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Power cables - how to measure


Guest rmpfyf

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11 minutes ago, bob_m_54 said:

looking at the voltage drop over 1M (2M return) of 14AWG power cable when drawing 10A, is about 170mV. Step it up to 12AWG will only bring it down to about 105mV.  So you'll gain an extra 65mV. So in reality, the gain there is 3/5 of 5/8 of SFA. Or less than 0.03% of the 230V input.

Thanks, Bob. Those are the sorts of figures I anticipated. (I was almost going to go out and buy a cheap kettle cord myself and measure the voltage drop across it when powering a 10A resistive load, but I don't think I'll bother.)

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14 minutes ago, Red MacKay said:

I think we are drifting from where we need to be lads.

The arguments about there being any significant voltage drop across a power cord under full load are weak, and so  we could perhaps turn to arguments relating to EMI.

 

Conventionally, it is isn't the design function of a power cord to attenuate EMI (other devices can do that if it is needed). However it is possible that some audiophile devices might fare measurably better than others when there is intense EMI depending on the particular power cord in use, and depending on where it was placed, e.g. most of its length coiled up near the power point.

 

I have suggested earlier in this thread that to get measurable differences in audio output quality, EMI might need to be artificially introduced, as ordinary levels of mains hash and of device generated EMI might not be enough of themselves to make a measurable difference (unless using an audiophile device very sensitive to incoming EMI).

Edited by MLXXX
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12 minutes ago, Red MacKay said:

 

What about DC on mains?  I have 243vAC here at the outlet, and 2.55vDC as well.

 

 

Just as a matter of interest, Red ... how did you measure your 2.55v DC?

 

Just putting the prongs of your multimeter into the 'Active' and 'Neutral' slits on the wall socket ... and selecting the 'DC Volts' range on the meter?

 

(I'd love to try measuring DC ... but I'm scared I might blow up the meter! :( )

 

Andy

 

Edited by andyr
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54 minutes ago, andyr said:

 

Just as a matter of interest, Red ... how did you measure your 2.55v DC?

 

Just putting the prongs of your multimeter into the 'Active' and 'Neutral' slits on the wall socket ... and selecting the 'DC Volts' range on the meter?

 

(I'd love to try measuring DC ... but I'm scared I might blow up the meter! :( )

 

Andy

 

Yes, exactly that.  My Fluke has no problems.

 

I was surprised that the AC volts have gone up here.  I have been in this home for 21 years and it's always been around 234-238V, never over that.

 

Mind you, John at his factory 1.2kms down the road regularly has 254V!

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59 minutes ago, andyr said:

 

Just as a matter of interest, Red ... how did you measure your 2.55v DC?

 

Just putting the prongs of your multimeter into the 'Active' and 'Neutral' slits on the wall socket ... and selecting the 'DC Volts' range on the meter?

 

(I'd love to try measuring DC ... but I'm scared I might blow up the meter! :( )

 

Andy

 

Sook.. LOL

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53 minutes ago, andyr said:

 

That's what I think, too.  :)

 

Andy

 

No problem measuring the DC level that way, providing there is something actually running off that circuit, to drop the voltage over. If there is no load, then anything you measure is basically floating, and means nothing.

 

As for worrying about blowing up your meter. Don't do it with an analog meter unless you make sure you start with it on the highest setting, or you'll peg your needle.

 

Most digital meters are fine, maybe some of the cheaper ones can't auto range quick enough, but no problem using a $600 Fluke.

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3 minutes ago, rantan said:

Electric shock

That nearly happened to a "qualified" electrician where I was working (as an electrician, unqualified) when he borrowed my multimeter to check if a circuit was live before working on it. He said "now I can see why it's not working, there's no voltage on the line" I had a look at the meter, switched the meter to AC, instead of DC, and said... well I wouldn't stick my fingers there...

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1 minute ago, bob_m_54 said:

No problem measuring the DC level that way, providing there is something actually running off that circuit, to drop the voltage over. If there is no load, then anything you measure is basically floating, and means nothing.

 

As for worrying about blowing up your meter. Don't do it with an analog meter unless you make sure you start with it on the highest setting, or you'll peg your needle.

