# Powering a box freezer

Solar Expert Posts: 208
Hi guys I have a 180 watt 9 cuft box freezer and I'm trying to keep powered 12 hours a day. I currently have a Trojan t-1275 12 v battery but wasn't sure wether I need to purchase a 12 v inverter and use one batteries or 2 batteries?

• Banned Posts: 17,615 ✭✭
Re: Powering a box freezer

The freezer runs on 12 VDC or 120 VAC? If the latter, you need an inverter. Most are 120 VAC so let's look at that scenario.
Next part; it uses 180 Watts for how long? Since freezers turn on and off through the day, you need some estimate of the daily Watt hour consumption in order to size the batteries.

For instance if it runs 1/2 the time then that's 180 * 12 = 2160 Watt hours. On 12 Volts that's 180 Amp hours, not including conversion and efficiency losses. If it runs 1/3 of the time that's 180 * 8 = 1440 Watt hours which is 120 Amp hours on 12 Volts. Again, no losses included.

Then you have to include those losses: the inverter is 90% efficient, perhaps, so that adds to the Watt hours: 1440 becomes 1600. The inverter uses, say, 20 Watts and is on constantly: that's another 480 Watt hours. If it has a standby mode you will save some there. But you are now over 2kW hours for the set-up and that means a minimum battery bank size of (2000 / 12 * 2) 334 Amp hours.

If this is attached to solar/wind/hydro/gen for recharging then some of the daily power can come from the charging source. But if you can't always count on it you need to make allowances for that as well.

The inverter is going to need to be large enough to handle the start surge, which is likely over 1000 Watts.
Re: Powering a box freezer

Are you trying to keep things cool (near freezing) or actually frozen?

Your usage can be anywhere from 0.25 kWH per day (cool) to 1.5 or even 2.0+ kWH per day (0F, -18C) (and depending on insulation/efficiency/ambient temperature). A huge difference in energy usage.

Inverter wise, you may need a minimum of 1,200 to 1,500 watt inverter to start the compressor.

Battery size, say you want to support 2 days of "no sun" and 50% maximum discharge for a 1 kWH per day power usage:

1,000 WH * 1/0.85 inverter eff * 1/12 volt battery bank * 2 days * 1/0.50 maximum discharge) = 392 AH battery bank @ 12 volts per 1kWH per day load

The smallest battery bank would probably be a 1 day and 50% load, or ~196 AH @ 12 volt battery.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 208
Re: Powering a box freezer

I have a 2000watt ryobi gas generator that gives me 5 hours on one gallon gas as a backup. I also think I can use my 24 v outback inverter instead then. I tought it would be too big of a inverter, that's why I mentioned getting a 12 v.
Re: Powering a box freezer

Look at the "tare" (unloaded) power consumption of the inverter... It could be in the 20 watt range--if left on 24 hours a day, would be ~480 watt*hours, or as much/more than than the freezer run as a refrigerator.

There should be a "search mode"--If this is a simple freezer without a defrost timer, that can work well and reduce the inverter's standby losses.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Banned Posts: 17,615 ✭✭
Re: Powering a box freezer

Outback inverters are all pretty much the same on self-consumption: 24 Watts. However they do have a standby mode which drops this to 6 Watts. So you have either (24 * 24) 576 Watt hours per day for the inverter, or some variation based on drawing 24 Watts when the freezer is cycling and 6 Watts when it is not. Again it becomes dependent on the freezer's actual running time.

Either the 2524 or 3524 will operate a freezer with no problem. And a lot of other stuff besides.
• Solar Expert Posts: 3,009 ✭✭✭✭
Re: Powering a box freezer

180 watts is a lot for a 9 cu ft freezer. My Energy Star 2 year old model uses roughly half that while it's running. Is it an old freezer, or by slim chance an absorption type? Does it have a compressor?
Re: Powering a box freezer

A Honda eu2000i would use about 1/2 that amount of fuel on a 400 watt or less load.

Figure out the fuel savings vs cost of bringing in a new genset.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 208
Re: Powering a box freezer

I just looked at the tag on the freezer and it actually says-
input power-240w
rated voltage ~110v
rated frequency 60hz
power consumption- 1.05 Kw/24h
charging of refrigerant R134a/175g
• Banned Posts: 17,615 ✭✭
Re: Powering a box freezer
castilloj wrote: »
I just looked at the tag on the freezer and it actually says-
input power-240w
rated voltage ~110v
rated frequency 60hz
power consumption- 1.05 Kw/24h
charging of refrigerant R134a/175g

Ignore that. Plug it in through a Kill-A-Watt and find out what it really uses.
• Solar Expert Posts: 208
Re: Powering a box freezer

Ok so I have it plugged in to killawatt and it shows
180 watts
1154 watts start for 3 seconds.
• Solar Expert Posts: 8,748 ✭✭✭✭✭
Re: Powering a box freezer
castilloj wrote: »
Ok so I have it plugged in to killawatt and it shows
180 watts
1154 watts start for 3 seconds.

Good start. Wow, 6x running current, needed to start! And the killawatt cannot capture the full surge, so we have to assume it's going to be even higher. Means your inverter will likely need to be able to surge to 2,000 watts to start the motor.
2KW @ 12V = 170 amps your battery and cables have to supply for 3 seconds without voltage sag.

So, lets leave the killawatt plugged in for a week, and see how many KW hours the unit consumes over time, and from that,
we can caculate the daily usage.
Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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• Solar Expert Posts: 3,009 ✭✭✭✭
Re: Powering a box freezer

Still shocked at the 180 watts consumption. It sucks!
• Solar Expert Posts: 280 ✭✭
Re: Powering a box freezer

Start capacitors are cool. I installed a Kickstart in my A/C and my swamp coolers came with start capacitors pre-installed. I wonder if they make inline start capacitor units for refrigeration (goes between the plug and receptacle)?
• Banned Posts: 17,615 ✭✭
Re: Powering a box freezer
Start capacitors are cool. I installed a Kickstart in my A/C and my swamp coolers came with start capacitors pre-installed. I wonder if they make inline start capacitor units for refrigeration (goes between the plug and receptacle)?

Nope.
Two things: starting capacitors have to be specific to the motor and they only go on the start windings. There is no way to make "generic, plug-in, one-size-fits-all" starting capacitor unit (although many companies try).
Chances are the motor already has a starting capacitor on it, providing the engineers who designed it have an I.Q. above that of the average chimpanzee. Compressor motors are inherently hard to start due to the nature of their operation (starting against a load).