Electric 1x1

When is it important and what for?

Anyone who has ever travelled independently in a camper or motorhome knows exactly how important it is to know the condition of the battery. Nobody wants to suddenly find themselves sitting in the dark. There are roughly two methods for monitoring the battery:

1. Measure the voltage.

This method is very simple and therefore not very precise. The current state of the battery is calculated using the battery voltage. This is possible because it decreases with the charge level. This is still fairly accurate for an AGM/lead-gel battery, as you can speak of an almost linear drop, but it is hardly applicable to a LiFePO4 battery, as the voltage remains very stable and only drops sharply at the end.

2. Counting the current.

The capacity is given in ampere hours Ah or watt hours Wh. Let's take a 100Ah LiFePO4 battery as an example, it can deliver 100A for one hour or 1A for 100 hours. We now need the option to monitor the outgoing and incoming currents of the battery and count them over time. This function is already integrated in many (required) battery management systems for LiFePO4 batteries and we can find out the state of charge, often SOC (State of Charge). The various manufacturers provide apps or interfaces for this. In our VAN PI system, Daly/JBD - Xiaoxing/Liontron are currently supported via cable or Bluetooth. Another method of monitoring the current is a shunt. This is a calibrated "resistance" - or rather an area in the circuit - where we can calculate the current using the resulting voltage drop. Such shunts have a typical voltage drop of 75mV for a certain current such as 100A. This voltage drop is linear and we can therefore calculate and monitor the currents precisely.

Shore power

If you are at home or at a campsite, you can charge the battery using chargers from a variety of manufacturers. Two things are particularly important here: firstly, the charging current should be sufficiently dimensioned and secondly, the type of battery used must be supported. Different batteries have different charging curves and end-of-charge voltages, all of which must be taken into account when making your selection.

Solar

Of course, it is possible to charge the battery via the solar system; you can find all important information under the heading "Solar".

Alternator - Booster

Charging via the alternator used to be a small thing. The internal resistance of lead-gel batteries prevents extreme current consumption, so second batteries could be operated in parallel with the starter battery without any major concerns. Of course there were "charging boosters" back then, but these were used much more to compensate for the voltage loss between the second battery and the alternator. Mostly for caravans, as the voltage reaching the car's battery is already very low. Back then it was actually still a boost - nowadays we only talk about a booster for marketing purposes. You know the drill ;)
When used with a LiFePO4, however, it is much more of a limiter - because unlike the old batteries, this new technology accepts much higher charging currents and does so until just before 100% charge. Our alternator would therefore run at 100% load all the time and would quickly fail due to overheating. The charging booster you choose should therefore provide a current that your alternator can provide without any problems and is large enough for you to charge the battery in a reasonable amount of time.

Example calculation: 200Ah LiFePO4 with a 25A charging booster

Our battery is empty and we want to charge it while driving on a warm day. The refrigerator is on. Ideally we would have to drive 200Ah/25A = 8h to fully charge the battery.

However, the following is often forgotten: the charging boosters reduce the power when the temperature is high and the device is warm. Often only 70-80% of the charging power is achieved. Furthermore, consumers such as the refrigerator draw power at the same time. This means that the charging current is only around 15A.

So the new calculation is 200Ah/15A = 13.3 hours of driving time to charge the battery from 0 to 100%. If we now use a larger charging booster, we can shorten the time, but we should make sure that it is not greater than 50% of the rated output of the alternator.

What do I have to pay attention to and how much solar do I need?

When it comes to quantity, the more the better :)
Above all, it depends on how much of the area on your vehicle you can and want to equip with solar panels. Often, a compromise has to be made between the roof rack and the solar area.

Let's do another example calculation: let's assume that we have installed solar modules with an output of 200W - that would be an area of ​​about 1 square meter. To calculate how much energy you can charge the battery in one day, you can use solar energy yield calculators. There you can use the coordinates to calculate the average yield over the year (don't forget to enter the inclination of 0°). With a 200W system you should therefore get about 22-25kWh in the summer months. That corresponds to a daily yield of about 750Wh or about 60Ah. However, this is the ideal case. In addition, there are shadows that are not taken into account, losses in the charging control and soiling of the solar modules. A realistic yield is probably more like 400-500Wh.

