Can u use a 0 ohm high power resistor in series to boost power dissipation - Page 1
Forum section: electronics / beginners

author: amateur_25
author_rank: Regular Contributor
timestamp: May 03, 2014, 10:34:46 pm
content: If I had a zero ohm 1W resistor in series with a 22 ohm resistor, will it give me the equivalent of 22ohm 1 watt resistor? Assuming it's exactly 22 ohm of course. Btw just an example these numbers.

author: Psi
author_rank: Super Contributor
timestamp: May 03, 2014, 10:35:38 pm
content: Its doesn't make sense to have a power rating on a 0R resistor.With resistors in series the wattage doesn't change.You still have two resistors, each with its own wattage, and they must be calculated separately given the current present and the resistors own resistance and vdrop

author: houdini
author_rank: Regular Contributor
timestamp: May 03, 2014, 10:37:51 pm
content: Yes, if the 22 ohm resistor is a 1 watt resistor.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 03, 2014, 10:40:23 pm
content: Quote from: houdini on May 03, 2014, 10:37:51 pmCorrect.And the "value" or "rating" of the zero-ohm "resistor" is a moot point as it doesn't really even factor into the equation at all. The question itself seem odd.

author: EEVblog
author_rank: Unknown
timestamp: May 03, 2014, 10:48:31 pm
content: No. All the power gets dissipated in the 22 ohm resistor, not the 0 ohm resistor. The 0 ohm resistor could be the physical size of a mountain and still make no difference.

author: c4757p
author_rank: Super Contributor
timestamp: May 03, 2014, 10:54:45 pm
content: Kirchhoff's Current Law (fancy-speak for "electron go in, electron go out") says that the current through the two resistors must be equal. Power dissipation is I2R, so the higher R will dissipate the higher power, and I20 = 0 anyway.

author: David_AVD
author_rank: Super Contributor
timestamp: May 03, 2014, 10:56:22 pm
content: As a side note, I had to look up the current rating of an 0805 zero Ohm resistor the other day. The brand I chose was rated for 2.5A (I think), but I can imagine that it will vary by manufacturer.

author: IanB
author_rank: Super Contributor
timestamp: May 03, 2014, 11:15:30 pm
content: Quote from: amateur_25 on May 03, 2014, 10:34:46 pmNo, but if you took four 22 ohm, 1/4 watt resistors, you could combine them to make a 22 ohm, 1 watt resistor (assuming you spaced them apart appropriately and allowed adequate room for cooling).

author: amateur_25
author_rank: Regular Contributor
timestamp: May 03, 2014, 11:45:29 pm
content: Ok cool thanks IanB. Having said that Dave did mention you could do that in his psu video. It's embarrassing but at least I understand now and I won't have a small fire. My desk is very very very bad place to start a fire. Full of pieces of paper and other combustibles like IPA. Not to mention I would tarnish my pretty breadboard I got for free.come to think of it it's a zero resistance so there nothing there to stop the current ROFL. I guess this was a dumb question LOL. But my mentor once told me there are no stupid questions, only stupid answers.However I got the idea from a critical mistake I made in my lm338 based psu. I whipped together a psu with 4 fixed voltage ranges using rotary switch to switch in a different R2 value. I was sick of buying 9v batteries!! not expensive but just a pain to have move my lazy ass. I know it seems like a hack and dumb idea but I couldn't really afford a bench supply because I'll get my head bitten off and still do even though it's money I've earned as a programmer.I wonder what expression dave had on his face when he show my post!! I bet double face palm lolAnways I ASSUMED that my output capacitor couldn't store a charge big enough to heat up the 1/4 bleed resistor. STUPID I KNOW. Luckily my mentor noticed it whilst I was soldering it together and gave me a 0.47ohm 5w resistor to put in series.

author: c4757p
author_rank: Super Contributor
timestamp: May 03, 2014, 11:57:11 pm
content: Quote from: amateur_25 on May 03, 2014, 11:45:29 pmYou really should consider moving those things. Put the combustibles where they won't combust. I wouldn't worry about paper, though it's probably best not to keep huge piles of it all over. Get the IPA the hell away from the burning resistors!QuoteNo, that's the wrong quote. It's: "There are no stupid questions, only stupidpeople."QuoteNah, an LM338-based PSU isn't a dumb hack, it's a good project for a beginner IMO. Lots of places to make mistakes (you see a stupid mistake, I see an educational mistake) but it's not so challenging that it requires experience.Dude, quit insisting you're being stupid! This is how we learn. You toast a few resistors here and there, maybe vent a cap or two, and eventually learn to be careful. Want me to send you the corpses of my burnt resistors as evidence? I'm sure I can find a few...I'm not so sure why your mentor had you install a 0.47ohm 5W resistor in series with a bleed resistor, though...... compared to the higher resistance of a bleed resistor, that might as well be zero.

