Mounting series capacitors on a pcb - Page 1
Forum section: electronics / beginners

author: Mp3
author_rank: Frequent Contributor
timestamp: January 23, 2021, 12:04:41 pm
content: How does one properly solder two capacitors in series to a PCB designed for a single capacitor?I only have one hole for each capacitor leg and i don't know how to properly mount two capacitors in this fashion. Do i solder one in with some leads exposed and solder to the legs of that?(I did google before asking, but only found diagrams in schematics, which i understand but don't help me solder properly.)

author: Ian.M
author_rank: Super Contributor
timestamp: January 23, 2021, 12:15:03 pm
content: If the pad spacing permits, use axial caps side by side, mounted vertically, with the top leads bent over 1/16" from the body and soldered together.If its too tight spacing to do that then its going to be a bodge job. Post a photo of the PCB top and bottom sides, and of the capacitors to be fitted, and give their dimensions and the distance between holes on the PCB, and we can make some suggestions that may or may not include drilling some extra holes off to one side.OTOH its probably preferable to get one capacitor of the correct value and voltage rating to replace the series pair, or possibly the next lower preferred value and make up the difference with a capacitor in parallel if the value is critical.

author: Mp3
author_rank: Frequent Contributor
timestamp: January 23, 2021, 12:19:58 pm
content: Quote from: Ian.M on January 23, 2021, 12:15:03 pmThanks!It was more for the added smoothing of a decoupling capacitor than to get a value I don't otherwise have. But, if that's the wrong way to go about it, please let me know.I don't have a problem I'm trying to solve. I have an audio DAC open for repairs and thought while i was doing it that I might as well try to see if anything noticeable happens.

author: Ian.M
author_rank: Super Contributor
timestamp: January 23, 2021, 12:23:34 pm
content: Caps in series REDUCES the value: Ctot=C1*C2/(C1+C2). If you want to INCREASE the value of a smoothing cap (or improve its frequency response) you need to add more caps in parallel.

author: Mp3
author_rank: Frequent Contributor
timestamp: January 23, 2021, 10:23:37 pm
content: Quote from: Ian.M on January 23, 2021, 12:23:34 pmYes and i thought if i use two 220's in series in place of a 100 then it's close enough?

author: Manul
author_rank: Super Contributor
timestamp: January 23, 2021, 11:17:00 pm
content: There is no benefit here to putseriescapacitors. Also you will roughly double the ESR, that will make smoothing worse, not better.Parallel - maybe. Yet, there could also in some cases be a catch. For example, some switching converters require a "window" of output ESR. Parallel nearly halves it. Most often it is safe. Still the question remains are there any audible spectrum frequencies to smooth there? In many cases resistor and active component noise floor is the limit anyway.

author: langwadt
author_rank: Super Contributor
timestamp: January 23, 2021, 11:57:57 pm
content: Quote from: Manul on January 23, 2021, 11:17:00 pmyou might want to put two electrolytic in series back-to-back to make a large non-polarized cap

author: ledtester
author_rank: Super Contributor
timestamp: January 24, 2021, 12:25:37 am
content: Quote from: Mp3 on January 23, 2021, 10:23:37 pmWhat's the purpose of the cap? And what's the unit on these 220s? micro-farads, nano-farads, pico-farads? It may not be a big deal.

author: srb1954
author_rank: Super Contributor
timestamp: January 24, 2021, 03:54:23 am
content: Quote from: Mp3 on January 23, 2021, 12:19:58 pmIf it just a supply decoupling capacitor it probably won't do any harm just using the larger value cap.