Help identify this capacitor, please? - Page 1
Forum section: electronics / beginners

author: petreza
author_rank: Contributor
timestamp: October 22, 2023, 02:40:29 am
content: in the attached picture the capacitor on the left is blowncould you please help me identify a replacement (as well as the one on the right, in case it was damaged too)thank you

author: Konkedout
author_rank: Frequent Contributor
timestamp: October 22, 2023, 02:56:33 am
content: I believe they are tantalum capacitors. The 686 should be 68 uF (looks like 25V?) and the 107 should be 100 uF (looks like 20V?). The big question which I do not know is the equivalent series resistance (ESR) which can be important. I recommend looking at some datasheets for tantalum capacitors from AVX and Kemet which are two of the biggest manufacturers and see if the case color and digits at the bottom can tell you anything.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 22, 2023, 08:08:06 am
content: +1 as stated by Konkedout.

author: srb1954
author_rank: Super Contributor
timestamp: October 22, 2023, 08:18:24 am
content: If you fit them in I would go for the next highest operating voltage for each of these capacitors. This will give you a bit more safety margin against future failures of this type.The failure rate of solid tantalum capacitors drops dramatically if they are derated well below their nominal rated operating voltage. It is generally considered desirable practice to operate solid tantalum capacitors at no more than 50% of their rated voltage. I even try to derate to 33% where ever possible.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 22, 2023, 08:44:13 am
content: I wouldn't worry too much about that, tantalums like to shortcircuit when getting old, simply replace them and forget for another 10-15 years.Tantalums have no acid in them so they won't leak or dry out, and have very high capacitance for their size.If physically fitting, normal electrolytics will probably work just fine here, they rarely fail this way.Might eventually dry out, though this will take decades unless exposed to heat 24/7.Just use high quality ones, so you have some reliability against leaking or other failures, Panasonic makes great caps.

author: petreza
author_rank: Contributor
timestamp: October 23, 2023, 08:58:47 am
content: thank you all for the help.so, it turns out it is a Kemet capacitor. The markings are as follows:M - either tolerance (+/- 20%), casing size (don't have it right now, so cannot confirm), or magnetic/non-magnetic (I guess for mounting)+ - polarity686 - 68microF25 - 25Vk - Kemet449 - date of manufacture - 2014, 49th weekwhen I filter at DigiKey for: Kemet, 68microF, 25V, SMD, size (7.3mm x 4.3mm (as opposed to 7.2mm x 6mm, which it is not))I get the following series:T491 - 700mOhmT494 - 300mOhmT495 - 125, 130, 150, 200mOhmT510 - 45mOhmWhich would you recommend? Here is the board:https://www.highpointscientific.com/celestron-motor-board-for-cpc-deluxe-series-telescopes-nxw444if the direct link does not work:https://www.highpointscientific.com/and search for: nxw444attached is a pictureI think this board is where the various external devices get plugged into the telescope - remote control, computer, etc. (sorry, not mine)It drives the motors of the telescope.Thanks!

author: Vovk_Z
author_rank: Super Contributor
timestamp: October 23, 2023, 09:55:02 am
content: "Sorry, you have been blockedYou are unable to access highpointscientific.com"I just guess it is not a DC-DC power supply unit. So you may use any general-use tantalum capacitor. If it is a power supply DC/DC converter, use any tantalum Low-ESR capacitor from your list. That's it (this is not rocket science. Or it is?)

author: petreza
author_rank: Contributor
timestamp: October 23, 2023, 04:05:58 pm
content: Quote from: Vovk_Z on October 23, 2023, 09:55:02 amedited my previous post to help with the broken link and attached a picture of the boardso anything in the T495 series - 120-200mOhm?

author: Vovk_Z
author_rank: Super Contributor
timestamp: October 24, 2023, 01:44:43 pm
content: I guess T494, T495 series should work ok.

author: petreza
author_rank: Contributor
timestamp: February 17, 2024, 12:42:45 am
content: Thank you all! I replaced the blown capacitor with:ESR 150mOhmhttps://www.digikey.com/en/products/detail/kemet/T495X686K025ATE150/1001005and it worked!The problem is, there is a high-pitched noise now coming from somewhere, which wasn't there before. This board drives the telescope motors (stepper motors, I guess - sorry, I am not there myself). Should I tell them to ignore it or are they risking burning out the motors? If I should replace the capacitor again, should I go with higher, or lower ESR?Sorry I cannot give you more relevant information. Just give me your best guess. Thanks!