Physical Capacitor Size - Page 1
Forum section: electronics / beginners

author: L0max
author_rank: Contributor
timestamp: August 07, 2020, 06:29:03 am
content: Hi,I am re-capping an old CRT monitor. Among other caps, I ordered a 4.7uF 50v Bi-Polar cap (in fact, it was this one:https://www.jaycar.com.au/4-7uf-50v-bipolar-electrolytic-capacitor/p/RY6806). When I removed the old 4.7uF 50V cap, I was surprised to find that it was considerably physically larger. So much larger, in fact, that alarm bells sounded in my mind. I have attached a picture of the new and old capacitors. New on the left, old on the right.Why the huge difference in size? Am I missing some critical spec regarding the new capacitor? Any help will be appreciated.'max

author: Siwastaja
author_rank: Super Contributor
timestamp: August 07, 2020, 08:15:10 am
content: Why are you replacing this capacitor? It likely isn't a part of DC/DC converter and not stressed to large ripple currents.What does "recapping" mean? Replacing all capacitors? Why? I'd see it as a huge risk because if you don't get the exact same original part number, you need to basically understand the full circuit and all it's details as well as the original designers. As a result, you likely get some part wrong. A lot of work and cost for mostly "fixing" working parts.Instead, identifyifyou have an actual problem, find the failed part, and dedicate your design efforts to fixing that.

author: Vovk_Z
author_rank: Super Contributor
timestamp: August 07, 2020, 08:21:34 am
content: Yes, if TS doesn't has ESR and RLC meters then I would afraid to change something.The larger one cap can have better current capacity.

author: Gyro
author_rank: Super Contributor
timestamp: August 07, 2020, 08:25:16 am
content: Quote from: Siwastaja on August 07, 2020, 08:15:10 amAgreed, blanket re-capping isn't a good thing to do.Looking at the photo, the original capacitor has a much higher ripple current rating than the Jaycar replacement, which probably wouldn't function at all in circuit. If youmustchange that particular capacitor then you could maybe look at metal film speaker crossover capacitor, but even then, their lower loss characteristics might prevent the circuit from working as originally designed.

author: Dabbot
author_rank: Regular Contributor
timestamp: August 07, 2020, 09:03:53 am
content: Quote from: L0max on August 07, 2020, 06:29:03 amIt IS from the CRT era and a quick peruse for similar specs returns caps which are only 10mm diameter. Though there are some 16mm diameter caps if you include obsolete offerings.Install the Jaycar thing and tell us all how long it lasts.

author: L0max
author_rank: Contributor
timestamp: August 07, 2020, 10:25:45 am
content: So why the difference in physical size?

author: Dabbot
author_rank: Regular Contributor
timestamp: August 07, 2020, 10:37:29 am
content: Quote from: L0max on August 07, 2020, 10:25:45 amThe larger cap is much older and likely uses obsolete tech. Even then, I wouldn't trust the Jaycar replacement.Here:https://www.digikey.com.au/product-detail/en/nichicon/UDB1H4R7MPM/493-16735-ND/2597783

author: silvestron
author_rank: Newbie
timestamp: August 07, 2020, 11:06:48 am
content: For everyone curious why, "recapping" or replacing all electrolytics is a thing that is done in retro-gaming circles, seehttps://console5.com/wiki/Identifying_Bad_Capacitors.Some people only do the ones that need replacing, some people replace them all.The only gaming CRT I can think of that has a 4.7uF 50v BP would be a Commodore 1084S monitor (if I'm guessing correctly), and the UDB1H4R7MPM that Dabbot linked is the common replacement in that case.

author: Gyro
author_rank: Super Contributor
timestamp: August 07, 2020, 05:09:43 pm
content: Quote from: Dabbot on August 07, 2020, 10:37:29 amNot just a matter of newer technology - there are more parameters than just voltage and capacitance value. There is ESR, dissipation factor, temperature range, lifetime etc. A larger capacitor package is much better at dissipating heat from high ripple / high AC current (in this case).If capacitance and voltage were the only relevant parameters, then the manufacturers' catalogues would be very short indeed.

author: Per Hansson
author_rank: Unknown
timestamp: August 07, 2020, 07:42:43 pm
content: "BP" in this context probably stands for "Bi-Polar"I.e. it is basically an AC capacitor.If you are recapping you buy better than original caps, for example higher temp rating, higher ripple rating to increase longevity.Not crap from Jaycar that this decades old cap is orders of magnitude better than