In order to determine the total amount of Amp Hours that you will use, you will need to go through this exercise for each and every electrical device that you plan to use and add up the Amp Hours for a grand total. Additionally, you cannot forget about the phantom loads in your RV. Phantom loads are all the items in your RV that are constantly drawing 12V power such as the CO2 detector, refrigerator brains, radio memory, etc. In some instances it may be difficult to find the amperage ratings for these devices; however, if you search through the owner’s manuals, you should be able to find them. If not, then you may just want to tack on an additional 10% – 20% at the end to account for all the phantom loads.
Following is an example of a worksheet. This is not a real worksheet and it is not all inclusive. Some of the numbers are made up for this example, so please don’t use them for your calculations. This worksheet is for demonstration purposes only. I have included a blank worksheet on this website for you to do your own calculations:
AC Appliances  

Item

Watts

Volts

AC Amps

0

DC Amps

Hrs per Day

Amp Hours

Sony HD Receiver 
35

110

.32

x 10

3.2

1

3.2

MotoSat Receiver 
156

110

1.3

x 10

13

1

13

Huges Modems 
64

110

.58

x 10

5.8

1

5.8

Laptop Amanda 
165

110

1.5

x 10

15

2

30

Laptop Steve 
165

110

1.5

x 10

15

2

30

Wireless Router 
55

110

.5

x 10

5

1

5

FP TV (Bed) 
165

110

1.5

x 10

15

1

15

Phone Charger 
14.3

110

.13

x 10

1.3

2

2.6

Phone Charger 
22

110

.20

x 10

2

2

4

Total

108.6

DC Appliances  

Item

Amps

Hrs per Day

Amp Hours

Lights 
.9

3

2.7

Water Pump 
8

.5

4

Radio 
2.5

2

5

CO2 Detector 
.2

24

4.8

Bath Fan 
1.5

.5

.8

Refrigerator 
.8

24

19.2

Total

36.5

Looking at the worksheets above you can see that I broke the calculations up between AC and DC items. The reason for this is because of the extra step you need to take in order to convert AC Amps into DC Amps. Now that I have an estimate of the total Amp Hours that I plan to use, I can add them together for a grand total. However, before I do that, I am going to take a couple more things into account. First I need to account for the efficiency loss of my inverter. Most inverters are 80% – 90% efficient (most good ones are 90%). So this means that if your appliance requires 1 Amp and your inverter is 90% efficient, then the inverter actually needs to draw an extra 10% from the batteries to account for the efficiency loss. So in actuality the inverter is drawing 1.1 Amp for every 1 amp that it is supplying. If it were only 80% efficient, it would have to draw 1.2 Amps from the batteries for each Amp that it supplies. Since only the AC equipment is going through the inverter, we only need to add 10% to the AC calculation (assuming we are talking about an inverter that is 90% efficient). The efficiency rating of an inverter is usually stated in the inverter’s documentation. Therefore, to account for the 10% efficiency loss you have to add 10% to your AC Amp Hours total.
108.6 Amp Hours x 1.1 = 119.46
Now that we have both numbers, we can add them together and get a grand total. Therefore, based on the calculations above, the grand total comes out to 155.85 Amp Hours per day (119.46 (from AC) + 36.5 (from DC) = 155.96). However, before we can say that we are done, there is probably one more thing that we should account for and that is the energy that we lose to resistance in the wiring and batteries, which can range anywhere from 510%. Since all of our appliances are using wires, it applies to all of our calculations, so I am going to use the grand total that we just arrived at of 155.96 and add 5% to it. Therefore, our final grand total comes out to 163.64 Amp Hours (155.96 x 1.05 = 163.76). Rounding up, we end up with a grand total of 164 Amp Hours. If you plan to install solar panels to recharge your batteries, you now know that you will need to replace 164 Amp Hours each day and can therefore size your solar panels accordingly. Now that wasn’t too bad was it?
Looking at the number that we just came up with, you may say “wow that is a lot of energy”. You are right, it is. It will take a sizable battery bank to power these requirements. However, the reality of the situation is that I probably over estimated on several of the items above. As I found out while I was traveling, I rarely had the desire to use my laptop every day. Similarly, even if I did, the battery in the laptop would usually last 3 hours and I did not always have it plugged in and would often end up at an RV park by the time it needed to be recharged again, at which point we were plugged in and I was not using battery power anyway.
Estimated Power Consumption Worksheet
Formulas to remember:
Amps = watts/volts
Volts = watts/amps
Watts = volts x amps
Step 1 – Determine Amp Hours used by AC Appliances
AC Appliances
Item  Watts  Volts  AC Amps  DC Amps  Hrs Per Day  Amp Hours  
Example Item  33  110  .3  x 10 =  3.0  X  1 hr  3.0 
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
110  x 10 =  X  
Total = 
Step 2 – Account for Inverter Efficiency
Once you have the total number of Amp Hours from your AC appliances you need to account for the inverter’s efficiency loss. If it is 90% efficient, then multiply your final number by 1.1. If it is 80% efficient, then multiply it by 1.2. It if it less than 80% efficient – buy a new one.
Step 3  Determine Amp Hours Used by DC Appliances
DC Appliances
Item  Amps  Hrs per Day  Amp Hours  
Item Example  2.5  X  2 hrs  5 
X  
X  
X  
X  
X  
X  
X  
X  
X  
X  
X  
X  
X  
X  
X  
X  
Total = 
Step 4 – Add the Totals Together From Step 2 and Step 3
Step 5 – Account for Resistance in the Wiring
Take the total from Step 4 and multiply it by 1.05 to account for a 5% energy loss from the wiring due to resistance. You should now have your final total estimate of the Amp Hours that you will use per day.
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