 

Most digital meters are fine, maybe some of the cheaper ones can't auto range quick enough, but no problem using a $600 Fluke.

Not sure if that part of the circuit is loaded actually. (laundry)  I never knew about the floating thing.

I will try in the kitchen a little later.

 

The Fluke was money well spent many years back.

 

I have triend many DC blockers here, varied designs but though they seemed to work re the trannies stopped humming - the trade off was a loss in dynamics and that is a trade off I am not willing to make.

 

I have a mate in Geelong with one of Anthony Holton's new DC Blockers.  His design is a completely different electrical concept and parts, so when (if ever) we get let out of our houses, my friend is going to bring it up and we will put it through it's paces.  I shall report my findings.  But keep in mind, if I like it, others will hate it.

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50 minutes ago, bob_m_54 said:

looking at the voltage drop over 1M (2M return) of 14AWG power cable when drawing 10A, is about 170mV. Step it up to 12AWG will only bring it down to about 105mV.  So you'll gain an extra 65mV. So in reality, the gain there is 3/5 of 5/8 of SFA. Or less than 0.03% of the 230V input.

I'm not talking about big differences here.

As I stated earlier $2 kettle cord is still fit for purpose in this situation and will boil water just fine.

My point being in relation to an earlier post  I was replying to is correct that there is a difference even if small.

 

BTW you're probably overestimating just how much copper is actually in a $2 kettle cord these days...

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21 minutes ago, Martykt said:

BTW you're probably overestimating just how much copper is actually in a $2 kettle cord these days...

Do you have an estimate, Martyky, of the voltage drop across a cheap kettle cord at 10 Amps RMS?

 

Please let us know what you think it might be.

 

I'm willing to go out and buy one and test it!

 

Here are some on sale at under $10. They are of different lengths:-

 

https://www.jbhifi.com.au/products/xcd-kettle-power-cable-2m

 

https://www.precisionaudio.com.au/products/kettle-cord

 

https://www.bunnings.com.au/jackson-1-2m-replacement-iec-power-lead_p4420134

Edited by MLXXX
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15 minutes ago, Martykt said:

I'm not talking about big differences here.

As I stated earlier $2 kettle cord is still fit for purpose in this situation and will boil water just fine.

My point being in relation to an earlier post  I was replying to is correct that there is a difference even if small.

 

BTW you're probably overestimating just how much copper is actually in a $2 kettle cord these days...

1.5mmsq

 

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

 

You can work out the rest.

Edited by bob_m_54
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55 minutes ago, bob_m_54 said:

No problem measuring the DC level that way

Correct me if I'm wrong but wouldn't the multimeter also be measuring the AC making any DC reading a digital meter somehow locks onto false?

 

With an analog multimeter when set to DC  connected to the mains the needle should follow the AC wave going up to 240(ish) then back down towards -240 until it hits its zero stop or decides life is too hard of course... 

 

To measure DC in the mains wouldn't you have to measure the actual wave with an appropriately connected oscilloscope looking at the flattening of the wave?

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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?

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3 minutes ago, Martykt said:

Correct me if I'm wrong but wouldn't the multimeter also be measuring the AC making any DC reading a digital meter somehow locks onto false?

NO

 

With an analog multimeter when set to DC  connected to the mains the needle should follow the AC wave going up to 240(ish) then back down towards -240 until it hits its zero stop or decides life is too hard of course... 

Depends on the meter type, but handyman meters, don't do it.

 

To measure DC in the mains wouldn't you have to measure the actual wave with an appropriately connected oscilloscope looking at the flattening of the wave?

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

 

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17 minutes ago, MLXXX said:

Do you have an estimate, Martyky, of the voltage drop across a cheap kettle cord at 10 Amps RMS?

Not off the top of my head.

 

29 minutes ago, MLXXX said:

I'm willing to go out and buy one and test it!

 

Here are some on sale at under $10. They are of different lengths:-

$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

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16 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. 

Voltage drop is not an issue with compliant to AUS standards

Quote

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. 

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.

Quote

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.

Basically the same as voltage drop as above

Quote

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?

We're talking power cables, not interconnects..

Edited by bob_m_54
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17 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?

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

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