EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: May 09, 2015, 12:35:29 am
content: Fundamental FridayDave explains why some designs have electrolytic capacitors connected in parallel. The answer is more in-depth than you might think.9 reasons are given and explained, and then some thermal camera fun on the bench.Rubycon capacitor datasheet:http://www.farnell.com/datasheets/1910904.pdfNOTE: Video #741 has been skipped for a reason.https://www.youtube.com/embed/wwANKw36Mjw

author: radioFlash
author_rank: Regular Contributor
timestamp: May 09, 2015, 02:03:47 am
content: Nice video Dave, but there is one quibble: the heat dissipation will be dominated by conduction and convection with air rather than block body emission at these low temperatures.

author: fusebit
author_rank: Contributor
timestamp: May 09, 2015, 02:04:48 am
content: When do we see the video about the LM741?

author: rs20
author_rank: Super Contributor
timestamp: May 09, 2015, 04:27:31 am
content: Great video, I learned a lot! One thing that still irks me is when I see a schematic published/shared that just shows "2x 470uF". If it said, "2x Panasonic 470uF model XYZ", or "1000uF with < 0.1 ohm ESR" then that would be somewhat rational. But otherwise, surely there's a wide range of performance characteristics for both 470uF and 1000uF capacitors -- there must be 1000uF capacitors out there with a way better ESR than 2x some marginal 470uF capacitors. If the original designer looked at what was available in the catalogue and concluded that 2x 470uF was the way to go back in 1973, isn't it likely that what's in the catalogues has changed since then? I'd almost (but not quite) go so far as to say that this is a question of component procurement and selection at the time of production, not something that belongs on a timeless schematic. Stating a max ESR seems like a far better approach.Or am I wrong, is there some sort of universal accurate standard for how much ESR a "decent normal" cap of a given voltage and capacitance has?

author: Barny
author_rank: Frequent Contributor
timestamp: May 09, 2015, 05:41:57 am
content: What happened with the DIY Current sink at the End of the Video?Is the 100mA Current raise to show the temperature diference better or is it drifted away?

author: Refrigerator
author_rank: Super Contributor
timestamp: May 09, 2015, 06:13:44 am
content: Dave you did it again ! Where did 741 go ?

author: Barny
author_rank: Frequent Contributor
timestamp: May 09, 2015, 06:35:15 am
content: Look at his twitter account:https://twitter.com/eevblog/status/596802022814384128He want to show a special video.

author: EEVblog
author_rank: Unknown
timestamp: May 09, 2015, 06:48:04 am
content: Quote from: radioFlash on May 09, 2015, 02:03:47 amShh, don't tell the nerds who are busy trying to calculate it

author: EEVblog
author_rank: Unknown
timestamp: May 09, 2015, 06:48:51 am
content: Quote from: Barny on May 09, 2015, 05:41:57 amOh, I upped them both to 300mA off camera but didn't do anything with that.

author: EEVblog
author_rank: Unknown
timestamp: May 09, 2015, 06:50:48 am
content: Quote from: rs20 on May 09, 2015, 04:27:31 amFor sure, massive differences.You'll see specific brand and models in the DC-DC converter datasheet like the one I showed, but without that you are left to guess why.

author: EEVblog
author_rank: Unknown
timestamp: May 09, 2015, 06:52:37 am
content: Quote from: fusebit on May 09, 2015, 02:04:48 amNo idea. We tried to build something novel but in practice it didn't work. So have to go with a whole new idea.David2 etched a board and everything.

author: errsu
author_rank: Newbie
timestamp: May 09, 2015, 08:33:42 am
content: The datasheet gives longer livetimes for larger diameters. This goes in the opposite direction of the temperature reduction when splitting into multiple capacitors. To know which effect is dominant, the actual dependency of the livetime from temperature would be needed, in numbers. Hmmmm...

author: Towger
author_rank: Super Contributor
timestamp: May 09, 2015, 10:19:54 am
content: Quote from: Refrigerator on May 09, 2015, 06:13:44 amThe same place as 666.

