Volts, amps and electric power supplies/components

Water is a garden hose travels at around a walking pace of below in mjy experience.

Reply to
ed
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Oh I disagree - no one things about electron flow, quantum events etc. They do think about flow of charge per second (amps) which is extremely analogous to flow of water - double both and you double the power delivered in classical terms.

No, the average person cannot run at 0.5c to practically c - they possibly can out stroll the speed of the agents carrying the electricity, who's average speed is after all zero for AC - but not the electricity itself.

Reply to
Tim Watts

that is, the electrons.

whose

I can't envisage electrons flowing at relativistic speeds down a wire; they'd smash every atom they came across. What is moving at such speeds is the electric field, i.e. the voltage.

See:

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and look at the numerical example: in a copper wire carrying 3 amps, electrons zoom around in all directions at about 1000mph. They have a net drift down the voltage gradient of some 28mm/sec, i.e. about an inch per second.

Reply to
Tim Streater

Whatever...

Indeed - which is to all intents and purposes what electricity is.

If I take a mile long bit of cable and have you hold the end while standing on wet grass in bare feet, and I connect the other end to the mains - it is entirely academic how fast the electrons move. The current will be flowing through you however long it takes to cover a mile at about half the speed of light[1]

[1] Speed of electrical signal propagation in some ordinary coax cable is around that sort of speed - actual undergrad physics lab experiment.

Which is irrelevant to "how fast the current starts flowing at the other end". It's more like Newton's cradle - the electrons do not need to move very fast, but the shock wave after changing the conditions at one end moves incredibly fast.

Anyway the original analogy is a good one.

If you have a full hose of water, and you tweak the tap open at one end a bit, water will start flowing out the other end almost immediately, even if the physical speed of the water is slow.

And if the hose is very wide, a slow speed of water can do an awful lot of useful work.

The electrons may be very slow and their charge tiny, but there's a bugger of a lot of them moving together.

Reply to
Tim Watts

Oh dear. Go back and read up a little more about the speed of a wave propagation versus the speed of the medium through which the wave propagates.

Reply to
The Natural Philosopher

Nope!

Reply to
Cursitor Doom

That was exactly my point in my other recent post.

Strewth - what is it with everyone. It's a bloody analogy FFS.

Reply to
Tim Watts

Yep.

with a 650V smoothing capacitor.

Reply to
The Natural Philosopher

I think whatever drug it is they coat the pages of the Guardian with, has been increased in dosage recently..

Reply to
The Natural Philosopher

That's it: "drift velocity." Well done, I couldn't recall the precise term after all these years.

Reply to
Cursitor Doom

ed is in fact correct. With 1 or 2 capacitors you can connect the BR to get 320 or 640v. It's power supply 101 stuff.

This thread has really brought out the confused.

NT

Reply to
tabbypurr

Which planet are you living on again?

Reply to
Julian Barnes

Perhaps I can help you, then. That's *voltage doubling* you're talking about I believe. Most PSU sections for goods sold in the UK and the US are switchable between 120v and 240v by inserting a couple of caps in the bridge. It's an extremely simple and cheap way of doubling the voltage. Do the same with 240VRMS in and you will get 644V out P-P alright, but that's *not* without doubling!

Reply to
Julian Barnes

The real one

Reply to
The Natural Philosopher

You're funny. There's no need to double anything, just 2 diodes from live to 2 caps and you're done.

Pointless talking about such 101 stuff really isn't it. Good luck with your electronic designs.

NT

Reply to
tabbypurr

Funny, because I read the Times mostly. WTF is your problem?

Reply to
Tim Watts

Well you prove my point. Its not you, its them.

Reply to
The Natural Philosopher

2 diodes + 2 caps in the right config forms a *voltage doubler* you muppet. Try googling "cockroft-walton network" it's just one stage of one of those ladder networks.
Reply to
Julian Barnes

also known as a half bridge..

Reply to
The Natural Philosopher

Indeed. But "ed" didn't mention anything other than conventional (ie full- wave) rectification in his erroneous remark:

"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."

This statement is prima facie incorrect. Conventional rectification will only get him *half* the p-p voltage.

Reply to
Julian Barnes

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