a datasheet for Vishay's 0Ω SMD resistor range.

    Note the fusible values range from 0.5A to 6.3A

    https://www.vishay.com/docs/31017/rcwp99.pdf

    Note also that although they are 'zero ohms' they actually have a value of 20 - 50 milli ohms hence a dissipation rating.
     
  8. shrtrnd

    shrtrnd

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    Didn't 'imply', mentioned what I've seen.
    And I'm back to say I've seen a lot of zero ohm resistors opened, that saved me a helluvalot of extra repair on adjacent boards.
    Perhaps, that is an unintended consequence of zero ohm resistor use(?)
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I don't buy that.

    I think I'm with you @shrtrnd.

    Is there an HP Journal article on the use of zero ohm resistors for board protection? :)
     
  10. jaredwolff

    jaredwolff

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    Jun 11, 2018
    I also often use 0 ohms in places where I can remove said 0 ohm to do series current measurements. Eventually, when going to production, ideally the 0 ohm jumpers get removed. That doesn't always happen though. ;)
     
  11. kellys_eye

    kellys_eye

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    ... to be replaced with..what?
     
  12. shrtrnd

    shrtrnd

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    I haven't ever actually looked for HP Engineering 'Bench Briefs' (the ones they used to turn-out during at least the 1970's) that might have mentioned zero ohm resistor use. I just mentioned my experience over the past 48 years of working HP T&M Instruments.
    I just checked the spec sheets from a couple of zero ohm manufacturers, and they all just list what kellys_eye repeated. The spec sheets list possible applications as jumpers, position holding locations on a board for possible or expected future modifications of a board, to jumper over trace on a board, or easy access test points like jaredwolff noted,.... mundane uses.
    I would suspect that no manufacturer would even consider mentioning their possible use as some kind of 'fusible link', because as kellys_eye noted, that would entail some kind of liability if the device didn't 'fuse-open' in some application if the manufacturer put that on their spec sheet.
    We've all probably seen zero ohm resistors. Because I saw a post about them again here, I just wanted to repeat what my practical experience has been, because in the HP gear, I often find a dozen of them or more; interestingly to me, specifically located on the output of one board, connected to the input of another stage board of the instrument. And I have often found them open, preventing damage to that second board.
    I'm not an engineer, I'm a bench tech who simply noticed this phenomenon, and maybe jumped to a conclusion that has no technical merit. Practically however, as a troubleshooting and repair tech, I have appreciated their use in the HP gear I mentioned.
    To me, this is like finding a second (maybe unintended) usefulness for something it was probably never originally designed for. I would never recommend using a zero ohm resistor as a fuse, it's just been a relief to me in troubleshooting, to see less damage to a circuit I'm trying to repair, because a zero ohm resistor got in the way.
    I can't argue with anybody, about what a zero ohm resistor is supposed to do, or be used for.
    I'm just mentioning what I've seen them do.
     
  13. kellys_eye

    kellys_eye

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    It's an interesting observation - not one in my experience but, then again, I'm not doing what you used to do! - but using parts for 'unintended purposes' is good thinking so kudos to whoever dreamt up the idea.

    I'll bear it mind for future self-notification should I come across anything that triggers me.
     
  14. KJ6EAD

    KJ6EAD

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    If one were looking for the former HP bench briefs now, I guess they would all be under the Agilent name, at least for test, measurement and power supplies.
     
  15. Chemelec

    Chemelec

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    Jul 12, 2016
    My 0 Ohm, 1/4 watt Resistors are a 24 AWG Wire, so Whatever Current is OK for that.
    Probably 6 to 8 Amps is safe. And I Like using them.
    0-ohm-.25W.JPG
     
  16. kellys_eye

    kellys_eye

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    I very much doubt that the 0Ω resistor you show is simply 24 AWG 'all the way through' - it's very likely that the body is an actual resistor with a metal film deposition to give 0Ω and will be rated according to the package dissipation (1/4 watt? 1/2 watt?) that the resistor is normally specc'd for.

    For example, you can get 0.1Ω resistors in such packages which are effectively 0Ω but you most certainly can't put 'lots' of wattage through them!

    Remember, even 'zero ohm' resistors actually have a value (25mΩ to 50mΩ for the SMD versions I linked to above but who knows what you actual resistor spec is?)
     
  17. Chemelec

    Chemelec

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    Jul 12, 2016
    Squeezing the heck out of it in a Big Vice, It is actually Solid Metal Inside. Other than the Lead Wires it is probably good for 50 amps. It Does Not even get Warm at 10 Amps on my Power Supply.
    It Measures .00056 Ohms at 1/4 Inch at Either Side of this Center Part. 0-ohm-0.25W.JPG
     
    Last edited: Jun 23, 2018
  18. kellys_eye

    kellys_eye

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    Wow! That's a real hunk'a'metal! Must say I'm surprised to see that as the insides - can't really see the point behind them making it so 'robust'.
     
  19. Chemelec

    Chemelec

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    Jul 12, 2016
    Yes, That SURPRISED ME ALSO.
    I bought this box of 1000 Pieces a few years ago at a wholesaler store in Vancouver, Canada.
    Doesn't say the Manufactures name, Just Says "0 Ohms, 1/4 watt Size and 5%".
     
  20. KJ6EAD

    KJ6EAD

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    Aug 13, 2011
    5% of 0? :rolleyes:
     
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