Components, Part 1: X Capacitors

With this article, I’d like to start a series about various electronic components: diodes, capacitors, resistors, varistors, and so on.
There are so many components, and they’re all different. I can’t shake the feeling that by the time I finish writing about them, something new will already have come out :)
I’ll start with X capacitors, especially since this article is a follow-up to my previous article about Y capacitors.

These articles are really meant to complement the videos. I don’t write scripts; I usually just talk about what I know, so there may be a few caveats or differences from the written version. But I’ll do my best to keep those differences to a minimum.
In this series, I’ll talk not only about the components themselves, but also about which circuits they’re best used in and why, and possibly discuss replacement options.
Also, if there are any particular components you’re interested in, I’ll try to make videos about those first. So I’d be glad to hear your comments and questions.

X capacitors are usually used together with Y capacitors. Both types are commonly used as interference-suppression components in filters. Of course, either type can also be used on its own.

They look like small blocks in various colors, usually gray, blue, or yellow. Each one should have the appropriate markings on it.


The mains supply has plenty of high-frequency interference and ripple, so the X capacitor’s job is to block as much of it as possible, essentially shunting it through the capacitor. The same goes for interference coming from the power supply. The diagram shows the path the interference takes and how it reaches the capacitor.
On the left of the diagram, you can see a 560 kΩ resistor. It’s there to discharge the capacitor after the power is switched off. If you leave it out and touch the power plug contacts after disconnecting the power supply, you could get a shock. Not a strong one, but still unpleasant. I once had a JVC camcorder brought in that could really “bite” like that.


X capacitors differ from ordinary capacitors in that they:
1. Work better with mains voltage
2. Can withstand voltage surges
3. Are less prone to catching fire.

In principle, you can replace them with ordinary capacitors, but that should be a last resort. Also, any replacement capacitors must be rated for at least 630 V. Someone might tell you that 400 V capacitors will do, and that they’ve used them many times without a problem. Don’t listen—630 V minimum!
So the right choice is the ones shown on the left in the photo.


Be especially careful with imported (read: Chinese) capacitors. The red ones on the left in the photo—I’ve seen them burst more than once, and they could easily have started a fire.


A little about the markings.
X1 – Used in industrial equipment connected to a three-phase supply. These capacitors are guaranteed to withstand a 4 kV voltage surge.
X2 – The most common type. Used in household appliances with a nominal mains voltage of up to 250 V; withstands surges of up to 2.5 kV.
Y1 – Operates at a nominal mains voltage of up to 250 V and withstands impulse voltages of up to 8 kV
Y2 – The most common type; can be used with mains voltages of up to 250 V and withstands 5 kV impulses

A quick tip
1. Y capacitors can be used in place of X capacitors, but X capacitors must not be used in place of Y capacitors.
2. Y capacitors usually have a much lower capacitance than X capacitors.
3. With X capacitors, higher capacitance is better, but Y capacitors should have as low a capacitance as possible. A typical value of 2.2 nF can already give you quite a jolt if you touch the power supply output and a grounded object at the same time.

Choosing the capacitance for X capacitors is simple: the higher, the better. For use in ordinary household devices, any class will do.

Sometimes Y capacitors can have the same case as X capacitors, so be careful when using them.


Also, as I mentioned above, Y capacitors can be used in place of X capacitors. What’s more, they’re sometimes marked for both types. You can even safely use a Y2 capacitor in place of an X1.
The one on the left is presumably the right capacitor, but since it doesn’t have a Y marking, it’s better not to use it—at least not as an interwinding capacitor.


You might be wondering why X and Y, rather than, say, W and Z. I’ll try to explain how I see the logic behind the markings.
On the circuit board, an X capacitor is installed as shown in the diagram: one lead connects to the input through one trace, and the other to the output through another. This is done to minimize the length of the conductors, since current always takes the shortest path.


But if we look more closely at these conductors, we can see that the X capacitor connection resembles the letter X, while the Y capacitors are arranged like the letter Y.
I won't claim that this was intentional, but it looks quite logical :)


Here’s what these capacitors look like in actual power supplies.
On the left is a power supply from a satellite receiver; on the right, one from a monitor. In the first case, capacitors are used both before and after the inductor; in the second, only before it. The first arrangement handles interference a little better, but the second has an additional inductor that reduces interference.


The inductor is visible just to the left and below the capacitor. The X capacitor is Class X2, with a capacitance of 0.22 µF.


Here’s another example: a computer power supply.


The input also has a Class X2 capacitor with a capacitance of 0.22 µF, but in this case that’s just a coincidence, since the capacitors in the satellite receiver’s power supply are 0.1 µF.


And here are those unusual Y-type capacitors I mentioned earlier. I hadn’t noticed before that they came in such an unusual package; I only spotted it recently.
By the way, the manufacturer’s marking, Astec, is visible on the left side of the board. At one time, it made very high-quality power supplies, which you may also have seen as phone chargers (for Siemens, for example). But later the company left the consumer electronics market. It’s a shame—their products were exceptionally well made. What’s more, they even made their own ICs.


Speaking of power supplies—and not just power supplies. As I mentioned, Class X capacitors are very reliable, so before you throw out an old power supply, take a look inside. You may be able to desolder them; they’ll most likely still be good.
In general, power supplies and other devices are great sources of parts, especially when you only need one or two. Sometimes it’s even convenient to store them intact.
For example, the standby power supply section below can be stripped for parts to make a low-power 5/12 V supply for powering something Arduino-like.


Or here’s the output section. You can easily salvage the cores for all kinds of voltage converters and filters—very handy. The coupled inductor used for cross-regulation can be especially useful.
Electrolytic capacitors may also come in handy, but if the power supply is “Chinese,” it’s better not to use them; they’re often junk.


Since I’ve started talking about power supply filters, here’s a filter from what I assume was a Soviet-era monitor. I found it on the balcony today.
You can see a large metal box, two fuses on the end (in switch-mode power supplies, it’s best to use a pair), and, unexpectedly, a perfectly standard modern power connector.


When I took it apart, I was shocked: it was just like typical Chinese mass-produced junk—a large enclosure with three components inside. And I mean literally three: an inductor, a capacitor, and a resistor.


By my estimate, the power supply connected after the filter was rated at 100–150 W. These days, you could easily fit a power supply and filter together in an enclosure that size. The photo shows a 100 W power supply for comparison.


Some power supplies also come with handy filters like this. This one also has three components: an inductor, a capacitor, and a resistor. Resolder the input connector and you can put it to use—compact, effective, and free.


That’s all for now; you can see the rest in the video. As I said, I’d be glad to hear your ideas, questions, and comments. It’s much nicer when there’s feedback from viewers and readers :)