Power Calculations For 2 Freezers

[Cass]

Basic math time. We have
1) 5.5 cubic foot chest freezer converted into a fridge. Kill-A-Watt shows 264 watts a day or 11 watts/hour (the temperature regulator turns the 'fridge' on an off and we've been monitoring the temp with a wireless thermometer. Our current AC voltage is 123. Watts when off are of course 0 and when the compressor is on around 120 watts but only for a few minutes.

2) 16 cubic foot upright chest freezer. It uses 1248 watts over a 24 hr period or 53 watts per hour. The watts vary from .3 constant to sometimes 100 watts while the compressor is running

I have an Ecoflow Delta 1300 and 2 x 100 Renogy Briefcase panels. For emergency power backup for just the 'fridge' and freezer I am guessing 10-12 hrs if fully charged and without the solar. The solar panels we have not tested yet but I am thinking with a good 4 hrs sun I can get another 6 hrs of freezer /ridge hrs? To be safe we're planning on estimating 12 hrs.

If the power outage is not widespread, we could always take the Ecoflow to a neighbor and recharge it there and bring it back. The biggest drawback with the Ecoflow is the 2 hr cool down and 2 hr recharge period = 4 hrs which might be pushing the fridge a bit. We have not yet tested how long the fridge can maintain its temp without power.

Any other tips/thoughts?

 

[svetz]

... 5.5 cubic foot chest freezer converted into a fridge. Kill-A-Watt shows 264 watts a day or 11 watts/hour

Sounds unbelievably low unless it's really cold already in that room. Refrigerators also tend to suck down a lot of power during the defrost cycle.

I'd double check those readings. Could be you're reading watts rather than watt hours, or the meter might be a bad one. I'd say try it on a light bulb of a known wattage. For example, an incandescent 75 watt light bulb should consume ~19 watt-hours if you meter it for 15 min (75 W x 15 min / (60 min / hr)). (If you have an ohm meter you can get fairly close to the exact wattage rating of the light bulb. V=IR, watts=VI, but R changes a bit when the bulb is hot.)

 

[Cass]

So putting aide the chest freezer numbers (more on that below). Will my set-up handle my upright freezer for 12 hours? Longer? I know there is some power loss going from DC Solar to AC and that the Ecoflow 1300 does not really offer 1260 watts - more around 950 watts

Re the chest freezer:
I checked Kill-A-Watt again - for the past 119 hours it averaged 12.2 watts per hour .

I took the Kill-A-Watt KWH number 1.458 KWH and divided it by 119 hours.

It has been much warmer in the garage (80s). I can see why this method is popular for off grid homeowners). I do not plan to run the freezer long term as a fridge - this would only be an emergency mode.

For a chest freezer to fridge conversion 12 watts per hour looks to be on high average - but it is possible that everyone else is calculating the wrong way as well?

290 watts day (12 watts per hour)

http://www.aselfsufficientlife.com/...on-the-most-energy-efficient-fridge-ever.html
150-180 watts day (7.5 watts per hour)

https://johnlvs2run.wordpress.com/2009/10/08/chest-fridge-conversion/
8 watts hr

https://permies.com/t/105709/grid-refrigerator-power
232 watts day (ca 10 watts per hour)

https://www.offgridbootcamp.com/poor-mans-super-efficient-off-grid-refrigerator/
Less than 200 watts day

https://intrepidhomestead.com/2009/09/11/first-days-with-the-chest-freezer-as-fridge/
440 watts day for a freezer that is three times the size (18.3 watts per hour)

 

[RCinFLA]

The 'got you' rarely taken into account powering refrig or freezers is Defrost cycle. Most refrigs do this about every 18 to 36 hours and the heater in the defroster can draw over 1000 watts. It can sink your battery capacity estimation. Defrost can last 15-30 mins but high current cycles On and Off during this period.

Also the compressor startup current can be upwards of 1500 watts or more even though run current is less the 200 watts.