author: rs20
author_rank: Super Contributor
timestamp: May 09, 2015, 12:42:35 pm
content: Quote from: errsu on May 09, 2015, 08:33:42 amAnoften-stated ruleis that electrolytic cap lifetime doubles for every 10 degrees C reduction in temperature. Interestingly, some solid electrolyte capacitorsclaim more than a tripling of lifetime for each 10 degree reduction in temperature, which really stacks up if your capacitor is rated at 105 deg C and you're actually using it at, say, 65 degrees (theoretically, 2000 hour cap at 105 degrees --> 32,000 hour cap at 65 degrees for normal cap, 200,000 hour cap for solid cap).So there you go, have a play with that model. Clearly, which effect is dominant depends on how hot the original single capacitor would get.But thanks for pointing that out, I hadn't considered that all the surface area of all those smaller capacitors actually means more surface area for them to dry out and age (who knows if that's really the underlying cause, but seems like a nice idea in my head). Key point is, using multiple smaller capacitors might be a strongly bad idea in some circumstances if you don't keep lifetimes in check.

author: EEVblog
author_rank: Unknown
timestamp: May 09, 2015, 02:07:40 pm
content: Quote from: rs20 on May 09, 2015, 12:42:35 pmYeah, I should have mentioned that one.On a look at the video again there is a lot of stuff I left out actually.

author: EEVblog
author_rank: Unknown
timestamp: May 09, 2015, 02:11:56 pm
content: Quote from: errsu on May 09, 2015, 08:33:42 amIf lifetime is your goal then you parallel up the best and longest life ones you can get, you wouldn't shoot for the smaller size just because you can.Higher voltage also gives longer life, so rise and repeat your options again and again for each design criteria.Messy business.

author: bktemp
author_rank: Super Contributor
timestamp: May 09, 2015, 02:45:26 pm
content: Quote from: wilfred on May 09, 2015, 02:30:06 pmA follow up would be great. Then you can go a bit more into detail how to calculate/estimate the ripple current and power dissipation inside a capacitor.Buy one of those, load it with the maximum specified current and measure the temperatur to show how not to design a circuit:https://www.eevblog.com/forum/projects/adjustable-buck-voltage-regulator-aliexpress-exiciting-finds/

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 09, 2015, 05:28:57 pm
content: On a related note, there's a similar reason to parallel batteries.

author: dentaku
author_rank: Frequent Contributor
timestamp: May 09, 2015, 08:12:55 pm
content: I love these educational videos.

author: smashIt
author_rank: Contributor
timestamp: May 09, 2015, 08:23:23 pm
content: Quote from: EEVblog on May 09, 2015, 06:48:04 amyou also didn't tell them to use the absolute temperature in kelvinI guess they will be really pissed

author: Tomorokoshi
author_rank: Super Contributor
timestamp: May 09, 2015, 10:01:12 pm
content: In parallel configuration, if the failure mode of one of the capacitors is lower capacitance then we have a nice way of constructing some redundancy into the circuit.What if the failure mode is a short?Can we rely on the increase in individual reliability to outweigh the increased chance in failure now that more parts are in the circuit?I wonder where the cross-over point is?

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: May 10, 2015, 04:20:18 am
content: I find that one big chunk of information about electrolytic caps is missing -Bipolar Capacitors. Where and why you may use them etc. Maybe it is a good subject for another capacitor video?

author: c4757p
author_rank: Super Contributor
timestamp: May 10, 2015, 04:35:38 am
content: Quote from: Tomorokoshi on May 09, 2015, 10:01:12 pmAluminum electrolytics generally do not fail short unless the failure is caused by overvoltage or reverse polarity.

