Used to power basics like lights, computers, TVs, and a DC fridge. Perfect for use in a van. The battery can also be charged from solar or the alternator with a B2B charger.
Components used
- 12V 230Ah lithium battery
- 12V 1200VA inverter
- 2x 195W solar panels
- 12-12V 30A B2B charger
- 40A charge controller or Victron alternative
- MRBF fuse with a 50A fuse for B2B and 125A fuse for inverter
- 20A DC circuit breaker for solar panels
- 12AWG 20ft solar cables
- 6AWG 20ft cable for DC to DC charger to battery
- 8AWG 10ft cable for charge controller to battery
- 4AWG 10ft cable for battery to inverter
optional:
Description
The maximum current the system will draw is: 1200VA/12V=100A
The total capacity of the battery is: 230Ah*12.8V=2,944Wh
The total solar power is: 200W+200W=400W on the roof of the van.
Now we can calculate how long it takes to recharge the battery with solar only.
The amount of sunhours (1000W/m²) we need to recharge the battery: 2,944Wh/400W=7.36 sunhours (thats about 2 days)
However, off grid design says that you should recharge your battery in one day. A winter day in Houston has only 3 sunhours. So, to supplement the battery charging, we can use the alternator.
The solar panels provide 400W*3hours=1,200Wh per day (on average)
So we need to recharge 2,944Wh-1,200Wh=1,744Wh per day from the alternator.
A Victron 12/12 30A B2B (Battery to battery) delivers: 12.8V*30A=384W
1,744Wh/384W=4.5 hours of driving/running the engine is required.
You can see it’s quite a lot. But you don’t have to use all the energy stored in the battery in one day.
In my opinion, charging through the alternator should not be relied upon but is a great backup energy source on the road during cloudy days.
Let’s say you have the following appliances:
- Laptop
- TV
- DC fridge (check my review video here)
- Lights
- Fan
And these are the power ratings and time you want to run them:
- Laptop: 30W – 4 hours
- TV: 30W – 2 hours
- DC fridge: 25W – 8 hours (30% duty cycle is normal)
- Lights: 15W – 4 hours
- Fan: 15W – 4 hours
If we now multiply the time and power we get watt-hours.
- Laptop: 120Wh
- TV: 60Wh
- DC fridge: 200Wh
- Lights: 60Wh
- Fan: 60Wh
If we add these all up we get a consumption of 500Wh per day.
And our battery is 2,944Wh, so we will have about 6 days of runtime on a single battery charge.
Remember that the solar panels produce 1,200Wh per day on average? That would be enough to recharge the battery every day with room to spare for cloudy days.
Questions? Send me an email here.