Power cables - how to measure

[Martykt]

11 minutes ago, bob_m_54 said:

NO

Are some meters able to ignore the incoming AC signal and be able to correlate the DC in the mains as a result?

How would this work?

 

15 minutes ago, bob_m_54 said:

I don't know what you mean by "flattening the wave" but using a CRO DSO,. NO.

I remember from somewhere though can't exactly remember where that what DC in the mains looks like is the peak of the wave being flat and as a result forming DC.

 

If you have any links on DC in the mains I'd be interested in reading further on it.

[bob_m_54]

Just now, Martykt said:

Are some meters able to ignore the incoming AC signal and be able to correlate the DC in the mains as a result?

How would this work?

 

I remember from somewhere though can't exactly remember where that what DC in the mains looks like is the peak of the wave being flat and as a result forming DC.

 

If you have any links on DC in the mains I'd be interested in reading further on it.

DC on the mains is an offset. ie the zero point of the AC waveform is at a DC level. flattening of the peaks is clipping, and I don't know what would cause that on a mains supply.

[Guest rmpfyf]

21 minutes ago, bob_m_54 said:

EMI protection on interconnects yes. On power cables, I can't see the point. Keeping **** out? your equipment filter circuits will sort that out. And there is a lot more cable in your house that will pick up even more ****...Keeping **** in? the effective radiated fields are very small. You'd have to have the power cable laying side by side to an unshielded interconnect to notice much.

 

There's a bunch of **** where my audio equipment is (TV etc) and the difference with/without a shielded cable is small but there. The rest of the cable in my home is not adjacent to my audio kit. Shielded cable is not expensive. If spending money on an upgrade of any sort, it's directionally correct and not expensive. 

 

21 minutes ago, bob_m_54 said:

Basically the same as voltage drop as above

 

No - the reference is in part to inductance - AC not DC, there are differing implications.

 

21 minutes ago, bob_m_54 said:

Voltage drop is not an issue with compliant to AUS standards

 

Australian mains and wiring standards specify an allowable voltage drop, they don't specify that voltage drop is or isn't an issue with your audio kit. The voltage drop permissible is quite signifcant, particularly in transients. As per my last post on this, no, I don't think the last stretch of cable is doing anything of significance here. Beyond something exceedingly poorly designed or a very overloaded cable, of whatever electrical properties a power cord assembly can realistically have I don't think resistance (in a practical range of compliant conductors) is a likely factor.

 

16 minutes ago, bob_m_54 said:

How can you use a techo word like Tribological (wtf that means?) and dampening in the same sentence

 

With ease.

 

As for your 'wtf' request - would you like me to handle that with about as much grace as you're carrying on here? 

 

There is no single subject domain expert in everything required to get to the bottom of this, but so far it's been 20 pretty good pages of having a go. That some of us have forgotten more than others may ever know in some aspects hasn't stopped an open discussion so far. Please consider how you might keep it going.

[Martykt]

31 minutes ago, rmpfyf said:

I don't think voltage drop is an issue, really, or you'd hear a difference when your system plugged in at different points in your home according to how far a GPO was away you were from your incoming mains. And audiophiles would have their houses redesigned so the incoming mains could be as close as possible to the street supply etc. Voltage drop is unequivocally not something a cable can help with - mega bandaid approach if so when you need a transformer. 

 

I don't think EMI is such an issue either. Cables should be shielded, that's just good practice. Broadband hash as mentioned is better than periodic hash, or you can go putting filters on everything else bar the audio circuits for completeness. 

 

Conductivity is just size of conductor, you could make a good argument for AC on skin depth that you don't necessarily want the smallest possible cross section. This is AC not DC after all.

 

I think inductance has a bit to do with it. Starts to make a theoretical argument for 'change in demand' performance factors, and theoretically why there may be a preference for solid core, or multiple solid cores individually insulated, twisted per conductor, maybe ideally shielded as twists? How would the earth best work in this imaginary scenario?

 

Tribological factors point towards dampening though yet to unpack what the real impacts might be.

 

What of capacitance?

Or it could be a combination of some or all of those factors.

[Martykt]

23 minutes ago, bob_m_54 said:

DC on the mains is an offset. ie the zero point of the AC waveform is at a DC level. flattening of the peaks is clipping, and I don't know what would cause that on a mains supply.

Yes that's what I'm confusing it with.

 

I'm still not sure how a multimeter set to DC would be able to measure this though?

