Talk:Ripple (electrical)

message: For an artistic project I am looking for a cross-section graph (z by x) of the shape that water's surface makes when a single object strikes the surface of a fluid. This would of course change over time and be dependent upon characteristics of the fluid, etc.
Lee De Cola 15:40, 16 November 2006 (UTC)
thread_title: Art project

message: I seem to remember hearing recordings of a man on the early BBC saying the words "Ripple testing. Ripple testing". Was this a test for this sort of ripple? Myrvin (talk) 17:59, 23 June 2010 (UTC)
replies: text: Unlikely.  There used to be an old test called a "ripple test" that had a similar purpose to VSWR and I would guess that is what it was.  Some version of this seems to have found a purpose in the modern world. SpinningSpark 19:04, 23 June 2010 (UTC)
replies: text: Turns out that the announcer may have made it up. Maybe he thought it sounded nice and had a rolled r and ps too. Myrvin (talk) 07:35, 16 November 2010 (UTC)
thread_title:  Ripple testing 

message: Nothing at all??  If it isn't here, then where?  Rather astonishing.  Sbalfour (talk) 22:02, 6 November 2017 (UTC)
thread_title:  Where's ripple current? 

message: The most common meaning of ripple in electrical science is the small unwanted residual periodic variation of the direct current (DC) output of a power supply... I don't like that at all.  First, the statement is unsourced. I wouldn't say most common; that depends on the application. Electrical science is a bit grandiose - electronics is better diction.  Nor is ripple necessarily small: the ripple voltage output of a rectifier is 100% of the peak voltage of the AC source.  Unwanted is judgmental and not strictly true: for battery charger applications, and even filament heaters (in general, resistive circuits) ripple is irrelevant - if it were unwanted, we'd get rid of it, but we don't.  Ripple isn't always present on the output of a power supply - in fact it rarely is, because most switch-mode power supplies are regulated.  Where we're most concerned with ripple is between the rectifier and power supply output.  And finally, ripple is not a variation in the direct current, but the DC voltage.  It's a high-schooler's definition, and omitted (until I added it below), any mention of ripple current.  Sheesh... Sbalfour (talk) 15:24, 7 November 2017 (UTC)
thread_title:  Description of ripple (lead) 

message: We state the formulas, with approximations rolled in, but give none of the derivation or development... that is, we omit all scholarship, and give formulas that experimenters would get from a lab manual when building a circuit, and need a component. Before we even mention approximations, which are superfluous to the topic, maybe we should describe how capacitors and chokes actually behave? I.e. something like "capacitors charge and discharge exponentially; the current delivered to the load over the relatively long discharge time must equal the current used to charge the capacitor in a short time, which leads directly to the phenomenon of ripple current."  Yah...  
The capacitor paragraph omits mention of yet another critical assumption, that output impedance of the capacitor/rectifier/transformer circuit should be much less than the input impedance of the following circuit.  That may be a dubious assumption in the case of a high voltage secondary winding with large DCR.  For old style oil capacitors, ESR could be a substantial fraction of the impedance of the cap at 120hz.  That also invalidates the formula.
In the inductor paragraph, unlike the capacitor paragraph where we use analytical representation of the constants, the magic number ".236" appears.  That looks suspiciously like  \sqrt 5 - 2 , but I've never seen  \sqrt 5 in such formulas.  It also says "with suitable approximations"... such as??  How about this statement: A choke has a filtering action and consequently produces a smoother waveform with less high-order harmonics.  If this, then that.  Why can't I substitute 'capacitor' in place of choke here? Capacitors have a filtering action; so do resistors, diodes, and other components.  Less high order harmonics than what?  A capacitor? We didn't mention a capacitor produced any harmonics.  If (lack of) them matters for a choke, then the presence of them should matter for a capacitor.  The statement is meaningless filler, and should straight up be deleted. However, we blatantly omit approximation formulas for p-p ripple for chokes. Why?? (probably because the original contributors didn't know how to describe what a choke does, and could manage linear approximations but not partial differential equations and integral calculus).
I'm going to take a stab at describing what a choke really does, and why it reduces ripple. The magnetic field of a choke is energized by current, rather than voltage like the electric field of a capacitor.  It resists change in current,i.e. it does not supply less when voltage falls, nor more when voltage rises as in-phase AC current does.  Because current lags voltage in a choke, current will tend to be higher when voltage is lower, and lower when voltage is higher.  Higher current will cause voltage to rise at the load, and fill-in troughs in the voltage waveform; similarly, lower current at the load will round off voltage peaks. Therefore ripple voltage will be reduced.
A grand omission with respect to both ripple factor formulas, is whether they are associated with full-wave or half-wave rectifiers, and whichever one they are for, where are the formulas for the other, since we explicitly detailed both just above?
For the rms value of the ripple voltage, the calculation is more involved as the shape of the ripple waveform has a bearing on the result.  For what waveform does the peak, derivative, integral, etc NOT depend on its shape??  If the imputation is that ripple is
not a simple sinusoidal waveform, then LET'S SAY IT; but that simply beggars the question - what shape does it have, and why is that
difficult to manage?  I think we should say that RMS is related to the area under the curve (between the curve and ordinate), and we might presuppose that the ordinate is the lowest point on the curve, when actually it isn't.  Exactly how is the ordinate defined?
I think most of the presentation (i.e.the approximation stuff) in this section is superfluous and ought to be moved into a sidebar or footnote. What's needed is a scholarly presentation of the subject, with analytical formulas developed starting with  dv/dt .  (Can't do calculus? tsk, tsk) Then mention reasonable approximations, but leave substituting such approximations into the formulae up to the experimenter.  The encyclopedia is not a lab manual. Sbalfour (talk) 17:47, 8 November 2017 (UTC)
thread_title:  Ripple voltage approximation forumlas 