author: bookaboo
author_rank: Frequent Contributor
timestamp: May 10, 2015, 08:39:19 am
content: Quote from: dentaku on May 09, 2015, 08:12:55 pmAgreed

author: VK3DRB
author_rank: Super Contributor
timestamp: May 10, 2015, 12:22:19 pm
content: A useful website for calculating the life out of a capacitor...http://www.illinoiscapacitor.com/tech-center/life-calculators.aspxDave hit the nail on the head over TV capacitors.To cut costs, many CRT TV brand names often used no-name branded capacitors. Typically in the vertical driver stage they were used to block DC, allowing the AC vertical signal to pass only to the vertical output amplifier (they were often 100uF to 470uF in size), and the AC currents (and heat) caused the electrolytic capacitors to dry up. The effect was a reduced vertical image size.Another area where dried caps were commonplace was in medium to low end audio amplifier power supplies. The symptom was a loud mains hum in the audio. In cheap audio amplifiers often found in radios and low end consumer amplifiers, electrolytic capacitors were used to block any DC from the power amplifier output getting into the speaker. Often, these capacitors passing a large AC current into an 8 or 16 ohm speaker would dry up and the effect was lack of bass in the audio. In real bad cases the entire volume would diminish or the sound would be very tinny.

author: VK3DRB
author_rank: Super Contributor
timestamp: May 10, 2015, 12:37:44 pm
content: Dave nicknames 100uF capacitors "100 mike caps". Maybe that is a Sydney term... I have no idea. I don't recall technicians and engineers using that term here in Victoria. Nothing wrong with it of course, because it is clear and not ambiguous.Here, 100uF capacitors are nicknamed "100 muff caps".100pF capacitors are nicknamed "100 puff caps".100nF capacitors are nicknamed "100 nano caps" or "Point one muff caps".

author: Dino KL0S
author_rank: Contributor
timestamp: May 10, 2015, 01:24:22 pm
content: Well, at least here in the U.S. WAY BACK in the day when we still called them "mmF" (micro-micro Farads) they were nicknamed "mickey-mikes"; "puff" remains in use but never heard of "muff" or "Point one muff". Although folks use the term "nano", that in between range never rings true with me and I have to mentally convert up or down since standard values are most often referred to as in terms of uF or pF.

author: station240
author_rank: Unknown
timestamp: May 10, 2015, 01:26:53 pm
content: mike is short for micro, as it's micro-farad.

author: EEVblog
author_rank: Unknown
timestamp: May 10, 2015, 01:37:24 pm
content: Quote from: Dino KL0S on May 10, 2015, 01:24:22 pmSame here, first time I've ever heard it called "muff". Muff means, err, a part of the female anatomySometimes "mu" or simply "you"Likewise nano can get shortened to just "n", like kilo gets simply "k"

author: Votality
author_rank: Contributor
timestamp: May 10, 2015, 01:58:20 pm
content: Quote from: EEVblog on May 10, 2015, 01:37:24 pmHahahah thanks for the laugh Dave .. Being from oz. I agree with your definition of a muff.Also am I paranoid or what or do tv manufacturers seem to stick all the power supply caps above the bulk heat sinks in the lcd's thus nicely warming them and reducing their operational life... Haven't they ever heard of convection.Planned obsolescence?.

author: Fungus
author_rank: Super Contributor
timestamp: May 10, 2015, 02:20:51 pm
content: Quote from: Votality on May 10, 2015, 01:58:20 pmThey call it that in the UK as well.PS: "Puff" can mean bad things in the UK. There's no escape.

author: donkey77
author_rank: Regular Contributor
timestamp: May 10, 2015, 02:54:30 pm
content: Quote from: Stupid Beard on May 09, 2015, 01:11:20 pmI wasn't the only one to notice this then!

author: DanielS
author_rank: Frequent Contributor
timestamp: May 10, 2015, 05:20:32 pm
content: Quote from: VK3DRB on May 10, 2015, 12:22:19 pmNo-name and low-cost Chinese caps are in many modern consumer electronics too. How many people have LCDs and PC power supplies that failed due to Fuhjyyu, SamXon and other Chinese brand capacitor failures or the power supply simply exceeds the capacitors' ripple current rating?

author: Paul Moir
author_rank: Frequent Contributor
timestamp: May 10, 2015, 11:34:23 pm
content: If electrolyte drying is the age failure, I would think that the ratio between the aluminium part of the can to the rubber stopper would have a big impact on lifespan, assuming that gross leaks in the seams aren't the real culprit. I wonder if that doesn't partly drive the trend towards tall narrow packages?