[bob_m_54]

2 minutes ago, rmpfyf said:

 

There's a bunch of **** where my audio equipment is (TV etc) and the difference with/without a shielded cable is small but there. The rest of the cable in my home is not adjacent to my audio kit. Shielded cable is not expensive. If spending money on an upgrade of any sort, it's directionally correct and not expensive. 

I don't know what you mean by "directionally correct"

2 minutes ago, rmpfyf said:

 

No - the reference is in part to inductance - AC not DC, there are differing implications.

 

You were specifying conductance, which is the reciprocal of resistance. Inductive reactance is a different thing again. And at 50Hz, in a mains cord, is not an issue

2 minutes ago, rmpfyf said:

Australian mains and wiring standards specify an allowable voltage drop, they don't specify that voltage drop is or isn't an issue with your audio kit. The voltage drop permissible is quite signifcant, particularly in transients. As per my last post on this, no, I don't think the last stretch of cable is doing anything of significance here. Beyond something exceedingly poorly designed or a very overloaded cable, of whatever electrical properties a power cord assembly can realistically have I don't think resistance (in a practical range of compliant conductors) is a likely factor.

 

 

With ease.

AS/NZS 4417 (don't quote me) states a 10A power cable as in a "kettle cord" must be 1.5mmsq

2 minutes ago, rmpfyf said:

As for your 'wtf' request - would you like me to handle that with about as much grace as you're carrying on here? 

 

There is no single subject domain expert in everything required to get to the bottom of this, but so far it's been 20 pretty good pages of having a go. That some of us have forgotten more than others may ever know in some aspects hasn't stopped an open discussion so far. Please consider how you might keep it going.

I'm not fussed about grace.. but I found it ironic that you used the term dampening, instead of damping, right after "tribology".

But are you talking about Tribology in the mechanical sense, or in the electrical sense? Way back in the dim recesses of my memory, I can remember there are certain factors relating to the effects of thermally influenced tribology between layers in a PCB. And they may have affected capacative and inductive properties of the PCB. But I don't remember anything about conductors in contact with each other.

 

In the mechanical sense it's about inter strand wear on conductors in flexed cables.

[bob_m_54]

26 minutes ago, Martykt said:

Or it could be a combination of some or all of those factors.

NO

[MLXXX]

1 hour ago, Martykt said:

 

 

$4.75... now see you're just not trying....

 

https://www.solutionsbybrandon.com.au/alogic-alogic-5m-aus-3-pin-wall-to-iec-c13-male-to-female-moq-6-mf-3pc13-05.html

That one is indeed very cheap at $1.86 (before postage) but at 5 metres is much longer than a standard kettle cord. I guess I could divide the voltage drop by 4 if testing a 5 metre cord to make it equivalent to a 1.25m cord.   I'm assuming the resistance of the connectors would not be material to that calculation.

I think the 1.2m cord from Bunnings might do, though it is only rated C13 and I have a lot of cables lying around the house used for pcs, computer monitors, printers, and powered speakers with the C13 connector.  I could simply measure 2 or 3 of those for voltage drop.

 

I'm not sure what the practice is in Australia, whether C15 cords (with their higher temperature rating) are used with kettles in preference to C13.  (The electric kettle I used this morning for testing mains source impedance has the power cord hardwired to the base onto which the kettle is placed.)

Edited October 16, 2020 by MLXXX

[MLXXX]

36 minutes ago, Martykt said:

I'm still not sure how a multimeter set to DC would be able to measure this though?

In the days of analogue meters I never dared to have the meter set to a low DC voltage range and connect it to 230 or 240V mains.

 

With digital meters how they'd react to a DC offset on a 50Hz AC waveform would depend on the circuit design.  What meters can do this successfully?

 

In an emergency if I needed to measure DC offset of the mains I'd be tempted to rig up an RC network with a long time constant and then measure the (almost ripple-free) voltage across the capacitor with a digital meter.  But that would be a once-off rather dangerous thing to do.  For one thing the resistor would need to be able to withstand mains voltage across it. For another, you'd want to include a bleed resistor to discharge the capacitor.

[Guest rmpfyf]

1 minute ago, bob_m_54 said:

I don't know what you mean by "directionally correct"

Good, if of unspecified magnitude.

 

1 minute ago, bob_m_54 said:

You were specifying conductance, which is the reciprocal of resistance. Inductive reactance is a different thing again. And at 50Hz, in a mains cord, is not an issue

I wasn't specifying either specifically. That anything isn't an issue to meet mains requirements does not qualify anything as a last-word device in a performance context.

