Explore europe in a campervan

Volts, Amps, Watts, 12 volt and 240 volt are all terms that many of us will recognize but not fully understand. However, once you get a campervan the electrical system is something you must get your head around.

The terminology

Volts: 12V DC low-voltage systems are powered by a leisure battery, 230V AC mains systems are powered as suggested through the mains electricity supply. Volts are somewhat like the pressure of an electrical system.

Amps: the amount of electricity needed. So lights will only require a small amount of electricity whereas a fridge will require a much larger amount of electricity.

Watts: the rate at which the electricity is used. It’s a combination of the pressure of flow (Volts) and the amount of current (Amps)

Watts = Volts x Amps
Volts = Watts / Amps
Amps = Watts / Volts

Leisure batteries

The 12V low-voltage system is primarily powered by a 12V leisure battery but is also linked up to your campervans 12V vehicle battery. Thankfully this comes with a switch so you shouldn’t accidentally discharge all the power in your vehicles battery.

Most campervan electrical systems have an integrated battery condition indicator so you can keep track of your available battery power. Ours doesn’t so we have bought a multi-meter that can be used to check the voltage reading of the battery.

Even though the leisure battery is rated at 12V if you take a reading of the battery using a multi-meter and it reads 12V that doesn’t mean it’s full! 12V or under means it’s discharged. When a leisure battery is charged it will read 12.5V or over. Below is a table to illustrate this:

Volts - State of charge

12.7V or over – 100%

12.5V – 75%

12.4V – 50%

12.2V – 25%

12V or under – Discharged

Leisure battery capacity

The capacity of a leisure battery is expressed in Amp-hours (Ah). This indicates how long it can provide output before needing a recharge.

For a rough estimate of how long your battery can supply your appliances before a recharge you must do the following calculation: Work out the Watt hours of your appliances (appliance Watt rating * hours in use) then dividing that by 12 will give you the number of Amp-hours that will be used.

Example: A frugal night’s usage for a 110 Ah battery.

One 8 Watt light running for 5 hours (8 Watt * 5 hours = 40 Watt hours)

Watch a 50 Watt TV for 2 hours (50 Watt * 2 hours = 100 Watt hours)

A total of 140 Watt hours then divided by 12 gives you 11.6 Ah.

So if you had a 110 Ah leisure battery and only run those two appliances as suggested, you could run them for about 9 consecutive nights before the battery would need recharging (11.6 Ah per night / 110Ah battery capacity = just over 9 nights).

There are also other factors that affect your leisure battery’s capacity. When battery manufacturers state that a battery has a capacity of 110 Ah they presume the battery will be operating where the ambient temperature is 25 degrees centigrade. For every 1 degree centigrade drop in temperature the battery capacity falls by 1%. A battery capacity also deteriorates when it gets older.

You must select appliances wisely. Usage for my two laptops differs greatly. The newer Sony vaio laptop uses 22.9 Ah for 3 hours usage and the Acer tablet laptop uses 12.5 Ah for the same 3 hours. I think this must be down to the 3 inch difference in screen size.

Charging your leisure battery

Your battery can be charged from either the engine’s alternator, a petrol generator or when your campervan is hooked up to the 240V mains electricity supply.

The time required to recharge a leisure battery can be calculated as follows. The recharge time in hours equals the battery capacity in Ah, multiplied by the Depth of Discharge in %, multiplied by 0.8, multiplied by 1.5, divided by 100 times the charger current rating in Amps, plus one hour. For example, a 110 Ah battery, discharged to 50%, on a 10 Amp charger, would take about 7.6 Hours.

This entry was posted on Wednesday, December 5th, 2007 at 12:14 am and is filed under Campervan. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.