Off road camper trailers are very light, or they should be! Because of this the amount of battery capacity is limited by space and weight. Typically with a fridge on board, most off-road camper trailers have 200 Ahrs capacity. What most people want to know is how long can I stay in a remote place without using a generator?
Nearly every off road camper trailer has solar to charge or freshen the batteries. At Kimberley, we have a small 25W panel on the front that will always charge providing there is sun on the panel. This keeps charging the batteries even when you are driving or pulled over for a beverage break and there is plenty of sun shine.
The next step up is a 100W folding glass panel “suitcase” that stores out of sight inside the front gullwing lid (see photo).
Even bigger still is the 220W Superthin solar attached to a rear awning that pulls out from the camper trailer when it unfolds (photo above).
Running a fridge uses between 25 and 60 Amp hours depending on the type and the brand. There is also increasing use of charging phones and laptops. An Ipad charger uses 2A on average at 13V so if left on charge for 3 hours there is 6 Amp hours. A Macair laptop uses a much greater 8A so for 4 hours there is 32 Amp hours. Phone chargers are far less at around 3 Amp hours.
So what is the best way to prepare for this?
This is our system: Calculate what you will use, decide on the battery capacity, purchase sufficient solar capacity. Then tune how you use this combination based on the actual solar power that you get!
- Here is a quick calculation of the items running on charge and the power they will consume in a 24 hour period “typically”. Fridge 40Amp hrs (well used) , LED lighting 15 Amp hrs, iPad Charger 6 Amp hrs, 2 x Phone chargers, 6 Amp hrs, Water pumps 5 Amp hours. This gives a total of 72 Amp hours every 24 hours.
- We recommend you start with a reasonable battery capacity of 200Amp Hours. The “usable” battery capacity for AGM batteries is half the nominal capacity for a reasonable battery life. So you will then have 100Amp hours and if using 72 Amp hours, you have a day and a half without charging.
- Select the folding suitcase capacity of say 125W, then you have roughly 8 amps going in for a typical “peak period” of 5 hours which is 40 Amp hours. (assuming the panels have good orientation to the sun). This will extend the battery capacity by about a day or two but not much more.
Lets step up to the 220W with good sun orientation: This will increase the charge capacity to 15 amps and so for 5 “peak hours” you should have 75 Amp hours going in. This would give you close to an indefinite period, providing the sun is good and you capture it well.
There is a catch though: The 220W awning can be slightly twisted during the day for maximum orientation but you will still loose some capacity because it cant be perfectly orientated to the sun. So you would be working hard to get the full capacity from it.
You can step up and have the 220W and the 125W suitcase. This should exceed your needs!
- Now the last part is the tuning. In the example above, you purchase 220W of solar but for the first few days, but it is overcast and you are not getting much solar power.
How long can you stay?
You need a meter to calculate this and not a Volt meter unless you are an electrical genius. The meter measures current flow in and out of the battery and then calculates the “state of charge” of the battery. After a day you can see how much capacity you have used and how much longer you can stay before charging with a generator.
There is a step up from this which is included in the Kimberley Platinum off-road camper trailer. The smart touch system measures the current (and therefore the power) coming in from the solar as well as the overall battery capacity.
It will give it to you in amp hours just like the calculation above. This allows you to see if you have less solar coming in as planned or if you are using more battery capacity than planned. Now you can really tune up how you use the power. If you are driving off in 2 days and the vehicle will fully charge the batteries on the upcoming trip, you can plan to juggle usage until then based on up to date solar readings. It makes it far easier to plan your days.
There is the alternative of a Fuel Cell. It is silent and can run in areas where generators are banned. Its output is pure water as well as power. These can produce up to 210 Amp hours per day, if you use this much but typically the smaller model with 140Amp hour capacity is well suited.
These Fuel Cells use a methanol liquid cartidge that last for 200hours at full capacity per cartidge for the 140 Amp hour model. If you only get 30-40 Amp hours from solar, then the remaining 30-40 Amp hours per day can be gained from the fuel cell. This would be 5-6 hours of run time from the 200 hour capacity per cartridge.
It is not an exact science while you are relying on solar power. Every day will be different. However, the technology available will make it easier for you to use and decide when to move on and how long to stay!