A/C Unit draws 50% more power on 50hz vs. 60hz

[mdsilvers]

Some more info. Here is a side-by-side screenshot of the load on the inverter with the main AC running.

[mdsilvers]

Here is the Dometic Service Manual. The footnote clearly states that the 120/60hz unit, if derated to 100v/50hz will work with a 17% loss in capacity.

The compressor is not labeled at dual 50/60 on the case, nor is it listed as dual 50/60 here in the service manual, but it appears that derating is 'OK' according to Dometic?

[Coolerking]

Derate 17% @50hz
Correct.

[valhalla360]

Are there any other loads on the inverter? 18amps for the 2 air/con units is already going to be around 2200w...that leaves only 300w before you hit the 2500w continuous load limit.

[Cadence]

Originally Posted by mdsilvers

Yes. I am checking both.

120v/50hz draws 17 amps
119v/60hz draws 11 amps

Where in the world is this? Is it possible your inverter is giving you a cleaner wave form and it has nothing to do with the CPS, hz if you like.

[mdsilvers]

Originally Posted by valhalla360

Are there any other loads on the inverter? 18amps for the 2 air/con units is already going to be around 2200w...that leaves only 300w before you hit the 2500w continuous load limit.

I'm only running one unit, not two.

[mdsilvers]

Originally Posted by Cadence

Where in the world is this? Is it possible your inverter is giving you a cleaner wave form and it has nothing to do with the CPS, hz if you like.

The inverter is tripping. Not the shore power. The inverter is 115v/60hz.

[mdsilvers]

I'll take the advice and stick with inverter. Working on getting that fixed.

I did test out the variable transformer, and it works great. 97v, 50hz and I draw the exact current at 115/60. So the power draw question is solved.

Thanks for all the advice.

[rbthorson]

With alternating current, current is not always in phase with voltage particularly when operating inductive loads such as motors and fluorescent lights. When you measure voltage and current with separate meters, you are actually measuring Volt-Amps which is not the same as wattage. You may want to consider a power factor correction circuit.

[Cadence]

Originally Posted by Cadence

Where in the world is this? Is it possible your inverter is giving you a cleaner wave form and it has nothing to do with the CPS, hz if you like.

My degree is 58 years old. It may be related to the compressor has a start run capacitor.. You might consider contacting the mfg. and see if they don't make a 50 and 60 cycle version which might be no more than changing out the capacitor. It probably looks like a can with terminals which causes a phase shift.

[Rothblum]

This quote from an on-line electrical course might explain the extra power draw when you are using the inverter, if the inverter is not a sine wave inverter, which hardly any high power inverters are: "Into the same load, a square wave will deliver twice the power as a sine wave of the same peak voltage. This is same as saying the square wave has an RMS voltage equal to its peak value; whereas a sine wave has an RMS value of 0.707 (actually sqrt(2)/2) times the peak value."

The transformer is a true sine wave machine, assuming the input is true sine wave.