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Inverter size for running fridge?
#1
Hello to everyone and thank you for all the resources you have made available here!
 
I am brand new to just about everything here and wanted to ask some questions to get some help and to verify what I am understanding correctly and what I have wrong.  Starting with, I hope this goes here, rather then the Battery Pack Planning forum!
 
 TLDR:  Is a 1000w continuous inverter enough to run a peak 864 watt fridge for ~24hrs? 

My goal is to build portable ~2KWh grid charged powerpack/battery to power my fridge for about 24h in case of a power failure.  By portable, I mean from the room I will keep it in, to my kitchen Smile
 
Here are my parameters.  
  • I live in an apartment and cannot make changes to my power panel etc. 

  •  Solar for charging is pretty much out as I hardly receive any direct sun.  I did buy one 75w panel to just see what it would do.  In summer I only get about 3-4 hours max that produced anything.

  • I live in Canada 
    • I am on 120v 60HZ 1 phase
    • Many things will not ship here
    • Many things are outrageously expensive to ship here
    • Many items are not available because of pandemic
 
  • I pretty much have to buy every tool I will need (and have started to do so).

  • I have a limited budget (doesn't everyone!) so I am trying to balance buying tools versus better parts etc.   

  • I want to do this one on as small as budget as is reasonable, so I can win over my wife for future projects!
 
 
On my fridge it gives these measurements:
Full load: 7.2 AMP
Max defrost sys: 468w
Max lamp fridge - 3x40w
Max lamp freezer - 3x40w
 
I have an energy monitor that I have had the fridge running on for about 4 days so far and this is what I have observed.



Average 1.5KWh per day 
  • peak of 560w
Current cycles between 0.58a - 1.22A
  • max of 4.63A

I own a 12v 500w modified sine inverter.  From what I've figured out so far, it is too small and not likely to work with my brand new fridge because of being a modified wave.  Any dissenting opinions (about the modified sine wave)?
 
I have ordered an OPUS charger and a yr1030.   I am planning to buy a 175w Weller soldering iron. 
 
What soldering supplies are essential to someone in the scope of this project?  Can I get it off AliExpress or there too much risk of it being … fake, garbage, etc., given that I am a total newb at this?
 
Originally I thought to build a 14s20p battery.   However, I am having a hard time finding a quality inverter that doesn't break the bank.  I have found a wider selection of inverters in the 12-24v range.  Given that this is solely for the powering my fridge, my reasoning is to select the best inverter I can get/afford then build my packs to match?  Does this make sense?  
 
According to the specs, the max wattage is 864w.  Is a 1000w inverter sufficient? I have come across some references that say for fridges an inverter should be able to handle at least 3x.  Anyone have some thoughts?
 
Maybe someone has some suggestions to widen my search beyond amazon, ebay?  invertersupply.com  - kills me on the shipping (and currency exchange).  Maybe some fellow Canucks have some "local" online store suggestions.
 
I have seen Reliable brand in my price point but they don't seem to have a great reputation on the board.
 
Thanks in advance!
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#2
One key thing about the fridge - does it have an inverter controller for the motor or just start with a bump?
It sounds like it is an inverter drive one (good because the start-up surge is much less).

"Modified sinewave" inverters are not good generally (the peak is lower, can cause motor heating + the fridge inverter & other electronics may not like this).
You should look for proper sine wave ones, even if they cost a bit more.

You should also target building a 24V system as the efficiencies are much better than 12V.

re the soldering iron, for 18650's the general thing seems to be about 80-100W with a bulky (thermal mass) tip is enough. If you go too big, you may start damaging the cells from excessive heat. There's a weller 100W model that looks ideal.
Running off solar, DIY & electronics fan :-)
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#3
+1 Redpacket

modified sine wave not good for "any" electric motor. You'll have a lot of buzzing and will increase heat generation (definitely not needed for a refrigerant based motor)

Also, a 1000W inverter may be fine if the surge wattage is 2000W or more. Otherwise, it'll have a hard time starting an 864W load.
When it comes to electric motors, the ratings on the tag are "running" values, not starting values. Generally speaking, an electric motor can consume up to 5x the rated power when starting up. A compressor style motor will most likely get closer to that than one like for a fan.
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#4
Check out the Victron ve.direct phoenix inverters. In the states the 1200va (1000w continuous) is around $400usd. It has a good surge and you can add the bluetooth dongle to configure and log from your phone if you desire. https://www.victronenergy.com/upload/doc...0VA-EN.pdf These inverters can be had in 12, 24 or 48v configurations.