 

[svetz]

WOW! Still can't believe it.... but if the numbers are right and includes any defrost power drains then ...

...Will my set-up handle my upright freezer for 12 hours?

Your power budget from the OP is:

Appliance	Duty (hours/d)	watts	Wh/d (=W x h/day)
5.5 cubic foot chest freezer	24	11	264
16 cubic foot upright chest freezer	24	53	1248
		35	1512

From this ref the ecoflow 1300 has: 1300 W continuous and 1260 Wh. I'll assume that's the AC watt hours (if not divide the numbers by the inverter's efficiency, that is if the inverter is 80% efficient then it will take 53/.8=67W to power the upright).

1260 < 1512, so that's not enough by itself for a full day for both freezers. But, for 12 hours, you'd only consume 756 Wh for both (624W for just the upright) and that is less than 1260 Wh. The inverter outputs 1300 W and you only need 35... so yes... the EcoFlow 1300 can keep you going for 12 hours.

You also have 2 x 100W Renogy Briefcase panels. Assuming your insolation is 4.5 (depends on where you live and can be found from an insolation map), you'd generate 200x4.5 = 900 Wh/d if they were aligned at the right tilt for the day less inefficiencies so call it 800 Wh/d. 1260+800=2060; which is greater than 1512 Wh/d... so yes... you'd have enough power for a day if you started out fully charged.

800 Wh/d isn't enough to recharge your batteries fully during the day, but it will stretch it out...looks like you could get two days plus some out of it.

 

[svetz]

Thanks for posting those links... I was still having trouble believing them (not like the links are scientific journals), but one of them cited energystar.gov and that's not as good as using a meter like you did...but generally pretty darn good. So I was flabergasted! Thanks for teaching an old dog a new trick!

So, here's the ES link setup for chest freezers and here's a few results:

Danby Designer - DCF081A1* - 8.1 cuft, 22 W, 2.66 W/cuft
GE - FCM11PH**** - 10.6 cuft, 25W, 2.34 W/cuft
Crosley - XCM22DM - 21.7 cuft, 40 Watts, 1.84 W/cuft

 

[Brewman]

The homebrew community is always turning chest freezers into kegerators.

 

[svetz]

Even some of the standard non-chest big-name fridge/freezers are pretty efficient and on par with the chest models w/cuft:

GE - GTE21GSH - 21.1 cuft, freezer on top, 45 watts, 2.14 W/cuft
LG - LTNS20220 - 20.2 cuft, freezer on top, 44.2W, 2.18 W/cuft
LG - LSXC22436* - 21.9 cuft, side by side, 60W, 2.7 W/cuft
Samsung - RT21M62*3** - 21.1 cuft, freezer on top, 45 W, 2.1W/cuft


Hmmm... wonder how long it would take the LG 20.2 to pay for itself. $600 on bestbuy. 12 cents /kwh. Assume current frig is 160 W at 40% duty ... so..
(160*.4-44.2) x 24 x 365 x .12 = $21/yr... so 600 / 21 = 28 years. Oh well...

 

[Cass]

I can say that I too was blown away with the results for the chest freezer -> fridge conversion. I ran it twice - 5 days each time into account for the defrost cycles and outside temp variation. There is a problem with condensation because there is no air flow - but for short term use it should be fine. I have switched the freezer back to freeze and removed the thermometer timer. The plan is to immediately switch it to fridge mode as soon as there is a power outage lasting more than 3 hrs and move the big fridge items over.

