What do you need?
How much power?
There are three sides to this question:
- How much power do you currently have?
- Is it enough to do what you currently do?
- Is it enough to do what you'd like to do?
These may be all the questions you need to ask yourself.
If you've got a wish list of things you'd like to run in your RV, it will help to know how much power each thing you want to run needs to start and how much power each needs to continue running. Then you need to work out how long you want to run each item each day.
If you currently run AGM batteries, you will know that you can only discharge them to 50% of their capacity before they suffer a serious voltage loss.
Lithium batteries don't suffer voltage loss, therefore, if you install half the amp hour capacity of lithium and get the same amount of power as your AGM. If you currently have enough power for your needs, this question is now answered. Half the capacity of lithium will cover your current needs.
Be aware, however, that once you get used to lithium, you may decide to run more appliances than you used to. If you've been running 240V household appliances only from mains power or a generator, some more lithium capacity and an inverter may allow you to leave the generator at home and run those appliances whilst free camping.
Can I run my air con?
I'm going to use a recent estimate for a customer as an example. This gentleman was looking at 300Ah lithium and had 480 watts of solar. He wanted to run a rooftop air con, so we looked up the specs for that make and model. Below are the pertinent figures (Max Rated Current-Heating was 7.4A, which is a lot, so we'll assume he'll use his diesel heater in the cold...).
How much power the air con requires
|Electrical Rating (single phase)||240V, 50Hz|
|Max Rated Current-Cooling @ 240V||5.6A|
|Max Rated Watts||5.6 X 240 =||1344W|
|+ 10% for the inverter draw||1344 x 1.1 =||1478.4W|
|Max Rated Current-Cooling @ 12V||1478.4 / 12 =||123.2A|
Now bear in mind that 5.6A is the maximum rated current, ie the air con is running at 100% load. Let's make the assumption that in a caravan, it wouldn't take long for the air temp to come down to the point where it only had to run half the time to maintain that temperature. NOTE: This is only an assumption and I may be wrong... it's happened before...
|50% Rated Current-Cooling @ 12V: ||123.2 / 2 =||61.6|
So, at 12V, once the desired air temperature has been reached, this air con requires roughly 62 amps per hour to run. Let's take a look at how much solar is needed to keep up with that power draw.
We see an average of 400 watts of solar among our customers.
So, 400 / 12 = 33 amps. You could run this air conditioner for roughly half an hour directly from the solar coming in. If you had a 400Ah lithium battery, assuming you didn't want to take the battery much below 50%, you could run this air conditioner for roughly 3.5 hours.
|400W solar / 12V =||33A of solar coming in|
|400AH lithium battery / 2 =||200AH we're prepared to use|
|200AH we're prepared to use + 33A coming in from the solar= ||233A to use on cool air|
|233A / 62A =||3.75 hours of blessed relief from the heat|
NOTE: If you had double the solar than the above example, ie 800W, you could run your air con without any drain on your battery!
What you're doing now, or have done in the past, need not determine what you do next or can do in the future.
- Ken Robinson