Help measuring Engel fridge power consumption

[Jman99]

My Engel 40L was running continuously in near 40 degree celsius heat with warm drinks added inside. Controlled tests.
Hour after hour my cheap common inline DC watt meter was displaying an average 2.8A draw and 37watts the whole time.
Since the compressor was running continuously, I would have thought the amphours and watthours accumulated in any given hour would be 2.8ah and 37wh.
Yet the readings were always around 1.7ah 22wh. from what I have heard the engel compressors actually draw a pulsed DC current that runs the 20vac sq wave inside.
So I ran the fridge on 240vac with an inline watt meter under the same conds, and the accumulated watthours was 44, roughly double,

So my questions are very simple

Which watthour readings (DC or AC) if any are accurate of power consumption?
Does this same apply to Danfoss type compressors? Or can I just take the DC watthours as accurate?

ta

 

[broncobowsher]

100% duty cycle, about 40W is correct.
Have no idea what math your cheap watt/amp hour meter is using. If it was powered on for 2 hours, but only hooked to the fridge for 1 hour, it might be trying to use that in the math? Maybe it does a rolling 24 hour average? You didn't tell us what you are using, so we have no idea.

But if you just figure 40W, that will get you close enough. If it draws slightly more and that is an issue, you didn't put enough buffer into it. If it draws less, you just have a little extra buffer.