Re the calculations above - one thing I have noted in all the reviews is that the Ecoflow does not deliver 1260 watts of power - most they deliver is around 900-950 watts. This is one of the biggest drawbacks of the Ecoflow. The big plus is that it can be quickly recharged from a AC wall outlet. So if the power outrage is not too widespread or, if it is, you have a friend with a gas generator who is willing to let you plug in, you can recharge it fast enough to get back to the fridge and freezer to avoid food spoiling. This would be 2 x a day

5 cubic freezer run as fridge 12 watts x 24 hrs = 288
16 cubic foot freezer 53 watts x 24 hrs = 1272
TOTAL power needed = 1560 watts - 900 Ecoflow = 660 watts

2 x 100 Renogy solar panels
Summer = 800 watts (using your numbers)
Winter = no idea will have to test

So we may barely squeak by 2-3 days in the summer

Here in Silicon Valley the online estimates assume 7 hrs summer light and 2.68 hours winter

Solar Irradiance Calculator

www.solarelectricityhandbook.com

In the winter 2.68 x 200 watt panels x .80 efficiency = ca 400 watts

So less than 1 day. I may be able to sequeak by with a 3rd solar panel - but the Ecoflow will only accept 65 volts in put so I might have to adjust the setup (again I am not well versed in solar panels/connections)

So lots of trade-offs. Until we get our solar panels we won;t be able to report on real life use

 

[Cass]

Quick update on the Ecoflow performance. Solar panels are still not here, so this is the AC wall charge

1. Recharge is as fast as they say 1.5 hrs
2. The 'cool down' period before recharge varies - 1.5-2 hrs - if it is not fully cool it will limit recharge input to 600 watts. I unplugged, gave it another 10 min and it started recharging again at 1000 watts
4. Performance - the 5 cubic ft 'fridge' is now converted back to a chest freezer which throws off the math, so I will only discuss the 16 cubic upright freezer

On a 95+ day inside the unheated garage with the freezer cycling on and off - 8 hrs
Cool evening/overnight 10 hrs

The Kill-A Watt only shows that the upright freezer 'used' 650 watts before shutting down both times...I am not certain how to square this with other reports that the Ecoflow holds 950 watts in real life.

 

[svetz]

...The Kill-A Watt ...shows ...the ...freezer 'used' 650 watts before ... [the ecoflow shut] down...I am not certain how to square this with ... the Ecoflow holds 950 watts [hours]

(Please double check my paraphrasing isn't making bad assumptions)
That is curious... if the 950 Wh is measured as battery capacity and the 650 Wh is AC, that would mean the inverter is only 650/950 = 68% efficient.

From the OP, it consumes 53 watts per hour, so that's about 12 hours of operation. So, not like you were pulling too high of a C-Rate.

Might be lemon, let's see what the hardware folks think. Personally I'd call tech support and ask them to explain it.

 

[Cass]

The Ecoflow has a rated watt storage of around 1260 watts. Various tests done by others said that they were only able to get 900-950 watts which they felt was a low efficiency. But for the unit's recharge speed, some felt it was a decent tradeoff.

I had expected to get around 900 watts power...but my Kill-A-Watt test last week seemed to show that the 16 cubic foot freezer pulled 650 watts before draining the battery. I am doing another test tonight in the cooler hours to see if that repeats. There is a possibility that both my Kill-A-Watt meters are defective (unlikely but that needs to be checked) so I may need to test with both before drawing any conclusions. Right now my setup is

Freezer ---->Kill-A-Watt (reset to zero at the start of the test) ---> Ecoflow AC outlet

My freezer is pulling around 119 Volts and of course the Amps go up and down with the Watts. Right now as I start the test, my Kill-A-Watts says the freezer is pulling in 87.2 watts during its cool cycle and the Ecoflow is registering 89 watts... ca. 2 watts delta, not enough to make a huge difference.

 

[SOFISINTOWN]

The 'got you' rarely taken into account powering refrig or freezers is Defrost cycle. Most refrigs do this about every 18 to 36 hours and the heater in the defroster can draw over 1000 watts. It can sink your battery capacity estimation. Defrost can last 15-30 mins but high current cycles On and Off during this period.

Also the compressor startup current can be upwards of 1500 watts or more even though run current is less the 200 watts.

The defrost cycle is also regulated by thermostat, so if there is no ice built, this cycle will be negligible.

 

[Cass]

My overnight test was even more disappointing. Cool evening, freezer pulled .490 KWH (490 watts). It ran for 11 hours but this is far below what it should be giving up. Am I reading the Kill-A-Watt incorrectly?

