Chest Freezer / Inver Configuration

Re: Chest Freezer / Inver Configuration

Looks like the thermostat triggers both the freezer compressor and inverter when needed, thus keeping the inverter off and not drawing power when it isn't needed. Should work, although some inverters' on/off controls do not remove all their power draw. It may be simpler to use one that has a standby mode and let it pulse, especially as not all inverters will like being turned on with a load present on the AC (the ones designed for standby do not suffer from this; they are designed to do it).

As for the power draw it's pretty much a matter of AC power factored by inverter efficiency plus inverter draw. So if the freezer uses 120 Watts @ 120 Volts (10 Amps) and the inverter is 90% efficient that's 134 Watts @ inverter Voltage (11.6 Amps @ 12 Volts) plus inverter draw (20 Watts perhaps - another 1.6 Amps) = 13.2 Amps.

But (and it's a big one) there will be extra power consumed on start-up, additional power loss in the wiring, and the ever-present Peukart Effect on the battery which makes the current draw non-linear as the battery Voltage changes (and alters the actual capacity as power is drawn). You can come close to predicting it by rounding the consumption numbers up, as in 12 + 2 = 14 Amps at nominal 12 Volts. 33% duty cycle over 24 hours would be 112 Amp hours per day, necessitating a minimum 224 Amp hour battery bank. Or, curiously enough, a couple of standard golf cart batteries in series.

Not that I've ever done that calculation before or anything. :roll:

Re: Chest Freezer / Inver Configuration

Hmanfl wrote: »

Thank you for your help !

I am looking on Craigslist for used freezers, small chest types and most of them are rated 1.3 to 2.0 amps.
I know the start up amps will be higher, but using the Johnson control to operate the freezer as fridge will
reduce the run time cycle.

So if the freezer / fridge is rated at 2 amps @ 120v = 240 watts , how many dc amps will it be pulling per hour for one hour of run time ??
Omit the inverter overhead and Peukart Effect for now.

I am trying to see if my current batteries can support this load and how long a run time they can handle.

Thank You

Omitting the fine details? It's simply a matter of dividing the Watts by the Volts to get the Amps. So 240 Watts / 120 Volts is 2 Amps, and the same 240 Watts / 12 Volts is 20 Amps. 20 Amps used for an hour is 20 Amp hours.

But when you do put in the inverter conversion efficiency it gets worse: 240 Watts on the AC side is suddenly 266 for the batteries to supply.

By the way, that isn't a very good power rating for that freezer. My 16 cu. ft. Frigidaire does better than that without any conversion. In fact it uses about 1/2 the power. I would not trust the numbers on the freezer's tag, but rather plug it in to a Kill-A-Watt and see what it really uses. I know; impossible to do until after you've bought it and then it's too late.

I hope you take some time to read through the thread on "How bad a small refrigerator is" in this section; there's a lot of real-world testing data in there you might find helpful.