ESR, i know, again... xD - Page 1
Forum section: electronics / beginners

author: 10101
author_rank: Contributor
timestamp: April 05, 2015, 03:30:34 pm
content: So i've been reading many stuff about the ESR measurement of capacitors, iv'e read all of this forum's threats, all youtube videos i could find + google searches and idk why i can't find a good explanation of it.So my doubt is how can we calculate the ESR ? because iv'e found some equations but idk how could i make a circuit how of them.Thanks in advance, 10101

author: Zero999
author_rank: Super Contributor
timestamp: April 05, 2015, 03:37:52 pm
content: You don't calculate ESR. It will be specified on the capacitor's datasheet.

author: 10101
author_rank: Contributor
timestamp: April 05, 2015, 03:42:56 pm
content: Then how ESR meters calculate / measure it ?

author: Zero999
author_rank: Super Contributor
timestamp: April 05, 2015, 05:00:22 pm
content: A capacitor's ESR is measured in a similar manner to any resistor. The difference is the capacitor's impedance is measured using a high enough frequency AC current that its resistance dominates. If the AC current and frequency remain constant, the voltage across the capacitor is proportional to the ESR.

author: kripton2035
author_rank: Super Contributor
timestamp: April 05, 2015, 05:35:57 pm
content: lots of examples on my repository ( link in the signature )some examples are very well explained.

author: Evil Lurker
author_rank: Regular Contributor
timestamp: April 05, 2015, 05:45:10 pm
content: Basically a capacitor's ESR is a measure of it's equivalent series resistance at a given frequency when subjected to electrical pulses or alternating current, such as on the output of a switch mode power supply. In other words when a capacitor charges/discharges it is not perfect and will behave a like very low value resistor and produce heat. Furthermore measuring a capacitors ESR is not an exact science, in fact it is all horseshoes and hand grenades, especially when you take in electrolytic's typical 20% tolerance. ESR will vary wildly amongst various capacitance values and among different series of capacitors from the same manufacturer in the same values. Not only that a lot of general purpose capacitors don't even list ESR values, only ripple ratings. The only thing you have to be careful of is when measuring them in circuit. If there are any ceramics or other caps in parallel it can seriously throw off your readings... the only "right" way to measure a caps ESR is by removing it from the PCB.Anyways it doesn't take long to get the hang of using one. Just measure a whole bunch of caps and which caps are good, which caps are still good but starting to go bad, and ones which should be replaced but have yet to vent will become obvious.

author: Shock
author_rank: Super Contributor
timestamp: April 05, 2015, 07:36:07 pm
content: Here is a good way to figure all these things out.If you look around for ESR meter circuits you can find a few with explanations of how they work. There is no one circuit that is superior, but there are circuits that have desirable features like in circuit testing, input protection, auto discharging, audible alert, digital display, multiple frequency support.As mentioned ideally you want to reproduce the datasheet test as close as possible, which happens to be on an expensive bench meter. The good thing is when electrolytics are going "out of tolerance" on ESR it's really obvious and the ESR reading can be many multiples greater than a new or "in spec" capacitor, so even inexpensive circuits are useful.Checking the ESR is only one factor in determining a capacitor falling out of spec, and each capacitor brand, series, capacity, voltage etc will have it's own ESR specification on it's datasheet. A capacitance, ESR and visual check will normally weed out any bad ones so capacitance by itself can be misleading.Reading test equipment operation and service manuals from good vendors will uncover reliable information on how these measurements are made and service manuals specifically have flow diagrams and explain operation. HP in addition to their manuals put out journals which digs deeper into various technologies.http://assets.fluke.com/manuals/PM6303A_umeng0200.pdfhttp://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/hpjindex.htmlIf you haven't seen it yet, check this video by w2aew.

