I never thought that an electrical system could be difficult to master, but here I testify that there are a lot of ‘gotchas’ that you can encounter when you are RVing and are not plugged into shore power.
First, know that you can get power from a number of places. The most frequent are shore power, aka, you plug into a wall socket somewhere. Now, this can translate into a 120v connection or a 240v connection plus you could connect to a 15amp circuit or a 30 amp circuit. Knowing your shore power limitations is vital.
But when you are not plugged into shore power can be equally tricky. For example, how will you have power when there’s no plug? For example you could be boon docking, or simply in the woods. First thing that comes to mind is a generator or batteries.
I’m lucky in that I have both options. Plus I’ve got a power converter that will change the 12 volts DC to 120 volts AC. But again, I have restrictions. On the generator, I get up to 4,000 watts of power at 120 Volts AC. So I can run everything including the air conditioning. But on the batteries and power converter, I only have access to about 1,200 watts of power. Enough for simple appliance but not for things like coffee pots, microwave and certainly not the air conditioning.
So it’s important to know what you can and cannot run and on what. The next thing to think about is your battery storage. I personally run two 6 volt batteries tied together in series, producing 12 volts across both of them. Now, the batteries in optimum condition can supply 220 amps of power before they are depleted. So, if I am running a laptop that needs about 100watts of power, lets see how long it will run before we are trouble.
The wattage of an item can be broken down by the voltage times the amperage.
So for the laptop, if it is taking 12 volts power and it is 100 watts when it is running, that means that it is using a continuous current of 8.33 amps. (amperage = wattage divided by voltage)
So, if I have a total of 220 amps of battery power, I can run my laptop for around 26.4 hours before the batteries are flat.
There are things that you have to think about that can catch you that you won’t think about though. My fridge in the bus is a multi-system fridge. In other words, it will take 12 volts and propane or 120 volts AC. In the automatic mode, it will select the 120 Volts over the propane to conserve propane.
I was noticing that my batteries were depleting pretty quickly when I was running on batteries and had the power converter turned on. I was actually a little ticked because I estimated the the batteries would be flat in about 4 to 6 hours. Hmmm, what the heck is going on here. Did I have bad batteries?
After thinking on it over the course of a day, it hit me. It was the fridge! I never before thought of this being a problem. so, I did a bit of Googling and discovered low and behold that the fridge will draw about 450 watts when it is running on 120 Volts! If you do the math that works out to about 5.8 hours before the batteries are toast!
It’s obvious when I mention this, but when you are in the situation, it can drive you batty. With the laptop running, a light running and the fridge running, the batteries were being depleted very quickly. And you never want to run your batteries to nothing either! This is a way to shorten the life of your batteries very quickly.
So when you hit the open road, really think about your electrical system. It can save you a ton of grief!