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Old 18th Feb 2016, 7:01 pm   #1
WaveyDipole
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Default Tiny electrolytics

I recently needed to recap a PSU. In addition to a number of caps of higher value, there were a couple of smaller electolytics (10uF and 2.2uF) that I figured on replacing at the same time. I had the correct values to hand but decided to replace them with 105deg types so when I placed my order with Farnell on Monday, I added these to the list, opting for Rubycon branded caps.

What I received was something of a suprise because whereas I am aware of the minature types used on SMD boards, I have never seen through the hole electrolytics this small other than Tantalums! There is no suggestion in the description that these might be 'minature' packages. The picture below illustrates. The two types are standing on opposite sides of a penny. The 2 'standard' caps are on the left and the two new Rubycon ones on the right. Capacitance rating is the same, but the 10uF Rubycon is rated 25v whereas the other one is rated at 50v. Both 2.2uF caps are rated at 50v.

The voltage rating is equal or exceeds the rating of the original caps so should be more than adequate, yet I am still hesistamt to use thse in the PSU!
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Old 18th Feb 2016, 7:49 pm   #2
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Default Re: Tiny electrolytics

All components are getting smaller, this is due to better manufacturing methods which are in due course pushed to make them cheaper by using less materials. They are probably better than the bigger ones. I am amazed that they can fit more than one million ohms into a resistor 10 x 20 thou (0.25 x 0.5 mm).
 
Old 18th Feb 2016, 7:53 pm   #3
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Default Re: Tiny electrolytics

Small is not automatically bad: in the case of electrolytics when used in switched-mode supplies being small can reduce inductive effects previously suffered by old 'spiral wound' electrolytics and give you a lower-ESR capacitor in a conveniently-smaller space.
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Old 18th Feb 2016, 8:17 pm   #4
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Default Re: Tiny electrolytics

those on the left are Nover, I see alot of them going high ESR in allsorts of things.

In my day job I automatically suspect any of those mini capacitors when I see them in power supplies, they seem to fail prematurely IMHO. Sometimes the specs for max temperature are time-constrained or for intermittent operation.
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Old 18th Feb 2016, 9:40 pm   #5
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Default Re: Tiny electrolytics

I sometimes find myself doing something of a double-take at this sort of thing, too- but I trust in names like Rubycon and, despite advancing years, I still have a degree of trust in genuine progress. I put it down to incremental improvement- I don't know if there's a Moore's law equivalent for electrolytic capacitors but comparing, say, a late '30s cathode decoupler of perhaps 50uF 25V with its modern counterpart is quite an eye-opener.

With things like mid-life SMPSUs, there's not much extra expense in "do the lot" while it's on the bench- and you might just keep your reputation!
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Old 19th Feb 2016, 4:15 am   #6
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Default Re: Tiny electrolytics

Please note that the allowed ripple current may be lower and the ESR higher for smaller capacitors. Double check this in any application that might be relying on this for a long capacitor life.
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Old 19th Feb 2016, 7:14 am   #7
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Default Re: Tiny electrolytics

hhmm Without upsetting Maarten, I would suggest that the Rubycons will be lower ESR and higher ripple.

Please bring back capacitors that you could feel in your pocket on the way home!!
Like five pennies in real copper

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Old 19th Feb 2016, 9:09 am   #8
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Default Re: Tiny electrolytics

I have used some micro electrolytics from LED lamps in power supplies and they have been fine. Don't know what make.
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Old 19th Feb 2016, 10:19 am   #9
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Default Re: Tiny electrolytics

In electrolytic capacitors, the dielectric constant of aluminium oxide is a given, and so is the breakdown voltage for a given oxide thickness.

What can be improved is the conductivity of the liquid component, leading to lower ESR.

What can also be improved is the surface texture of the aluminium foil leading to greater surface area for a given amount of foil. So capacitors get smaller for the same energy capacity (half*C*Vsquared) The liquid component has to be wetting and mobile enough to fill voids.

What can also be improved is the number of taped brought out from the rolled foils to the terminals, reducing ESL

What can also be improved is the quality of sealing, leading to slower loss of the water content of the liquid.

I think they've been making steady progress on all of these fronts., but the properties of aluminium oxide remain.

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Old 19th Feb 2016, 10:31 am   #10
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Default Re: Tiny electrolytics

Ok, I put my hand up. These Rubycon ones ARE described as 'miniature', a fact that I managed to miss twice! The ESR is not stated. Ripple current is 18mA. I opted for these because of the reputation of Rubycon and their stated lifetime was the longest - 3000hrs. I might otherwise have opted for Panasonics (2000hrs). I'm not so sure I trust the cheaper Multicomp but am curious about members experiences of those?. The PSU in question is the Thurlby PL320 I recently purchased, not SM but linear so I guess the ESR is not so critical.

