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Old 09-18-2018, 01:30 PM   #1
Mini-Skoolie
 
Join Date: Aug 2018
Posts: 20
Calculating Amp Hours for Boondocking/Off Grid

Using this chart
https://www.wholesalesolar.com/solar...gy/power-table to figure out the average Watt/hour needed for appliances I think I've successfully charted out how many Amp hours I need per day.

You can check it out here:
https://docs.google.com/spreadsheets...it?usp=sharing

I multiplied the total Amp hours by 2 (since you don't want to drain the batteries below the 50% mark) and tried to see how many days in a row I'd like to boondock. And yikes, deep cycle batteries are expensive!
I figure if I want to boondock 2 days in a row, I need around 730 AH

2 days= 730 AH
3 days=1092 AH
4 days= 1456 AH

After snooping on these threads, I plan to get a generator, alternator to battery charger, charge controller, 4x250W solar panels, and whatever amount of batteries I need for those Amp Hours.

Am I doing this all wrong? Does anyone who has successfully (or unsuccessfully) used off-grid have recommendations?
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Old 09-18-2018, 05:04 PM   #2
Skoolie
 
Join Date: Jun 2018
Location: Pacific NW
Posts: 120
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Looking over your numbers, I think you're estimating very high on some of your electrical usage, and making some fundamental errors in calculations. For instance a 60 watt equivalent LED light bulb only draws 10 to 13 Watts. I highly doubt the microwave gets used for an hour of run time per day. No way do laptops actually draw 200 Watts. Also, some of your amp calculations are based on 120, and some (chest freezer) on 230.

Your methodology gets a little confusing for me at that point, it's important to consider that an amp of 120v electrical carries with it a lot more power than 12 or 24v. Your amp-hour numbers are just added up regardless of voltage, which is incorrect.

I would standardize your calculations on power usage while running, If these are appliance you already have, consider plugging them into a Kill-a-Watt meter for a couple days each and seeing actual power usage, and multiply that by expected hours of usage to give yourself watt hours or kilowatt hours (kWH) per day. Then you can see how many amp hours of battery it will take to supply those kWH without dropping below 50%
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Old 09-18-2018, 11:35 PM   #3
Almost There
 
Join Date: Feb 2018
Location: Fort Collins, CO
Posts: 71
Fox,



I agree that your Amps are getting mixed up. An Amp at 12V does not equal an Amp at 24V does not equal an Amp at 120V.


That spreadsheet is a great start, but you should

1. calculate the W-h of all the appliances (multiply watts by hours per day the appliance will run)
2. sum all of the W-h, then

3. divide by the battery bank voltage (probably 12V or 24V).
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