Author Topic: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel  (Read 28367 times)

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Offline EEVblog

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Fundamental Friday
Dave 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.pdf
NOTE: Video #741 has been skipped for a reason.

https://www.youtube.com/embed/wwANKw36Mjw
« Last Edit: May 09, 2015, 12:38:45 am by EEVblog »
 

Offline radioFlash

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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.
 

Offline fusebit

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When do we see the video about the LM741? :-+

 

Offline rs20

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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?
« Last Edit: May 09, 2015, 04:35:54 am by rs20 »
 

Offline Barny

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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?
 

Offline Refrigerator

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Dave you did it again ! Where did 741 go ?
Just started a blog at http://brimmingideas.blogspot.com/ . Not much in it as of now but more is sure to come :)
 

Offline Barny

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Look at his twitter account:
https://twitter.com/eevblog/status/596802022814384128

He want to show a special video.
 

Offline EEVblog

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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.

Shh, don't tell the nerds who are busy trying to calculate it  ;D
 

Offline EEVblog

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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?

Oh, I upped them both to 300mA off camera but didn't do anything with that.
 

Offline EEVblog

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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

For 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.
 

Offline EEVblog

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #10 on: May 09, 2015, 06:52:37 am »
When do we see the video about the LM741? :-+

No 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.
 

Offline errsu

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #11 on: May 09, 2015, 08:33:42 am »
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...

[rsu]
 

Offline Towger

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #12 on: May 09, 2015, 10:19:54 am »
Dave you did it again ! Where did 741 go ?

The same place as 666.
 

Offline rs20

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #13 on: May 09, 2015, 12:42:35 pm »
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...
An often-stated rule is that electrolytic cap lifetime doubles for every 10 degrees C reduction in temperature. Interestingly, some solid electrolyte capacitors claim 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.
« Last Edit: May 09, 2015, 12:45:37 pm by rs20 »
 

Offline Stupid Beard

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #14 on: May 09, 2015, 01:11:20 pm »


:-DD
 

Offline EEVblog

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #15 on: May 09, 2015, 02:07:40 pm »
An often-stated rule is that electrolytic cap lifetime doubles for every 10 degrees C reduction in temperature.

Yeah, I should have mentioned that one.
On a look at the video again there is a lot of stuff I left out actually.
 

Offline EEVblog

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #16 on: May 09, 2015, 02:11:56 pm »
The datasheet gives longer livetimes for larger diameters. This goes in the opposite direction of the temperature reduction when splitting into multiple capacitors.

If 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.
 

Offline bktemp

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #17 on: May 09, 2015, 02:45:26 pm »
An often-stated rule is that electrolytic cap lifetime doubles for every 10 degrees C reduction in temperature.

Yeah, I should have mentioned that one.
On a look at the video again there is a lot of stuff I left out actually.

Do a follow up.
A 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/
 

Offline NiHaoMike

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #18 on: May 09, 2015, 05:28:57 pm »
On a related note, there's a similar reason to parallel batteries.
« Last Edit: May 09, 2015, 05:30:55 pm by NiHaoMike »
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Offline dentaku

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #19 on: May 09, 2015, 08:12:55 pm »
I love these educational videos. :-+
 

Offline smashIt

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #20 on: May 09, 2015, 08:23:23 pm »
Shh, don't tell the nerds who are busy trying to calculate it  ;D

you also didn't tell them to use the absolute temperature in kelvin
I guess they will be really pissed :D
 

Offline Tomorokoshi

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #21 on: May 09, 2015, 10:01:12 pm »
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?
 

Offline Alexei.Polkhanov

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #22 on: May 10, 2015, 04:20:18 am »
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?
 

Offline c4757p

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #23 on: May 10, 2015, 04:35:38 am »
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?

Aluminum electrolytics generally do not fail short unless the failure is caused by overvoltage or reverse polarity.
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Offline bookaboo

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #24 on: May 10, 2015, 08:39:19 am »
I love these educational videos. :-+

Agreed
 

Offline VK3DRB

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #25 on: May 10, 2015, 12:22:19 pm »
A useful website for calculating the life out of a capacitor... http://www.illinoiscapacitor.com/tech-center/life-calculators.aspx

Dave 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.
 

