Basic RV Electrical System Guide 2021

When traveling by RV, what RV users care most about is the power system on the RV. All kinds of AC equipment such as AC air conditioners, induction cookers, refrigerators, audio multimedia systems and even electric water heaters, require the power supply system to work stably. In addition to AC appliances, there are also DC devices that draw power directly from batteries, such as DC air conditioners, DC refrigerators, DC LED lights, and DC monitors. If you are an RV user and hope that these devices can provide stable power for your every trip, it is very important to have a basic understanding of your RV power system.

When you fall in love with RVs and use RVs frequently, understanding the power system, internal structure and logical structure will be of great reference significance for you when choosing various products. Most importantly, if there is a problem, you will know where the problem is and troubleshoot it quickly. We know that not all riders are electrical engineers, we will use the simplest language to describe.

What are RV electrical system’s keywords?

First, let’s take a look at the professional terms in the RV power system.
DC load power (W) = battery voltage (V) * load ampere (A).
If it is a 12V system, the battery voltage is 12V
AC load power (W) = AC voltage (V) * load ampere (A).
If it is used domestically, the AC voltage is 220V or 120V
Battery capacity (WH) = battery voltage (V) * charging and discharging ampere (A) * hours (H)
We heard that many RV users directly talk about how much AH is when talking about the battery capacity. In fact, this understanding has somewhat deviated. Let’s take the lithium iron phosphate battery as an example. The surface of the battery is nominally 12.8V / 460AH, then the capacity of this battery is: 12.8V*460AH=5888WH=5.89kWh, kWh is actually the same as our electricity meter at home, which is often said to be 5.89 kWh instead of directly reading 4.6 kWh.

Can you put LiFePO4 batteries in parallel for RV electrical system?

Now that we have talked about 12.8V, let’s deepen the understanding of lithium batteries. The nominal voltage of a single cell of lithium iron phosphate is 3.2V. When we use a 12V system, we connect four cells in series, so 12.8V is obtained. Many RV users are also very confused about the full voltage and the discharge voltage. This is very simple. The nominal value of a single battery cell is 3.2V. Generally, the maximum voltage of the built-in protection board is 3.65V, and the empty voltage can be up to 2.5V, but the basic setting is 2.8V. The conclusion is drawn: 4*3.65V = 14.6V when fully charged, and the voltage is 4*2.8V=11.2V when the battery is less than 10%.

Here a question that most concerned about are: If we feel that the battery in my RV is not enough, can I buy another set to increase the capacity? We see that many users are chaotic. For example, if they have a 400AH battery and a 600AH battery, the ideal state is to reach 1000AH, but this is not the case in actual use. When lithium batteries are connected in parallel, they will be based on the maximum capacity to calculate the cumulative value. Similar to the above parallel method, the number obtained should be 800AH, and this parallel method is not scientific and is prone to problems. So why is it so? Let’s explain. Assuming when you charge a 400AH battery, the single-cell voltage is 3.2V/400AH (multiple blocks in parallel) and a 600AH battery, the single-cell voltage is 3.2V/600AH (multiple blocks in parallel), you are charging two sets of batteries at the same time, and the capacity of the battery is related to the voltage. The built-in protection board also judges whether the battery is overvoltage. Under the same conditions, when the 400AH battery is charged to 3.65V, it starts the protection, feedbacks the battery voltage to the charger, and lets it stop charging. At this time, the 600AH battery is only charged to 400AH, it cannot reach 3.65V.

What is CC and CV in LiFePO4 battery charger in RV electrical system?

Charging power (W) = voltage (V) * charging current (A). The selected AC charger or MPPT, PWM solar control charger is nominal A. For example, the battery is a 12.8V lithium iron phosphate battery; because there are two stages in the charging process (lead-acid has three stages), the first stage is called CC mode (constant current). When the battery voltage is lower than 14.6V, the charger will charge with the maximum current until when the battery voltage reaches 14.6V, it will switch to CV mode (constant voltage). At this time, the charger voltage remains unchanged at 14.6V, while the charging current naturally decreases, until the charging current drops to 10% of the rated charging current, the charging is completed. Note that unlike lead-acid batteries, lithium batteries do not require a floating charge function (FC). The floating charge will affect the number of cycles of lithium batteries.

Is RV electrical system AC or DC?

After understanding some basic common sense, we will know that there are actually two power systems in our RV, one is a 12V DC (battery) system, which supplies some DC loads, such as DC air conditioners, DC refrigerators, and USB chargers, 12V LED lights in the RV, etc. There is also a 220VAC or 120VAC power system (through an inverter) for some large electrical appliances, such as induction cookers, microwave ovens, ovens, multimedia audio-visual systems, etc.

