Why aren't dry electrolytic caps made anymore? - Page 1
Forum section: electronics / projects

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: August 08, 2022, 01:56:08 pm
content: The dry electrolytics seem the be one of very few caps that usually are still fine after ~60+ years, so why are they not used anymore?

author: rooppoorali
author_rank: Regular Contributor
timestamp: August 08, 2022, 02:17:19 pm
content: I'm not sure, sorry. Are you looking for these or anything else?https://www.indiamart.com/proddetail/capacitors-24377081748.html

author: strawberry
author_rank: Super Contributor
timestamp: August 08, 2022, 04:51:46 pm
content: Quote from: rooppoorali on August 08, 2022, 02:17:19 pmAluminium Electrolytic Ceramic ?

author: JohanH
author_rank: Frequent Contributor
timestamp: August 08, 2022, 05:22:21 pm
content: Some old aluminium electrolytic capacitors did have a gel-like electrolyte with low water content and were called "dry" capacitors. Seehttps://en.wikipedia.org/wiki/Electrolytic_capacitor#%22Dry%22_aluminum_capacitorOn the other hand, a modern polymer aluminium electrolytic capacitor has a solid-state electrolyte (a solid-state electrolyte is chemically a thing). That could be called a modern dry electrolytic capacitor. Now when these are available, there is no reason to use any old stuff, because they have extremely long service life (over 50 years claimed).

author: wraper
author_rank: Unknown
timestamp: August 08, 2022, 07:12:20 pm
content: Why do you need that obsolete garbage to begin with?

author: wraper
author_rank: Unknown
timestamp: August 08, 2022, 07:33:05 pm
content: Probably more than half a century passed since they were made. So assuming they will be more reliable than modern parts is wishful thinking. "Dry" capacitors on alibaba are just film caps.

author: jpanhalt
author_rank: Super Contributor
timestamp: August 08, 2022, 08:09:48 pm
content: Don't the most common tantalum capacitors ("solid") use a dry electrolyte?Source:https://www.vishay.com/docs/40058/ldtintro.pdfQuote

author: uer166
author_rank: Super Contributor
timestamp: August 08, 2022, 08:58:34 pm
content: Quote from: ELS122 on August 08, 2022, 07:24:04 pmYour post doesn't make any sense. Just because some of those caps survived doesn't mean they're more reliable than modern options (survivor bias), and they will certainly not have any better performance/size/cost.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 08, 2022, 10:04:42 pm
content: They're all "dry"... they dropped the specifier when "wet" (read: sloshy liquid in a can) types were obsoleted. About a century ago.There are "wet" and "dry" tantalums, if you like; but that's not very useful for the things you've been working with.Tim

author: CaptDon
author_rank: Super Contributor
timestamp: August 09, 2022, 12:36:17 am
content: With a good capacitor analyzer and looking at several parameters I can't say any of the 'dry' capacitors still meet any kind of good quality spec after 60 years. High ESR, high leakage, 'twitching' the leakage current meter when tested at near original rated voltage. If I were rebuilding an old table radio with those filter cans marked 'dry electrolytic' they would be getting gutted and a modern replacement cap hidden inside!!

author: abquke
author_rank: Regular Contributor
timestamp: August 09, 2022, 12:49:17 am
content: Why drive a car? Horses were in use for thousands of years.

author: Colt45
author_rank: Contributor
timestamp: August 09, 2022, 01:04:21 am
content: Yeah, "dry" as in the same sense of 'dry cell', which still has electrolyte.

author: TheMG
author_rank: Frequent Contributor
timestamp: August 09, 2022, 01:59:45 am
content: Quote from: ELS122 on August 09, 2022, 12:32:59 amElectronics from 50-60 years ago were a lot more forgiving than modern electronics. Switching power supplies/regulators weren't even really a thing back then. SMPS depend on low ESR for proper operation and the high switching frequencies and currents place a heck of a lot more stress on the capacitors than linear regulators that were common 50 years ago.Take those 50-60 year old capacitors and press them into service in a modern SMPS, see how long it lasts (prediction: not very long).As for tantalum capacitors, there were a few types over the years that were more prone to failure, but the vast majority are actually extremely reliable parts when one takes care not to stress them beyond their ratings (less forgiving than other capacitors in terms of voltage transients and such). I know of a lot of hardware with SMD style tantalum caps still going strong with no tantalum cap-related failures in over 2 decades. There are also "Tantalex" style "solid" electrolyte tantalum caps still in 24/7 service for 30+ years with no problems at all still within spec!Sure, there are some low-grade electrolytic capacitors that are not very reliable, and electronics (mostly consumer electronics) manufacturers that stress the parts to their absolute limits in order to cut costs and this leads to short life of the capacitors in the product, but this does not mean modern aluminum electrolytic capacitors aren't good. A good quality brand, and choosing the right capacitor for the job, careful design of the circuit and overall product (such as adequate cooling), modern caps can last a very long time indeed.

author: ejeffrey
author_rank: Super Contributor
timestamp: August 09, 2022, 02:32:24 am
content: Quote from: ELS122 on August 09, 2022, 12:32:59 amGood quality electrolytic capacitors that are rated appropriately easily last longer than 10 years.

author: JohanH
author_rank: Frequent Contributor
timestamp: August 09, 2022, 07:31:24 am
content: Quote from: ELS122 on August 08, 2022, 07:11:08 pmPolymer caps don't go high in voltage, at least yet, or they become really expensive (it's the latest capacitor tech after all).If you need high voltage, use modern common electrolytics, or for one-off projects where space and cost doesn't matter, film caps such as polypropylene (or cheaper polyester/PET). Film caps will last an eternity.

author: JohanH
author_rank: Frequent Contributor
timestamp: August 09, 2022, 07:54:59 am
content: If you have to use tantalums, consider polymer tantalums (which are dry or solid-state). Alongside polymer aluminium electrolytic, they are also the latest tech with best specs of any tantalum or aluminium variant (long life, low ESR, wide stable impedance range, best temp characteristics etc.). Best of all, they only need about 10-20% voltage de-rating (much better than traditional tantalums). These are almost exclusively SMD for now. If you need through hole with almost as good specs, use polymer aluminium electrolytic.

author: Miyuki
author_rank: Frequent Contributor
timestamp: August 09, 2022, 10:15:21 am
content: Quote from: TheMG on August 09, 2022, 01:59:45 amThere are two things, old electrolytic caps (from the 70s and 80s) are about 5 to 10 times bigger than today with the same capacity. This with use in linear design with really low ripple makes them live a really low-stress life. And have plenty of electrolyte to spare, might be even designed this way.Another thing is in cheap consumer designs capacitors are commonly stressed way over maximum ratings yet still holding few years.But you can get modern electrolytic capacitors with like 20k hours rated life at full temperature, but they are not cheap. This gives you like 600k hours/68 Years of running life at 50°C (as they tell in the datasheet) even with full ripple. In linear design, it will last almost forever.It is just about what quality/price you target

author: Bassman59
author_rank: Super Contributor
timestamp: August 09, 2022, 04:52:59 pm
content: Quote from: ELS122 on August 09, 2022, 12:32:59 am"perform fine?" What were the tolerances on those ancient cap? +80%/-20% or something equally vague? And what are the values now? How much have they drifted beyond even those original crappy specs?The only time "modern' parts start to see problems after just ten years is when they were incorrectly specified for the environment and the use case. That's generally just the accountants getting ahold of the BOM and demanding cheaper parts.