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Power system

The power systems on motorhomes are nothing more than these: external mains, generators, and solar power generation. Advantages of external mains: no noise, basically unlimited power consumption; Disadvantages: It is not easy to find a place to connect to the power when you are away from home. Advantages of generators: basically unlimited power consumption at any time, as long as there is oil; Disadvantages: high noise. Advantages of solar power generation: no noise, power generation can be generated as long as there is sun; Disadvantages: low power generation efficiency, only enough for lighting or refrigerator power.

Power storage system

There are two types of power storage systems: lead-acid batteries and lithium batteries. Advantages of lead-acid batteries: safe and cheap; Disadvantages: small storage capacity, heavy weight, cannot be deeply discharged, and relatively short life. Advantages of lithium batteries: large storage capacity, light weight, can be deeply discharged, and relatively long life; Disadvantages: safety is worth paying attention to and high price.

Power transmission and power consumption system

The power transmission system is mainly composed of various wires and cables or copper bars, etc., and the wire diameter needs to be calculated according to the power consumption demand.

The power system includes 12V power and 220V power. The lighting and refrigerator in the RV are generally powered by 12V, and the TV, air conditioner, socket and other common household appliances are powered by 220V.

Electrical demand estimation

Everyone should know that energy is conserved. The total demand of our power system plus the loss of the transmission system cannot be greater than the maximum limit that the power system can provide. Therefore, we reversely infer what kind of power supply or power storage system is needed based on the power demand. In addition, we can reversely infer what kind of wire diameter is safe based on the power demand. The following example uses the calculation of Battery Chargers capacity, which is mainly for electrical literacy estimation. Professionals please ignore it.

Use simple junior high school physics knowledge to help us estimate electrical demand, P (power) = U (voltage) × I (current), for example: 1W = 1V × 1A. Watt (W) - unit of power, commonly used kilowatt (kW) or 1000W as a unit. Kilowatt-hour (kW·h)——1kW·h=1 kWh (1kW of power for 1 hour), Volt (V)——unit of voltage, Ampere (A)——unit of current.

First, you need to understand the power of your electrical appliances. The accurate value can be obtained from the label behind the appliance.

Common RV electrical appliance power estimation: air conditioning heating is generally around 2500W (electric auxiliary heating); air conditioning cooling is generally around 800W; induction cooker is generally around 2500W; electric kettle is generally around 1500W. Note: It is not recommended to use high-power electrical appliances in RVs. The power of a single electrical appliance should be less than 3000W, and high-power electrical appliances should not be used at the same time as much as possible. This is determined by the maximum power that the generator or inverter we can carry can provide.

Let's take the air conditioner that everyone is most concerned about and has the largest single power as an example. If you want to turn on the air conditioner for 10 hours in summer, the energy required is: 800W×10h=8kW·h (8 kWh), based on the formula: power×usage time=power consumption.

The above calculation is a theoretical value. Other electrical appliances can be deduced in the same way. The total energy consumption of all electrical appliances is the total power demand. The power demand should be estimated according to the larger value to ensure that the reverse power supply is sufficient.

Through the above estimation, you can calculate the power consumption of your individual electrical appliances according to your personal needs and add them up to get the total demand. 

For example:

Watching TV for 5 hours ≈ 280W×5h=1400Wh=1.4kW·h=1.4 kWh; using a rice cooker for half an hour ≈ 800W×0.5h=0.4 kWh; using an air conditioner for 10 hours ≈ 800W×10h=8 kWh; total power demand: 1.4+0.4+8=9.8 kWh.

Estimation of the energy that a battery can provide

Calculation method (taking 120Ah as an example, that is, discharging at 120A current for 1 hour), (12V×120A×1h)/1000=1.44 kWh, based on the formula: (voltage×current×discharge time)/1000=provided power.

Note: The above is a purely theoretical calculation. It is impossible for a car battery to discharge all its power. Lead-acid batteries cannot be deeply discharged and need to be discounted by 50% to 60%, 1.44×0.5=0.72 kWh; lithium batteries can be deeply discharged and also need to be discounted by 20%, 1.44×0.8=1.152 kWh.

In summary, taking common lithium batteries as an example: 240Ah≈2.304 kWh; 500Ah≈4.8 kWh; 600Ah≈5.76 kWh; 800Ah≈7.68; 800Ah≈10 kWh.

Choose batteries according to demand

Through the above example, we know that our electricity demand is 9.8 kWh. According to demand, we see that lithium batteries with at least 800Ah can meet our needs. Of course, this is only a theoretical calculation. We ignore many low-power electrical appliances, such as lighting, refrigerators, mobile phone charging, laptops, etc.; and we do not consider the losses during power transmission and inversion. The real calculation is much more complicated than our example, so we will not discuss it. Here we only provide self-estimation for electric novice. When choosing a battery charger for car , you should also consider safety, price, life, ambient temperature, weight (affecting the weight of the RV) and other practical factors. I will not expand on them here.

Power transmission system

Here we mainly introduce the selection of various wires, cables and circuit breakers. The most unstable factor in the circuit is current. Excessive current will cause heat, which will cause fire. The wire diameter is thin, the safe current it carries is small, and it is easy to heat up. If the joint is not connected properly, it is easy to heat up. If the wire is short-circuited, it will heat up extremely. Therefore, the most important thing in the power transmission system is to calculate the current and select wires or cables of corresponding thickness and circuit breakers according to the calculated current.

Current calculation

For example: Using 220V to power a 3000W air conditioner, I=P/U, that is, current=power/voltage, 3000W/220V≈13.64A. Note: Both 12V DC power supply and 220V AC power supply can be calculated in this way. Check the national standards to find out the safe current carrying capacity of copper core cables.

Although we see that 1.5 square wires can already carry, considering the service life and heat generation of the wires, we can enlarge the selection and give a safety margin.

Wire selection

During decoration, 1.5 square wires are often used for lighting, 2.5 square wires are used for sockets, and 4 square or 6 square wires are used for air conditioners, because the thicker the wire, the greater the safe current carrying capacity and the less heat it generates. In order to save costs, some RV manufacturers often use thinner wires with rough joints. There may be no big problem in short-term use, but if used for a long time, the effect will be unsatisfactory.

 I give an example here, which is a simple theoretical calculation. It does not take into account the simultaneous coefficient and power factor. It is only for the electrician's estimation reference. Professionals please ignore it. In short, we choose the corresponding wiring and circuit breaker according to the calculated current. Remember, the thicker the wire, the safer it is. Of course, the wire joint process must be in place. Virtual connection and short circuit can easily cause excessive current and cause fire.

Inverter selection

You need to choose an inverter according to your power consumption. If you need a battery to drive an air conditioner or induction cooker, choose an inverter of at least 3000W. If you only need to use a rice cooker or electric kettle, at least an inverter of 2000W. Some manufacturers' original 300W inverter. The inverter must be pure sine wave, not modified wave. The wires from the battery tender charger to the inverter must be thick (you can calculate the specific amount yourself). Due to limited space, we will not discuss the inverter in detail.