message: We jump into measurement of smoothing before defining what ripple is.  The article as written assumes a monolithic kind of ripple, when in fact ripple is a complex phenomenon of signal transmission, and requires fourier analysis to define exactly what we're looking at.  There's the presence of potentially many higher harmonics, divided into even and odd with possibly different implications.  In multi-phase current, there's cis- and trans- phase order rotation harmonics.  Mixed harmonics also result in sum-and-difference frequencies and their harmonics (i.e. non-harmonic or intermodulation distortion) which may also have to be considered.  This article needs a firm mathematical and theoretic foundation before we do anything. Sbalfour (talk) 23:54, 10 November 2017 (UTC)
thread_title:  Ripple definition 

message: We dutifully compute the RMS value of capacitor-filtered ripple, which is considered to be a sawtooth wave, using an approximation formula, and insert it into the computation of \gamma.  A sawtooth wave incorporates odd harmonics of the fundamental, which are not actually present in the rectifier output, so the resulting RMS estimate will be high.  We painstakingly computed the RMS value of unfiltered rectified ripple above, starting from first principles, using the integral calculus.  Not too many assumptions were made.  We know that a filter reduces alternating voltage (RMS unless otherwise specified) as a voltage divider according to Kirchoff's law, and Kirchoff's law is not itself an approximation - it's exact. The proper way, and patently more accurate way, to compute the filtered ripple is according to the familiar formula Vrms' = Vrms * Xc/Zl where Vrms' is the filtered voltage, Vrms is the rectified AC component, Xc is capacitive reactance, and Zl is the impedance looking into the load.  The complex impedance of the load is a vector quantity whose value is \sqrt {Rl^2 + Xc^2}. The DC component of gamma, which is now higher because we just converted some more of it, is \sqrt {Vlrms^2 - Vrms'^2}, where Vlrms is the RMS value of the voltage across the load, which doesn't change as we shift the ratio between the AC and DC components (except via dissipative losses which are not accounted for here).  This value is also computed above.  We normally can make the assumption that Xc >> Rl where ">>" is 10X or more, frequently as high as 50X.  The rule is often stated another way, \tau (RC in this case) > 1/f where f is frequency of the ripple, 100 or 120 hz. 
The following table gives the computed and estimated values of gamma for a range of relative capacitance impedance ratios:
Xc/Rl:    .02    .1     .2   .333        
  gamma  .0087   .043   .087  .146
~gamma .0091   .045   .091  .151
gamma is computed using Kirchoff's law; ~gamma  is computed using sawtooth approximation.  The approximation based on the constant .453  is consistently high by 4% for values Xc << RL.  It suggests that a constant 4% lower should be used. That is in fact correct: the actual constant is .4352, accurate to about 1 part in 10,000.  
For the RMS value of the ripple resulting from choke input, another unrelated approach is apparently used: an approximation ostensibly based on the first non-constant term of the Fourier expansion of rectifier output is used (the source is a 50-year old non-descript book, no longer available and hence not verifiable).  In contrast to the saw tooth approximation of capacitor ripple, the Fourier term discards all higher harmonics of the ripple so the resulting estimate of RMS will be low rather than high, a bothersome incongruency between approaches.  Several
successive approximations were applied to the resulting integral to reduce it to the stated formula, and I'm dubious. I'm working on a presentable derivation, since the math is daunting.  I also get a better approximation by starting with the analytical geometric approach detailed in the capacitor input paragraph.
Sbalfour (talk) 18:26, 14 November 2017 (UTC)
thread_title:  RMS approximations 

message: 90% of this article is concerned with a rather minor parameter of ripple, the ripple factor (RF, or \gamma).  There are at least a handful of quantification measures of voltage ripple, and their relationships to diode current, DC voltage, transformer VA, and other quantities.  The various diode rectifier topologies also have distinct implications.  Real rectifiers differ from ideal rectifiers, especially for tube diodes and other non-SS diodes. No coverage of ripple current or 3-phase rectification.  Rectification in switch-mode power supplies has some unique implications.  In rectification circuits, there's a trade-of between ripple reduction and voltage regulation (capacitor vs inductor) - need to cover here or in rectifier#rectifier output smoothing section.  Keep in mind that this whole article except for the frequency domain stuff, is slated to be merged into the foregoing article/section.
I propose an organization thus:
1. Definition of signal
2. Properties of rectifiers
*  center-tapped, bridge, voltage doubler; half-wave and full-wave
*  ideal vs real (diode forward voltage, dissipation, HF switching noise, and switching time (non-continuous current flow)
3. Fourier decomposition
4. Quantification of ripple
* peak-peak, RMS value,  signal equation, approximation (i.e. sawtooth), ripple factor, form factor, rectification ratio, transformer utilization
5. filtering: capacitor, choke, LC & RC sections, \pi filter
*  This is a summary; considerations of filter theory should (filter types, Butterworth, etc, corner frequencies, frequency domain ripple,  etc) should be handled in low pass filter article
6. 3-phase rectification
7. ripple current
*  (this section could become a whole other article - primarily concerned with input to rectifier rather than output)
Sbalfour (talk) 17:26, 14 November 2017 (UTC)
thread_title:  Structure of article