10 hrs 48 minutes
.49 kwh
The freezer was running at 119-120V (when it ran, as it cycled on and off as needed)

 

[Cass]

The defrost cycle is also regulated by thermostat, so if there is no ice built, this cycle will be negligible.

The 'got you' rarely taken into account powering refrig or freezers is Defrost cycle. Most refrigs do this about every 18 to 36 hours and the heater in the defroster can draw over 1000 watts. It can sink your battery capacity estimation. Defrost can last 15-30 mins but high current cycles On and Off during this period.

Also the compressor startup current can be upwards of 1500 watts or more even though run current is less the 200 watts.

If I am using a Kill-A-Watt to measure the actual freezer usage over multiple days it should catch the defrost cycle. But estimates aside, my latest test shows that the actual battery capacity of the Ecoflow is less than 1/4 of their advertised rate - and 1/2 of what Will and others were getting. Unless I am doing something wrong in the measurement, which is possible.

 

[svetz]

Did you test your power meter with a known resistance to double check the accuracy (see post #2)?
BTW: My meter loses it's reading and resets to 0 if the power goes out... could someone be unplugging it for a few seconds to use the socket for something else not realizing it resets (e.g., running the vacuum)?

 

[Cass]

We don't have any incandescent bulbs nor an Ohm meter. We have 2 Kill-A-Watt meters and used both in our tests. It is the kind that does not reset when the power goes out or is unplugged. You must click on the reset button. And I am the only person who has access to the units or the room they are in. I am trying to think of an item we have readily available in the house that has a known wattage. Are LEDs comparable?? (they always talk about equivalents....)

 

[gnubie]

Cheap LED lights usually have horrific power factors, not good for checking inverter run times etc.

 

[Cass]

Did you test your power meter with a known resistance to double check the accuracy (see post #2)?
BTW: My meter loses it's reading and resets to 0 if the power goes out... could someone be unplugging it for a few seconds to use the socket for something else not realizing it resets (e.g., running the vacuum)?

OK a neighbor gave us their 100 incandescent watt bulb.

We did 2 tests using the same Kill-A-Watt meter

1. Running the bulb from the house AC. We saw 122 Volts, it recorded an average 91-92 watts. For 30 minutes minutes it used .04 kwh (or 40 watts). I waited an extra minute to see if it would tip over to .05 but it did not

2. Running the bulb from the Ecoflow. We saw 120V volts and an average 88-92 watts. For 30 minutes it used .04 kwh (or 40 watts). I waited an extra minute to see if it would tip over to .05 but it did not. The Ecoflow claimed it was outputting 86 watts when the Kill-A-Watt said 88 watts

I am assuming the difference in watts as it was running may have to do with the varying Voltage rate

House AC measurement 80/100
Ecoflow AC measurement 80/100

Even assuming my Kill-A-Watt is only capturing 80%...I might let the 690 watts slide based on the 950 number Will and others saw ...but the 490 watts is ridiculous and far below the 1260Wh Capacity & 1800W

 

[svetz]

Most likely the 100W bulb was weak, they're cheap and not overly precise, but once they hit temperature they should be fairly consistent.

From the Watt Meter:

I = W / V = 91.5 / 122 = 0.75​

R = V / I = 122 / 0.75 = 162.7 Ω​

From the Ecoflow:

I = V / R = 120 / 162.7 = 0.74​

W = V x I = 120 x 0.74 = 88 ​

​

The numbers are close enough that you can confirm A) you're not doing anything wrong with the test measurements, and B) the test gear is working.

So the EcoFlow Delta 1300 has 1260Wh capacity, that's the DC capacity so you lose some wh based on inverter efficiency.
Your test was pulling < 60 Watts for ~11 hours before it shut down at 690W, so 54% efficiency. Was the EcoFlow hot to the touch or something?

This definitely sounds like a lemon to me. I'd call them and ask them for a replacement or refund.