Nowadays we use a variety of electronic devices. On an excursion with the motorhome, the caravan or the camper, we do not want to miss them.
This can include the mobile phone, an electronic hob, a refrigerator and many other devices. However, since these devices now consume electricity and have to be charged, a utility battery in your vehicle is necessary. But what capacity does the battery actually have to have?
Here we have put together a small guide to the capacity calculation of utility batteries, which can help you choose the right capacity.
Capacity calculation for utility batteries
In our invoice, we assume that there is no solar power inverter in your vehicle and that all electronic devices are operated with a voltage of 12v inverter. An explanation for this procedure can be found below.
- Collect performance of your electronic devices
First, write down the power in watts of all your electronic devices that you are likely to want to run on the utility battery. The wattage numbers are easily marked with a “W” on each device.
Example: A radio requires a power of 12 watts.
- Determine overall performance
Since we assume a voltage of 12 volts in our calculation, we can determine the total power of the devices at this point. For this purpose, all performance values are added together. In this case, there is no need to perform individual invoices for each device.
Example: Radio 12 watts + TV 30 watts + refrigerator 60 watts = 102 watts
- Calculation of amperes
In a next intermediate step, we now have to calculate the current A of our devices to be operated. To do this, we divide the total power W with the voltage V.
Example: Total power 102 watts / voltage 12 volts = 8.5 A
- Estimation of the useful life per day
Determining the useful life of all electronic devices per day is essential for calculating the required capacity. Estimate how much time you spend on your devices during the day.
Example: We assume that all devices must be operated autonomously via the battery for more than 8 hours.
- Calculation of ampere-hours
The ampere-hours can now be calculated using the following formula:
Ampere-hours (Ah) = Ampere (A) * Useful life
Thus, our results from steps 3 and 4 give the following example:
Example: Ampere 8.5 A * Useful life 8 hours = 68 Ah
- Factor in the safety factor
At the end of the calculation of the actually required capacity, a safety factor should always be taken into account. Because a utility battery should never be deeply discharged. The battery can suffer considerable damage and life expectancy is also shortened.
Since the different battery technologies are differently resilient, the safety factors also differ. We recommend that you use the following values for the calculation:
Lead-acid battery: 1.6
AGM & Gel batteries: 1.4
Lithium batteries: 1.2
In our example, we calculate our capacity for an AGM battery. The invoice looks like this:
Example: Ampere-hours 68 Ah * Safety factor 1.4 = 95.2 Ah
This means that you should choose an AGM battery with a minimum capacity of 95.2 Ah to cover your daily requirement on the road in a motorhome, caravan or boat.
You want to live self-sufficient for several days. You are probably wondering why we have calculated the required capacity in our example based on just one day and why the refrigerator should only be operated for more than 8 hours?
Quite simply: Unfortunately, it is not easily possible to live independently for several days at a time with only one utility battery. Because such a battery, as already mentioned above, should never be deeply discharged. Conversely, this means that your supplier must be charged!
There are several ways to do this: On the one hand, you can stop at suitable campsites with a power connection for shore power during your trip. So you can charge your vehicle comfortably during the night. On the other hand, you could charge the battery on the go via a solar panel on your mobile. This would be particularly suitable for self-sufficient travelers. Another interesting solution is charging via the alternator or generator. In this case, you could even switch on a booster in between, which charges the battery even faster.
12 volts? I need more!
In our calculation we assume a voltage of 12 volts. However, there are also devices that require a voltage of 230 volts. If you want to use such devices, you either have to wait for a power connection that provides you with exactly this voltage or you install an inverter in your vehicle.
In this case, however, it should be noted that you have to calculate the capacity of all devices individually and add them up at the end. This can significantly increase the required capacity.
Do I need an inverter?
An inverter is a matter of taste. If someone wants to travel very self-sufficiently, has a solar power generator system and, for example, can not do without his hair dryer, which is operated with 230 volts, then an inverter can be quite useful. Someone who stops at campsites anyway and gets shore power via an extra access to the vehicle can also use his 230-volt hairdryer.
It is therefore not absolutely necessary to install an inverter. Also because most devices for the camping area are now designed for 12 volts. You can buy a 12 volt deep cycle battery for your daily needs. In addition, it should be noted that in addition to the normal power consumption, the inverter also requires electricity for voltage conversion. So there is another safety factor to be included in the capacity and a higher power loss is present.
With our battery consultant to the right supply battery
The calculation of the capacity of the utility battery is essential in order to be able to charge all batteries when traveling. If you follow our instructions for calculating capacity, you will have a perfect orientation for the required capacity in your vehicle. Whether this happens with or without inverters is entirely up to you. If you will use some high-power appliances, I suggest you buy a 3000 watt inverter.