Ripple and caps - Page 1
Forum section: electronics / beginners

author: cs.dk
author_rank: Unknown
timestamp: June 29, 2014, 03:17:37 pm
content: Yet another beginners question- Have a PSU with high ripple voltages, and alot of caps in the junk-box.Should the cap be placed seriel or parallel on the output? And what size should I aim for? Got a 25V 2200uF, guess it should be OK?I've attached some images of the ripple!

author: TheRuler8510
author_rank: Regular Contributor
timestamp: June 29, 2014, 04:27:15 pm
content: Answers:Should the cap be placed seriel or parallel on the output?parallel.And what size should I aim for?Depends on current range of use and final ripple desired.Got a 25V 2200uF, guess it should be OK?Are you regulating after it? If not, you need some idea of desired ripple. Try it and see.

author: cs.dk
author_rank: Unknown
timestamp: June 30, 2014, 01:18:39 pm
content: Thanks for your answer - Tried a 470 uF, and a 2200 uF, it does not seem to work. The ripple is the same?

author: 128er
author_rank: Regular Contributor
timestamp: June 30, 2014, 03:12:13 pm
content: Some more information could be very helpful.-Please show us the PSU you are measuring.-Draw a small schematic of how you attached the probe.-And maybe the way you was trying to connect the caps

author: cs.dk
author_rank: Unknown
timestamp: June 30, 2014, 04:29:31 pm
content: It's just a simple multi-tab transformer, and a rectifier. I suspect the rectifier could be faulty.I saw that theres allready a 1000 uF cap build in - Measured it, and it seems fine. That explaines why the extra cap doesn't work.The banana's you see is a meter measuring current, a meter measuring voltage, and the scope via a banana-BNC adapter, and of course a load.I have some 1N5822 diodes - Thinking of making my own retfier - Guess i just can solder them together for a test?

author: cs.dk
author_rank: Unknown
timestamp: June 30, 2014, 07:04:43 pm
content: So, did budge a home-made rectifier in - Allmost the same ripple

author: SeanB
author_rank: Super Contributor
timestamp: June 30, 2014, 07:26:04 pm
content: I think your 1000uF capacitor is very dead, you probably should replace it with the 4700uF unit and try again.

author: kizzap
author_rank: Unknown
timestamp: July 01, 2014, 10:49:44 am
content: the different rectifier isn't going to be doing a damn thing in lowering the ripple voltage. The amount of ripple revolves entirely around the amount of capacitance you haveafterthe bridge rectifier,beforethe output. The caps charge when the voltage out is higher then their charge, then dump their stored charge into the circuit when they are at a higher potential then the output of the transformer. The amount of capacitance you need to filter the AC that you need depends on a number of factors:The amount ofCurrentdrawnThe output voltage of the transformer at peakThe frequency the transformer is operating atThe amount of ripple which you can work withMake note of that last one. There will generally always besomeripple. That is just the nature of the beast. if you need a pure 100% DC with no ripple, you are going to have to put some kind of regulator on the output.Oh just as a note, on a project I am working on, drawing 3A or so, with the ripple kept to less then 5V, I need over 8800uF if you want less then that, you are going to be talking in the order of 50,000uF at a guess.