What Watts are What?

[not so old china hand]

32 minutes ago, Dave Hounddriver said:

1 hour ago, OnMyWay said:

 

Thanks.  I was looking at a few "universals" like that, but when I look close they usually say 50 Hz when operating at 220+ Volts and 60 Hz when operating at 110 -120 volts.  That seems to be the standard.  But I will look more closely at that one.  

But for now I will give it a rest and look in the local hardware stores tomorrow.  Oh that's right, may be closed tomorrow because of some kind of strike.  Well we shall see.

It's been a long, long, time since I studied physics at college but AFAICR frequency does not make any difference to the measurement of voltage or current and hence power. OK we were using moving coil instruments and maybe (just maybe) digital instruments need to make a correction for frequency. If that were the case (and I think it's not) the meter would need to sense the frequency and correct for changes in the frequency of the supply.

This is a long winded way of saying that the more I think about it the more I'm inclined to think that the frequency in the spec does not matter. JMHO

An afterthought, why do they quote frequency ranges? I think ecause it is useful to be able to measure the actual frequency since some devices are sensitive to frequency.

Edited October 15, 2017 by not so old china hand

[Dave Hounddriver]

36 minutes ago, not so old china hand said:

some devices are sensitive to frequency.

Yeah, I was worried that my air conditioner would be sensitive to frequency and I was scared of putting something in the 220/60hz plug that specs out at 220/50hz  If its not going to hurt it then I can get lots of local devices that say they work on 220/50, but would it give a correct reading and would it work?  

[not so old china hand]

45 minutes ago, Dave Hounddriver said:

Yeah, I was worried that my air conditioner would be sensitive to frequency and I was scared of putting something in the 220/60hz plug that specs out at 220/50hz  If its not going to hurt it then I can get lots of local devices that say they work on 220/50, but would it give a correct reading and would it work?  

IMO the meter would do no harm to the air con since a meter only senses the current; it does not change it. As to the accuracy of a device rated 230v 50Hz  on a 220 60 Hz supply my feeling is it would give the same accuracy at both frequencies: but I can't backup that feeling with hard figures.

[Gary D]

Frequency will affect the phase angle hence the power factor, that's why VA is quoted in cases rather than Watts. A motor or transformer designed for 50Hz can run faster and hotter when given 60Hz

[AlwaysRt]

Order this one today and it might even be in your hand by the weekend.  http://www.lazada.com.ph/digital-watt-meter-power-meter-power-reader-with-overcurrentprotection-and-back-light-220v-max-10a-14549715.html?spm=a2o4l.search.0.0.KlyTvn&ff=1

Edited October 16, 2017 by AlwaysRt
If I remember correctly that inverter has a power factor somewhere between .9 and .93

[Dave Hounddriver]

3 minutes ago, AlwaysRt said:

Order this one today and it might even be in your hand by the weekend

I'll have a look but let me just say I have been watching videos and reading articles about batteries and meters and inverters all weekend and quite honestly, the more I learn the less I know 

[Jake]

14 hours ago, not so old china hand said:

IMO the meter would do no harm to the air con since a meter only senses the current; it does not change it. As to the accuracy of a device rated 230v 50Hz  on a 220 60 Hz supply my feeling is it would give the same accuracy at both frequencies: but I can't backup that feeling with hard figures.

I concur with Terry on this one.  The device plugged into the wall to monitor power consumption for any load (AC unit, appliances, rice cooker, etc) will not affect the operation of the load.  It's like a tachometer measuring RPM's will not affect the operation of the engine.  

It would be interesting to compare power consumption, say within a 24 hour period between your 3/4 HP AC unit and the 1 HP AC  unit.  The monitoring device's specs of 50Hz or 60Hz should not matter.  It's all relative -- you're just using it for comparison.  

[not so old china hand]

On 10/15/2017 at 8:20 PM, Gary D said:

Frequency will affect the phase angle hence the power factor, that's why VA is quoted in cases rather than Watts. A motor or transformer designed for 50Hz can run faster and hotter when given 60Hz

Indeed. AFAICR induction motors are prone to this. However the question is whether a so called Universal Meter would be capable of measuring the maximum current and power factor accurately at 220V 60Hz.

And as Jake says it might not matter anyway if one is just looking for relative values.

[Dave Hounddriver]

For those following my "meter mayhem" I found one in a shop in Dumaguete today, but the male plug in the back of it would not fit the female socket in the wall.  Since I want to test an aircon that draws a lot of power I did not feel comfortable jury rigging it through a couple of 25 peso adapters.

Plan B is to find a similar digital watt meter that gets wired in line.  That way I can wire my own plugs on the ends  so still playing with the idea.  

[allancomeau]

Normally what is given on appliances is the NOMINAL current.

Especially for motor driven appliances (fridge, A/C, etc) the motor requires a large initial rush of current. This surge can be five to ten times the nominal power though it is very brief, without that current being supplied the unit can not turn on (properly).

Your A/C manual should state the turn-off surge current.