Zero ohm resistor... - Page 1
Forum section: electronics / general

author: strangersound
author_rank: Regular Contributor
timestamp: December 03, 2016, 07:38:28 pm
content: http://www.analog-eetimes.com/news/why-zero-ohm-resistorhttp://hackaday.com/2016/12/03/the-zero-ohm-resistor/Sounds a bit odd, but makes sense. But is it really zero ohms?

author: Zero999
author_rank: Super Contributor
timestamp: December 03, 2016, 08:11:56 pm
content: Of course, they're not really zero Ohms. They have resistance, some inductance, even a tiny capacitance and a self-resonant frequency. Apart from bridging a track, they're also used where there may or may not be a resistor in different versions of the same product, with the same PCB.

author: tatus1969
author_rank: Super Contributor
timestamp: December 03, 2016, 08:16:50 pm
content: they're also used to code something, for example a pull-up or pull-down to enable different functionality of a board.

author: linux-works
author_rank: Super Contributor
timestamp: December 03, 2016, 08:33:49 pm
content: I have a preamp (my own board) and its meant for diy use. the builder can configure a final op amp to have gain or be unity. for unity, you use the 0 ohm R. works fine

author: Howardlong
author_rank: Super Contributor
timestamp: December 03, 2016, 08:45:18 pm
content: They're also useful for allowing debug points for signal injection and measurement.In RF applications I sometimes use PCB mount micro-miniature coax jacks with lands co-located for a coupling cap for production. The cap has no electrical design function other than they're much cheaper than coax jacks. Coupling caps are even cheaper than zero ohm resistors ;-)

author: @rt
author_rank: Super Contributor
timestamp: December 04, 2016, 01:42:27 am
content: You mean to tell me my thru hole superconducting resistor stock is obsolete?The term "0 Ohm Resistor” almost seems a paradox in itself

author: BravoV
author_rank: Super Contributor
timestamp: December 04, 2016, 01:47:58 am
content: Quote from: @rt on December 04, 2016, 01:42:27 amHow bout this ?A psu that supplies a zero volt ..

author: Brumby
author_rank: Unknown
timestamp: December 04, 2016, 01:48:26 am
content: Quote from: @rt on December 04, 2016, 01:42:27 amSend those back.They're way outside the tolerance limits.Edit:Unless theyaresuperconducting, of course.

author: @rt
author_rank: Super Contributor
timestamp: December 04, 2016, 02:21:12 am
content: It’s the current that kills you not the voltage.. don’t you watch YouTube?Quote from: BravoV on December 04, 2016, 01:47:58 am

author: Brumby
author_rank: Unknown
timestamp: December 04, 2016, 03:06:41 am
content: One very valid application I have seen for zero ohm resistors is in the sender unit for LPG fuel tanks.In some installations, the sender is matched to the vehicle's petrol gauge, with that gauged being switched between the petrol and LPG tanks. Other times, a separate segmented LED display is used.The resistance range that drives the gauges varies - and there are half a dozen commonly encountered ones (in Australia, at least). One might be 0 - 90 ohm and another 110 - 40 ohm. An inverse taper and with different end points and curve can make for a manufacturing headache - except it is solved with zero ohm resistors...There is one mechanical and PCB design, with the difference simply being the placement of SMD resistors - including zero ohms ones.

author: AG6QR
author_rank: Frequent Contributor
timestamp: December 04, 2016, 03:15:39 am
content: Quote from: BravoV on December 04, 2016, 01:47:58 amWell, a zero ohm resistor IS a zero volt power supply.

author: jeroen79
author_rank: Frequent Contributor
timestamp: December 04, 2016, 03:56:39 am
content: So, how much current will flow through a zero ohm resistor when connected to a zero volt power supply?

author: AG6QR
author_rank: Frequent Contributor
timestamp: December 04, 2016, 04:05:09 am
content: Quote from: jeroen79 on December 04, 2016, 03:56:39 amLet's see, I * R = V, so we need to determine the value for "I" that satisfies I * 0 = 0Looks to me like 3.42 amps works.