author: DanielS
author_rank: Frequent Contributor
timestamp: May 10, 2015, 11:55:08 pm
content: Quote from: Paul Moir on May 10, 2015, 11:34:23 pmThe "bung" is intended to be permeable to hydrogen so hydrogen gas which may form during heavy load and fail to recombine can percolate through it instead of blowing the casing off the bung or bursting the pressure relief valve which would create a much worse leak and potentially more spectacular failure.As for the tall form factor, I think the main drive for it is lower PCB footprint cost: almost everything inside PSUs is getting smaller except inductors and capacitors. Once your board size is basically dictated by the size of your electrolytic capacitors, the only way to shrink the PCB is to use taller caps. In most PC PSUs I have opened up, the output caps are tightly clustered, packed about as close as their footprint will allow. If the original caps were 8mm diameter, there rarely is enough room to fit 10mm caps. At least not neatly.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: May 11, 2015, 12:45:02 am
content: Thank you very much DanielS. That is very interesting: it explains why more hermetic systems are not used on electrolytic capacitors. I had presumed it was for cost savings since the packaging appeared simpler to make.

author: Votality
author_rank: Contributor
timestamp: May 11, 2015, 12:47:29 am
content: Quote from: DanielS on May 10, 2015, 05:20:32 pmBut not only that why in so many designs are the caps orientated directly above the heatsinks in the convection path.

author: DanielS
author_rank: Frequent Contributor
timestamp: May 11, 2015, 02:18:17 am
content: Quote from: Votality on May 11, 2015, 12:47:29 amThe simplest answers to that would be:1- because that's where the output rectifiers are, especially in flyback converters where you need to minimize stray inductance2- layout constraints (connectors, heatsinks and other mechanical or structural components have predetermined locations on a predetermined board size)3- the final orientation was unknown and could not be taken into consideration for board placement4- it simply makes sense to put them there from a PCB routing flow point of view5- they simply put them where they had spare space6- they simply didn't careI'm sure there are many more possibilities.

author: LabSpokane
author_rank: Super Contributor
timestamp: May 11, 2015, 03:48:35 am
content: http://www.chemi-con.co.jp/e/catalog/pdf/al-e/al-sepa-e/001-guide/al-technote-e-140701.pdfNippon Chemi Con's app note on electrolytic capacitors.Incidentally, one of Chemi Con's aluminum foil factories is located in Moses Lake, Washington about an hour and a half away. I'm hoping I can score a tour some day. (We have the world's lowest power rates here, so we traditionally have had a lot of aluminum plants in the area.)

author: errsu
author_rank: Newbie
timestamp: May 11, 2015, 06:09:57 am
content: Quote from: rs20 on May 09, 2015, 12:42:35 pmInterestingly, this rule is what I remember from school for the general speed of chemical processes.So, in Daves example, the diameter-dependent livetimes are 5000 and 7000 hours. The temperature difference where smaller gets better is then 10*log2(7000/5000)=4.85 K. A little more than in the example, but probably a common case in high-power setups.

author: free_electron
author_rank: Super Contributor
timestamp: May 11, 2015, 02:09:39 pm
content: Quote from: donkey77 on May 10, 2015, 02:54:30 pmcould have been worse ... wwwank ... world wide wa... let's not go there.

author: m100
author_rank: Regular Contributor
timestamp: May 11, 2015, 03:45:18 pm
content: What never ceases to amaze me is the failure rate of cheap no recognisable brand caps in so called quality consumer equipment that clearly runs at relatively low temperatures, supplied by external linear or switch mode power supplies. They seem to degrade to useless in a few years when operated at something not much above UK room temperatures.Despite the drive for lower and lower costs I'd have thought that by now everyone in the business of manufacturing caps would have got some idea how to manufacture something that could withstand life outside the component drawer. It feels like the failure rate now is an order of magnitude or two above what it was in say the early 80's

author: djQUAN
author_rank: Frequent Contributor
timestamp: May 11, 2015, 03:50:31 pm
content: I think it has something to do with engineered obsolescence or whatever it is called.

