Capacitor Size Vs Rated Voltage - Page 1
Forum section: electronics / beginners

author: Bskitter
author_rank: Regular Contributor
timestamp: November 01, 2016, 06:10:26 pm
content: Hey Guys so, I am replacing some old caps on a Kenwood Amplifier,There are two caps I am replacing.0.01 uF Ceramic +100% -0%0.15 uF Mylar +- 10%Now all was fine until I bought the replacement caps and noticed both are incredibly smaller than the old ones, here is a photo of the two side by side of the new onesThe top ones are 0.15 uF.The replacement I bought is rated at 100V 10%The bottom ones are 0.01uF (103), the big blue one is rated @ 3kV and the small blue one is rated at 100v 10%Now looking at where they are located on the circuit the 103 caps are for some high frequency filtering of some sort, I have no idea why the caps that were put there are so big since the output on the TF is 50V RMSOn the other hand the 0.15uF caps look like some sort of snubber from the output of the `power transistors there is a 2 Watt resistor before the cap.Here are the diagrams for both.The parts sheet for this amp mentions nothing about the rated voltage for these capacitors only the tolerance.Basically will the small capacitors be fine in this situation ?RegardsByron

author: wraper
author_rank: Unknown
timestamp: November 01, 2016, 06:21:03 pm
content: First of all I don't understand why you would want to change them at all. And second why would you want to change them with crappy unstable ceramic capacitors.

author: Bskitter
author_rank: Regular Contributor
timestamp: November 01, 2016, 06:25:43 pm
content: Well this is why I am asking kind sir, What capacitors are suitable if ceramic are "unstable" ?

author: wraper
author_rank: Unknown
timestamp: November 01, 2016, 06:26:40 pm
content: Quote from: Bskitter on November 01, 2016, 06:10:26 pmNo, not fine. On top of that 0.15uF capacitor unlikely to be 100V rated. More like 25-50V. Never change film capacitors with ceramic, especially with Z5U or Y5V crap you bought.

author: wraper
author_rank: Unknown
timestamp: November 01, 2016, 06:29:33 pm
content: Not replacing them is the best. The is no good in changing them. Film capacitors should be replaced with film capacitors (if there is actual reason to do so).

author: singapol
author_rank: Frequent Contributor
timestamp: November 01, 2016, 06:36:09 pm
content: If none of the caps are shorted or open I think you can put them back where they belong.Have you measured their capacitance value and are they in spec?

author: Bskitter
author_rank: Regular Contributor
timestamp: November 01, 2016, 08:53:13 pm
content: Thank you for the info, but this is the beginners thread and I am just college student trying to repair my amp, no need for hate.I tested the caps, one of the 103's is not picking up on the tester. Is the smaller 103 an acceptable replacement ? I doubled checked the product code vs the data on the suppliers site. its rated @ 100 Volts.Is the size of the cap just old technology, and from till now we have made them smaller ?Byron

author: wraper
author_rank: Unknown
timestamp: November 01, 2016, 09:10:40 pm
content: Quote from: Bskitter on November 01, 2016, 08:53:13 pmNo and yes. They are smaller because of the newer technology but not only. Completely inferior parameters compared to the 0.15 uF film capacitor, likely lower voltage rating too. 10n capacitor most likely have lower voltage rating, original could be somewhere about 200V IMO. For AC you need at least twice of the DC voltage rating (+ some margin of course.)Those capacitors are not good as replacements at all. And original 10nF capacitors certainly are not a source of the fault, even if they are faulty themselves, what is very very unlikely. More likely either you tried to measure it in circuit or there wasn't good contact between the capacitor and multimeter probes. They just don't fail unless something extraordinary happens.

author: Rerouter
author_rank: Super Contributor
timestamp: November 07, 2016, 09:32:22 am
content: C59 and c60 should remain film caps because they are in the signal path, equally they will be that size because they will dissapate some heat.The other 4 near the bridge rectifier can be ceramic, and likely are not too critical to the operation of the device.

author: danadak
author_rank: Super Contributor
timestamp: November 07, 2016, 09:55:52 pm
content: Capacitor technology is a study unto itself. Here is an excellent startingapplication note that will help.The dielectric and geometry and construction make capacitors solve differentproblems with different types, eg. the best characteristics. For example in noisework ESR a very important parameter, ceramics, multilayer ceramics, polymerTantalum, etc.. Another focus could be leakage, where film, Teflon, polypropylene,and others shine at low dielectric leakage. Then you have caps for timing circuitswhere C vs V of the cap, temp drift.....you can easily make a career out of justCapacitor technology. RF work has a whole technology area itself, air spaced, piston,silver button mica,........http://www.kemet.com/Lists/TechnicalArticles/Attachments/6/What%20is%20a%20Capacitor.pdfThe .01, .001, to ground, are typically for noise suppression. Usually ceramic disk.Or these days multi layer ceramic (MLC).Regards, Dana.