How much power do I need in my Camper Van ?

The leisure electric system that you design and fit into your camper van is in my opinion, the most important part of the campervan conversion process. Without power a camper van is fairly useless, no lights, fridge or water pump !

I believe the vehicles battery and the leisure system should be separate so that no mater how you use your leisure electrics, your vehicle will always be able to start. The other reason for keeping them separate is that you will use a different type of battery, as its usage is totally different.

I wanted my van off grid with the ability to be mains hooked up. Lets look at off grid and work out how much power I will use. This can then be used to determine the battery bank capacity and thus its physical size.

I planned to have the following electrical appliances in my van :

• 12v Compressor fridge - (40 watts)
• Water pump - (10 watts)
• Lights (LED) - (15 watts)
• Battery monitor - (0.4 watts)
• Gas alarm - (0.4 watts)
• Laptop (12v charger) - (80 watts)

I obviously would not be using all of these all day, so we need to calculate what the average daily consumption of power will be. In power systems we calculate the total amount of energy consumed over a certain period in Amp hours (Ahr). E.g. .one amp consumed for 5 hours has used a total of 5 Ahr of power.

To be able to calculate our Ahr's we need to be able to convert between the common measures of power i.e. Amps, Watts and Volts.

• Volts: Electrical force of pressure behind the electrons in a circuit. Analogous to water pressure or PSI, it tells us the system voltage (12, 24).
• Amps: The number of electrons flowing past in a second. Like litres per second in a pipe, it defines the electrical current in a wire.
• Watts: Total amount of electrical energy, per second.

The conversion formulas are:

• Watts = Volts times Amps
• Volts = Watts divided by Amps
• Amps = Watts divided by Volts

Therefore 40 Watts (Fridge) divided by 12 Volts equals 3.33 Amps. Take this 3.33 Amps and multiply it by the number of hours it will be consuming power (estimated to be 16hrs for each 24 hour period) equals 54 Ahrs (Max of 80 Ahr, if running continuous for 24 hrs.).

I therefore calculated my average 24 hour period power usage as follows :-

• 12v Compressor fridge (40 watts / 12v = 3.33 Amps) * 16 hours = 54AHr
• Water pump (10 watts / 12v = 0.84 Amps) * 1 hours = 1Ahr
• Lights (LED) (15 watts / 12v = 1.25 Amps) * 3 hours = 3.75Ahr
• Battery monitor (0.4 watts /12v = 0.03 Amps) * 24 hours = 0.75AHr
• Gas alarm (0.4 watts /12v = 0.03 Amps) * 24 hours = 0.75AHr
• Laptop (12v charger) (80 watts / 12v = 6.66 Amps) for 2 hours = 13.5AHr

This totals 74 Amp Hours of power, the standard rule of thumb, is to then add on 25% to allow for battery deterioration, poor charging etc. My total was 92.5 Ahr.

Leisure batteries should only ever be 50% discharged to avoid damage. So I would need a battery pack of 92.5Ahr * 2 = 185Ahrs.

Given these calculations I installed two 110Ahr batteries linked in Parallel, ie a 220Ahr battery !

Posted July 2018