1. ## Re: Just how bad a small 'frige is

Ah, but the upside is the 48 Volt system is every-so-slightly more efficient than 12 Volt.
And most inverters will run around 90% efficiency these days.

So the 1200 Watts hours is 1333 on the DC side, plus the 480 Watt hours of the inverter being always on (20 Watts per hour) = 1813 Watt hours. Divide by 48 Volts and you get roughly 38 Amp hours per day to run the 'frige.

Some caveats: the refrigerator's actual use will vary from day to day due to changes in ambient temperature and how often the door is opened; the current draw from the batteries is not fixed because of the Peukart Effect (more current as the battery goes down in Voltage - calculating it at system nominal gives an advantage as that should be the minimum Voltage seen); panels recharging during the day should take some of the load entirely, further reducing the battery draw (except on days when there is insufficient sunshine).

That's the reason for the fudge factors; adjust the numbers the right way and you get enough margin for error to make it work all the time.

2. Frequent Poster
Join Date
Jan 2012
Posts
52

## Re: Just how bad a small 'frige is

I just got back from a week at the cabin I am building. The need for refrigeration with low power consumption and low initial cost led me to the so called freezer conversion. I used a separate thermostat and a 5.0 cu ft. freezer rated at 193 KWH annually. Keeping track with a kilo-watt meter my numbers came out like this. Elapsed time was 181 hours. KWH usage was 1.39. If I did my math correctly, that comes out to about 185 WattHours [-Bill] per 24 hour day. I kept the temp at 40 degrees which seemed cold enough for me. Ambient temps were about 60 at night and 75 to 80 during the day.
Last edited by BB.; August 6th, 2012 at 9:14 PDT. Reason: add "hours". -Bill

3. ## Re: Just how bad a small 'frige is

Another one for the books:

Old Admiral 15 cu. ft. chest freezer (came with the house).
Start-up 4.99 Amps, 562 Watts max.
3.7 Amps running, 280 Watts (on 120 VAC lousy PF!)
Averages 5.8 kW hours per day (pretty hot weather here just now: highs over 30C).

4. ## Re: Just how bad a small 'frige is

Originally Posted by Cariboocoot
Averages 5.8 kW hours per day (pretty hot weather here just now: highs over 30C).
That's HORRIBLE!

We have a little 6 or 7 CF chest freezer that is rated at somewhere between 1.2 and 1.5 KWhr/day. I haven't tested it with the kill-a-watt yet, but I bet it's close. Is your freezer in a location that the sun shines on it, or could something else be wrong?

5. ## Re: Just how bad a small 'frige is

Originally Posted by Cariboocoot
Another one for the books:

Old Admiral 15 cu. ft. chest freezer (came with the house).
Start-up 4.99 Amps, 562 Watts max.
3.7 Amps running, 280 Watts (on 120 VAC lousy PF!)
Averages 5.8 kW hours per day (pretty hot weather here just now: highs over 30C).
My Mom once had a SEARS 15 cu ft freezer that sucked back at least 5 Kwh/day. Horrible!

6. ## Re: Just how bad a small 'frige is

Nope: it's just been very, very hot.
The freezer is located in a ventilated "cold room" under the carport. The interior temp has been near outdoor high, so I've added a thermostatically controlled vent fan to draft air through. The running of the fan should decrease the interior temp and allow the freezer to run less. Naturally the weather has gotten cooler now. But I will test it some more. The power factor is still dreadful on the thing.

7. ## Re: Just how bad a small 'frige is

Update:

Retested in cooler weather with the fan evacuating air from the room.
3.1 kW hours per day, which is still terrible. The running Watts being twice a typical refrigerator is one issue.

Still a caveat for anyone thinking of doing a chest freezer to 'frige conversion: make sure the freezer is economical to begin with!

8. ## Re: Just how bad a small 'frige is

Frigidaire 20.3 cu. ft. upright frost free freezer.
Energy Star rated @ 763 kW hours per year
5.0 Amps @ 115 VAC

Running on 122 VAC
Idle draw: 0.1 Amps, 10 Watts
Max Amps: 4.99, Max Watts: 565
Running average (not in defrost): 1.89 Amps, 147 Watts
Consumption: 1.92 kW hours per day (700 per year, so not too far off the rating)

9. Solar Panda
Join Date
Jun 2012
Location
Ottawa, ON
Posts
221

## Re: Just how bad a small 'frige is

I'm wondering if anyone has any experience with the Steca 5.9 DC Freezer/Fridge? http://www.uniqueoffgrid.com/App_Use...9_EN_17458.pdf

They claim:

POWER CONSUMPTION When operating as a Fridge: 57-110 Watt Hours/Day
(25C/77F AMBIENT): When operating as a Freezer: 300-570 Watt Hours/Day
Subject To A 10 Month Consumer Evaluation In A Moderate
Climate, Usage Averaged 120 Watt Hours/Day As A Freezer

10. Fizzycist
Join Date
Jun 2012
Location
Northern CA, 2400 ft. elevation
Posts
1,718

## Re: Just how bad a small 'frige is

Originally Posted by Cariboocoot
The latest numbers:

Unexpectedly, the start-up surge remains at 4.99 Amps despite the refrigerant being cooled down. This is contrary to my experience with larger refrigerators. Perhaps the lesser volume of refrigerant equates to the motor/compressor being the main contributing factor; the change in refrigerant temp (being of such small volume compared to full-size units) not being a significant percentage of the work done.
As the motor starts up, the pressure differential across the compressor is zero (hot side pressure == cold side pressure) and will stay low until a significant volume has been pumped. By the time that point is reached the motor will be out of its startup surge RPM range, so the effect will not show up there.
I suspect that you are thinking of the problems in starting a compressor under load, as when it has been running and is shut off and then restarted before the pressure has had a chance to equalize slowly though the expansion valve. In that case you would get the same initial surge current with the motor RPM at zero, but because of the pressure differential the motor may not produce enough torque to get up to operating speed at all. It is the duration of the surge current that trips out the motor overload or the CB in that situation.

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