I should be able to do the calcs but it’s decades since I used any of that theory. All I know is that when I followed the logic above when looking at the wattage of my chiller display and freezer for the market stall, it didn’t work. IIRC the chiller was 120w and the freezer 400w, so a max load of 500w (not that simple as the compressors don’t run continuously but when they do start, they draw a lot so for worst case I assumed a constant draw of 400w). With my 2000wh of power-bank, that nominally gave me 5 hrs run time. First time I used it in anger, I still had 25% of one 1000 wh battery left, the other was full, after 8 hours of use and with additional string lights permanently on.
You've got too many variables going on there to provide anything more refined than your estimate. The biggest of which is the weather -If it's a 30 C roaster of a day when you're running your market stall, those chillers are going to be running continuously. If you're outside in winter, they'll barely run at all. Also if trade is brisk, and you're constantly opening the chiller door to get product, that'll have a huge impact versus, say, if you set up at a vegan music festival. Remember, the absolute worst thing you can do in a power cut is keep opening the freezer door fretting over how quickly your meat is defrosting... All that said, It seems you're fine with your battery capacity.
If you'd still rather get a better idea...Maybe your inverter has a function, hidden in a menu somewhere, to show you the average power draw over the course of the day, which should enable you to work out a endurance with a bit more accuracy. Or even use a plug-in watt meter.
Thread stealing, Ok, so I need a bit of help on working out power requirements.
2 x 5Ahr batteries 18v. My chainsaw. How big a station would be needed to charge the batteries, 5 times?
This is what I have worked out,
90 w/hrs per battery per charge? So 1,000 w/hrs min or 560 m/amps? Would that be about right?
Im not a sparky, but I think you are mixing up battery output (volts and amps) rather than charger input (volts and amps) or what the charger draws from the wall when you plug it in. These aren't the same because of inefficiency/wastage/heat.
18v chargers draw anything from 1amp to 8amps for fast chargers. UK mains is 230 volts AC. Watts = amps x volts. The other thing you need to know is how many hours it takes to charge one battery. It might be easier to just buy more batteries.
Gah I typed the below whilst you and muddy had already updated the thread. Might as well post it now as I reckon there may be some useful additional context...possibly.
As muddy has said, you need to tell us the model of the charger you're using - that is what will determine how many charging cycles your will get off your powerbank. Power tool chargers are not 100% efficient - far from it, and a lot of them will run fans to cool the battery. The other variable here is how hard you run your saw, and by that I mean do you swap batteries as soon as the saw starts complaining the charge is low, or do you carry on making that final cut till the battery protection kicks in and shuts the tool down - from another thread you said you were limbing so I would assume the former, which is A) better for tool battery life but also b) will require less energy to charge, as power draw vs time is not a straight line.
It's also important to remember, for the sake of understanding, Watt Hours is a multiplication of the 2 units, not Watts per Hour as you've typed.
