Any Electricians? (idle curiosity)

Page may contain affiliate links. Please see terms for details.
Switched-mode supplies (which most modern consumer electronics use) are notoriously bad for having a large IV phase difference due to the inductors used as part of the switching process. Very few consumer manufacturers bother with active PFC as it adds significant expense to the cost of the power supply.

Absolutely. As you say, it costs to get it right, and the legacy of a poor supply is a large IV phase difference - with effectively 'wattless' current - but still not chargeable! The problem is that the cables are still taking the load and - quite rightly, fuses need to be specified accordingly.

Another interesting point is the IV phase of a tungsten filament lamp (the ones before these new-fangled energy saving things). When attached to a dimmer, for part of the mains cycle they act as an inductor, and for part as a resistor (due to the way most modern dimmers work, switching at the zero-crossing point of the AC waveform).

Gosh, this is interesting. The point you make about the inductive nature of a coiled tungsten lamp is fascinating. I hadn't heard/thought of that before. I can quite see why the lamp would behave as an inductor when the current slew rate was high.

However, surely that's not quite right about the dimmer. Modern lighting dimmers switch midway through the half-cycle, the exact point determined by the level of lighting required. For full lighting, the dimmer switches at the beginning of each half-cycle, and remains on until the end. When at half power, the device switches on when voltage is at peak, and then - as before - remains on until the end. It is the switch at peak voltage, presenting dI/dt at maximum when the dimmer is in 'Grand ol' Duke of York' mode (neither up nor down!) that causes interference and characteristic dimmer buzz - and often, in theatres etc, cross couples to audio circuits if cable routes have not been selected carefully. And surely, it's this switch at peak voltage, with a very high dI/dt, that brings out the inductive characteristic of the light bulb that you bring to our attention.

Zero-voltage switches are used in order to ensure that any device is only switched on at the beginning of a half-cycle, and are used - for example - for heating loads. Proportional heating control can be effected by cycle counting with a zero-voltage switch, so - for example - a heater can be set at half power by switching 'on' for 25 half cycles, and then 'off' for the next 25. Zero voltage switching does, in this way, reduce dI/dt to the minimum - improving the capability of the triac, and reducing the need for suppression components and cable isolation. However, such a device couldn't be used on a lighting circuit because the flicker over the resultant (1/2 second) duty cycle would be absolutely intolerable. Heating applications are fine, because of the thermal inertia of the element and room.
 
1. can be checked with a screwdriver ... :)

2. Most likely the cables were purchased from another cable supplier before Pioneer boxed the system prior to dispatch - in fact was probably done by the exporting or importing distributor to have the correct plug.

Spot on with number 2... Pioneer Europe import the DVD players from China or Japan from one of their factories... then once they have arrived in Belgium, Pioneer Europe source the mains cables for the european region of the players destination... UK, Italy, France, Russia etc... ( I beleive most of the Pioneer DVD Players are figure of 8) with the fuse normally rated for the cable... in this case 5amp.... incase you unplug the cable from the DVD Player and insert it into something that draws more power....
 
Spot on with number 2... Pioneer Europe import the DVD players from China or Japan from one of their factories... then once they have arrived in Belgium, Pioneer Europe source the mains cables for the european region of the players destination... UK, Italy, France, Russia etc... ( I beleive most of the Pioneer DVD Players are figure of 8) with the fuse normally rated for the cable... in this case 5amp.... incase you unplug the cable from the DVD Player and insert it into something that draws more power....

Of course in Europe / Russia / most of the rest of the world, the plugs don't usually contain fuses anyway. This is one of the reasons that our electrical system is deemed one of the safest in the world.
 
Geoff,

I think I can help here.

Electricity meters measure the product of voltage, current and time, giving a figure in Kilowatt hours. This is a measurement of energy used. If the voltage is decreased, then - yes, the current decreases - and the kettle takes longer to boil. However, the total amount of energy used, and hence the cost, will remain the same. If this were not the case, then those at the end of a cable run - where voltages are subject to signficant depression within specified tolerances - would be paying more for their energy. They don't. Electricity meters measure energy = voltage x current x time.

I hope that helps.

Simon

PS. An interesting discussion point may be the phase angle between voltage and current - and the devices that distort this. If you've ever wondered, for example, why there is a capacitor directly across the supply terminals of a flourescent tube - it's there to counter the effects of the inductor which is in series with the tube itself, and to ensure that the whole device appears to the electricity supply a near as possible like a pure resistor.

Thanks for that, and for those who are worried, I was a draughtsman so nothing dangerous:D but, I must ask, why would the current drop? If an appliance needs x amps to operate, surely it will still take x amps. The main reason why electricity is "shipped" around the country at 400kv and above, is to reduce the amperage to give the required end product when transformed down. I never did any work on meters so I am a bit thick when it comes to how they work, please excuse me and not just apss some off the cuff coments as some of you did. We are not all geniuses
 
>>why would the current drop?

It's Ohm's Law, V=I*R

The resistance (R) of the kettle's element is unchanged, so, if the voltage (V) reduces, so must the current (I).

You can go on, and look at Ohm's law in a more general way for AC curcuits, where the resistance is more properly termed impedance, and can include reactance as well as resistance, which leads to the possibility of phase between voltage and current, and the desire for power factor correction, but, I don't think doing so helps answer your more fundamental question.
 
A plumbing analogy

Thanks for that, and for those who are worried, I was a draughtsman so nothing dangerous:D but, I must ask, why would the current drop? If an appliance needs x amps to operate, surely it will still take x amps. The main reason why electricity is "shipped" around the country at 400kv and above, is to reduce the amperage to give the required end product when transformed down. I never did any work on meters so I am a bit thick when it comes to how they work, please excuse me and not just apss some off the cuff coments as some of you did. We are not all geniuses

Geoff,

Sometimes it's helpful to think of electrical circuits in the analagous terms of plumbing. The equivalent of voltage is pressure and that of current is flow rate. The higher the pressure difference between one end of a pipe and another, then the greater volume of water will flow through it per second. A resistor, which is what a kettle element really is, is merely the equivalent of a piece of thin pipe. So, in the same way, the greater the voltage difference applied across the element, then the greater the current flow. This is normally expressed in the relationship Current = Voltage / Resistance. For a given resistance, then the higher the voltage the higher the current. The power dissipated in the element = Voltage x Current. We know that Current = Voltage / Resistance and so we can re-write this as:

Power = Voltage x Voltage / Resistance

In other words, power is proportional to the square of the voltage.

If we doubled the supply voltage, then the power would quadruple. If we halved the supply voltage, then power would be one quarter. A more likely 10percent reduction in supply voltage will cause a 19% reduction of power, and therefore - for a given amount of water in the kettle - a 23% increase in the time taken to boil. However, going back to your original point, the overall amount of energy used will be exactly the same, and the electricty meter - which multiplies voltage, current and time - will show the same cost.

It's just that you'll have to wait longer for that much needed cuppa...... and that's giving me a thought right now!

All the best,

Simon
 

Users who are viewing this thread

Back
Top Bottom