I don't mean to answer for Peter, and I'm sure he will have good "real world" info because he has used these systems in an egg. But I'm going to suggest a way that you can calculate based on your trailer and your electrical
usage. It's still a good idea to make up your own power usage calcs, because you will never be exactly the same as anyone else, and also it helps you to understand how it all works, and what it means when you turn on a light
, or fire up the laptop.
Basically, each electrical
item that exists has a set amount of power it draws when it's on. So you look at each of your electrical
items (or their manuals), and you can see exactly what it draws. If it says, say, 2 amps, that means two amps for every hour
you are running it.
So you get a list going (because this will be different for everyone). Something like this:
(if on 12v) ---- 14 amps
Laptop (with 12v adapter) - 16 amps
Reading lights----------------1 amps (each)
Fan--------------------------- 2 amps
And so on.
Then you figure how many hours per day you are likely to use each of these. You have to guess, of course. When in doubt, round up. Now multiply to get the total number of amps per day.
Kitchen light, 1 hour = 2 amps
, will run on propane
= 0 amps
Laptop, 2 hours = 32 amps
2 of them x 4 hours =8 amps
Fan, 8 hours = 16 amps
So, your total number is 58 amps for a 24 hour period. Aren't you glad you have a furnace with no fan, and a propane refrigerator
Now let's say you round up to 65 amps. (And now you know why people get LED lights
, because they draw next to nothing. Also something like a Hella marine fan will draw .5 amp.)
You don't want to draw your battery down by more than 50%, because that will kill it much sooner, so you want to keep that in mind when sizing your battery. Of course if you have constant solar power
going back in, that's also a factor (you can figure out about how much they put back in, too). Or, with no solar, but if you plan to go out for two days and not charge witha charger until you get back, then you will be using 130 amps. For that you would want about 260 amps in your battery bank.
You can see there are variables on what battery size you need, depending on your recharging methods, but what you do know
is that you need to "give back" 65 amps per day, somehow, and at some point in time. If you had a 1300 amp bank of batteries (not practical! I'm just saying), you could go 10 days without giving any back. etc.
Sometimes appliances list watts not amps, but you can easily convert.
Amps = Watts divided by Volts (use 12 for 12-volt items).
For figuring in a solar panel it gets a bit more complicated, because although they will have a certain power rating, of course you aren't getting power from them when it is dark or very cloudy (or reduced power input). So it becomes a game of estimation and trial and measurement. But if you are figuring for a system with a 110 volt charger putting power back in (like when you get home), of course you can be more precise.
If you're doing trips on just weekends, it would probably make sense to start with a good battery bank and a charger to plug in when you get home during the week, and then add solar later. But solar is nice to have, absolutely
When I lived on a boat we had a 360 amp house bank of batteries, one solar panel of about 150 watts, and a wind generator
. That was nice but it would be a bit hard to cram that all in to a 13-foot Boler
. We still had to be parsimonious with our power usage.