Volts, amps and electric power supplies/components

On 11/12/15 12:55, Julian Barnes wrote:

y do you knowitall trolls always change the subject when someone is about to prove you wrong?
I know perfectly well what they are. The point is that what they are is absolutely NOT '*implies a certain mode of operation*'.
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On Fri, 11 Dec 2015 16:03:15 +0000, The Natural Philosopher wrote:

Oh dear. Sounds like someone's been on the gin again. ;->
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On Friday, 11 December 2015 16:03:16 UTC, The Natural Philosopher wrote:

We seem to have got ourselves a new troll :/ He's acting the idiot in s.e.d as well.
NT
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On 10/12/2015 15:20, The Natural Philosopher wrote:

What are you trying to prove? Giving a partial description of a device and out of context as well doesn't prove a point. There are hundreds of terms that you can do this with such as Foster (seeley discriminator);Black (level clamping);Line (flyback EHT) or Line (output level) . Doesn't prove anything.
Have you heard the one about the man who bought two 9v batteries and connected them in series to make a voltage doubler?
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On Sat, 12 Dec 2015 13:21:02 +0000, george wrote:

Did it work? ;->
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On 10/12/2015 13:44, TomSawer wrote:

Its the fact that it makes use of both positive and negative halves of the waveform, that makes it a full wave rectifier.

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On 10/12/2015 12:42, snipped-for-privacy@gmail.com wrote:

Well you see, the reason many people describe such circuits as doublers, is because you stick in an AC signal with a peak voltage of V in, and you get out DC at 2V. This is contrary to the usual behaviour of a linear unregulated supply where it will have a no load voltage output of only V.
You can find similar circuits that can give triple or greater multiples too.
Do a web search for "voltage doubler", and you will find many circuits like that which you describe.
Now why everyone is throwing toys out of the pram over the precise naming of these circuits escapes me, since its bleeding obvious that while "voltage doubler" is indeed in very common use, there are different names and terminologies commonly in use as well.

A dubious claim IMHO, but not relevant, so let's skip that.

Yes, and calling it a doubler is also perfectly acceptable.
However don't take my word for it, see fig 1.78 and following explanation:
http://wiki.diyfaq.org.uk/index.php/File:VoltageMultipliers1.gif
http://wiki.diyfaq.org.uk/index.php/File:VoltageMultipliers2.gif
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On Thursday, 10 December 2015 12:42:53 UTC, snipped-for-privacy@gmail.com wrote:

A constant current source and a current limit are two differnt things. Not sure how or where sample and hold comes in to it as the key here seems to be to use passive devices rather than active.
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On 10/12/2015 12:42, snipped-for-privacy@gmail.com wrote:

You're not coming over as being very bright.
With just the one rectifier, would you be the sort of person to call this circuit a "voltage halfer"?
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On Fri, 11 Dec 2015 22:09:45 +0000, Fredxxx wrote:

He's clearly never heard of the proverb, "when you're in a hole, stop digging."
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On Monday, 7 December 2015 16:42:43 UTC, snipped-for-privacy@gmail.com wrote:

How ? Can you also rectifiy it to a tin of hot tomoto soup,? I'd believe that more
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On 07/12/15 16:37, Cursitor Doom wrote:

depends on how you rectify it.
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On 06/12/2015 20:01, snipped-for-privacy@makewrite.demon.co.uk wrote:

Explain how you would obtain 650v directly from a 230v rms supply.
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On Mon, 07 Dec 2015 18:36:20 +0000, TomSawer wrote:

File:Sine_wave_voltages.svg

I wouldn't hold your breath waiting for an answer. Seems some folk here don't know the very considerable (x2) difference between peak voltage and peak-to-peak voltage. I suspect that's the root of their comprehension problem, anyway.
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On 07/12/2015 18:36, TomSawer wrote:

Ed's description was fine - the pedants might argue at the use of the word "bridge" while describing the half wave rectification, but it ought to be clear what was intended:
D1 ---------+----->|--------+----------- +V peak | | | | | | + 230 | --- C1 VAC | --- | | | | | | ------------------------+ | | | | + | --- C2 | --- | | | D2 | -----|<--------+----------- -V peak
On the positive half of the cycle, D1 conducts and C1 charges to the peak of the supply voltage. On the negative portion of the cycle, D2 conducts and charges C2 to the peak of the supply voltage. The voltage measured over the series pair of capacitors will now equate to the peak to peak voltage (i.e. twice the peak voltage)
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Mathematically yes, but try grabbing a live wire that has an average of zero....
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Six stages of married life:
1: Tri-weekly
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On Sat, 05 Dec 2015 10:51:42 +0000, The Natural Philosopher wrote:

Well, that saved me the bother of putting you straight on that 'schoolboy howler'. :-)

