I have a residential refrigerator that draws 1.5a at 120vac with the compressor running. The inrush current is 22a with almost no voltage drop when plugged into the mains. I measured these values with a 2-ch oscilloscope and current clamp taking simultaneous current and voltage measurements. The 22a lasts for only 263ms and goes down to about 15a for another 600ms. The entire inrush event lasts about 900ms and the current drops to typical 1.5a running.
I have a 12v LifePo4 battery (13.6v actual resting voltage) and was wanting to use a Victron Phoenix 12/1200 120v inverter to run my fridge for several hours during a power outage so I didn’t have to keep the generator running the entire time, then run the generator to top off the battery. I’m concerned though that the inrush of 2,640 watts (22x120), even though that lasts 263ms, is more than the peak power of 2200 watt rating for the Phoenix 12/1200. Can that inverter handle that since it’s only over peak for 263ms, or is it too small? Seems like the larger inverters are way overkill for this 1.5a normal load and they have a high idle power draw.
Should I wait and hope the 12/1600 makes it to the USA in a 120v version?
@AndrewW Hello Andrew. It is great to have the real world numbers for the inrush current for the compressor for the fridge. I wonder is that reading the RMS value of the current? It seems a bit high to me as I would have guessed maybe an inrush of probably 8- 10 times the quiescent current but that is closer to 15. I dont know the answer to your question but keen to hear what you learn.
Firstly, thank you for taking time to ready my question! I replied outside your question so I’m not sure if that notified you or not but I was actually wondering if I needed to use peak or RMS when sizing for inrush. All the measurements I gave are Peak current measured from the waveform on the oscilloscope, not RMS. I saw something from Fluke that said their meters look at around 5 cycles to determine inrush and take the RMS, and other models take the peak value, so I didn’t get anywhere looking at how some other tools measure inrush.
If I translate my peak measured current to RMS it is 15.5a (22 x 0.7071), which is still a little higher than I was expecting. That looks to be about 1860 watts, which would be within spec of the 12/1200. Too good to be true?
I’ve seen from videos on Victron’s YouTube where some Victron inverters have an overload period of 30 cycles for the most severe overloads before shutdown. The period of 22a peak lasts for about 17 cycles, then drops down to 15a peak for ~30 cycles before settling at the 1.5a normal running current. Without clarification on whether to use use peak or RMS for inrush I didn’t want to assume I could use RMS and risk the inverter going into low-voltage overload, or even worse frying it.
@AndrewW For the purposes of evaluting the capacity to handle the inrush the measurments should be RMS. The reason is the true RMS value provides the equivalent heating value of the waveform. If we use peak, the equivalent heating value may change depending upon the distortion of the waveform. At least that is my plausable story for the reasoning… I think the 12/1200 will do the job nicely. The short duration of the inrush I don’t think will be a problem.
I think the 12/1200 will do the job nicely. The short duration of the inrush I don’t think will be a problem.