author: Fungus
author_rank: Super Contributor
timestamp: May 11, 2015, 03:56:51 pm
content: Quote from: errsu on May 11, 2015, 06:09:57 amWe used to call itQ10

author: Len
author_rank: Frequent Contributor
timestamp: May 11, 2015, 04:16:23 pm
content: Quote from: djQUAN on May 11, 2015, 03:50:31 pmI think so too. In the last few years I've had a few devices that failed due to bad electrolytic caps, but they were all past their warranty period. (Some not very far past.) From the manufacturer's point of view, that's proper value engineering. Sigh.

author: tszaboo
author_rank: Super Contributor
timestamp: May 11, 2015, 08:10:20 pm
content: Quote from: rs20 on May 09, 2015, 04:27:31 amBecause that information doesn't belong to the schematic, that is the Bill of Material.One thing which should have been mentioned, is that you cannot just mix capacitors and hope for the best. Meaning if you are using 5 electrolytic for 1000uF, they have to be the same type (unless very carefully investigated) they cannot be like 4x 100uF and 1x 560uF. ESR is different, ripple current is different and so on.Otherwise, excellent reference video.

author: Smokey
author_rank: Super Contributor
timestamp: May 11, 2015, 09:00:25 pm
content: Quote from: EEVblog on May 09, 2015, 06:52:37 amDid you make him hand tape the layout as well? Carve the BOM in stone tablets?

author: rs20
author_rank: Super Contributor
timestamp: May 12, 2015, 02:01:57 am
content: Quote from: NANDBlog on May 11, 2015, 08:10:20 pmWhich one? Do you mean this?:-- Schematic should say "1000uF with < 0.1 ohm ESR"-- BOM should say "2x 470uF"

author: GoldSrc
author_rank: Contributor
timestamp: May 12, 2015, 08:31:43 am
content: Could you eliminate the ripple at almost any load if you use a lot of capacitors in parallel to get close to 1 Farad?

author: rs20
author_rank: Super Contributor
timestamp: May 12, 2015, 09:44:16 am
content: Quote from: GoldSrc on May 12, 2015, 08:31:43 amQ: Could you lift almost any load if you use a lot of cranes teamed up to get close to a total lifting capacity of 1 million tonnes?A: Uh sure, any load up to about a million tonnes.

author: tom66
author_rank: Super Contributor
timestamp: May 12, 2015, 02:56:40 pm
content: Quote from: GoldSrc on May 12, 2015, 08:31:43 am1 farad capacitors generally have high impedance and low voltage ratings. Sure, if you found one that had low impedance (they do exist.)Also note the frequency response of the cap comes into play as well, I would imagine the capacitor would have rather poor response due to high internal inductance.

author: Fungus
author_rank: Super Contributor
timestamp: May 12, 2015, 03:19:21 pm
content: Quote from: tom66 on May 12, 2015, 02:56:40 pmTranslation: They are expensive.Quote from: tom66 on May 12, 2015, 02:56:40 pmYou could parallel it up with other types of capacitor with different frequency responses.

author: SeanB
author_rank: Super Contributor
timestamp: May 12, 2015, 04:02:47 pm
content: 1F low ESR will do horrid things to diodes, imagine the peak current per cycle, only being limited by the very low inductance and resistance of the transformer secondary and the wiring. You would probably be in the region of using a 100A diode just to have the peak handling capacity with a 5A DC load.

author: PA3BNX
author_rank: Regular Contributor
timestamp: May 12, 2015, 07:47:53 pm
content: Hello EveryBody,Nice lecture Dave about Caps.But why didn't you also talked about the leads (copper stripes) from rectiflier to the capsThey have big currents and also big resistor losses hi...The peak currents to caps are much higher then the averaged current withdraw from the caps.

author: GoldSrc
author_rank: Contributor
timestamp: May 13, 2015, 12:52:11 am
content: Quote from: tom66 on May 12, 2015, 02:56:40 pmI guess you could get around that frequency response by using different capacitors.Anyway, thanks for the answers.