What is the best type of battery for an RV electrical system ?

Know about the power consumption of the RV, you can more clearly choose the type and capacity of the battery.

Judging from the configuration of more than 100 RVs we have contacted, there are now basically very few lead-acid batteries available. Lead-acid batteries are heavy, bulky, and wear fast; while lithium iron phosphate(LiFePO4) batteries have the advantages of high safety factor, small size, and high cycle times (generally greater more than 2000 times, long life), etc., that are chosen by more and more users. The density of the ternary lithium(LiMn2O4) battery is higher than that of lithium iron phosphate, so it has the advantages of lighter weight and smaller volume than lithium iron phosphate, but also very obvious weaknesses. The safety performance is not as good as that of lithium iron phosphate, and the number of cycles is 600. The price is higher than lithium iron phosphate.

What I have to mention here is that there is a key parameter that will be ignored by all RV riders, that is the charge and discharge coefficient of lithium batteries, usually expressed as ?C. We take the 12.8V/460AH battery as an example. If the marked discharge coefficient is 1C, which means it can withstand a maximum discharge capacity of 460A. The battery can withstand 1 hour to discharge the battery, and it does not damage the battery life. If it is marked as 0.5C, it means that it can only withstand a maximum of 2 hours to discharge the battery without harming the battery; some even only have 0.2C. If the battery cell is only 0.2C, then even if your BMS or protection board can withstand charging and discharging more than this current, it will cause damage to the battery.

The same is true for charging. Lithium iron phosphate batteries on the regular market now generally have a discharge coefficient of 1C and a charge coefficient of 0.5C; that is, it can support 1 hour to discharge, and 2 hours to fully charge. This will be an important reference parameter when choosing a lithium iron phosphate battery, of course, this statement also applies to ternary lithium batteries.

What size battery does my RV electrical system need?

After understanding the battery type, we began to simply calculate the power consumption in our RV. For example, in a 102-liter DC refrigerator A, we calculate according to the nominal display 0.39KWH/24H, the 24-hour power consumption is 0.39KWH which we commonly use. A 12V DC air conditioner B, the power of the compressor is 300-900W, we calculate it according to half the time the compressor works (if the temperature drops, the compressor will automatically stop): 900W/2*1H=0.45KWH, which means if the air conditioner used for 1 hour, it is about 0.45 kWh of electricity.

These devices are all DC devices, directly derived from the battery, and the loss is very small. In addition, there are some LED lights, which are quite small loads and can be ignored. After calculated the DC load, we calculated the AC equipment. Usually, the most used by RV users should be induction cooker C, electric kettle D, we also give an example, the maximum power of the induction cooker is 2100W, because the induction cooker is AC equipment, so its power supply is inverted from the battery through the inverter, the conversion efficiency of the inverter is very important here.

The most popular ones on the market are the low-frequency inverter with integrated charging and inversion and the normal high-frequency inverter. In the state of 12V, the conversion efficiency of the low-frequency inverter is much lower. The conversion efficiency of the normal low-frequency inverter 12V3000W is about 80%, while the quiescent current reaches 150-200W, and the conversion efficiency of the high-frequency inverter is 88%, and the quiescent current is about 300W. If you are using a low-frequency inverter, the power consumption of a 2100W induction cooker is 2100W/0.8*1h=2.6KWH. In other words, the induction cooker consumes 2.6 kWh of electricity for one hour. The power of an electric kettle is about 1200W. Usually, we can boil a pot of water in 7 minutes. 1200W/0.8*0.12= 0.18KWH, which means that 0.18 kWh of electricity is required for boiling water.

Knowing this calculation method, do you understand the power consumption in your RV? Choosing a battery with a reasonable capacity will bring enough power for your RV trip.

How do I charge my RV electrical system battery？

How to properly configure the charging method of the life battery in the RV?
There are basically three parts to charging the living battery in the RV:

1. Car motor charger
2. MPPT/PWM solar control charger
3. AC charger

There are two types of car chargers

A. Dual battery isolator: The charger that charges the "car battery" from the engine compartment at the same time charges the life battery. This kind of application is very efficient and easy to install. It charges two batteries at the same time when charging, and separates them when only the life battery is used instead of the "car battery". According to the power of the car generator, you can choose 80-120A. If your car generator supports a charging current of 120A, then 120A*12V*1 hour=1.44KWH, which means that the life battery can be charged 1.44KWH for 1 hour of driving.

