Kettle on Gas vs Electric Kettle

Gerry1

Astria said:

For example, if a wireless charger for a toothbrush or mobile phone is similar (I don't know if it is or not), they typically draw 2A from the wall to put 1A into your phone.

Some very wonky maths there.  You can't just compare the current (amps) because the voltages are very different.  A charger using 2A at 240V would be drawing 480W.  The charger and / or the phone would melt !

doodling

Hi,

Captainkirk54 said:

doodling

"The stuff above about reactive loads is largely wrong because in the case of hobs they are required to have a power factor near 1, achieved by power factor correction (PFC) on the input, and in the case of phone chargers they are supplied by DC (admittedly from a switching power supply which may or may not have PFC).  I don't know whether electric toothbrush inductive chargers operate at 50Hz so can't comment on them but they aren't very big loads anyway."

Most AC reactive loads were required to be PF corrected to between 0.8 and 0.9.
False unity (1) should not be obtained artificially due to the danger of the destructive resonance condition.

It depends heavily on how you're doing your PFC. In general PFC is mandated for domestic equipment not because of the issue of reactive power but more due to a risk of flattening the peaks of the supply sine wave due to the use of rectifiers on lots of loads.

PFC in domestic electronic equipment is usually achieved through the use of a boost converter after the bridge rectifier, operated so as to force the current drawn by the equipment to be a sine wave in phase with the supply voltage. This method can easily achieve very high power factors with no risk of resonance.

Capacitors or not normally used, except where there is a truly inductive load of more or less fixed inductance - there are not many of those in a domestic setting.

In the specific case of induction hobs the design will generally have a input rectifier followed by a PFC boost converter which will generate a DC voltage of around 500V, this is then chopped by suitable power electronics to produce whatever frequency they want the hob to run at.

Traditionally inductive loads have been corrected by connecting capacitors as you say, as capacitance is the direct polar opposite of inductance. Both of these conditions are known as reactive power. You can reduce the effect of wasted reactive inductive energy by installing capacitors but these also use reactive power/energy which you have to pay for.

Power companies used to meter and charge PF penalties to large power users. Now we just all pay for poor factor in the form of high electricity prices.

Traditionally, in a domestic setting, inductive loads have not been power factor corrected. I do not recall mentioning capacitors in any of my previous posts in this thread. Having said that, if you do correct the power factor using capacitors then there is no reactive power to pay for and supply I2R losses are reduced (give or take the ESR loss in the capacitors).

You do not pay for reactive power draw on a domestic supply. Commercial users still pay for reactive power, that hasn't changed. Electricity prices are not particularly affected by domestic power factor - gas costs and green levies are the driving factors there.

[...]

Unity - Artificially achieved cancellation of (XL) inductive reactance and (XC) Capacitive reactance.

That is an unusual definition of unity power factor. Are you saying that pure resistances don't achieve unity power factor?

[...]

The induction hob involves changing electrical energy into magnetic energy (Reactive Power) then changing magnetic energy into heat energy - corrected by capacitors using Reactive Power. All of these are energy losses which you have to pay for.

The majority of the losses are resistive losses in the power electronics, not as a direct result of the energy conversions. Reactive power has little to do with the efficiency or otherwise of an induction hob.

Of course the induction hob is not more efficient than an electric element which is directly

immersed in water.

Agreed, as I stated in a follow up post.

I do not know enough about phone and toothbrush charger technology to comment - only that in the electrical trade we attract a number of queries about bathroom shaver sockets overheating when used to charge toothbrushes which do not charge fully.

This has been addressed in the trade by the provision of beefed up dual bathroom shaver sockets, which have both charger and shaver logos on them. This issue does not occur when the charger is plugged into a normal 13A socket.

I suspect that the issue with electric toothbrushes is that shaver sockets have historically not been continuously rated.

Spies

So I just got an actual stove top kettle today, the time it actually takes to boil is 4 minutes which is quite a bit longer than electric! As some have said, you need to consider if its actually worth your time waiting around for it to boil.

I needed one for when we go camping anyway so it's not a waste if I don't use it. 

Spies

Updated my post with more accurate figures, boiling on stove until whistle starts actually used 0.19kWh, not 0.17kWh as previously specified

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