author: retrolefty
author_rank: Super Contributor
timestamp: December 04, 2016, 04:18:12 am
content: Quote from: jeroen79 on December 04, 2016, 03:56:39 amAC or DC voltage?

author: Brumby
author_rank: Unknown
timestamp: December 04, 2016, 04:21:52 am
content: DCAC current will be a bit less, I think.

author: brucer37
author_rank: Contributor
timestamp: December 04, 2016, 04:22:18 am
content: Quote from: @rt on December 04, 2016, 01:42:27 amHhmmmm.I think 10% would be better. Just think of the possibilities and uses of the ones found on the negative side of the bell curve.Breakout the volt meter.

author: Carl_Smith
author_rank: Frequent Contributor
timestamp: December 04, 2016, 04:39:47 am
content: Are those zero ohm resistors really 1/4 watt?

author: @rt
author_rank: Super Contributor
timestamp: December 04, 2016, 04:57:18 am
content: Online parallel and series resistor calculators do get thrown off with (ALL) zero values... I checkedI also checked my Jaycar China multimeter says 000.0 Ohms, so it must be true!Is the power supply so called just because a sinusoid has zero mean value?

author: SeanB
author_rank: Super Contributor
timestamp: December 04, 2016, 05:44:08 am
content: Quote from: Carl_Smith on December 04, 2016, 04:39:47 amThey do have a current limit, so must have a power rating.

author: @rt
author_rank: Super Contributor
timestamp: December 04, 2016, 05:47:51 am
content: I think it’s meant that zero ohm resistors don’t loose energy as heat due to resistanceQuote from: SeanB on December 04, 2016, 05:44:08 am

author: JPortici
author_rank: Super Contributor
timestamp: December 04, 2016, 06:13:33 am
content: (they were also used back in the day of single sided through hole, a zero ohm resistor could be machine assembled by the same tool used for resistors, unlike a wire bidge)

author: Carl_Smith
author_rank: Frequent Contributor
timestamp: December 04, 2016, 06:56:37 am
content: Quote from: SeanB on December 04, 2016, 05:44:08 amIf you suppose that these zero ohm resistors really have maybe a maximum resistance of 50 milliohms, then you would dissipate 1/4 watt with 5 amps of current. But the other question is, are they rated 1/4 watt because that is all they can handle, or because they are in a 1/4 watt resistor package?

author: SeanB
author_rank: Super Contributor
timestamp: December 04, 2016, 08:40:32 am
content: Many are a simple lead through a ceramic former, with a glaze applied to hold the wire into the hole, while others are an actual resistor element, but with a thick sputtered aluminium coat and no spiral cut. The first is basically a wire ( with the same current rating as that wire in normal operation, depending if it is a steel or copper tinned wire used) while the second is actually a very low value resistor. The current rating is generally the rating for the lowest value resistor the manufacturer will supply in the 0.25W package, as that is the only part they make that is tested for this, as opposed to the "0" ohm version, which only has a basic continuity test in manufacture to ensure it actually was coated and has ohmic contacts.

author: george graves
author_rank: Super Contributor
timestamp: December 04, 2016, 08:52:31 am
content: Quote from: SeanB on December 04, 2016, 05:44:08 amThat's the first thing I thought of - can't they be used as a "poor-man's" fuse if you had to cut corners? Kinda handy that you can get them in SMD sizes. I know I've purchased some buck regulators, and some had a small fuse, others had a zero ohm resistor.

