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Yeah he probably means ripple voltage, but ripple current is also sometimes needed to be known in order to ensure the cap can handle it but that's the ripple current going through the cap not exactly what we see at the output in the load.
We built up a ripple voltage detector circuit a long time ago but im not sure if i have it anymore. It was basically a AC peak detector circuit with a little calibration to make up for the nonlinear diode part which was a Schottky diode.
The main problem with measuring the ripple voltage is although it is basically just an AC voltage riding on a DC level, most meters that measure AC are made for lower frequencies like power line frequencies so most are not adequate for measuring the normally much higher switching frequency of a typical switching power supply. Building a higher frequency detector addresses this issue so that we can get a good idea what the real ripple voltage is. Since the detector uses a high pass filter followed by a rectifier diode and low pass filter it captures the peak to peak ripple. If the ripple is extremely low however a scope is a better choice and that works for all cases.
The audio input of a sound card (buffered of course) can probably be used to measure power supply ripple fairly well. A while back I built such a buffer to use my sound card as a makeshift oscilloscope. It works pretty good, though I had an issue with noise being generated by my buffer it's self. Strategically placed filter capacitors fixed that quickly though.
For voltage, just probe + on the power supply to one input channel, and supply ground to the audio ground.
For current, make sure there is a resistance on the line, and measure the voltage across that.
In both tests, make sure to run the system through all four edge conditions.
Max load, max input.
Min load, min input.
Max load, min input.
Min load, max input.
Another possible way to see ripple is to make a high pass filter to a rectifier and capacitor. If there is any AC on the supply above the cutoff, it will pass through the filter, get rectified, and charge the cap. The circuit needs to be designed properly if you want to get a correct reading of course. You need to have a way to discharge the cap too, otherwise you may get false readings from spikes and turning it on and off and so forth.
First question: Are you talking Switch Mode or Linear.
Second question: What Currents are we talking from the Secondary side.
Two basic questions. Answer them properly and we can help.
Then and then only. Ripple Currents are dependent on application.
Ripple current is relatively easy to measure on Linear supplies. I LOVE LINEAR. Reliable...always. No nasty surprises.
On SMPS, another matter altogether. You are dealing with high speed switching on them. A totally different ball game.
That is why caps dry out, explode, bulge etc on the Secondary of SMPS. They have heaps of work to do smoothing stuff at high frequency.
They run hot doing their job.
Poor buggers. That is why a 105 Degree cap is always better than a 85 Degree cap doing Secondary smoothing. Depending on Cap quality too.....
Personally, for me after years of messing about with rubbish, Rubycon is the ONLY one I trust. They make the most reliable Electrolytic out there.
Bar none.
And they cost very little more than the other rubbish available. PLUS, Rubycon wrote the book about Electrolytics..........
Low ERS "solid electrolytic" Polly caps are all the rage for output filtering. Though a good SMPS design will just have low ripple from the start anyway. Increasing the size of the inductor can reduce ripple just as well.
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