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yogesh jain · Mar 23, 2009, 01:00 AM

How to measure ripple in dc system

Perito · Mar 23, 2009, 03:59 AM

Two ways. #1 (best way): Oscilloscope. #2: Voltmeter on the AC scale. The internal capacitor will block the DC and only the AC (the ripple) will be measured.

yogesh jain · Mar 23, 2009, 04:42 AM

Originally Posted by Perito

Two ways. #1 (best way): Oscilloscope. #2: Voltmeter on the AC scale. The internal capacitor will block the DC and only the AC (the ripple) will be measured.

That's so nice of you sir/madam , what is % ripple

Perito · Mar 23, 2009, 06:19 AM

Gee. No one has referred to me as "sir" in ages. Usually, it's "Yo. You, there...".

The "percent ripple" is usually described as the RMS AC voltage (what you would measure on most voltmeters on the AC scale) divided by the DC component of the voltage -- expressed as a percentage. So, if you had a 12.00 volt power supply with a 1 volt (RMS) AC voltage superimposed on it (a ripple), you would have 1/12 * 100% = 8.3% ripple.

yogesh jain · Mar 23, 2009, 06:47 AM

Originally Posted by Perito

Gee. No one has referred to me as "sir" in ages. Usually, it's "Yo. You, there...".

The "percent ripple" is usually described as the RMS AC voltage (what you would measure on most voltmeters on the AC scale) divided by the DC component of the voltage -- expressed as a percentage. So, if you had a 12.00 volt power supply with a 1 volt (RMS) AC voltage superimposed on it (a ripple), you would have 1/12 * 100% = 8.3% ripple.

Dear Perito,

You have great knowledge are you a professor

KISS · Mar 23, 2009, 07:16 AM

Most voltmeters will not measure ripple correctly.

1. frequency of the ripple (picture a 1 MHZ DC-DC converter)
(the frequency response isn't there)

2. Most voltmeters are peak responding, RMS reading. They are only correct for sine wave inputs. You need a TRMS (True RMS) voltmeter with the proper frequency response. Crest factor can come into play for some meters as well.

Generally ripple is measured in p-p or peak to peak. RMS values of ripple are quite meaningless.

An Oscilloscope where the signal is AC coupled should work.

Signal analysis tools such as those capable of doing FFT's (Fast Fourier Transforms) might be able to give a more accurate picture.

Example spec:

http://www.murata.com/power/spec/s11e1.pdf

yogesh jain · Mar 23, 2009, 09:44 PM

Originally Posted by KeepItSimpleStupid

Most voltmeters will not measure ripple correctly.

1. frequency of the ripple (picture a 1 MHZ DC-DC converter)
(the frequency response isn't there)

2. Most voltmeters are peak responding, RMS reading. They are only correct for sine wave inputs. You need a TRMS (True RMS) voltmeter with the proper frequency response. Crest factor can come into play for some meters as well.

Generally ripple is measured in p-p or peak to peak. RMS values of ripple are quite meaningless.

An Oscilloscope where the signal is AC coupled should work.

Signal analysis tools such as those capable of doing FFT's (Fast Fourier Transforms) might be able to give a more accurate picture.

Example spec:

http://www.murata.com/power/spec/s11e1.pdf

Dear sir ,

Thanks for the reply if you can tell what is the effect of high or low ripple and how does it effect the system we are using , to be specific I am concerned to the battery charger with 220v , or 48v rating

KISS · Mar 23, 2009, 11:31 PM

In a strictly battery charging application such as a golf cart, ripple doesn't matter.

If it were for a telephone system then the noise should be out of the hearing range, this is why frequency of the ripple matters.

Usually the battery acts as a big capacitor and dampens the ripple considerbly.

Basic answer is low ripple is usually better, but the application dictates the effect.

Alternator whine in a radio in a car is a typical detrimental effect of ripple.