author: Howardlong
author_rank: Super Contributor
timestamp: December 04, 2016, 09:22:35 am
content: A potential problem of using a zero ohm resistor as a safety fuse is that they're generally neither designed nor characterised for that function or failure mode, although admittedly taken to the extreme they're always going to blow open, but perhaps not before your PCB traces or other parts have fried. They may specify a maximum current carrying capabilty of, say, 0.5A but they might blow at 0.51A or 5.1A.Furthermore, even if you have run your own characterisation on a given part, whereas you average resistor can almost always be safely substituted for another one of the same value, your fuse characterisations may not apply to another part number, or even the same part from the same manufacturer but from a different batch made with a different process (but still conforming to the same datasheet).It's still a valid use case for last resort protection and is possibly better than nothing, but if you're skimping on costs to that extent, you might just use a skinny bit of PCB track, it's even cheaper than a zero ohm resistor: in that market segment your device is unlikely to be one that anyone would deem economically repairable in the event of failure anyway, certainly not at component level. If you want a fuse to protect your device you should use a fuse characterised for the job, like one of these:

author: N2IXK
author_rank: Frequent Contributor
timestamp: December 04, 2016, 03:45:38 pm
content: Another use I have seen for the thru-hole ones is as configuration jumpers intended for (one-time) user modification.MUCH easier/safer for a user to snip out a thru-hole 0-ohm than to desolder and remove an SMD type, and they are also cheaper than the reusable header pin and removable shunt type.

author: amyk
author_rank: Super Contributor
timestamp: December 04, 2016, 04:13:35 pm
content: I've never seen any 0H inductors or 0F capacitors advertised as such.

author: SeanB
author_rank: Super Contributor
timestamp: December 04, 2016, 04:32:42 pm
content: Depends what you regard a zero. A 1pf capacitor at DC or under 20 kHz will look about the same as an open circuit, along with a 0.1nH inductor looking like a short.At 10GhZ the roles likely will be reversed.

author: MaxSantos
author_rank: Newbie
timestamp: December 04, 2016, 07:03:22 pm
content: Can they act as a fuse in some application?

author: SeanB
author_rank: Super Contributor
timestamp: December 04, 2016, 08:03:47 pm
content: Quote from: MaxSantos on December 04, 2016, 07:03:22 pmShort answer is no. Long answer is that the current rating is not well defined, the characteristics of how it goes open circuit, the emission of flames and smoke are not part of the spec, and there is no consistency between different suppliers of them. If you want a cheap fuse then choose a low value low power fusible resistor ( they also come as SMD parts) and put it in the power lines, but be aware they are limited as to withstand voltage when blown, and the voltage drop while blowing can be limited to reduce arcing. A SMD fuse or polyfuse is a lot more repeatable there.All that you can be sure of with the resistor is that at 200A for 30 seconds it will blow open circuit, though the PC board traces and the PC board itself might be on fire before it fails, and it might fail by melting itself off the board.

author: Carl_Smith
author_rank: Frequent Contributor
timestamp: December 06, 2016, 12:35:42 am
content: On the subject of fuses, at a previous job at a company that manufactured electric forklifts, I found an extreme case of fuses not limiting current to what the fuse is rated at. There was a normal white ceramic cylindrical 5 amp fuse on these forklifts on the power to the main control board. These forklifts ran off a 36V battery that weighed a ton and under normal use could dump about 1500 amps into the drive motors and could probably supply 5000 amps for a short while if shorted out.I found that if you dead shorted the power after that 5 amp fuse that it literally disappeared in a blue flash. So I decided to hook up the Tek current probe to the oscilloscope and sacrifice a few more fuses to the electrical gods to see how much current flowed through that blue flash before the fuse vaporized. Turns out you can dump several hundred amps for a few milliseconds through a 5A fuse before it's molecules are scattered to the wind.

author: PointyOintment
author_rank: Frequent Contributor
timestamp: December 06, 2016, 03:00:35 am
content: Quote from: SeanB on December 04, 2016, 08:03:47 pmWhen a fuse opens, is it considered to have failed or to have succeeded?

author: @rt
author_rank: Super Contributor
timestamp: December 06, 2016, 03:20:40 am
content: That depends on how confident you were of clearing the board when it happened.Ie. how far you were from any ghosts, how many power pellets you had left, ect.

