Electrical engineers needed

DVardysShadow

stevemcol wrote: »

If we are correct that it is the power factor that's being distorted then no, you can't influence the amount of power you are using (other than by switching off appliances). Simple power monitors just measure current which is an approximation of the power consumed (volts x amps). However, your main meter measures true power** (volts x amps x power factor).
So your simple power monitor may report higher or lower current but your meter would be ignoring these 'apparent power' changes.


**I'm only 90% certain of that fact and would be interested in other views.

Main meter measures and integrates instantaneous voltage * current and there for measures true energy consumption.

Note that switchmode and even rectifier circuits offer the potential of power factors in excess of 1 [sometimes on the internet this causes a terrible row, but it is true]. With Sine wave volts and amps, the max power factor is 1.

stevemcol

DVardysShadow wrote: »

Not that switchmode and even rectifier circuits offer the potential of power factors in excess of 1 [sometimes on the internet this causes a terrible row, but it is true].

Can you elaborate? It implies power is being created (true power greater than apparent power).

DVardysShadow

stevemcol wrote: »

Can you elaborate? It implies power is being created (true power greater than apparent power).

Far from it. The true power transmitted is in excess of the aparent power transmitted.

Bear in mind at unity power factor, true power = rms volts * rms current

Now consider what happens if the waveform is not sinusoidal, but a rectangular wave where the current only flows when the instantaneous voltage is above the rms value. This will give you a power factor in excess of 1

Wig

I just measured the speakers power factor, came out as 1.00
I'll have to check the computer PF when it is next switched off.

Just checked the computer, and it too has a power factor of 1
This might indicate the power factor function on the meter is broken or it might be me not knowing how it is supposed to function. It might for example only give a final reading once you have disconnected the appliance.

Oh and one other thing I noticed with the computer & everything on standby it was 25W when I connected the speaker power it did go up to 33W, so I got that part wrong sorry..... I will cross it out on the OP.

sharkie

DVardysShadow wrote: »

Now consider what happens if the waveform is not sinusoidal, but a rectangular wave where the current only flows when the instantaneous voltage is above the rms value. This will give you a power factor in excess of 1

It has been a long time since i was at college, but a mains pf above 1???:eek: are you sure??? Whether one leads or lags the other, the pf range has to be between 0 and 1. Anything above 1 generates free energy, and you will become a very rich man .

It is AC and has to be sinusoidal otherwise the rms calculation no longer is valid. All the rms calculation does is to convert the amount of sinusoidal voltage to get a DC heating equivalent.

Sure you are not thinking about switched mode, duty cycles, or surge currents, spikes?

victor2

DVardysShadow wrote: »

Now consider what happens if the waveform is not sinusoidal, but a rectangular wave where the current only flows when the instantaneous voltage is above the rms value. This will give you a power factor in excess of 1

Backing up what sharkie says, the RMS value for a sine wave is
a/√2 (a over root 2) and for a square wave it is just a, where a is the amplitude, so the power factor can never exceed 1.

stevemcol

victor2 wrote: »

Backing up what sharkie says, the RMS value for a sine wave is
a/√2 (a over root 2) and for a square wave it is just a, where a is the amplitude, so the power factor can never exceed 1.

Until I started researching further, I agreed with that statement. However, apparently the RMS value for a modified square wave is back to being peak/√2 (from wiki so it has to be true). I'm going to keep my oar out until I've one a bit more digging. That's those metaphors well mixed.

DVardysShadow

I did say

DVardysShadow wrote: »

Note that switchmode and even rectifier circuits offer the potential of power factors in excess of 1 [sometimes on the internet this causes a terrible row, but it is true]. With Sine wave volts and amps, the max power factor is 1.

sharkie wrote: »

It has been a long time since i was at college, but a mains pf above 1???:eek: are you sure??? Whether one leads or lags the other, the pf range has to be between 0 and 1. Anything above 1 generates free energy, and you will become a very rich man .

It is AC and has to be sinusoidal otherwise the rms calculation no longer is valid. All the rms calculation does is to convert the amount of sinusoidal voltage to get a DC heating equivalent.

Sure you are not thinking about switched mode, duty cycles, or surge currents, spikes?

I did say

DVardysShadow wrote: »

Note that switchmode and even rectifier circuits offer the potential of power factors in excess of 1 [sometimes on the internet this causes a terrible row, but it is true]. With Sine wave volts and amps, the max power factor is 1.

victor2 wrote: »

Backing up what sharkie says, the RMS value for a sine wave is
a/√2 (a over root 2) and for a square wave it is just a, where a is the amplitude, so the power factor can never exceed 1.

I did say

DVardysShadow wrote: »

Note that switchmode and even rectifier circuits offer the potential of power factors in excess of 1 [sometimes on the internet this causes a terrible row, but it is true]. With Sine wave volts and amps, the max power factor is 1.

stevemcol

DVardysShadow

Can you post a link to a waveform diagram showing shapes / phase relationship?

DVardysShadow

stevemcol wrote: »

DVardysShadow

Can you post a link to a waveform diagram showing shapes / phase relationship?

Sorry not got the facilities ready to hand. But easy enough form the description.

• Voltage is sine wave, because we are talking about mains
• Current is a rectangular wave where the current only flows when the instantaneous voltage is above the rms value.