B. 12 to 12v DC charger, the advantage of this product is that it supports a wide front-end voltage input, usually 10.5-16V, similar to a dedicated charger, it can be charged in CC/CV mode. But its price will be much more expensive than dual battery isolators, and generally does not support high power.

How to configure solar panels for RV electrical system？

MPPT/PWM solar controller (MPPT is maximum power point tracking, usually 20-30% higher than PWM power generation).
There is a certain space on the top of the RV to install solar panels. According to our survey, the solar panels of the general RV are 400W-800W. Here we will share the most reasonable RV solar panel power generation design. Usually, we choose even numbers when installing solar panels, because we need to involve series and parallel. If your RV is a 12V system, the best working voltage of the MPPT solar controller is 24V-36V. Of course, many MPPT controllers also say that it can work at 3V higher than the battery, but the RV is not like an off-grid solar system. The lighting and installation angle are both extremely demanding for RV, so we choose a slightly higher one. We have also checked a lot of solar panels used in RVs, which are basically around 18V, so we suggest 2 pieces in series and then parallel. If you use an 800W solar panel, it is most ideal to choose the 12V/80A MPPT solar charge controller. We have seen a lot of solar panels installed, but the actual controller did not reach, and it still can’t generate much electricity. Because of the different lighting in various places and the different parking positions of the riders, it is impossible to give an accurate answer to how much electricity the 800W solar panel can generate. However, we investigated most of the RV users who installed 800W, and they can generate about 2 kWh of electricity in 3 hours from 11:00-14:00 noon.

Here, let me share with you the experiments we have done. In fact, we have seen many RV users install a lot of solar panels on roofs of different shapes and sizes. Most users will find that 800W solar panel installed, but only has a charging capacity of more than 200W or even more than 100W. Here is my experience, because most of the single solar panels on the RV have a voltage of around 17-21V, so many users and even RV factories connect two pieces in series and then in parallel. An important theory here is that if solar panels with different power are connected in series, the current is output at the smallest piece. In layman's terms: 150W and 100W are connected in series, the actual effect is only 200W but not 250W, so when doing the test, the actual power generation of one group of 150W+100W and the other group of 100W+100W are the same.

We saw a lot of users installed some very small pieces on RVs. If this pieces is 20W and another piece of 100W, it can only be 40W, which will be a lot of waste. Will the parallel connection of multiple groups of different powers have an impact? For example, we have one group of 150W+150W, and two groups of 100W+100W. Seeing that the power is 700W, but the actual power generation efficiency has not been reached.

The reason is that the parallel of solar panels with different powers into the MPPT will affect the maximum power tracking. Therefore, the suggestion is to install an even number of boards of the same size on the top of the RV, so that the power generation effect can be highest. Composed of a double number in the smallest unit, for example, it is recommended not to install 100W in some places and 50W in some places. just install at 50W. In our actual test, if the installation is reasonable, use the MPPT with good performance, the power generation efficiency can reach more than 50% when the sun is not particularly good, and it can reach more than 85% when the sun is big occasionally.

Therefore, when choosing to install solar panels for RVs, you must pay attention to this detail. Don't reduce the overall power generation efficiency just because you want to increase a small piece of usable space.

Summary: When installing solar panels on the roof of your RV, choose an even number of solar panels of the same model to achieve the best condition.

How to charge battery while it is connected to grid in RV electrical system?

AC charger for RV battery

The AC charger is connected to the mains when parking the RV to charge the battery. Commonly, there are chargers that come with the inverter. Generally, the charging current is small. If it is a low-frequency inverter, it may also be marked as 50A-80A. The charging current 12.8V of a single charger is only 100A. What does charging current mean? If there is a 12.8V/460AH battery, it takes 4.6 hours to fully charge by using a 12.8V/100A charger. The calculation formula is 460AH/100A=4.6H. It should be noted that it must use a matching charger to charge the battery. The charger parameters of different batteries are different. For lead-acid, the voltage of CC must be 15.5V. Although the lithium battery has a protective plate for protection, it is still risky and dangerous.

A summary of charging:
1. Review your general information of habits, driving time and parking time
2. A simple calculation is required for the power consumption in the RV when parking
3. If the above three charging methods are installed in the RV, get to know about the approximate distribution of the various charging methods.

What is the best power inverter for RV electrical system?

After explaining the three charging methods, I believe everyone has a certain understanding of the charging methods of RVs. Next, we will talk about inverters.

The choice of the inverter is the most critical for the RV. When the RV user is parked and resting, all the large electrical appliances in the RV run on the inverter. For example, AC air conditioners (including overhead air conditioners and household air conditioners), induction cookers, kettles, televisions and so on. If there is a problem with the inverter, it all becomes a fantasy.