author: Emil
author_rank: Regular Contributor
timestamp: May 13, 2015, 08:18:44 am
content: QuoteWhat about caps which are electrically in parallel but are located in different places on a board, for example for decoupling? Since the trace resistance will be in the milli ohms, much less than the ESR of the caps, won't the same apply?

author: rs20
author_rank: Super Contributor
timestamp: May 13, 2015, 10:51:40 am
content: Quote from: Emil on May 13, 2015, 08:18:44 amDecoupling caps are probably spread around the board because of trace inductance, not so much trace resistance. At high frequencies, the inductance will dominate.

author: DanielS
author_rank: Frequent Contributor
timestamp: May 13, 2015, 07:16:25 pm
content: Quote from: SeanB on May 12, 2015, 04:02:47 pmThat depends on the power supply topology.In a flyback design, the diode will not see any more current than the primary current after turn ratio conversion. In a forward converter design, the immediate current change will be limited by the filter inductor. In a current-fed forward converter, current will be limited by the primary-side current-setting inductor. In nearly all topologies, current on the primary or secondary side can be limited on a per-cycle basis so long as the application does not mind the slower voltage ramp rate.

author: eneuro
author_rank: Super Contributor
timestamp: May 29, 2015, 12:08:11 am
content: Watching Flir E8 in action, had a lot of fun when notepads had to be used to see anything on its displayThe first thing I've made in custom SeekThermal software was... interface to set manualy temperature min/max ranges and let operator decide to automatic mode or fixed values, etc

author: jp430bb
author_rank: Contributor
timestamp: September 29, 2015, 03:02:57 am
content: When I came across this board in a scrap bin, EEVblog #742 immediately came to mind. It's a bunch of LT1084 regs and a load of Nichicon caps. It probably doesn't set any records, but it would be interesting to see a board with more electrolytics per unit area.

author: drago
author_rank: Contributor
timestamp: September 29, 2015, 12:31:19 pm
content: Wow. What this was for?

author: jp430bb
author_rank: Contributor
timestamp: September 29, 2015, 11:11:28 pm
content: It is marked Cabletron Systems. I suspect it was part of a networking equipment rack, since there was old fiber-optic communication equipment in the bin nearby.

author: bookaboo
author_rank: Frequent Contributor
timestamp: September 30, 2015, 11:30:12 am
content: Quote from: eneuro on May 29, 2015, 12:08:11 amThe Flir has this as standard with no messing about, would have been better if Dave had manually set the span to minimum.Adding the cheap external lens hack (see E4 thread) make the Ex range incredible for PCB work, I've seen a modified E4 (with lens) side by side with a Flir E60 and Fluke Ti32 and if anything the E4 was better.

author: crispy_tofu
author_rank: Super Contributor
timestamp: September 30, 2015, 11:43:24 am
content: That is a LOT of caps!

author: CamBeezie
author_rank: Newbie
timestamp: February 29, 2016, 04:01:49 pm
content: Just watched this video. Good stuff! Got a question though that maybe somebody can help me with. When Dave first measured the voltage across the caps with the oscilloscope after applying the 200mA loads he says he's measuring the ripple current (Around 28:20) when obviously he means voltage (he corrects himself later), but then goes on to say that the two circuits have the same ripple current, when what we are actually seeing is that they have the same ripple voltage.Ripple voltage is ripple current multiplied by total ESR, so couldn't the two circuits have had different ripple currents but the same ripple voltages if the ESR's were also different? For instance the ripple current of the 10 10uF parallel caps could have been half that of the single 100uF cap, but if that circuit had twice the total ESR it would produce the same magnitude of output ripple voltage. I checked the datasheet Dave linked but it doesn't give the ESR's of the caps.(5 minutes later)Looking at it again, the ripple voltage Dave displays is a result of I = C*dV/dT capacitive discharge. ESR would have negligible impact at 200mA unless ESR's were up in the ohms range.

author: iXod
author_rank: Frequent Contributor
timestamp: March 02, 2016, 04:07:44 pm
content: Quote from: rs20 on May 09, 2015, 04:27:31 amOr, possibly, back then 2 x 470uF was cheaper than one high-spec 1000uF cap.