Assuming the speaker is rated to handle 7KW transients, you might have to endure 50Hz at high SPL for several seconds before the plugtop fuse blows or the voice coil releases its magic smoke with a side order of pyrotechnics.
More realistically, with 50 to 100 watt rated units, the magic smoke with pyrotechnic display event is likely to occur in less than quarter of a cycle (5ms) so more a 'crack' and a flash of light with a side order of magic smoke than a deafening thump.
It really depends on the size and rating of the speaker drive unit involved. With smaller 2 inch half watt units, the flexible voice coil tails will probably act as fusewire, rapidly curtailing any speaker cone excursions and pyrotechnics.
It's only interesting the first time around with most domestic sized speaker drive units. Beyond that, it all becomes somewhat predictable and therefore a bore, unless you're paying Russ Andrews prices - then the transactions on your bank account will be where the real action lies. :-)

Even assuming the use of a 250Vac X class capacitor (typically also rated for a maximum stress rating of 630VDC and intended to be connected directly across the mains input terminals) in a mains filter designed to act as an LPF with a cut off transition frequency of 90 or 130 Hz, you're likely to suffer a spectacular failure from voltage magnification generating kilovolts within the filter circuit.
I could've added that rather obtuse acronym, DAMHIK, made more obtuse by the lack of the qualifying phrase, "I just know :-)"[1] but I won't :-).
Quite simply, when I was trying to eliminate what I thought were troublesome 2nd and 3rd harmonics from a petrol generator emergency supply [2], I designed and made up a LPF using mains voltage rated capacitors which I'd had the foresight to test on a 6 VAC supply before trying to use them in anger. After measuring ac voltages in the range of 30 volts and above, I swiftly realised this wasn't going to be the right solution [3] for me. :-)
I assume Brian's "Mains Filter" was the more prosaic "EMI" filter designed to filter out 100KHz and above noise and transients on a 240v 50/60Hz mains supply where the magnification effect only applies to a few hundred millivolts worth of unwanted HF energy that might be present on the supply. I'm guessing Brian simply overlooked the fact that the equivalent DC voltage rating for a capacitor to safely handle 250 volts ac typically being in the region of 630 to 650 vdc.
[1] This is a dig at posters who, unconscionably, use the acronym, DAMHIK *without* that all important phrase, "I just know :-)".
[2] The implication, often made in the literature accompanying most UPS kit, that it's the 'poor quality' of mains voltage produced by such emergency gensets which makes them unsuited for use with their UPS kit (or a reference to a sensitivity adjustment that needs to be lowered to mitigate such problems of "poor quality" emergency supplies), is rather misleading in the extreme.
The truth of the matter is that all such gensets are extremely susceptible to capacitive loading on their output over-riding the AVR causing them to over-volt considerably (4.7microfarad capacitor across the terminals of a 230v 2.8KVA genset resulting in 280v AC ouptut - the 2KVA Line Interactive UPS in question switching some 9 microfarads across the supply when in pass mode, dropping it when switched to battery - you can imagine the consequences of this set up - I didn't have to, endless cycling between battery and 'mains power').
The problem of "Poor Quality" has nothing whatsoever to do with harmonic content (2nd and 3rd harmonic and the sub-harmonic component resulting in the use of a single cylinder 3000 rpm prime mover imposing its own 25Hz modulation along with windings slot ripple effects). Nor has it anything to do with the less than perfect frequency and voltage regulation performance of such emergency gensets. It's all to do with capacitive loading sensitivity of the AVR leading to uncontrolled overvolting.
A 'heads up' for those thinking of supplementing their whole house UPS protected circuit mains sockets with an emergency genset is that the *only* type that's free of this capacitive loading overvolting effect is the "inverter" type such as the now classic Honda E3000 (or 3000E ... whatever!) which uses a highly efficient permanent magnet alternator to generate a DC voltage feeding a 50/60Hz 230vac inverter.
Luckily, Honda no longer hold a monopoly in the inverter genset market and it's now possible to buy a brand new 3KVA inverter genset for less than £1000 these days. The last time I checked pricing a couple or three years ago, I was contemplating a spend of 600 quid or so for one such genset before common sense prevailed.
It was one thing to buy a 2.8KVA petrol genset from Aldididle 6 or 7 years back for a bargain price of 150 quid (now down to 130 quid in more recent offers) as a worthwhile supplement to my emergency backup supply system but a totally different thing when looking to spend 4 or more times that amount to get a 'solution that will *actually* work as "imagined").
For anyone contemplating such a genset upgrade to their existing battery backed UPS arrangements, it's important to realise that a basic genset that uses a conventional 50/60Hz alternator driven by a 1500/1800 or 3000/3600rpm prime mover will be a complete waste of money unless you're considering a 20 to 30 KVA monster to backup the whole house supply where the 'protected' loading is less than a quarter of the genset's rating.
[3] Have you seen the price (and size and availability) of inductors and capacitors rated to handle 30 kilovolts or more? I haven't but I figured if I had to ask, I didn't need to know. :-)
--
Johnny B Good

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wrote:

Or even the square root of 2 - which you seem to have done.
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On 10:01 5 Dec 2015, The Natural Philosopher wrote:

As you mentioned it, what sort of electrical qualifications do you have as an an electrical engineer. Just not sure if you mean electronics or main electrical supply.

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pamela

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On 05/12/15 11:07, pamela wrote:

Both.

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