Ok, as promised. The "suitcase" I used was exactly the same one I described in my For Camping thread. The attached PDF data sheet also specifies the hardware. I hooked everything up yesterday and let it run for 24 hours. Caveats: the freezer has an external thermostat on the power line to regulate the temp between 30* and 34*. It was pre-chilled on line power before starting this series, wanted to get 'running' power usage as opposed to startup. The freezer was empty. It's generally accepted that a fridge/freezer with contents stabilizes the internal temp and runs less frequently. The freezer was never opened. In the real world, frequent open/close increases run time. I tried to take all battery reading with the freezer was not running, so as to get 'resting' battery voltage.
The purpose was to see exactly how much power was required to run a small fridge in order to properly size a system adequate for Tbird's emergency assistance thoughts. I was surprised myself at the actual numbers. Cliff Notes: the freezer as configured draws about 1050W on startup, less than I thought. Running usage was about 70W. After running a few numbers, the overall power usage for 24 hours works out to about 10W per hour, less than .3KWH over 24 hours. After losing charge power in the evening and running all night, the battery was still at 12.5VDC in the morning, which is 90% charged for an AGM. I did notice surge/sag voltage drops to about 10.9VDC, but I'm sure they were short lived and of no real concern. Because the battery was still pretty full, the charge rates from the PV and charger were pretty low, around 15W, once in a while as much as 90W. In the AM, the charge rate jumped to 160W, but the battery charged up quickly and by 11AM cut back to 15W again. The takeaway.... LOTS of spare charge power available. LOTS. Instead of a 3.5cf (100litres) unit, I would, using this setup, opt for something around 7cf (198L) or 2-3 smaller units and could easily charge multiple batteries. All from a single 270W panel.
But we need to step this up a bit. This morning I disconnected the small freezer and connected a full size kitchen fridge with top freezer, a 10 year old Kemnmore 21cf. Again, pre-chilled it on line power before testing. Results encouraging! Power on surge was around 1300W, running usage around 100W. A couple of interesting notes..... when the big fridge kicked on, the solar charger kicked into high gear, with charge rates in excess of 190W from the panel, 14.0A to the battery. The charge rates topped of the battery in no time at all, and cut back to float charge while the fridge was still running! The only down side was the run time. Where the little freezer/fridge had runtime cycles of 4-5 minutes, the big fridge ran for 25-30 minutes per cycle. Still low wattage, but much more of it required.
Takeaway: the system as used is more than adequate for a small freezer or dorm fridge with plenty of excess power for charging device like phones, laptop, cordless drills. If a large fridge is to be powered, I would upgrade the inverter to a minimum of 2000W, 3000 preferable, and add 2-3 more battery capacity to cover night time usage. Replacing the AGM with Lithium would also provide more long distance power. If using a large fridge, you might think that a new energy efficient one would work well, but keep in mind many have auto-defrost features and ice makers. Both take power. A fridge without these features (or turned off) would extend battery life.
And that's what I did on my summer vacation.
