What kind of capacitor is this - Page 1
Forum section: electronics / beginners

author: giosif
author_rank: Frequent Contributor
timestamp: March 17, 2020, 11:28:15 pm
content: Hi,Could someone please help me understand what type of capacitor this is (if indeed a capacitor)?It's first time I encounter such format and I'm wondering if there is anything particular to it.Thanks!

author: wizard69
author_rank: Super Contributor
timestamp: March 18, 2020, 05:17:49 am
content: The first thing I thought of was battery holder even though it obviously isn't. I'm almost thinking a sealed crystal.

author: golden_labels
author_rank: Super Contributor
timestamp: March 18, 2020, 05:54:46 am
content: A power diode or possibly some kind of a thyristor (it has three pins, though one seems to be unconnected in this device)?

author: floobydust
author_rank: Super Contributor
timestamp: March 18, 2020, 06:04:37 am
content: It's a button-style capacitor, wet tantalum 220uF 50V used in military applications. These are good for -55°C to +125°C. SeeVishay CA2 seriesbut this one is likely made by Arcotronics.I'd consider solid polymer to replace it in SMPS use. The board likely needed a low ESR part and maybe went nuts putting this one in?It's not super reliableNASA Reliability of New Wet Tantalums

author: Zero999
author_rank: Super Contributor
timestamp: March 18, 2020, 09:11:50 am
content: Yes, it's a wet tantalum capacitor. I've seen one before and probably have one tucked away somewhere.

author: Gyro
author_rank: Super Contributor
timestamp: March 18, 2020, 09:29:36 am
content: Quote from: floobydust on March 18, 2020, 06:04:37 amI've certainly seen leakage of old Arctronic CA2 series wet Tants in storage before now, accompanied by very high esr. Granted, they were old, but unused - the smell in the drawer in the garage was 'unpleasantdistinctive'. The CA2 caps are pressure crimped plastic (polythene?) seals, like button cells, rather than the hermetic glass-metal seals of the axial types. Personally, I've never had one of those leak physically or electrically.P.S. Without knowing more about the board it's hard to know why they would have used it, but judging from the 1973 vintage commercial spec W005 bridge rectifier next to it, maybe somebody had one lying around and bodged it on at some time (it certainly looks bodged).

author: giosif
author_rank: Frequent Contributor
timestamp: March 18, 2020, 09:54:41 pm
content: Thank you, all!This cap is in the power supply section of a Micromaster LV48 programmer I'm trying to bring back to life.The power brick connecting to the mains provides around 17 VAC into this board, which is then rectified by the bridge rectifier you see in the background.Our cap is the smoothing cap, after the bridge rectifier.And, yes, it kind of looks like a bodge but, OTOH, there is another PCB sitting on top of this one, so there are some clearance restrictions that might have played a role here.Based on your input, I've decided to replace this cap (feels quite heavy for its size, BTW).I am thinking a normal electrolytic should be just fine as a replacement, would you agree?Cheers!

author: Zero999
author_rank: Super Contributor
timestamp: March 18, 2020, 10:26:15 pm
content: Looking at the Vishay datasheet linked to above, it doesn't appear to be anything special ESR wise, but it does have a lower leakage current, than most aluminium electrolytics. It can also work down to an ambient pressure of just 1kpA.Assuming it's just used for bulk filtering and you don't need to take it to the edge of space, an ordinary aluminium electrolytic will do.

author: giosif
author_rank: Frequent Contributor
timestamp: March 19, 2020, 08:09:59 pm
content: Ok. Replaced the cap with an electrolytic with the same main specs and all seems the same.Now, back to trying figure out what's wrong with this programmer.If only there was some service manual...

author: David Hess
author_rank: Super Contributor
timestamp: March 20, 2020, 05:49:56 am
content: Quote from: floobydust on March 18, 2020, 06:04:37 amWet tantalum capacitors are not particularly low ESR but they have a high ripple current rating compared to the alternatives. A polymer tantalum or polymer aluminum electrolytic capacitor will have a much lower ESR which may or may not be a problem depending on the circuit requirements.