[Newbie] Using 50V cap with 30-0-30. safe?

nina · 30th August 2005, 03:07 PM

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,

Jorge · 30th August 2005, 03:10 PM

I don't think they would blow on you, but their life will be shortened.

UrSv · 30th August 2005, 03:11 PM

Absolutely no problem at all IMHO. Go ahead.

nina · 30th August 2005, 03:23 PM

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?

wxn · 30th August 2005, 03:43 PM

IMHO it's more dependent on such factors as temperature and physical damage.

jacco vermeulen · 30th August 2005, 04:03 PM

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

(i had a Bearded Collie named Niña, but that is Spanish

)

Jorge · 30th August 2005, 04:15 PM

Some electrolytic life guidelines:

http://www.capacitorindustries.com/SEI/guidelines.htm

Lsharptec1 · 30th August 2005, 05:01 PM

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

guzzler · 30th August 2005, 10:46 PM

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

nina · 31st August 2005, 02:41 AM

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.

30th August 2005, 03:07 PM	#1
nina diyAudio Member Join Date: Apr 2005 Location: Earth	[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,

30th August 2005, 03:11 PM	#3
UrSv diyAudio Member Join Date: Jan 2002 Location: Sweden	Absolutely no problem at all IMHO. Go ahead. __________________ UrSv Those who say it can't be done should not stop those who are doing it.

30th August 2005, 03:43 PM	#5
wxn diyAudio Member Join Date: Sep 2003 Location: Vilnius	IMHO it's more dependent on such factors as temperature and physical damage. __________________ Nothing is as simple as it seems

30th August 2005, 04:03 PM	#6
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, just under Rotterdam	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 (i had a Bearded Collie named Niña, but that is Spanish ) __________________ Looks like Sponge Bob has killed another thread.

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30th August 2005, 03:10 PM	#2
Jorge diyAudio Member Join Date: Apr 2001 Location: Brazil	I don't think they would blow on you, but their life will be shortened.

30th August 2005, 04:15 PM	#7
Jorge diyAudio Member Join Date: Apr 2001 Location: Brazil	Some electrolytic life guidelines: http://www.capacitorindustries.com/SEI/guidelines.htm

30th August 2005, 05:01 PM	#8
Lsharptec1 diyAudio Member Join Date: Oct 2004	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

30th August 2005, 10:46 PM	#9
guzzler diyAudio Member Join Date: Feb 2003 Location: Scotland	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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