 

2 minutes ago, bob_m_54 said:

AS/NZS 4417 (don't quote me) states a 10A power cable as in a "kettle cord" must be 1.5mmsq

Yes (not sure the relevance of this)

 

6 minutes ago, bob_m_54 said:

But are you talking about Tribology in the mechanical sense, or in the electrical sense? Way back in the dim recesses of my memory, I can remember there are certain factors relating to the effects of thermally influenced tribology between layers in a PCB. And they may have affected capacative and inductive properties of the PCB. But I don't remember anything about conductors in contact with each other.

 

In the mechanical sense it's about inter strand wear on conductors in flexed cables.

Could be inter-strand wear on conductors, could be sheath-to-insulation behaviours. There's an alternating current at play. Excitation to any notable end I guess would require a magnetic field. There are people who believe certain types of insulators used in power cables make for discernable, audible differences in their rigs. In lieu of any data proving otherwise this thread exists to entertain all.

 

3 minutes ago, bob_m_54 said:

I'm not fussed about grace.. but I found it ironic that you used the term dampening, instead of damping, right after "tribology".

You're nitpicking over a typo? That's your soapbox moment - that someone mistyped something? 

 

I'm fussed about keeping an open discussion, and if you can't support that best you start another thread that doesn't require it.

[Steffen]

2 hours ago, bob_m_54 said:

OK. Comparing a standard "kettle cord" which has to be a minimum of 1.5mmsq, to a 2.5mm sq power cable

 

1M x 1.5mmsq cable - 230VAC - 10A - voltage drop = 236mV or 0.1% of 230V

1M x 2.5mmsq cable - 230VAC - 10A - voltage drop = 142mV or .06% of 230V

 

Sure, but will the tea taste the same? And how much better would it taste if you used an audiophile power amp cord? That’s the sort of question an audio forum should be concerned with...

 

(the amp calling the kettle black?)

[aussievintage]

 

 

Oh dear.  We have managed to prove this is all pointless I fear...

[Steffen]

3 minutes ago, aussievintage said:

 

 

Oh dear.  We have managed to prove this is all pointless I fear...

Wasn’t that purpose of this thread? In a nutshell, if you spend hundreds or thousands on audio power cords (rather than on better speakers, amps or listening environment) you’re wagging the dog.

[aussievintage]

1 minute ago, Steffen said:

Wasn’t that purpose of this thread?

Absolutely not.

[Steffen]

Just now, aussievintage said:

Absolutely not.

Sorry, my mistake. Carry on then.

[MLXXX]

18 hours ago, rmpfyf said:

I think inductance has a bit to do with it. Starts to make a theoretical argument for 'change in demand' performance factors, and theoretically why there may be a preference for solid core, or multiple solid cores individually insulated, twisted per conductor, maybe ideally shielded as twists?

There certainly could be odd things happening at higher frequencies, such as resonances at radio frequencies in parts of the cable; that could have hard to predict consequences for EMI radiation to or from adjacent equipment, or for the transmission of EMI along the power cord conductors (or along the shield, if a shield is present).

 

But down at 50Hz, any inductive reactance contributed by the power cable would be over an order of magnitude less than the inductive reactance of the wiring from the power point back to the switchboard [and beyond].

 

A lot is sometimes made of the supposed "suddenness" of the inrush of current when reservoir capacitors are topped up near and at the positive and negative peaks of the AC waveform. But there are factors that limit the rate at which that topping up will occur. And the more limited the rate of rise in the demand for current, the less the impact of inductance.

 

___________________

 

[What follows is intended for more technically inclined readers of this thread.]

 

For example, assume an audio power amplifier, powered by a linear power supply, is being tested at full output power before clipping. It will discharge its power supply reservoir electrolytic capacitors appreciably after each positive peak of the mains such that  when the next negative peak has almost arrived  there will be an appreciable inrush of current through 2 of the 4 bridge rectifier diodes.  The build-up of forward current through those diodes will be gradual at the beginning of that inrush even if it might look somewhat  abrupt on an oscilloscope at the slow timebase required to display a 50Hz or 100Hz signal.  Why will it be gradual?

 

Stray inductance in the linear power supply transformer windings will temper the rate of any fast build-up of current, but most important is the very fact that a sinusoidal power supply is not a square wave and the rise time of the top section of a peak of the AC waveform has a distinct slope to it.  The source resistance of the mains combined with the considerable resistance of the linear power supply transformer windings will make for a "soft start" to the recharging of the reservoir capacitors (rather like a classic RC filter with only a low voltage initially applied).

