Selection of miniature low esr electrolitics - Page 1
Forum section: electronics / repair

author: gmac34
author_rank: Regular Contributor
timestamp: February 06, 2025, 11:45:23 am
content: I'm "refurbishing" an old Sartorius scale 3862 MP8-1 from around the mid-'80s. The scale was mostly functional, but it needed a few capacitors replaced in the power supply.When I do this kind of work, I tend to treat electrolytics as a consumable and apply the "while I'm there" approach. I'm sure many will disagree, but I prefer tackling an old piece of equipment apart only once every 30y.Apart from the large filtering caps on the power supply, the designers of this scale made large use of 7mm x 4mm 1.5uf 50v decoupling caps with a relatively low ESR of 5ohm (maybe even less 40y ago), they are all over the board. As far as I can see, they are just local decoupling.The thing is, I'm struggling to find a proper replacement. Small electrolytes like that are not that common today and have probably been replaced by better options like tantalum or ceramic.So all I find in this format are higher ESR caps in the 10-15ohm range (likehttps://industrial.panasonic.com/ww/products/pt/aluminum-cap-lead/models/EEAGA1H1R5) or larger caps 11x5mm in the 2/3ohm range, but these will not fit properly on the board.Attached is a schematic of a similar scale; you can see all the 1.5uf caps around.I wonder if I should- Leave it be, it will work for now; all the capacitors that I pulled for testing were fine, but I do have a similar scale, 6-7y older, where the same caps were almost all bad (in that case I used phisically larger caps but it wasn't pretty )- Use higher ESR capacitors, possibly ok as most of them are paired with 100nf ceramics- find a non electrolytic replacement, ceramic or tantalum, with all the caveats that that entailswhat do you think?

author: benj38
author_rank: Frequent Contributor
timestamp: February 06, 2025, 05:09:00 pm
content: Where did you get the 5-Ohm ESR value from? If you measured it with your ESR meter there is a good chance that there is very little correlation between that value and what is specified in the data sheets. To get a meaningful value you must try and duplicate the measurement conditions, and method used by the test instrument, that the manufacturer employed for producing the datasheet values.The issue of how comparable or meaningful ESR measurements produced by different ESR and LCR meters are was discussed with passion multiple times in this forum.If you have not read these threads before, get some popcorn, search for these threads, sit down to read, and enjoy. Once you have digested the information, come back to your current problem.

author: gmac34
author_rank: Regular Contributor
timestamp: February 06, 2025, 05:23:38 pm
content: I measured all with the same ESR Meter, both the original, the new Panasonic EEAGA1H1R5 as well as a larger 5x11mm low ESR.https://www.peakelec.co.uk/downloads/esr70-datasheet-en.pdfThe ESR si tested at 50kHz i find it is usually comparable to what a datasheet says if tested in the 50 to 100khz range, would be very different if tested in the 100hz range as larger caps are often measured.

author: benj38
author_rank: Frequent Contributor
timestamp: February 06, 2025, 05:39:15 pm
content: Quote from: gmac34 on February 06, 2025, 05:23:38 pmI see. The original post gave the impression you only measured the original ones, and was comparing that reading to the published data for the other caps.As for your original question, I for once would not replace them. Given that you don't have an easy path for obtaining direct replacements, why not cross this bridge when (and if) you get to it? I am sure opening the unit up again in the future will take you much less time than resolving this riddle now

author: wraper
author_rank: Unknown
timestamp: February 06, 2025, 05:49:27 pm
content: You don't need low esr capacitors for this to begin with.