author: 10101
author_rank: Contributor
timestamp: April 05, 2015, 10:11:04 pm
content: Quote from: kripton2035 on April 05, 2015, 05:35:57 pmYeh iv'e seen your repository it's in almost all threats about this on this forum xD and still couldn't understand from thatQuote from: Shock on April 05, 2015, 07:36:07 pmI've seen 90% of the internet's ESR content this video included xDAfter reading your explanations i might have figure it out.So from what i understood the ESR is the resistence measured - the capacitive reactance right (ESR = Rmeasured- Xc) ?Thanks for all the help, 10101

author: dannyf
author_rank: Super Contributor
timestamp: April 05, 2015, 10:34:30 pm
content: QuoteNot exactly. But if you get Xc sufficient small, ...

author: 10101
author_rank: Contributor
timestamp: April 05, 2015, 10:53:11 pm
content: Quote from: dannyf on April 05, 2015, 10:34:30 pmTell me what's missing please

author: Dave
author_rank: Super Contributor
timestamp: April 06, 2015, 02:32:08 am
content: Quote from: 10101 on April 05, 2015, 10:11:04 pmZ = ESR - j*XcESR is at a 90° angle to Xc, so you can help yourself with Pythagoras's theorem.ESR = sqrt(|Zmeasured|2- Xc2)

author: 10101
author_rank: Contributor
timestamp: April 06, 2015, 02:37:46 am
content: Quote from: Dave on April 06, 2015, 02:32:08 amCould you enlight me a bit more on this please ?Quote from: Dave on April 06, 2015, 02:32:08 amJust to be sure the Zmeasuredis what i called Rmeasuredright ?

author: Dave
author_rank: Super Contributor
timestamp: April 06, 2015, 03:16:23 am
content: Quote from: 10101 on April 06, 2015, 02:37:46 amTake a purely resistive load (ideal resistor) and you have an impedance with only the real component. If you apply a sinusoidal voltage to this load, it is going to produce a sinusoidal current that is in phase with the voltage.If your load is not purely resistive (everything else than ideal resistors - components with inductance and capacitance), the current is going to have a phase angle towards the voltage. We write these kinds of impedances as complex numbers. Voltage on an ideal capacitor would be exactly 90° behind current. If you had an ideal inductor, voltage would be exactly 90° ahead of current.I suggest you read up on complex impedance, because it is absolutely essential in electrical engineering.Quote from: 10101 on April 06, 2015, 02:37:46 amYou may call it R, but it's just not correct, simple as that.

author: 10101
author_rank: Contributor
timestamp: April 06, 2015, 10:46:36 pm
content: Quote from: Dave on April 06, 2015, 03:16:23 amSo i've read a bit about it and i found something that sounded weird, why the need of using complex numbers (be gentle with the math)Thanks to everyone who tried/is trying to help me

author: Dave
author_rank: Super Contributor
timestamp: April 06, 2015, 11:17:35 pm
content: Quote from: 10101 on April 06, 2015, 10:46:36 pmI can't say for sure, but my best guess would be that it was chosen because it makes a mathematical model that allows for very simple analysis of linear circuits.Quote from: 10101 on April 06, 2015, 10:46:36 pmHappy to help.

author: dannyf
author_rank: Super Contributor
timestamp: April 06, 2015, 11:43:55 pm
content: QuoteTo describe complex things,

author: Grapsus
author_rank: Regular Contributor
timestamp: April 07, 2015, 12:01:19 am
content: The w2aew video is by far the best explanation on the subject I have seen, it has everything, the practical side and the theory. No need to look for other videos or explanations, it won't get any simpler, just pause at each step, make sure you understand exactly what's going on, redo the calculations, etc.

author: Zero999
author_rank: Super Contributor
timestamp: April 07, 2015, 07:51:20 am
content: Don't worry about the complex numbers for now.At low frequencies, say 1Hz, the impedance of a capacitor XCis dependant on it's capacitance which limits the current to such as low level that the ESR is insignificant.XC= 1/(2pi*FC).A 100µF capacitor will have an impedance of 1.6k Ohms at 1Hz, even if its ESR is as high as 10R, it's insignificant compared to the 1.6k due to its capacitance.To measure the ESR we need to use a much higher frequency. At 100kHz an ideal 100µF capacitor has an impedance of 16m Ohm, but our real capacitor will has an ESR of 10 Ohms, which is now much greater than the tiny 16m, Ohm due to the capacitance so can be easily measured.