 

The red line in the diagram below shows the ripple in the DC supply at the reservoir capacitors. Full-wave rectification has been used, resulting in both the negative and positive peaks of the mains waveform contributing to the rectified DC voltage. There is not an intense spike of current flow right at the top of each half cycle of the incoming mains. Rather, current first starts flowing before the peak, when there is only small potential difference between the instantaneous mains voltage at the secondary of the power transformer and the voltage remaining across the reservoir capacitors.

 

Mains ripple does not have a fast risetime.  The theoretical diagram below illustrates this:-

 

 

 

(From https://blog.powerandtest.com/blog/know-your-power-supply-jargon-ripple )

 

 

Below is a real world example of mains ripple, at 120Hz.  As in the theoretical diagram, it will be noticed that the replenishment of the charge on the reservoir capacitor does not occur in a brief instant. Particularly when the load is high, a considerable portion of the AC waveform is devoted to the replenishment of the reservoir capacitor. 

 

 

 

 

 

 

Edited October 17, 2020 by MLXXX

[allthumbs]

If I was to purchase a recognized audiophile power cord for testing, I have one in mind, where would I be better off deploying the cable to get the most powerful impact as far as audibly hearing the difference in my system, would it be my integrated amplifier or my CD player?

[Ittaku]

20 minutes ago, allthumbs said:

If I was to purchase a recognized audiophile power cord for testing, I have one in mind, where would I be better off deploying the cable to get the most powerful impact as far as audibly hearing the difference in my system, would it be my integrated amplifier or my CD player?

This is probably the wrong thread to ask that since we can't even agree that they do anything. We keep going offtopic enough as it is.

Edited October 16, 2020 by Ittaku

[allthumbs]

8 minutes ago, Ittaku said:

This is probably the wrong thread to ask that since we can't even agree that they do anything. We keep going offtopic enough as it is.

You may be right Ittaku but I am new to this and thought I'd enter into the spirit of the thing just to see. I can only afford one cable and am looking for best slam for buck as to deployment from those who have the most experience with these types of cables.

 

It is not too off topic.

[Ittaku]

1 minute ago, allthumbs said:

You may be right Ittaku but I am new to this and thought I'd enter into the spirit of the thing just to see. I can only afford one cable and am looking for best slam for buck as to deployment from those who have the most experience with these types of cables.

 

It is not too off topic.

I would recommend you don't buy one at all, as it will equally make no difference regardless of where you put it, as any perceived effect is psychological so where you put it will be entirely random, and expect the research in this thread to discover they make no measurable difference (again). I'd recommend buying affordable non-audiophile branded shielded power cables only if they're in close proximity to other sensitive cables and equipment. There's my recommendation, and I've tried to somehow make it relevant to the thread.

[Marc]

13 minutes ago, Ittaku said:

I would recommend you don't buy one at all, as it will equally make no difference regardless of where you put it, as any perceived effect is psychological so where you put it will be entirely random, and expect the research in this thread to discover they make no measurable difference (again). I'd recommend buying affordable non-audiophile branded shielded power cables only if they're in close proximity to other sensitive cables and equipment. There's my recommendation, and I've tried to somehow make it relevant to the thread.

But, your opinion serves no benefit to what is trying to be achieved by this thread. If you're a non-believer, instead of trying to turn the thread upside down why not just give it a wide berth? Why not allow others to go on a journey and discover this for themselves, or discover it via a thread with a goal that is at least trying to prove/disprove it. 

[Ittaku]

4 minutes ago, Marc said:

But, your opinion serves no benefit to what is trying to be achieved by this thread. If you're a non-believer, instead of trying to turn the thread upside down why not just give it a wide berth? Why not allow others to go on a journey and discover this for themselves, or discover it via a thread with a goal that is at least trying to prove/disprove it. 

Why? Because I've tried to help the science, to help prove they do jack. To me that's a worthwhile reason. I even did some measurements to kick off the discussion before anyone else.

Edited October 16, 2020 by Ittaku

[Guest]

Simply because they won’t disbelieve regardless of any proof or whatnot. 
 

It’s a faith based belief, and faith based beliefs are exceptionally  hard to remove. When it come to personal experience, you can’t disprove a negative. 

[davewantsmoore]

10 hours ago, aussievintage said:

Oh dear.  We have managed to prove this is all pointless I fear...

I don't understand why you would say that.   SNR is more than a common problem.   

[davewantsmoore]

9 hours ago, MLXXX said:

There certainly could be odd things happening at....

Yes, this is why it is simply impossible to generalise results for "power cords", or "power conditioners" in a typical audio systems (multiple boxes, cords, etc.)

 

It's why I prefer to think about how to fundamentally avoid the issues.... rather than quantify them or fix them.   Same applies for many other issues in audio.