Apex power readings

[Turkeysammich]

Hello
I noticed this and maybe I’m wrong in my math.
If I do the math on my apex. The numbers are all wrong.
Amps X volts = watts
4 amps X 117 volts = 468 watts
But on the apex it’s different.
Also. When I do the same equation on the kilowatt meter. It’s off too. Can someone explain what am I doing wrong ? I’m confused

 

[thesassyindian]

Its rounding off the P/V/I to the nearest integer.
The actual current draw is likely a float (in this case, 411/117 = 3.51A) which is why its displaying it as 4A.

 

[Turkeysammich]

Oh ok. So apex rounds it up. But what about the kilometer ?
Here’s my example with the kilometer.
The meter reads. 60.3 watts @ 118.8 volts @ .85 amps.
If I take the amps X volts = watts.
.85 X 118.8 = 100.98
That’s way off from the 60.3.
That’s my confusion.
So which one is correct ? The 60.3 or the 100.98 ?

 

[thesassyindian]

Oh ok. So apex rounds it up. But what about the kilometer ?
Here’s my example with the kilometer.
The meter reads. 60.3 watts @ 118.8 volts @ .85 amps.
If I take the amps X volts = watts.
.85 X 118.8 = 100.98
That’s way off from the 60.3.
That’s my confusion.
So which one is correct ? The 60.3 or the 100.98 ?

What is the refresh rate of the Kilometer?
The Apex power PVI readings are refreshed at a very low rate. So Its likely that the Kilometer is reading faster and the Apex is just not refreshing fast enough to display those readings.

 

[Turkeysammich]

the numbers are consistently changing. Not by a lot but .05 ish. Up and down.

 

[thesassyindian]

OK so two things come to mind.
1. If the current is changing by 0.05A, that is about 6W at 117V.
2. If you are plugging the Kilometer in to the wall, and connecting the EB832 to it, it is also measuring the power drawn by the power bar itself, plus the head unit, plus all the peripherals (including those on the Aquabus). The current required to actuate/latch relays is higher than you'd expect.

These measurements are all missed by the power display on Apexfusion, which only shows the power drawn by the 8x sockets.

 

[rygh]

With a lot of switching power supplies as loads, you can get a lot of transient current draw.
That make is hard to measure average current.
It also distorts the local sine wave on your power line, making it hard to measure true RMS voltage.

So basically : Most likely neither of them are particularly accurate.
You need much fancier test equipment.

It is pretty sad that the P=IV calculation is off by some 40% though.