# Capacitor a/c or dc

Discussion in 'General Electronics Chat' started by spike47, Aug 13, 2009.

1. ### spike47 Thread Starter Member

Mar 11, 2009
22
0
HI

I have a conponent marked 103 1kv , I think it is a ceramic capacitor , it is off the power board section of a LCD tv PCB , there is a fault in that the red stand by light is flashing on and of and a small blue button capacitor as marked above is clicking away .

I have found that a shottky rectifier is at fault which I have ordered , but I wanted to replace this capacitor as well , but I dont know if it is a/c or dc , I have checked on the web , and found some that are either dc or a/c and some are are saying high voltage and some are saying low voltage , so I am a bit , well a lot confused .

I have made a schematic drawing of the circuit in excell but I am having problems uploading to here .

any help on this would be highly appreciated

regrds
spike

2. ### ELECTRONERD Senior Member

May 26, 2009
1,146
16
A capacitor can be used either for AC or DC. It's just that they respond in different ways. You should read how a capacitor reacts to DC and how it reacts to AC as well. It would be helpful if you knew the part number for the capacitor, because then you could find the maximum peak-to-peak voltage and the maximum DC voltage. 103 means that it is 0.01uF 1,000V capacitor. 1kV is very high so i'll bet that capacitor is fairly big. I would just replace it in the DC value because 1,000V DC is higher than 1,000V AC. 1,000V AC RMS actually would be 707V DC.

3. ### russ_hensel Distinguished Member

Jan 11, 2009
820
47
Caps are not AC or DC quite, but are polarized or non-polarized which is similar. On a polarized cap the negative lead must be kept negative with respect to the other lead.

I would guess you have a high voltage supply with a filter cap and that a polarized cap would do fine, but you can always substute a non polarized cap ( of the right cap. and voltage ).

The circuit would help.

4. ### spike47 Thread Starter Member

Mar 11, 2009
22
0
HI

here is the schematic

cheers

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5. ### davebee Well-Known Member

Oct 22, 2008
539
46
Is there a reason you want to replace it? Does it look burned, or does it measure as shorted, or something?

If it isn't damaged then why not just leave it alone?

(Edit - I just re-read your first post - the capacitor is clicking? Can you see a spark?)

Last edited: Aug 13, 2009
6. ### Audioguru New Member

Dec 20, 2007
9,411
896
No.
103 does not say the voltage rating.

No.
A 0.01uF/1kV ceramic capacitor is fairly small because its value is small.

No.
A capacitor rated for 1000VAC will work with peak voltages of 1414V which is a lot higher than 1000VDC.

7. ### spike47 Thread Starter Member

Mar 11, 2009
22
0
its about 8mm diam in size .

here is a picture of the actual pcb arrow points to 103 1kv(blue button)

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8. ### spike47 Thread Starter Member

Mar 11, 2009
22
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Here is a better view .

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9. ### ELECTRONERD Senior Member

May 26, 2009
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I didn't say that it did. 103 means that it is a 0.01uF capacitor 3 is the multiplier so you add three zeroes. So it looks like this 10000. Then you go back six decimal places to get the value in uF. He said that it was 1kV.

0.01uF is a small value, but the voltage is very high. I read in the Electronic Design Magazine about supercapacitors. They said that to retain a small size you either have high voltage and low capacitance or high capacitance and low voltage. Look up many of the supercapacitors to date and you'll notice that they don't have very high voltage ratings.

10. ### ELECTRONERD Senior Member

May 26, 2009
1,146
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In that case, I doubt that it is 1kV. That seems too high for such a small cap.

11. ### peranders Well-Known Member

May 21, 2007
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The voltage rating is most likely DC and 10 nF. The application seems to be voltage doubler. The size seems quite OK for a 1kV 10 nF.

12. ### spike47 Thread Starter Member

Mar 11, 2009
22
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It is marked 1kv !! , here is a probable replacement .

just another point , as per my first post , what symtems could cause a capacitor to start making a clicking sound .

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13. ### rspuzio Active Member

Jan 19, 2009
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> what symtems could cause a capacitor to start making a clicking sound

One thought that comes to mind is that, should capacitor plates come
loose, then the electrostatic forces could move them around or bend

14. ### cryosar Active Member

Apr 2, 2009
40
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This capacitor is used in the clamp circuit of the SMPS

15. ### ELECTRONERD Senior Member

May 26, 2009
1,146
16
I had the same problem on my power supply, it would make this "clicking" sound and I didn't know what was wrong. Until I noticed I had my CD player nearby and when I turned that off it stopped. Not sure that's the same situation with you.

16. ### spike47 Thread Starter Member

Mar 11, 2009
22
0
Hi

I have found the problem to be a short in the Switch mode transformer , I desoldered the cap , and the noise was still there although now very faint , so the short was puting a load on the cap ! .