Father-in-law's solar system

[Cipro 6,202]

The inrush current problem is because of Power Factor. With an inductive load the wave form of the current and voltage are out of phase. The inductive current current lags the applied voltage. 

 

A parallel capacitor supplies current that isn't dependant on the mains (or inverter supply) to realign the waveforms and so reduce inrush current. This capacitive load will lead the voltage and tend to reduce the Power Factor.

 

In large industrial systems, we use caps to correct PF but they are disconnected during start-up. I remain unconvinced that having caps on the line full time would fix this start issue without introducing an issue during normal operation, at the very least. 

[Cipro 6,202]

Since you have a clamp meter available, you should do a test on your fridge. See if the results matches with the rated specs sticker on/in your fridge.

 

 

Unfortunately it's not that simple. 

 

Inrush is particularly complex because you're dealing with a power draw that changes rapidly over a brief time. When this is reported on a sticker, the goal is not generally to report the biggest spike, it is generally done with a goal of helping people to understand how they should size the circuit and circuit protection. 

 

Most circuit breakers or fuses have an implicit functional characteristic that integrates demand over time, with different devices having different characteristics. The goal for these devices is to protect the wires in the circuit from damage due to heat from over current. Thus, being able to sustain an over current for some time is a desirable characteristic, and not dangerous. 

 

The limits imposed by a solid state DC-AC inverter are vastly different; the inverter is concerned with protecting the switching devices, which are much more sensitive to current transients than wires or a simple motor. 

 

Thus you will often find an apparent mismatch between the ratings, and the consequent advice to oversize the inverter for such hard to start loads. 

[thebob 18,260]

 

 

I remain unconvinced that having caps on the line full time would fix this start issue without introducing an issue during normal operation, at the very least. 

 

I agree that it isn't optimal but it is the easiest "kludge" I can think of to get it to run. It is a difficult problem because each time the compressor motor starts the AC waveform is likely to be in a different place, so even measurement is difficult.

 

 

 

Inrush is particularly complex because you're dealing with a power draw that changes rapidly over a brief time. When this is reported on a sticker, the goal is not generally to report the biggest spike, it is generally done with a goal of helping people to understand how they should size the circuit and circuit protection. 

 

This is a problem that I don't think is being addressed by the DIY solar community. Safety, efficiency and practicality are often at odds with each other.

 

Unfortunately running a large inverter partially loaded isn't efficient, but is needed for starting conditions. Perhaps a separate inverter that is switched in for starting but not for running would aid efficiency, but practically "aligning" the output of multiple inverters isn't trivial. Not to mention the necessary predictive sensing, to allow the inverter to boot. 

[Paul 55,114]

 

 

Unfortunately running a large inverter partially loaded isn't efficient, but is needed for starting conditions. Perhaps a separate inverter that is switched in for starting but not for running would aid efficiency, but practically "aligning" the output of multiple inverters isn't trivial. Not to mention the necessary predictive sensing, to allow the inverter to boot. 

 

It is quite common, especially concerning off-grid systems, to have two separate voltage inverters. One runs lighter, smaller loads during off-peak times, while the larger inverter is connected to the heavier loads in the home / cabin. 

[Ozepete 9,569]

I see. Okay. Different appliances.

 

 

 

 

You are correct, in that it should. However, in testing many appliances over the past six months, I have found that most are not drawing the same rated power that are stated on their labels. More often than not, they have drawn more than what was stated on the label.  

 

Very small refrigerators, for example - what we called "dorm refrigerators" in the states, often draw as much as a full sized energy efficient refrigerator. 

 

These "dorm" fridges are most likely 'Peltier systems'  This is a most inefficient form of refrigeration that should be avoided. (Or banned) They can use as much as eight times as more power than a compressor system.

Operating AC appliances via inverters is quite inefficient and don't be too convinced of the virtues of so called 'Pure sine wave' as the term is loosely used. There are many factors that come into play when an electric motor (compressor) is applied to a power source. Firstly the THD factor (Total Harmonic Distortion, a factor which relates an inverters THD to the theoretically perfect THD. And most don't get within a bull's roar!). Peak voltages, pulse width etc are all involved. 

 

We have developed a 3cc DC compressor with driver and controller system that runs at 74watts (12VDC) and has no start-up current rush. 

[Cipro 6,202]

These "dorm" fridges are most likely 'Peltier systems'  This is a most inefficient form of refrigeration that should be avoided. 

 

My little fridges (before I gave them away) had tiny little compressors in the back and tiny little heat exchanger tubes in back too.  

as for Peltier devices, I like them for specific applications, and if they are running off a solar array I don't see what interest the public has in banning my solid state fridge being driven by my solar cells.