A few capacitors and how they affect a converter’s ripple level

Recently, I wrote that I’d bought a bunch of different electronic components at a local shop. Among other things, I picked up several types of electrolytic capacitors for a small modification to one of my converters. Today I’ll show how simply replacing a capacitor can significantly change the performance of a converter—or a power supply.



This will be a short review. There probably isn’t much to say about capacitors, but I think even a brief look at them will be useful.

You’ve already seen the converter board in one of my reviews. Since I do want to put it to its intended use, I decided to make a few modifications, which is why I bought these capacitors.



I bought five types of capacitors in total, from two manufacturers, with several options for rated voltage and capacitance. I got them from the Kosmodrom store in Kharkiv, along with a bunch of other small parts.


First up are my favorite Samwha capacitors from the RD series. These are 330 µF, 63 V models, and they cost about 20 cents each. They’re inexpensive and quite good quality, which is why I use them so often.


It’s worth noting that these aren’t low-impedance capacitors. They’re simply a high-temperature version of the more familiar SD series. Even so, they work very well in switching power supplies.


For all the capacitors, I’ll list the measured parameters in the same order:
1. Photo of the vent pattern on the top and the shape of the insulating sleeve
2. Weight—in this case, of two capacitors, so divide the result by 2.
3, 4. Overall dimensions.

Why bother? Capacitors are often counterfeited, and to get at least some idea of what genuine ones look like, you need some kind of

Parameters for both capacitors at 100 Hz and 7.8 kHz.


Another Samwha, but from a different series: WL. Capacitance is 1000 µF, rated voltage 35 V. They cost about the same 20 cents each—link.


These are low-impedance capacitors, so they’re perfectly suitable for use in converters and switching power supplies. They’ve already appeared in my review of the lighting modifications.


The sleeve shape, vent pattern, and overall dimensions. These capacitors are fairly large.


Capacitance and ESR.


Next up are Panasonic capacitors. I’ll start with the most compact ones in this review: 470 µF, 35 V.
They’re a bit more expensive, of course, at around 30–35 cents each—link.


These are also low-impedance capacitors, as stated in the datasheet.


The vent pattern on the top has a distinctive shape, although the sleeve looks very similar to Samwha’s.


Besides their good performance, here’s an interesting detail: if you look at the photo, you’ll see that the Samwha markings are positioned so the positive lead is on the right (viewed with the leads pointing down), while on the Panasonic it’s the other way around, with the positive lead on the left.



Another Panasonic from the same series, also rated for 35 V, but with a capacitance of 820 µF. These cost 80 cents each—link.


The vent pattern on the top is the same as on the previous ones, but the sleeve shape is noticeably different.


The specs are simply excellent. I definitely recommend them. The datasheet gives the parameters at 100 kHz, but my meter can’t measure at that frequency :(


And the third Panasonic looks a little different: the markings are gold-colored, and it has an "M" logo. They cost a little over a dollar apiece - link.


The stamped shape and insulator are exactly the same as on the previous ones; the only difference is the marking itself.


Compared with the Samwha RD, these are certainly much better in terms of specs, but the price difference is substantial too.


The modification is simple and straightforward: desolder the original capacitors and install the new ones. The original part was a Chinese "Sanyo" rated at 470 µF, 50 V.
Of the five types shown above, I chose two: a Samwha RD 330 µF, 63 V for the input and a Panasonic 330 µF, 50 V for the output. At first I thought of using a 330 µF, 50 V capacitor on the input and either a pair of 470 µF, 35 V capacitors or a single 820 µF, 35 V capacitor on the output, but I decided to play it safe: the input will be around 48–50 V, and I don't want to lower its voltage rating, while 35 V capacitors would be right at the limit on the output. The Samwha WL was too large; it barely fit, so I decided not to use it.
In general, there's very little choice when it comes to small-diameter capacitors rated for 50–63 V with a capacitance of 330 µF or more. I wanted something with higher capacitance, preferably a quality part with low ESR, but no luck...


Of course, I could have left it at that, but I was really curious whether there would be a difference in the end, and if so, how much. So first I powered up the board with the original capacitors and measured the output ripple, then replaced the capacitors and ran the same test under the same conditions.
The input voltage was around 22 V in all cases. The output was:
1. 3.3 V, 8 A
2. 6 V, 8 A
3. 15 V, 3.5 A.

Before the modification is on the left, after it on the right. Though I think you've already figured out "which is which" :)


And here are the measurements for the original capacitors, the worst and the best ones. The third one's specs are somewhere in between. In short, they're about on par with ordinary capacitors, such as the standard 85 °C Samwha series. I do have some doubts about their longevity, though; I think Samwha will be more reliable.


So, I can say the results are clear and quite impressive: ripple dropped by about 5–6 times, even though the output capacitance was 940 µF before the modification and is now 660 µF. So we reduced the capacitance and the ripple, and I hope reliability has improved significantly too.

In short, I really liked the Panasonic capacitors—all of them. I liked the Samwha ones too, but I've known that brand for a long time and more or less knew what to expect. If you want quality, though, Panasonic is still the better choice. In this case, it was the FC series.


As always, comments and questions are welcome. I hope you found this review useful.