author: jeroen79
author_rank: Frequent Contributor
timestamp: December 06, 2016, 03:42:38 am
content: Quote from: PointyOintment on December 06, 2016, 03:00:35 amThat depends on why it opened.If it opened due to it's rated current passing through it for the rated time then it succeeded.If it opened for some other reason then it failed.If the zero ohm resistor really is a few tens of milliohms, can we consider that to be ESR?

author: aargee
author_rank: Frequent Contributor
timestamp: December 06, 2016, 04:44:41 am
content: I don't think @rt can take those back, Dick Smith sold his last lot to him (and I).It might be interesting to do a test on them to see how much current/time those 1/4W *shaped* links can take.

author: Brumby
author_rank: Unknown
timestamp: December 06, 2016, 06:03:10 am
content: Quote from: Carl_Smith on December 06, 2016, 12:35:42 amSounds about right.Fuses fail/(succeed?) because they heat up and melt (or vaporise). It takes time to heat stuff up.

author: Zero999
author_rank: Super Contributor
timestamp: December 06, 2016, 11:27:09 am
content: Quote from: Carl_Smith on December 06, 2016, 12:35:42 amIt sounds like you were exceeding the breaking capacity of the fuse, which should never be done because it's very dangerous.The breaking capacity, is the maximum current the fuse can safely interrupt without, reaching a dangerous temperature, catching fire or exploding. It depends on the open circuit voltage, whether it's AC or DC (a interrupting AC is easier, since there's time for the arc to quench during the zero crossing) and the inductance, which is important at DC because the high voltage back EMF keeps the current flowing. If the breaking capacity is greatly exceeded, then bad things can happen: the fuse may never interrupt the current, causing an arc to form, the battery to overheat, a fire and explosion.The resistance of the wiring and power supply should limit the current to below the breaking capacity of the fuse. For example, if the voltage is 36V and the breaking capacity of the fuse is 500A, then the resistance of the wiring and power supply need to be greater than 36/500 = 72mOhm. If the resistance is lower than this, then the prospective fault current (maximum short circuit current) will be higher than the fuse's rating, so a larger fuse should be used or a suitable resistor, with a high enough peak power rating and low inductance connected in series with it, to limit the current to a safe level. If the wiring and battery have a resistance of 22mOhm, then a >50mOhm resistor can be used and needs to be able to dissipate the power/energy both at the maximum load and for the length of time it takes for the fuse to interrupt the current.

author: Neilm
author_rank: Super Contributor
timestamp: December 06, 2016, 08:18:32 pm
content: Quote from: Hero999 on December 06, 2016, 11:27:09 amThe other thing to consider is the inductance of that wiring - at 500A just work out how high the voltage will rise once the fuse opens with only a small amount of inductance. You will be surprised

author: Zero999
author_rank: Super Contributor
timestamp: December 06, 2016, 10:26:50 pm
content: Quote from: Neilm on December 06, 2016, 08:18:32 pmI did mention the inductance. Please re-read my post.Yes, the back EMF can be considerable. In theory, if the fuse interrupts the current immediately, then the voltage will be infinite but in reality that won't be the case. The fuse needs to be able to quench the arc and dissipate the energy stored in the inductance safely.

author: tszaboo
author_rank: Super Contributor
timestamp: December 06, 2016, 10:36:46 pm
content: Quote from: Carl_Smith on December 06, 2016, 12:35:42 amfuses have maximum current rating and also maximum voltage rating. But dont be suprised when batteries are involved. I've seen 10KA rated fuse blown. Meaning, it was rated to carry 10KA, without blowing for a minute, and it was dead.And they make fuses in 0603 and even 0402 packages, so please just use them.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 07, 2016, 04:59:59 am
content: Quote from: amyk on December 04, 2016, 04:13:35 pmIt would be really hard to tell a 0 Henry inductor from a 0 ohm resistor. And hard to detect the absence of a 0 Farad capacitor, except through visual inspection.