Understanding Capacitors ESR  - Page 1
Forum section: electronics / projects

author: GoatZero
author_rank: Regular Contributor
timestamp: December 29, 2013, 02:43:35 am
content: Hello, i have been measuring with an ESR metter all my capacitors, but before going in a nonsense rampage of throwing all the ones with high ESRI've been trying to figure out this ESR thing,it's not making too much sense. I know that 0 ESR would be a perfect capacitor with no resistance whatsoever. But we all (most of us), know that all capacitors, ceramic or electrolytics, have resistance.What I don't understand is how this affects a power supply or a circuit.If you have less ESR, how does this affect a power supply?I'm set up my protoboard with the circuit in the picture and took the following meassurements of 4 capacitos that are supposed to be rated the same 1000uF 25V however most of my meassurements seem to be pretty close even in the low Farad CapacitorI really hope anyone here could make any sense of my meassurements (in picture) and explain to me fairly simple how does ESR affect my capacitors/circuitsThanks in advance.

author: GoatZero
author_rank: Regular Contributor
timestamp: December 29, 2013, 03:03:53 am
content: damn wrong form i wanted to post in begginers not in proyects

author: mariush
author_rank: Super Contributor
timestamp: December 29, 2013, 03:17:45 am
content: edit: Did you exclude the resistance of the leads of your multimeter? Use the REL feature if your multimeter has one.See PA4TIM's blog post about ESR, hopefully it can explain more about it in simpler terms:http://www.pa4tim.nl/?p=3775Also see these pdf's besides the one I attached:http://www.low-esr.com/QT_LowESR.pdfIntroduction to capacitors, the terms, formulas etc:http://www.vishay.com/docs/28356/alucapsintroduction.pdfYou don't see the effect of the ESR because you're working at low frequencies.ESRis the DC resistance of the inner parts of an electrolytic capacitor - the lead wires, the aluminum foil, the electrolyte (the electrolyte is not the dielectric).Impedanceis the overall resistance of the part to AC current, of which ESR is a part.Impedanceis the vector sum of the ESR (DC) and thereactance(capacitive reactance minus the parasitic inductive reactance of the leads and foils).______________Z= ? (ESR2 + (Xl-Xc)2At low frequencies (e.g. 100Hz or 120Hz) the capacitive reactance dominates so ESR is irrelevant;In the 10s of KHz the ESR dominates;In the 100s of KHz the inductive reactance becomes relevant and begins to dominate. You can see this effect in the impedance vs. frequency charts in the datasheets of many/most low impedance electrolytic capacitors.Switching power supplies run at 40-60 kHz, some work at up to 200-400 kHz. Either way, they usually work above what the human ear can hear, which is around 22kHz.Dissipation factor(tan ?)or DF is defined as the ratio of the ESR and capacitive reactance. It is theDissipation factor is also known as the tangent of the loss angle and is commonly expressed in percent.Recognized standards express the dissipation factor at specific frequencies typically 120Hz for Aluminum electrolytic and Tantalum capacitors while for film capacitors is 1 kHz and 1 MHz for ceramic capacitors.DF=ESR/Xc or tan ?Equivalent Series Resistance or ESR for short is the sum of the ohmic losses of the dielectric, materials and connections used in the construction of the capacitor.ESR=DF*Xc=DF/(2* ?*f*C)ESR is normally expressed as a maximum value at specified frequencies, 120 Hz and 100kHz for aluminum electrolytic and tantalum capacitors and 100kHz for film capacitors.Impedance is the total resistance the capacitor represents to alternating waveforms. This includes theinductive and resistive components.______________Z= ? (ESR2 + (Xl-Xc)2An important observation is the Fr parameter. Fr is the self-resonant frequency. Defined as the frequencywhere Xl and Xc are equal._____Fr=1/[2*?*? (L*C)]At this frequency the impedance is equal to the ESR.Below self-resonance the Xc component is dominant and the capacitor behaves like a capacitor. Above the self-resonant frequency the inductive component is dominant and the capacitor behaves more like an inductor.Aluminum electrolytic and film capacitors have the impedance specified as a maximum at a specific frequency normally at 100 kHz and 20°C for aluminum electrolytic and 70°C for film capacitors.note: fragments of texts above are copy pasted from forum posts and pdf's I saved locally and I don't have the sources anymore. Better than typing from memory.

author: c4757p
author_rank: Super Contributor
timestamp: December 29, 2013, 03:20:37 am
content: Quote from: GoatZero on December 29, 2013, 02:43:35 amSimple way to answer this: if there is a high current flowing in and out of the capacitor, the ESR dissipates the usual I2R, making the capacitor hot if the ESR is high.It's not incredibly important in low frequency / low ripple current circuits.

author: AG6QR
author_rank: Frequent Contributor
timestamp: December 29, 2013, 05:14:37 am
content: Quote from: c4757p on December 29, 2013, 03:20:37 amRight. An ideal capacitor dissipates zero energy, while a capacitor with nonzero ESR dissipates nonzero energy.Furthermore, the heat produced by lots of AC going through a high ESR electrolytic capacitor may cause the electrolyte to start to boil off, further increasing ESR (and probably reducing capacitance eventually). Once ESR increases beyond a certain point, you can get a positive feedback loop where high ESR results in heat resulting in boiled electrolyte resulting in increasing ESR. This can become a "death spiral" toward a failed capacitor.Often, a capacitor is placed in a circuit to provide a low-impedance path for AC, while blocking DC. As the ESR increases, the impedance increases, so the capacitor no longer provides a low impedance path for AC. This might show up as more ripple in a power supply. More complicated results can happen if the capacitor's purpose is more complex.

author: Skimask
author_rank: Super Contributor
timestamp: December 29, 2013, 05:23:46 am
content: Quote from: c4757p on December 29, 2013, 03:20:37 amI never thought about the heat factor in high ESR.Is there normally a thermal dissipation rating for cap's? Kinda like there is for regulators, etc., like a temp rise...ugh...what do they call that... where the temp rises X degrees per watt dissipated, then a person could calculate what kind of volts/current/etc you'd have to pass before you get close to the 85C or 105C (or whatever) rating of the cap...

author: Zero999
author_rank: Super Contributor
timestamp: December 29, 2013, 10:19:38 am
content: The specification you're looking for is ripple current which is the maximum current rating.There's also the dielectric loss which causes heating too but it's more important at higher frequencies.