# Powering a deep freezer



## Rob30

I am looking for a way to power a deep freezer. I am currently using a generator, but it is loud. Does anybody know if I could power it with batteries and an inverter? It needs to run for a minimum of 6hrs, but 9 hrs would be best.


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## Michael Kawalek

Hi Rob
The first thing to do is get a handle on how many watts your freezer will be consuming. There should be a panel on the back that tells you either the watts or the amps consumed while running. Multiply amps X110 volts to get watts.

When you say the freezer would be running for 6-9 hours, do you mean the you'll be using the freezer for that amount of time, or the compressor motor will be running for that amount of time. Normally a freezer will cycle on and off periodicly to maintain it's set temperature.

Once you know how many watts your unit will consume per day you can create a system to power it. Lets work our way back from the freezer. Say its consumption is 750 watts. You should have an inverter that is rated at least twice as much power as you are going to comsume. First, startup loads for anything with a motor will be about double the average consumption. Secondly, inverter ratings tend to be rather generous and state things like "produces 1000 watts for 5 minutes, or 800 watts continous". So, you want something bigger than what you think you need.

Take another step back to your batteries. You want deep cycle batteries like golf cart batteries. They survive repeated charge/discharge cycles. Also assume that they should never be drained less than 50% of their capacity. More than that and their life is rapidly shortened. Let's say you need 100 amp hours of power per day. You'll need at least 200 amp hours worth of battery capacity, and 400 is more reasonable. Assuming a single large battery is worth about 100 amp-hours, you'd need 4 batteries.

Next comes the charge controller. That takes the watts from the panels and charges the batteries at just the right voltage to fully charge the batteries. Without a controller, batteries can be quickly ruined from incorrect charging. 

Finally, we get to the panels themselves. They will never produce their rated capacity except under perfect conditions; that is a perfectly clear day exactly at noon. Assume that a panel will likely produce about 5-6 times its rated watt hours per day. That is, if you have 100 watt panel, expect it to produce a total of about 500 watthours over the course of the day. The amount of power your panels will produce per day needs to excede the amount you'll be consuming per day. Also, your charge controller needs to be sized in accordance with your panel output. A little controller handles a maximum of about 7 amps, which is what a 100W panel will produce at noon. Again, the controller needs to be sized larger than the largest charging current it will recieve.


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## artificer

How are you going to charge the batteries? No mention of solar, so are you just going to run the generator? (which would be the cheapest in the short run)

When you pick an inverter, its best to get a full/pure sine wave one. Some motors and compressors don't like the modified square wave ones (the cheap inverters), so the freezer would last longer with the sine wave inverter.

Why do you need to run this off of a battery? I get the feeling its for a farmers market situation, but that might just be my imagination.

An example of a small chest freezer is what we have out at the property. 5cubic foot, and it takes 850 watts to start, and that drops back to 110 watts to run. That power drops lower as the freezer gets colder. If you're trying to freeze material, it'll be running full time, so use more power. If you put frozen materials into the freezer, and just try to keep them frozen, it'll use less power. The best thing to get its a kill-a-watt, and see what your actual usage is, so you can have a properly designed system.

Michael


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