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Old 13th July 2006, 06:39 AM   #1
beppe61 is offline beppe61  Italy
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Location: torino
Default Ripple current in capacitors.

Dear Sirs,


first of all I have to say that I am quite ignorant in electronics.
Then please excuse me if this question has been already asked a number of times.
I searched the forums but I did not find a straight answer.
I see in the capacitors' specs the Ripple Current figure.
What is that ?
Moreover, can this figure be taken as a measure of the quality/performance of a cap ?
I mean, I see remarkable differences from brand to brand for same values of uFs and working Voltage.
My interest is driven by a very simple DIY project of linear PSU to use with a power amp (transformer+diodes bridge+filter caps).
And a last question: if I keep the same transformer and replace the two main filter caps with other bigger and better ones what kind of improvements could I expect in the final sound?
Better bass maybe (a very important point to me) ?
Will these improvements be substantial ?

Thank you very much indeed.
Kind regards,

beppe
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Old 13th July 2006, 11:55 AM   #2
AndrewT is offline AndrewT  Scotland
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Hi Beppe,
I see you are still trying to learn.

Ripple current is the current flowing into and out of the capacitor. It can be from the charging pulses coming from the rectifier or it could be the current demand pulses from the output stage.

As the current flows in and out it passes through the ESR and causes heating.

Basically the lower the ESR the higher the ripple rating. Similarly the bigger the surface area of the cap the more heat it can dissipate. Both these features cost money to manufacture, so one tends to find that good ripple rating costs more and due the the way it is achieved it is a rough indicator of cap quality. Notice I said rough.

Careless selection of smoothing caps can lead to overheating and very short life due to high ripple during operating conditions.

A cheap way to improve the ripple rating is multiple parallel lower value caps. It's about lower ESR and more surface area.
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Old 13th July 2006, 12:25 PM   #3
beppe61 is offline beppe61  Italy
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Join Date: Feb 2005
Location: torino
Quote:
Originally posted by AndrewT
Hi Beppe,
1) I see you are still trying to learn.
2) Ripple current is the current flowing into and out of the capacitor.
It can be from the charging pulses coming from the rectifier or it could be the current demand pulses from the output stage.
As the current flows in and out it passes through the ESR and causes heating.
Basically the lower the ESR the higher the ripple rating.
Similarly the bigger the surface area of the cap the more heat it can dissipate.
Both these features cost money to manufacture, so one tends to find that good ripple rating costs more and due the the way it is achieved it is a rough indicator of cap quality.
Notice I said rough.
Careless selection of smoothing caps can lead to overheating and very short life due to high ripple during operating conditions.
A cheap way to improve the ripple rating is multiple parallel lower value caps. It's about lower ESR and more surface area.
Hello dear Mr. Andrew,

thank you very much for your kind and valuable advice, as always.
1) It is quite clear that my comprehension ability is limited.
I try always to "trivialize" topics in the hope to understand that a little better.
2) Thank you for your kind explanation.
To be more specific I have some huge Sikorel caps (15.000uF/100V) at hand that I would like to use to replace the existing ones in an amp (it has two 7.200uF/50V old Mallorys),
The dimensions of the Sikorels is going to make the replacement not the easiest mod to perform.
I wonder if this mod is advisable.
Would I get any sonic improvements all other things kept the same ? in which way ?

Thank you so much again.
Kind regards,

beppe
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Old 3rd September 2006, 09:34 AM   #4
beppe61 is offline beppe61  Italy
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Join Date: Feb 2005
Location: torino
Quote:
Originally posted by AndrewT
Hi Beppe,
I see you are still trying to learn.
Ripple current is the current flowing into and out of the capacitor. It can be from the charging pulses coming from the rectifier or it could be the current demand pulses from the output stage.
...
.
Dear Mr. Andrew,

I thought about your words a lot before putting another maybe trivial question.
If filter caps with a low current ripple are used in a power amp power supply could they act as a bottle-neck for the current that should reach the output devices of the amp?
In this case a replacement of all the filter caps with others with better current ripple figure should be always extremely beneficial for the overall performance of the amp.
Much more, for instance, than a transformer replacement/upgrade keeping the original caps.
Am I misunderstanding badly the all thing?

Thank you so much as always.
Kind regards,

beppe
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Old 3rd September 2006, 10:01 AM   #5
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
Hi Beppe,
nothing is ever too trivial, but you will know from some of my postings that I do not suffer lazy fools gladly.

Quote:
filter caps with a low current ripple are used in a power amp power supply could they act as a bottle-neck for the current that should reach the output devices of the amp
yes. But think about the two sides of ripple in the main smoothing bank. Which is worse? the ripple from the charging pulses or the ripple from the output load current demands? Improving the ripple rating may (or will?) have a direct effect on the capacitor reliability.
Quote:
replacement of all the filter caps with others with better current ripple figure should be always extremely beneficial for the overall performance of the amp
that is likely to be overstating the improvement potential. Take out always extremely and you could be nearer the truth.
Quote:
Much more, for instance, than a transformer replacement/upgrade keeping the original caps
again overstating the case. I believe it depends on how the designer has skimped on the specification of both the transformer AND the smoothing capacitors to save both cost and space. Improvement may come from either upgrade but equally the result from the upgrade could be worse than the original if the designer has voiced the COMBINATION of PSU and amplifier to sound just right (to his ears and those of his intended market).
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Old 3rd September 2006, 11:37 AM   #6
beppe61 is offline beppe61  Italy
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Join Date: Feb 2005
Location: torino
Quote:
Originally posted by AndrewT
Hi Beppe,
nothing is ever too trivial, but you will know from some of my postings that I do not suffer lazy fools gladly.

yes. But think about the two sides of ripple in the main smoothing bank. Which is worse? the ripple from the charging pulses or the ripple from the output load current demands? Improving the ripple rating may (or will?) have a direct effect on the capacitor reliability. that is likely to be overstating the improvement potential. Take out always extremely and you could be nearer the truth. again overstating the case.
I believe it depends on how the designer has skimped on the specification of both the transformer AND the smoothing capacitors to save both cost and space.
Improvement may come from either upgrade but equally the result from the upgrade could be worse than the original if the designer has voiced the COMBINATION of PSU and amplifier to sound just right (to his ears and those of his intended market).

Thank you sincerely again for the kind and thoruogh advice.
As always it is a much more complex issue than how it looks to an uneducated eye.
I should just stop to play with low level equipment hoping to upgrading them to an acceptable level and take a more serious approach to the problem.

Kind regards,

beppe
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