For what you need I'd say 7s (24v) would be the smallest you should go. Keep in mind that while you are logging 1.5kwh of daily use it will vary depending on room temp. I have a chest freezer in a room that isn't very insulated. When the avg temps are in the 40's it only uses around 500wh per day. In the peak of summer when the ambient temps in the room average around 90 it uses more like 1.2kwh of power. It is fully stuffed so it is running at it's max efficiency. You should also consider the theoretical pack capacity vs usable capacity. Especially with used cells and the smaller cycle range that we tend to use. Maybe consider planning for a pack capacity around 3kwh to get through 24 hours.
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#5
(06-21-2020, 03:56 AM)Redpacket Wrote: One key thing about the fridge - does it have an inverter controller for the motor or just start with a bump?
It sounds like it is an inverter drive one (good because the start-up surge is much less).

"Modified sinewave" inverters are not good generally (the peak is lower, can cause motor heating + the fridge inverter & other electronics may not like this).
You should look for proper sine wave ones, even if they cost a bit more.

You should also target building a 24V system as the efficiencies are much better than 12V.

re the soldering iron, for 18650's the general thing seems to be about 80-100W with a bulky (thermal mass) tip is enough. If you go too big, you may start damaging the cells from excessive heat. There's a weller 100W model that looks ideal.

I never realized they had inverter fridges so never knew they existed.  They must be rare and on expensive models. But for the conventional fridges with hard starts, yes they take 3x the rated to start the pump. The labels may only record max running amps and not the starting amps. Actually most motors take up to 6x or more amps. Typically doesn't blow a breaker because they usually have a time delay for such cases. I run my fridge, which states a 6.3A and it just about makes it with my 2.4kw inverter (which carries a 2x surge to 4.8kw). It's a chinese inverter so the surge rating may be debatable. But the fridge does take a wallop just to start so I wouldn't even consider a 1kw inverter.
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#6
Yeah lots of recent fridges use "inverter" motor control, they're quite common here in Australia.
They vary the motor speed & make the start-up much more gentle.
Korishan likes this post
Running off solar, DIY & electronics fan :-)
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#7
Ahh, kinda like a soft-start system
Proceed with caution. Knowledge is Power! Literally! Cool 
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#8
(06-21-2020, 01:16 PM)Korishan Wrote: Ahh, kinda like a soft-start system

Nah more like variable speed. Not common here in the US yet (or maybe i haven't realized it). Look like common on the japanese and asian imports. Same stuff they use in the mini split ac units. I've heard of heat pump dryers, but I never thought it went into fridges but does make sense.
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#9
(06-21-2020, 02:32 PM)not2bme Wrote:
(06-21-2020, 01:16 PM)Korishan Wrote: Ahh, kinda like a soft-start system

Nah more like variable speed. Not common here in the US yet (or maybe i haven't realized it). Look like common on the japanese and asian imports. Same stuff they use in the mini split ac units. I've heard of heat pump dryers, but I never thought it went into fridges but does make sense.
Exactly - variable speed (internal inverting) is present on our new 4ton Lennox heat pump - the power starts at 1a@240v and gently rises to 2a, 3a, 4a etc over minutes.  No inrush or large surges of power up/down.
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#10
With a "peak of 560w" from a measurement average of I'm presuming a 1 second sample time or longer the difference between inverter based and bump start will be massive.

With a 500W compressor unit the surge currrent spike is going to be large enough to blow virtually every 1kW rated inverter. From some values I have seen on motor starts about 7x is possibly closer and also factor in the accidental incident of the fridge being re-powered too quickly with compression back pressure on the fridge, which will either stall the compressor or cretae a lot longer surge. If the inverter is already close to it's limit then this is what may well push it over the edge.

If it's bump start then most high frequency inverters below about 2kW are going to fail with a 3.5kW surge for a second.

If it's inverter based, completely different issue as it may revolve around the spike from the input capacitor charging when first plugged in. The way around this is to have the fridge plugged into the inverter as you power the inverter up and if the inverter has a soft start (rising output voltage over 1-3 seconds) this smooths out any capacitor charging spike.
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