There are currently two types of inverters on the market: low-frequency inverters and high-frequency inverters. The modified inverter is no included, and the inverters referred to are all sine waves.

1. Advantages of low-frequency inverter
Three times the peak power, strong load capacity, strong shock resistance, and a high-power charger Disadvantages of low-frequency inverter Large size, heavy weight, low conversion efficiency, large no-load loss, large heat generation.

2. Disadvantages of high-frequency inverter
Double times the peak power (some manufacturers have provided triple peak power), and the load capacity is weaker than the low-frequency. Generally, there is no charger or low-power charger.
Advantages of high-frequency inverter, small size, light weight (only about 20% of low frequency inverter), high conversion efficiency (about 10% higher than low-frequency inverter), low no-load loss (only about 15% of low frequency machine), low heat generation. The long-term working shell temperature is not higher than 40 degrees (when the ambient temperature is 25 degrees).

After comparing the advantages and disadvantages, we found that the low frequency inverter is stronger than the high frequency inverter in impact resistance, and will come with a high-power charger, which makes the installation much easier.

However, it is also obvious to find that the advantages of high-frequency inverters may be more suitable for use in an RV, because the inverters are mostly installed under the seat, under the bed, or in the storage box at the rear of the car; the location of the inverter installed is small and not ventilated.

Most manufacturers are not particularly professional circuit engineers. they only think that will be fine they can put down the inverter. In fact, this enclosed space is extremely unfavorable to the inverter.

After the ambient temperature rises, it cannot be dispersed for a long time, resulting in that the components inside the inverter are aging quickly. If they are maintained at high temperature for a long time (although the inverter has over-temperature protection), the internal components are also prone to failure, causing the inverter to be damaged and unable to output.

We have seen a lot of low-frequency inverters installed by RV users, when the air conditioner is turned on, the inverter over-temperature protection does not work in the middle of the night, or the charging module is broken. Some users suggested that if you don’t need a large load, you need to turn off the inverter, because if you don’t turn on the load, the low frequency inverter has a loss of 100-200W, and it consumes 0.1-0.2KWH electricity in one hour. This has created a very difficult decision for many users.

Therefore, when choosing an inverter, we recommend that a more reasonable configuration of the inverter will make your RV AC power supply smoother.

What is configuration suitable for RV electrical system?

Which plan is more suitable for you? Let's recommend a set of configurations (12V/3000W system):

1. 3000W high frequency sine wave inverter with bypass function.
Advantages: When the main supply is connected, the electricity in the RV will be directly transferred to the mains supply, the inverter will no longer work, and there will be no self-loss and heat generation. Usually not connected to the mains, the high-frequency sine wave inverter has the advantages of high conversion efficiency, low self-loss, and low heat generation. The actual 6000W peak power of 3000W inverter can start most of the large electrical appliances in the RV, overhead air conditioners, household air conditioners, kettles, audio-visual systems, etc.

2. MPPT solar controller 12V/24V/48V adaptive 60A.
Advantages: Why choose 12V/24V/48V adaptively? The reason is that in case you change the 48V system on a whim, you can still use it. The 48V/60A MPPT solar controller can support up to 876W (14.6V*60A) solar panels, but in fact, even if we install 800W solar panels on the RV, under normal circumstances, it cannot reach such a large power. But if your configuration is too small, you will not be able to achieve the maximum effect. The 60A MPPT solar controller can meet most of the DC load, even if the weather is not so good, the electricity generated is enough for the DC refrigerator.

3. 12.8V LiFePO4 dedicated mains charger 100A.
Advantages: When connected to the mains, quickly charge the life battery in the RV. We mentioned this charge and discharge coefficient when we talked about the battery above. If the lithium battery is 200AH and the charge factor is greater than 0.5C, it only takes 2 hours to fully charge the battery when it is connected to the mains. The advantage of the independent AC charger is that it has its own fan and over-temperature protection function, which is more stable and safer in the state of mains charging.

4. 12V to 12V dual battery isolator 120A.
Advantages: I personally think that this will be the best and fastest charging method. If our car generator has a charging current of 100A, when this dual battery isolator is installed, it can charge 1.2kWh every 1 hour when driving. For RV users, it is the most comfortable state to drive for 3 hours per trip and rest for one night at the station. If equipped with dual battery isolators, it can fully meet the electricity needs of one night. So please don't ignore this key configuration.

Should I disconnect my RV battery when plugged in?

It depends on the design of the electrical system in your RV, especially the selection and design of the AC charging and inverter determine if that operation is needed.

