[Newbie] Using 50V cap with 30-0-30. safe? - diyAudio
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Old 30th August 2005, 03:07 PM   #1
nina is offline nina  United Kingdom
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Default [Newbie] Using 50V cap with 30-0-30. safe?

Sorry for this dummy question:

I have many good electrolytic cap rated 50V. I wonder if it can be used "safely" with the power 30-0-30V ( ~ 44Vdc) ?

Thanks,
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Old 30th August 2005, 03:10 PM   #2
Jorge is offline Jorge  Brazil
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I don't think they would blow on you, but their life will be shortened.
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Old 30th August 2005, 03:11 PM   #3
UrSv is offline UrSv  Sweden
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Absolutely no problem at all IMHO. Go ahead.
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Old 30th August 2005, 03:23 PM   #4
nina is offline nina  United Kingdom
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Quote:
Originally posted by Jorge
I don't think they would blow on you, but their life will be shortened.
Thanks UrSv and Jorge.

When saying their life will be shortened. How bad it is?
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Old 30th August 2005, 03:43 PM   #5
wxn is offline wxn  Lithuania
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IMHO it's more dependent on such factors as temperature and physical damage.
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Old 30th August 2005, 04:03 PM   #6
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No dummy question, very good question.

30Vac = 42.43 Vdc, with rectifier losses a 50Vdc capacitor has nearly 20% reserve for voltage surge and unloaded voltage increase.
Which is more than enough for any transformer.
Using higher voltage capacitors will only cost you extra money without returns.
Reforming the ones you have is far more important than having some with extra spare volts.

If you like the tech stuff, read some pages on (re)-forming capacitors.
Pooge posted some excellent links to some recently:
http://www.diyaudio.com/forums/showt...989#post705989

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Old 30th August 2005, 04:15 PM   #7
Jorge is offline Jorge  Brazil
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Some electrolytic life guidelines:

http://www.capacitorindustries.com/SEI/guidelines.htm
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Old 30th August 2005, 05:01 PM   #8
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Rectified and filtered DC voltage is 1.414 times the AC voltage.

So, 30 VAC X 1.414 = 42.42 VDC positive and negative rails.

Larry
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Old 30th August 2005, 10:46 PM   #9
guzzler is offline guzzler  Scotland
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All the above is correct, but forgetting the fact that the transformers voltage is usually rated at maximum output. An unloaded transformer will easily put out 10-20% higher voltage than actually specced. As always when dealing with high voltage/current, play safe.

Go double the voltage rating of the transformer for some margin of safety, ie 63V
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Old 31st August 2005, 02:41 AM   #10
nina is offline nina  United Kingdom
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Quote:
Originally posted by guzzler
All the above is correct, but forgetting the fact that the transformers voltage is usually rated at maximum output. An unloaded transformer will easily put out 10-20% higher voltage than actually specced. As always when dealing with high voltage/current, play safe.

Go double the voltage rating of the transformer for some margin of safety, ie 63V
guzzler,

I plan to put 2.2K-10K 5W Bleeder resister in parallel with the filer cap. Will it help?

Thanks.
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