EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: TheRuler8510 on April 26, 2014, 04:34:29 pm
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Capacitor Experts: Please Explain this Disconnect...Axial vs. Radial Electrolytic
Sources are datasheets on Digikey, and my own measurements.
Disconnect #1: As a general rule, axials seem to have much higher ESR/Impedance compared to radial, and lower ripple current capability. Why is that?
Disconnect #2: I measure significantly lower ESR than what the datasheet says. Example is Vishay 22uF MAL202138229E3, measures at 0.8 ohms, compared to datasheet at 5.8 ohms. WTF?
Disconnect #3: There a large price difference; radial is much cheaper. You would otherwise think there were two massively different technologies being compared.
Is it because Axials are dying out? It seems to me, it would be just as easy to manufacture an axial compared to a radial...what am I missing?
Regards,
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Axial are older components design wise, and the higher ESR is from the construction with a long metal tab being used to connect the one foil to the bottom of the can, this being folded in during assembly. As well with the older design the ripple current rating is lower, as the paper used is thicker and the electrolytes are slightly different.
As to ESR this is a maximum value, they generally will only reach this at around end of life, so are much lower when new.
As to price, radial is a more commonly used part, and thus is a larger volume produced with a corresponding lower unit cost for plant and machinery overhead. As well axial are small volume, and are likely stock that is quite old, or is produced in older process plant that has a much higher hand assembly in the production, or which has older machinery that needs more maintenance with spare parts that are getting expensive to buy or make.
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I agree with SeanB with the exception of why axial construction yields higher ESR. There were old axial capacitor series which *did* have low ESR and high ripple current capability, the Sprague 30D series comes to mind, but they were not advertised that way because the applications which would take advantage of that, switching regulators, were not as common back then.
It is easy for machine insertion to handle radial capacitors. Axial capacitors are much more difficult.
My solution when replacing these parts, they wear out with age also, is to use a radial capacitor that will physically fit and bend one lead around.
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Radials seem to be where the R&D efforts go, in fact it seems like the manufacturers would like axials to just disappear. Look at your choices in radials- low esr, low leakage, super miniature and 37 other types. Now look at your choices in axial- general purpose.
Measuring esr to match a data sheet is difficult if you can't duplicate the conditions exactly, and the typical hand-held esr meter probably won't give the right answer. Everybody today wants to talk about esr, but traditionally the number was only of interest to switching supply designers. Dissipation factor is easier to measure accurately with bridge or phase techniques and more useful, once you understand how to use it.
IMO, data sheet maximums don't have much to do with typical parts. Most parts were far better, but today I see some that crowd the limits. Oddly, some very long life parts (for LED lighting applications) have surprisingly high dissipation factor, and some low esr parts have surprisingly high DC leakage currents. My guess is parameters are a trade-off and you have to pick what's important at the expense of what isn't.
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Yeah, I would second (third?) age and various aspects of manufacturing.
If you need a low profile, you can always toss in more radials, or find "squat" aspect ratios.
Tim
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Had a scrap axial today so took it apart. Easy to see the long negative tab, and the issue of this being the one lead.
1000uF 63V 85C REC branded cap.
(https://www.eevblog.com/forum/projects/capacitor-experts-please-explain-this-disconnect-axial-vs-radial-electrolyti/?action=dlattach;attach=91313;image)