RV owners need to use the AC equipment in the car when they stay in the car, especially in summer, the temperature inside is very high and it needs to turn on the air conditioner for a long time, but many owners have refrigerators running 24 hours; this time the battery will not be enough, the power of the solar system in the RV is limited, or there is not always good sunshine to support the power generation, then it will be necessary to plug in the mains in the premises or basic to charge the battery and powering the load at the same time. In this case, should I disconnect my RV battery when plugged in? we need to talk about two cases, which have the difference between inverters with bypass function and DC to AC inverters.

1. With bypass inverter
If your inverter has bypass function, there is no need to do anything when plugged in to the grid. When the grid is detected, the inverter with bypass function will automatically switch to grid to provide the power for the load in the car, the BP series with bypass inverter has a switching time <19ms. We highly recommend using our BP series with bypass inverter + Ares series battery charger, when the bypass inverter switch to grid, also the Ares series battery charger will charge the battery, it is a very smart solution for RV power charging and electricity system. And the Ares series battery charger provides a maximum charge current of 12.8v 100amps, even if you have a 12.8v/1000ah battery, it only takes 10 hours to be fully charged, which is a very good choice.

Caution:

Inverter with bypass function generally has two modes, a. Grid priority b. Battery priority . Choose the corresponding mode according to your situation. If you are using inverter charger, some models will also have bypass mode, such as our BP with charger series, but we also found some cheap inverter charger in the market, just DC to AC inverter + ac charger does not have bypass mode, please pay attention to the choice.

2.DC to AC inverter
Many caravan manufacturers or conversion plants, in order to reduce costs, in the caravan only installed DC to AC inverter, it is completely separate from the grid, and will be installed a converter at the same time. If grid plugged in before the inverter is off, and then the converter to the mains. Operate correctly, otherwise the gird plugged in will burn the inverter, but there is no relationship with the battery, it will not damage the battery .

Why high frequency inverters are suitable for RV electrical system?

Why is such a configuration more reasonable? I believe that everyone has no doubt on AC chargers and dual battery isolators solar controller, so why not directly use low-frequency inverters? Because the self-loss of the low frequency inverter is too large, calculated based on the average hourly power consumption of 0.15 kWh, it can consume 3.6 kWh of electricity in 24 hours.

According to the law of conservation of energy, the consumed electricity will be converted into heat. However, most of the RVs are passively cooled where the inverter is placed, and the heat is very difficult to dissipate, which will eventually lead to an increase in the failure rate of the inverter. Many RV users will say that I turn off the inverter or enter the sleep mode when I am not using it. Of course, this is fine, but it cannot solve another problem, which is the low conversion efficiency of the low-frequency inverter.

After testing, the conversion efficiency of the lower frequency inverter in the 12V system is basically within 80%, while the high frequency inverter is about 88%. This 8% efficiency can make your battery run 8% more time, which is also an indirect cost saving; and the problem caused by low conversion efficiency is the problem of heat generation.

According to the law of conservation of energy, the loss of the inverter directly generates heat when inverting, which increases the heat. For a small space, the difficulty of heat dissipation is once again increased. In addition, there is also a key indicator of weight. Usually, the weight of a 3000W low frequency inverter with integrated charging and inversion is 25kg, and a high-frequency inverter is only 9kg. Even if you add 5.5kg of the 12.8V/100A AC charger, it is only 14.5KG. The driving weight is also a very important indicator for RV users.

Summary: 1. The self-loss is large, the conversion efficiency is low, and the battery usage time is reduced. 2. In the space where the heat is large and it is not easy to dissipate the heat, it is extremely easy to cause the inverter to malfunction. The high-frequency inverter with mains switching function and the independent AC charger has independent fan and over-temperature protection functions, which will ensure a more stable operation of the AC charging and discharging system in the RV. If you have a better solution, you can also contact us, and we will discuss a better RV power solution together.

We spent a lot of time describing the advantages of installing high-frequency inverters with mains switching functions in RVs. We also talked about how to choose the type of battery suitable for RV users. Of course, we also talked about the selection and function of various charging methods. If you think it is enough, then I will talk about the key link that is an easily neglected-the choice of wire diameter between the various devices. This is the most easily overlooked link. If the diameter of the wire you connect is too thin, the loss will increase, and the cable will easily heat up. To a certain extent, it may cause a fire. There will also be a large voltage drop at the DC end. We often see that the voltage on the battery terminal is 13.5V, and the inverter terminal is only 13V. In addition to the normal voltage drop, the thick wire diameter can also cause this problem.

Author: Rico Chen by CNBOU

Basic RV Electrical System Guide 2021