# Volts, amps and electric power supplies/components

Hello All.
Is it at all useful (or accurate) to think of volts as being "pushed" aroun d a circuit by the power supply and amps as being "drawn" by the components fed by it? In other words, is it right to work on the assumption that a po wer supply that exceeds the voltage rating of the components its feeds migh t damage them, but will probably not get damaged itself. Conversely, workin g on the assumption that a power supply whose maximum amperage rating is be low that of the components its feeds might itself get damaged, but that the components will not.
Is that broadly correct, or have I got the wrong end of the stick?
Thanks. Terry.
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On Saturday, 5 December 2015 07:05:19 UTC, snipped-for-privacy@gmail.com wrote:

und a circuit by the power supply and amps as being "drawn" by the componen ts fed by it? In other words, is it right to work on the assumption that a power supply that exceeds the voltage rating of the components its feeds mi ght damage them, but will probably not get damaged itself. Conversely, work ing on the assumption that a power supply whose maximum amperage rating is below that of the components its feeds might itself get damaged, but that t he components will not.

Think of an analogy to water in a hosepipe. The pressure is equivalent to Volts. The amps is equivalent to the amount of water moved.
Too high a pressure will force too much water through and destroy/damage th e equipment. Simple explanation here. http://www.explainthatstuff.com/electricity.html
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wrote:

Yes.

Too much pressure is more likely to burst something and that is a better way to look at it.

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I think one of the problems whe we talk about AC equipment is that the volts measured are often not the peak at plus or minus, but the average. as i found out quite early on, if your mains is nominally 220volts at 50 hertz, even a capacitor rated at 230v can just get blown up.
I was building a mains filter at that time. Brian
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On 05/12/15 09:51, Brian-Gaff wrote:

??
I suppose aas a fully qualified electrical engineer I cant even believe no one else kinows this.
240V mains peaks at 415V typically. Its common to use 630V DC rated capacitors or those designed for 250V *AC*
More interesting is mains straight across an 8ohm loudspeaker...

--
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diverted our attention away from what really matters to our existential
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On 05/12/2015 10:01, The Natural Philosopher wrote:

Not quite as high as 415 volts, AC voltage at 220V RMS (Root mean sqaure) will have a peak to peak voltage of +311V to -331V
(to get from RMS to peak voltage, multiply by the square root of 3)

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On 05/12/15 10:43, I love spam wrote:

No. Multiply by the square root of 2...
sheesh... you will be telling me next that Pi=4.
But you are nearly correct. Its about 350v peak
415v is the RMS difference between two 240V phases on 3 phase...

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diverted our attention away from what really matters to our existential
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On Saturday, 5 December 2015 10:51:44 UTC, The Natural Philosopher wrote:

Drivel. As usual.
RMS value of a sine wave is 0.707 x peak value.
Average value is 0.636 x Peak value.
Different for different wave forms.
https://en.wikipedia.org/wiki/Root_mean_square#/media/File:Sine_wave_voltages.svg
I don't suppose a janitor can be expected to know such stuff.
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On Saturday, 5 December 2015 16:53:45 UTC, harry wrote:

Er, the average value is zero.
NT
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On 05/12/2015 19:02, snipped-for-privacy@gmail.com wrote:

The average value refered to is the half-cycle average.
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On 05/12/15 19:08, TomSawer wrote:

actually it isn't. Its the root mean square average
Defined as 'the DC voltage that would heat a resistor up the same as what this AC stuff does.'
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diverted our attention away from what really matters to our existential
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On 05/12/2015 19:19, The Natural Philosopher wrote:

Actually it is!
It is the average of the Instantaneous values of the half-cycle.
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On 05/12/15 19:27, TomSawer wrote:

No, it isn't.
Oh, are you bending the argument to reference the .636 value?
--
the biggest threat to humanity comes from socialism, which has utterly
diverted our attention away from what really matters to our existential
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On 05/12/2015 19:37, The Natural Philosopher wrote:

What argument are you going on about?
As far as I can see the posts are about Sine waveforms. The average value for the half cycle of such a wave is 0.637 of the peak. A simple graph of a sine values between 0 and 180 degs will show you this.
Also see
http://www.electronics-tutorials.ws/accircuits/average-voltage.html
for a detailed explanation.
This is not "bending" any argument!
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On Saturday, December 5, 2015 at 7:52:43 PM UTC, TomSawer wrote:

Having read this thread I can see there is a bit of an argument from nowhere.
1) 230V a.c. without appreciable harmonics has the same effect on a resistive load as 230V d.c.
2) A 230V a.c. without appreciable harmonics waveform will have a peak voltage to Earth/Ground/Neutral of about 325V.
3) Since 10ms later the peak will be -ve this will have a maximum negative voltage of about -325V to Ground/Earth/Neutral.
4) The +peak to -peak voltage therefore of any one phase of 230v a.c. is about 650V and one can bridge rectify between line and neutral and get that voltage.
I think I have done the subject to death.
E
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On Sun, 06 Dec 2015 12:01:34 -0800, ed wrote:

Nope!
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On 06/12/15 23:12, Cursitor Doom wrote:

Yep.
with a 650V smoothing capacitor.
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diverted our attention away from what really matters to our existential
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On Sun, 06 Dec 2015 23:18:21 +0000, The Natural Philosopher wrote:

Which planet are you living on again?
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On 07/12/15 00:17, Julian Barnes wrote:

The real one
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diverted our attention away from what really matters to our existential
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On Mon, 07 Dec 2015 00:31:33 +0000, The Natural Philosopher wrote:

Strictly speaking, CD is correct. Ed's minor error re item 4 was the reference to a bridge rectifier instead of a voltage doubling two diode two capacitor circuit (which can also be made up using a bridge rectifier of adequate PIV rating and two smoothing capacitors).
Incidentally, unless the situation regarding the uptake of PFC upgrades to SMPSUs has vastly improved in recent years, the conversion coefficient to translate rms voltage to peak voltage approximates closer to 1.4 than it does to the the more accurate 1.414 value.
The last time I had occasion to sample the mains supply waveform, some 4 or 5 years ago, I did notice it was a little flat topped compared to a true sinewave. I presumed it was all that loading from smpsu powered kit not incorporating any PFC circuitry to spread the HT rectifier packs' conduction angle further away from the waveform crest (the 'flat top' had a slight upward slope).
--
Johnny B Good

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