The Nover caps were leftover from a purchase I made over 18 months ago for hobby projects. They were rather cheap and I'm not convinced of their quality - a suspicion apparently supported by the comment above - which is why I did not want to use them for any serious application. I would like the PSU repair to last...

I take the point that small is not necessarily bad and given the reputation of the Rubycon brand these will probably serve well, but I just wanted to check whether there would be any obvious drawbacks. The detailed analysis of the possible manufacturing improvements is also interesting.

Thanks for all the comments. Much appreciated.

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Old 19th Feb 2016, 10:32 am   #11
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Default Re: Tiny electrolytics

The interesting unknown and unspecified parameter is just how well very small capacitors will cope with extreme age.

Left unused for a few years there is bound to be a little reformation required. Their small size suggests there may not be much electrolyte to spare as if not tightly controlled you loose a bit of electrolyte on reforming.
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Old 19th Feb 2016, 11:38 am   #12
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Default Re: Tiny electrolytics

GMB, that's an interesting thought and I guess only time will tell.

Incidentally, has anyone come across these yet?

http://uk.farnell.com/webapp/wcs/sto...=128%20SAL-RPM

The largest (at least at Farnell) appears to be 68uF, but although these look like Tantalums, they are actually aluminium electrolytics. The voltage drops with increasing capacity - I guess that is the trade-off to keep the package size compact, but are rated for 125deg and appear to have extermely long life spans (20,000hrs). A bit pricey though!

I came across these while searching for ordinary electolytics but again, have not seen them before.
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Old 19th Feb 2016, 1:17 pm   #13
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Default Re: Tiny electrolytics

Quote:
Originally Posted by Maarten View Post
Please note that the allowed ripple current may be lower and the ESR higher for smaller capacitors.
ESR depends on several factors, largely value and voltage rating. This is a chart showing typical benchmark values.
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Old 19th Feb 2016, 3:24 pm   #14
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Default Re: Tiny electrolytics

Quote:
Originally Posted by WaveyDipole View Post
Incidentally, has anyone come across these yet?
They do look interesting, solid electrolyte, and reverse DC and AC allowed...
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Old 19th Feb 2016, 4:35 pm   #15
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Default Re: Tiny electrolytics

I guess it's fair to say nobody will be restuffing those Rubycon miniature ones in 60 years time Although who knows - maybe some new type of capacitor technology will come along...
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Old 19th Feb 2016, 8:11 pm   #16
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Default Re: Tiny electrolytics

re the Vishay capacitors mentioned in #12, it is interesting to read, under the heading "Mounting" on page 1 of the data sheet that you can download via the linked page, the following:

"Completely sealing the component’s body or use in an oxygen-free environment has a negative impact on useful life."

I don't suppose this would be a problem in domestic equipment, which, unlike some of the radio equipment I remember from my days at Plessey, is not normally hermetically sealed. It might be something to consider if using them to re-stuff old electrolytics.

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Old 20th Feb 2016, 11:44 pm   #17
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Default Re: Tiny electrolytics

Quote:
Originally Posted by WaveyDipole View Post
Incidentally, has anyone come across these yet?
Early solid state capacitors, appeared at least 30 years ago in the Philips catalogues so the fact that they are still on the market after take over by Vishay and rationalisation of the product portfolio says something about their quality.

Quote:
Originally Posted by AC/HL View Post
ESR depends on several factors, largely value and voltage rating. This is a chart showing typical benchmark values.
That chart was probably taken from the Bob Parker meter, which I own and use as well. I have found the chart to be at most semi useful.

Interestingly, working voltage and capacitance seem to only have an indirect correlation to impedance. The first rough indication is the series (other etching and electrolyte is used depending on working voltage range, impedance range, temperature, etc.). Within a series, can size is what matters most (in Panasonic datasheets for low impedance capacitors there is an actual table for impedance versus can size). Of course, can size is indeed determined by working voltage and capacity.

Last edited by Maarten; 20th Feb 2016 at 11:54 pm.
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Old 21st Feb 2016, 12:40 am   #18
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Default Re: Tiny electrolytics

Quote:
Originally Posted by WaveyDipole View Post
Incidentally, has anyone come across these yet?
New to me. However, I have been given a few bags of 0.47, 1, 2.2, 3.3 and 4.7 uf miniature film capacitors of various brands (mostly, WIMA MKS2 and Roederstein MKT1826). They all have 5mm between the leads and often fit perfectly in place of electrolytic caps of those values. So far they seem to work well as replacements in every place I'm used them. They claim to last a very long time (200,000-300,000 hours), have high voltage and temperature ratings, and aren't hugely expensive.
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