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I was cleaning my 36v dc 5.5 amp SMPS today. I was playing around with the wires and goofed up. A spark happened and later I found that a Y Cap had cracked.

This cap value is: Yf222m 2200pf 250v x1:400v y2:250v

I went to the component store and the guy searched his inventory and handed me what he had. The only info given on this cap is:

E 222m 2kv

I argued with him whether this was compatible and he "guessed" or hoped that it did.

Now I'm back home wondering if I should solder this component in my smps and hope that it doesn't blow up.

edit:

Yes, the one I got from the store looks like a Y cap but it may not be a Y cap.

Anyway, even though the 2kv range is much higher than the original 250v ac rating, I have gone ahead and soldered it in and it seems to be working. This smps is part of my sound amplifier. I have a tiny active voltage monitor module installed on the amp front display and the reading i'm getting is 36.0v constant +/- 0.1v as before.

I initially took the smps out because I was not getting FM reception. Initially, I thought my USB fm audio playing module was broken. Then I took my amp closer to the FM broadcast area(within 5km) and was able to get good FM reception albeit with tiny dots of noise(like the noise in old projector films) so I figured the class D amp was increasing noise and lowering the chances of getting FM reception. The amp used here is a class d chinese tda7498 commonly found on aliexpress. After reading around on the internet I found that almost all class D amps kill the FM reception and the tda7498 is, as I found out in my experiment, is a confirmed FM killer. I will have to get back to internet radio again.

I can order the correct rated Y cap from aliexpress but unfortunately, it will take a month for it to arrive so haven't bothered to order one yet.

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    \$\begingroup\$ It's not a clearly marked Y cap, do not use. \$\endgroup\$
    – Matt Young
    Commented Mar 5, 2017 at 14:42
  • \$\begingroup\$ Might work. It's not a Y cap, but 2kv should be OK. Back in the day the Japanese used 1500 V caps for line filtering in audio stuff. That seemed to work. \$\endgroup\$
    – Robert Endl
    Commented Mar 5, 2017 at 15:09
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    \$\begingroup\$ It may meet the voltage requirement, but the capacitor MUST fail open when it fails. I wouldn't replace that Y capacitor with anything except an equally good or better Y capacitor of the same capacitance or lower. \$\endgroup\$
    – Oskar Skog
    Commented Mar 5, 2017 at 15:17
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    \$\begingroup\$ If I'm not mistaken, the Y capacitor is only there for EMI noise suppression, and it's Y rated because it's connected across the transformer. I think the SMPS will work fine without that cap, but you might annoy someone with the EMI. \$\endgroup\$
    – Oskar Skog
    Commented Mar 5, 2017 at 15:20
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    \$\begingroup\$ DON'T! When your non-Y-rated cap fails, it will create a short from primary to secondary, potentially killing anyone whi come in touch with it. \$\endgroup\$
    – winny
    Commented Mar 5, 2017 at 20:33

1 Answer 1

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The replacement part is unlikely to be a Y capacitor.

The failure of a Y capacitor leads to an electric shock hazard, and no fuse blows. For example, a surge on the AC power line is likely to damage the Y capacitors. A typical surge might be due to a direct or indirect lightning strike.

All Y capacitors must have an AC rating. The 250V rating on the replaced part is an AC RMS voltage. In addition, there is a DC rating for types Y1, Y2, and Y4. The original part is type Y2, which means that it has a DC rating of 5000V. I wouldn't install the replacement. Use a real Y2 capacitor.

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