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Inverter size for running fridge?
#31
Sorry but don't think that wouldn't really help - the surge on a non inverter type compressor draws many amps over several cycles of the 50 or 60Hz AC.
Caps like that can be used to help with power factor correction of steady inductive loads (not electronic type loads) ie to get the current drawn back in phase with the voltage.
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#32
(06-25-2020, 11:12 PM)Redpacket Wrote: Sorry but don't think that wouldn't really help - the surge on a non inverter type compressor draws many amps over several cycles of the 50 or 60Hz AC.
Caps like that can be used to help with power factor correction of steady inductive loads (not electronic type loads) ie to get the current drawn back in phase with the voltage.

I beg to disagree. All air conditioners and refrigerators use a smaller oil filled cap to start  and run the compressor. The size of the cap is sized 

     for barely enough to fit them in a normal sized circuit breaker and be able to start them.
 
If you had  enough capacitance  to equal or exceed  the startup requirement . the startup would just be a small blip on a meter.

Compressors are not a steady inductive load , ie temperature changes , starting.

The power factor on a compressor is a .9 at best after startup

While the unit is on or starting up the capacitor will smooth out the draw whether it comes from a utility or inverter

A inverter compressor does a better job at smoothing out starting up and running , but taxing a battery inverter you have to look at
   
     starting watts , I agree with You can't trust the ratings on a high frequency inverters from China.

The Ebay load conditioner is just capacitors and lights and a fancy box and maybe a circuit breaker. A 50-100mfd capacitor will melt a 16

      penny nail and give you a light show you'll want to forget



Jim jr
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#33
Thank you to everyone!  I really appreciate the detailed responses, they really help me to not just get an answer but understand all the factors that go into it.  

A question about energy monitors and these starting spikes.  Are they generally viewed as sensitive enough to catch them?  I'm using a Blue Planet EM100.  I have now had it running for 10+ days and it has still never gone over 560w/4.6A.  Over 10 days my compressor has to have cycled many times.  Do compressors always have the same kick when starting or does it vary?  Assuming my energy monitor is accurate enough, is it possible that over 10 days my compressor has just never done a big kick?  

Is my reasoning correct:  I've noticed 3 phases to my fridge, 1. uses about 10w, 2. uses about 90w and 3. uses about 140w.  I assume I would use the larger 140w/1.16A for to calculate 2-3x working load.  This means at least 4A load.  Now I know since I know that I fridge is labeled with a 7.2A max, so if I leave more headroom at look at 1500w/12.5A+ (true capacity, not just surge) I think I will be good.  Did I miss any steps in my logic?

Jim can I ask what you mean by "power factor on a compressor"?
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#34
Your logic looks good. It'll mean you can have some other loads on at the same time & it'll cope.

The three different current draws are probably:
1) Idle, electronics only
2) 90W = door edge heaters (for icing/condesation control)
3) compressor running

Since your fridge DOES have an inverter, the "big" start-up surge won't be happening.
The inverter drive electronics does a "soft start" - probably drawing only the 560W/4.6A peak you're seeing.

So "power factor" is a calculation related to the timing & shape of current vs the voltage (of the AC mains, a sine wave).
With something like a resistive heater, the current & the voltage are in phase & the same sine wave shape.
But other loads, eg like a simple electric motor might be quite inductive load due to the coils in the motor. So this makes the current lag (be delayed) by up to 90 degrees from the voltage - the shape is still a sine wave.
Electronic loads tend to draw a pulse of current at the peaks of the voltage waveform not smoothly up & down the curve.
Power factor affects transformers & the wider power grid too but also an inverter trying to run your gear.
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#35
(06-27-2020, 12:30 AM)Dax Wrote: Jim can I ask what you mean by "power factor on a compressor"?

Mr Redpacket is correct in his answer. He gives it from having a better back ground in electronics than me .

A compressor changes its load on changes on starting to opening up the frig door to outside air temp to seeing a blob of oil going into the compressor.

Since you have a inverter style compressor , you won't see a large surge with it.  The only thing is there are more parts to  fail.

I am still using a 1959 compressor as a vacuum pump.


Jim Jr
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#36
(06-26-2020, 03:35 PM)Jim Jr. Wrote:
(06-25-2020, 11:12 PM)Redpacket Wrote: Sorry but don't think that wouldn't really help - the surge on a non inverter type compressor draws many amps over several cycles of the 50 or 60Hz AC.
Caps like that can be used to help with power factor correction of steady inductive loads (not electronic type loads) ie to get the current drawn back in phase with the voltage.

I beg to disagree. All air conditioners and refrigerators use a smaller oil filled cap to start  and run the compressor. The size of the cap is sized for barely enough to fit them in a normal sized circuit breaker and be able to start them.
 
If you had  enough capacitance  to equal or exceed  the startup requirement . the startup would just be a small blip on a meter.

......

While the unit is on or starting up the capacitor will smooth out the draw whether it comes from a utility or inverter

...
A 50-100mfd capacitor will melt a 16 penny nail and give you a light show you'll want to forget

Jim jr

Motor run or motor start capacitors across AC voltages "store energy" only for up half a cycle of the AC wave.
They do not smooth out current draw, they change the phase of the AC current into a 2nd start or run winding.
Just putting a large cap across the AC feeding a motor will not help the startup current draw which is over several cycles until the rotor is up to speed.
A little while back, I looked into the startup surge of my own fridge in detail, built a motor control circuit & did several posts of it a while back & came to understand AC motors pretty well there.
https://secondlifestorage.com/showthread.php?tid=6043

Agree one of these caps can store quite a bit of juice (think camera flash energy ++)
Caps in DC circuits, sure they store energy much longer because of the circuit.
Running off solar, DIY & electronics fan :-)
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