author: ejeffrey
author_rank: Super Contributor
timestamp: May 04, 2014, 05:11:36 am
content: Quote from: amateur_25 on May 03, 2014, 11:45:29 pmPlenty of people come in here with bigger misunderstandings about electronics. You posted in the beginners section, you asked a clear and specific question, and (most importantly) you didn't then turn around and attack the people trying to help you and insist that your original idea was correct. That is pretty good in my book.

author: KC0PPH
author_rank: Unknown
timestamp: May 04, 2014, 06:53:11 am
content: Ill save you one more... I only say it because I have seen it--- Black is not ground on a line cord and does not get connected to the chassisWe all have days where we think or say something crazy---

author: amyk
author_rank: Super Contributor
timestamp: May 04, 2014, 10:36:40 am
content: It's worth remembering that ideal components don't exist in reality, that's why 0 ohm resistors have a power rating - they're not actually 0 ohms. Push enough current through one and they will dissipate enough power to burn up. Nothing has no resistance (except maybe superconductors, but even those have a maximum current density.)This thread is a good read:https://www.eevblog.com/forum/beginners/0-ohm-resistors/Quote from: amateur_25 on May 03, 2014, 11:45:29 pmMine was

author: Jeroen3
author_rank: Super Contributor
timestamp: May 04, 2014, 10:53:19 am
content: Sure it's better to calculculate manually. But hey.http://mustcalculate.com/electronics/parallelresistance.phpNote you cannot actually use 0 in Ohms calculation. There is no such thing as 0 Ohm the EE world, you should ask the Quantum mechanics department for those magics.In the normal world it will result in a divide by zero, and that makes the world stop.

author: David_AVD
author_rank: Super Contributor
timestamp: May 04, 2014, 09:28:46 pm
content: Quote from: amyk on May 04, 2014, 10:36:40 amI'm yet to see a zero Ohm resistor with a wattage rating. In the data sheet for a particular resistor series, the zero Ohm version is usually noted as having a max current rating and is not part of the normal listing / chart.They are all listed together in the series (say 0.25W) of course, but common sense tells you that the zero Ohm one is a special case.

author: digsys
author_rank: Unknown
timestamp: May 04, 2014, 10:44:23 pm
content: Quote from: David_AVDAgreed. They're usually just a length of wire with a body to match the "series" you wish to be compatible to. In the "old" days, of single-sidedvs double-sided cost differences, and wave soldering, it made design / assembly much simpler. I still use them quite a lot, often as a"place mat" in case I need to do in-circuit debug or changes.

author: ampdoctor
author_rank: Frequent Contributor
timestamp: May 05, 2014, 12:30:03 am
content: I've seen power ratings on 0 ohm resistors on any number of occasions. Since it's not much more than a piece of copper encapsulated in a ceramic body, when you push enough current through the wire it will heat up and that ceramic has to dissipate the heat. As such I'm going to assume that has something to do with the rating. How exactly they derive the value would be anybody's guess.With regard to usage, I typically see them in old double sided boards with no solder mask. Run a trace under a jumper and you'll get a short. Instead they use a 0 ohm resistor and call that good enough.

author: David_AVD
author_rank: Super Contributor
timestamp: May 05, 2014, 02:15:19 am
content: Quote from: ampdoctor on May 05, 2014, 12:30:03 amIt's a bit hard to derive a wattage when the resistance part of the equation is zero.That's why the good data sheets have a current rating instead for the zero Ohm part.

author: SeanB
author_rank: Super Contributor
timestamp: May 05, 2014, 05:03:08 am
content: Wattage rating is more due to the size, thus giving a wattage rating associates it with a size of the substrate, and allows you to use the common parameters like dimensions for the range. That it has a power rating is normally a current based on the max allowable current for the lowest resistance value in the range. It will handle the current, and will fit in pick and place machinery set for the series size with no problem.