Offline VK3DRB

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #26 on: May 10, 2015, 12:37:44 pm »
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".


 

Offline Dino KL0S

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #27 on: May 10, 2015, 01:24:22 pm »
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.
 

Offline station240

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #28 on: May 10, 2015, 01:26:53 pm »
mike is short for micro, as it's micro-farad.
 

Offline EEVblog

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #29 on: May 10, 2015, 01:37:24 pm »
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".

Same here, first time I've ever heard it called "muff". Muff means, err, a part of the female anatomy  ;D
Sometimes "mu" or simply "you"
Likewise nano can get shortened to just "n", like kilo gets simply "k"
 

Offline Votality

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EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #30 on: May 10, 2015, 01:58:20 pm »
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".

Same here, first time I've ever heard it called "muff". Muff means, err, a part of the female anatomy  ;D
Sometimes "mu" or simply "you"
Likewise nano can get shortened to just "n", like kilo gets simply "k"

Hahahah 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?.
« Last Edit: May 10, 2015, 02:22:43 pm by Votality »
 

Offline Fungus

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #31 on: May 10, 2015, 02:20:51 pm »
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".

Same here, first time I've ever heard it called "muff". Muff means, err, a part of the female anatomy  ;D
Sometimes "mu" or simply "you"
Likewise nano can get shortened to just "n", like kilo gets simply "k"

Hahahah thanks for the laugh Dave .. Being from oz. I agree with your definition of a muff.

They call it that in the UK as well.

PS: "Puff" can mean bad things in the UK. There's no escape.

 

Offline donkey77

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #32 on: May 10, 2015, 02:54:30 pm »


:-DD

I wasn't the only one to notice this then!
 

Offline DanielS

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #33 on: May 10, 2015, 05:20:32 pm »
Dave hit the nail on the head over TV capacitors.

To cut costs, many CRT TV brand names often used no-name branded capacitors.
No-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?
 

Offline Paul Moir

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #34 on: May 10, 2015, 11:34:23 pm »
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?

 

Offline DanielS

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #35 on: May 10, 2015, 11:55:08 pm »
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?
The "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.
 

Offline Paul Moir

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #36 on: May 11, 2015, 12:45:02 am »
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.

 

Offline Votality

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #37 on: May 11, 2015, 12:47:29 am »

Dave hit the nail on the head over TV capacitors.

To cut costs, many CRT TV brand names often used no-name branded capacitors.
No-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?

But not only that why in so many designs are the caps orientated directly above the heatsinks in the convection path.
 

Offline DanielS

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #38 on: May 11, 2015, 02:18:17 am »
But not only that why in so many designs are the caps orientated directly above the heatsinks in the convection path.
The 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 inductance
2- 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 placement
4- it simply makes sense to put them there from a PCB routing flow point of view
5- they simply put them where they had spare space
6- they simply didn't care

I'm sure there are many more possibilities.
 

Offline LabSpokane

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #39 on: May 11, 2015, 03:48:35 am »
http://www.chemi-con.co.jp/e/catalog/pdf/al-e/al-sepa-e/001-guide/al-technote-e-140701.pdf

Nippon 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.)
 

Offline errsu

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #40 on: May 11, 2015, 06:09:57 am »
An often-stated rule is that electrolytic cap lifetime doubles for every 10 degrees C reduction in temperature.

Interestingly, 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.

[rsu]
 

Offline free_electron

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #41 on: May 11, 2015, 02:09:39 pm »


:-DD

I wasn't the only one to notice this then!
could have been worse ... wwwank ... world wide wa... let's not go there.
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Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 

Offline m100

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #42 on: May 11, 2015, 03:45:18 pm »
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
 

Offline djQUAN

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #43 on: May 11, 2015, 03:50:31 pm »
I think it has something to do with engineered obsolescence or whatever it is called. :-//
 

Offline Fungus

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #44 on: May 11, 2015, 03:56:51 pm »
An often-stated rule is that electrolytic cap lifetime doubles for every 10 degrees C reduction in temperature.
Interestingly, this rule is what I remember from school for the general speed of chemical processes.

We used to call it Q10
 

Offline Len

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #45 on: May 11, 2015, 04:16:23 pm »
I think it has something to do with engineered obsolescence or whatever it is called. :-//

I 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.
 

