whats ripple current of c

johndiy · 1st September 2006, 12:10 AM

hi

what is ripple current of a capacitor
the one quoted in the ratings of a capacitor

john

sreten · 1st September 2006, 09:01 AM

Hi,

A power supply may draw constant current but the capacitors
will charge only at the peaks of the incoming AC, so the charging
current is much higher but shorter time, this is the ripple current.

/sreten.

AndrewT · 1st September 2006, 09:47 AM

Hi,
the ripple current is responsible for most of the heating in a smoothing capacitor.

The ripple rating varies with ambient temperature. Keep your capacitors COOL. Locate then away from hot heatsinks/sources and provide ventilation.

You can use PSUD11 to investigate the ripple current in your proposed application, but do try to use as little of the permitted rating as possible.
Multiple parallel caps offer a solution to high ripple currents but have other downsides and a few upsides.

AKN · 1st September 2006, 10:00 AM

Specified ripple current capability on a capacitor is specified in Arms, peak currents can be higher.

bremen nacht · 1st September 2006, 10:38 AM

this will give you an idea of what ripple-current rating your caps will need

http://www.duncanamps.com/psud2/index.html

mikeks · 1st September 2006, 02:56 PM

Alternatively, see Vishay

cpemma · 1st September 2006, 10:42 PM

Quote:

Originally posted by AndrewT
You can use PSUD11 to investigate the ripple current in your proposed application...

That confused me and Google.

PSUD-Latin 2 as per bremen nacht's link?

johndiy · 1st September 2006, 11:26 PM

Hi and thanks
i still dont understand it, i know it relates to ripple but why
is it useful, how do you apply it to power supply design

high ripple currents c's are they better than low ones?

thanks

john

AndrewT · 2nd September 2006, 08:05 AM

Hi,
high ripple capacity rating is better than low ripple capacity rating.

Using less than the ripple capacity rating is better than using all the ripple capacity rating.

Overstepping the ripple capacity rating is dangerous (if continued for more than a brief moment).

sawreyrw · 2nd September 2006, 11:37 AM

All caps have a finite resistance. Typically it is called ESR - equivalent series resistance. The power loss is I^2 * R and the power heats up the cap. The temperature rise is a function of the thermal resistance (from the cap hot spot to the surrounding air) and the life of the cap is strongly related to it's hot spot temperature. So, in general, lower ESR make for longer life.

1st September 2006, 12:10 AM	#1
johndiy Banned Join Date: Aug 2006	whats ripple current of c hi what is ripple current of a capacitor the one quoted in the ratings of a capacitor john

1st September 2006, 10:00 AM	#4
AKN No snake oil diyAudio Member Join Date: Aug 2005 Location: In the middle of Sweden	Specified ripple current capability on a capacitor is specified in Arms, peak currents can be higher. __________________ / Anders

1st September 2006, 10:38 AM	#5
bremen nacht diyAudio Member Join Date: Feb 2004 Location: england	Useful tool for power supply design this will give you an idea of what ripple-current rating your caps will need http://www.duncanamps.com/psud2/index.html __________________ All this radio needs is a fuse

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1st September 2006, 09:01 AM	#2
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, A power supply may draw constant current but the capacitors will charge only at the peaks of the incoming AC, so the charging current is much higher but shorter time, this is the ripple current. /sreten.

1st September 2006, 09:47 AM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, the ripple current is responsible for most of the heating in a smoothing capacitor. The ripple rating varies with ambient temperature. Keep your capacitors COOL. Locate then away from hot heatsinks/sources and provide ventilation. You can use PSUD11 to investigate the ripple current in your proposed application, but do try to use as little of the permitted rating as possible. Multiple parallel caps offer a solution to high ripple currents but have other downsides and a few upsides.

1st September 2006, 02:56 PM	#6
mikeks Account Disabled Join Date: Jun 2004 Location: Animal farm	Alternatively, see Vishay

1st September 2006, 11:26 PM	#8
johndiy Banned Join Date: Aug 2006	Hi and thanks i still dont understand it, i know it relates to ripple but why is it useful, how do you apply it to power supply design high ripple currents c's are they better than low ones? thanks john

2nd September 2006, 08:05 AM	#9
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, high ripple capacity rating is better than low ripple capacity rating. Using less than the ripple capacity rating is better than using all the ripple capacity rating. Overstepping the ripple capacity rating is dangerous (if continued for more than a brief moment).

2nd September 2006, 11:37 AM	#10
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	All caps have a finite resistance. Typically it is called ESR - equivalent series resistance. The power loss is I^2 * R and the power heats up the cap. The temperature rise is a function of the thermal resistance (from the cap hot spot to the surrounding air) and the life of the cap is strongly related to it's hot spot temperature. So, in general, lower ESR make for longer life.

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