Offline NANDBlog

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #46 on: May 11, 2015, 08:10:20 pm »
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.
Because 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.
 

Offline Smokey

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #47 on: May 11, 2015, 09:00:25 pm »
...
David2 etched a board and everything.

Did you make him hand tape the layout as well?  Carve the BOM in stone tablets? 

:)
 

Offline rs20

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #48 on: May 12, 2015, 02:01:57 am »
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.
Because that information doesn't belong to the schematic, that is the Bill of Material.

Which one? Do you mean this?:
-- Schematic should say "1000uF with < 0.1 ohm ESR"
-- BOM should say "2x 470uF"
 

Offline GoldSrc

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #49 on: May 12, 2015, 08:31:43 am »
Could you eliminate the ripple at almost any load if you use a lot of capacitors in parallel to get close to 1 Farad?
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Offline rs20

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #50 on: May 12, 2015, 09:44:16 am »
Could you eliminate the ripple at almost any load if you use a lot of capacitors in parallel to get close to 1 Farad?

Q: 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.
 

Offline tom66

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #51 on: May 12, 2015, 02:56:40 pm »
Could you eliminate the ripple at almost any load if you use a lot of capacitors in parallel to get close to 1 Farad?

1 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.
 

Offline Fungus

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #52 on: May 12, 2015, 03:19:21 pm »
Could you eliminate the ripple at almost any load if you use a lot of capacitors in parallel to get close to 1 Farad?

1 farad capacitors generally have high impedance and low voltage ratings. Sure, if you found one that had low impedance (they do exist.)

Translation: They are expensive.

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.

You could parallel it up with other types of capacitor with different frequency responses.

 

Online SeanB

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #53 on: May 12, 2015, 04:02:47 pm »
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.
 

Offline PA3BNX

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #54 on: May 12, 2015, 07:47:53 pm »
Hello EveryBody,

Nice lecture Dave about Caps.

But why didn't you also talked about the leads (copper stripes) from rectiflier to the caps

They 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.





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Offline GoldSrc

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #55 on: May 13, 2015, 12:52:11 am »
Could you eliminate the ripple at almost any load if you use a lot of capacitors in parallel to get close to 1 Farad?

1 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.

I guess you could get around that frequency response by using different capacitors.
Anyway, thanks for the answers.
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Offline Emil

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #56 on: May 13, 2015, 08:18:44 am »
Quote
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.

What 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?
« Last Edit: May 13, 2015, 08:26:26 am by Emil »
 

Offline rs20

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #57 on: May 13, 2015, 10:51:40 am »
What 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?

Decoupling caps are probably spread around the board because of trace inductance, not so much trace resistance. At high frequencies, the inductance will dominate.
 

Offline DanielS

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #58 on: May 13, 2015, 07:16:25 pm »
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.
That 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.
 

Offline eneuro

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #59 on: May 29, 2015, 12:08:11 am »
Watching Flir E8 in action, had a lot of fun when notepads had to be used to see anything on its display  :-DD



The 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  :popcorn:
12oV4dWZCAia7vXBzQzBF9wAt1U3JWZkpk
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Offline jp430bb

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #60 on: September 29, 2015, 03:02:57 am »
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. 
 

Offline drago

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #61 on: September 29, 2015, 12:31:19 pm »
Wow. What this was for?
 

Offline jp430bb

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #62 on: September 29, 2015, 11:11:28 pm »
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. 
 

Offline bookaboo

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #63 on: September 30, 2015, 11:30:12 am »
Watching Flir E8 in action, had a lot of fun when notepads had to be used to see anything on its display  :-DD

The 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  :popcorn:

The 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.
 

Offline crispy_tofu

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #64 on: September 30, 2015, 11:43:24 am »
That is a LOT of caps!  :wtf:
 

Offline CamBeezie

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #65 on: February 29, 2016, 04:01:49 pm »
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. 
 

Offline iXod

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Re: EEVblog #742 - Why Electrolytic Capacitors Are Connected In Parallel
« Reply #66 on: March 02, 2016, 04:07:44 pm »
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?

Or, possibly, back then 2 x 470uF was cheaper than one high-spec 1000uF cap.
 


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