What is the electricity we generate in summer enough for?

Roughly speaking, the calculated power is enough to run a compressor cooler for around 15 hours. Longer periods of autonomous operation are therefore only possible in conjunction with a large battery. This is because other consumers such as lights or charging cell phones and laptops continue to discharge the battery. The cooler is often turned off at night, but 200W is usually not enough to generate a positive charge in the battery. However, with a suitable charging booster (more on this below), for example, the missing power can be quickly recharged by the alternator.

Wiring and charge controller

Let's start with the charge controllers. MPPT (Maximum Power Point Tracking) has become established on the market and is more efficient than the outdated PWM technology.

What do I need to look for in an MPPT charge controller?

The charge controllers always have two important parameters: the PV (photovoltaic voltage) and the maximum charging current. Using the example of the Victron Smart Solar 75/15, this means: the voltage of the solar system can be a maximum of 75V and the controller can then achieve a maximum charging current of 15A. This controller can therefore be used for 220W solar systems. 15a (14.4V*15A).

How should I design the solar panels?

Solar panels come in a variety of dimensions and circuits. The most important thing here is the PV (or open circuit voltage) and the nominal current. If we now design a solar system for the solar controller mentioned above, we can use solar modules with a maximum voltage of 75V. This voltage seems very high, but you could now connect three solar modules with 100W and an open circuit voltage of 20V in series and have an open circuit voltage of 60V.

But we can only achieve a maximum of 220W with the solar controller (75/15), so why 300W solar on the roof?

The solar panels reach 300W at peak power, i.e. with optimal alignment and a bright blue sky. However, since we install the modules flat on the vehicles and not at an angle, experience has shown that only 50% of the peak power is achieved - in this case 150W. It therefore makes sense to dimension the solar system somewhat above the solar controller.

What is the most effective way to switch on the solar modules?

The advantage of connecting solar panels in series is the low currents. The voltage is added, but the current remains the same. This means that thinner and lighter cables can be used. But there are also other controllers that cannot handle as much voltage. Or combination devices that are charging boosters and solar controllers in one, such as the Renogy DCC50s. This can only be operated with a maximum PV voltage of 25V. Here the solar modules would have to be connected in parallel. This means that the voltage remains the same and the currents add up.

Regardless of whether it is connected in parallel or in series, the solar system must be connected with appropriate cables and the fuse must not be forgotten under any circumstances!

Pure sine or modified sine

A normal 230V socket on the road makes many things easy. To implement this, we now need to convert our 12V on-board power supply. We do this with an inverter. This converts the direct current to alternating current and thus increases the voltage. You often read about pure sine wave and simplified/modified sine wave. What does that mean?

In our normal power grid, we have an alternating frequency of 50 Hz. This means that the voltage and therefore the current change direction 50 times a second. This happens in a nice sine wave. This is the crux of the matter: pure sine wave inverters reproduce this curve 1:1 and are no different from normal shore power - modified sine wave inverters do not have a curve, but change the voltage in a step shape. The circuit is much simpler and these devices are therefore cheaper.

Which devices should definitely get a pure sine wave inverter?
These include, for example: coffee pad machines (such as Philips Senseo), televisions, chargers, audio amplifiers. Sensitive devices such as chargers could be damaged by a modified sine wave inverter. However, opinions differ here - many report years of use without any defects.

What performance?

Here it is of course important to know which devices are to be operated. If you only want to charge your laptop, camera, etc., inverters with low power are sufficient. If we assume a 250W inverter, for example, you can easily charge or operate a laptop and two other small devices.

However, if large consumers such as coffee machines, kettles or similar are planned, the output of the inverter must be very high.

Here is an example calculation for a vehicle with an induction hob and a 200Ah LiFePO4 battery.

1. Required inverter:

Our hob has 2000W power -> Therefore we need an inverter with at least 2000W continuous power. The peak power that can be accessed for a short moment is then usually 3000-4000W.

2. Cable cross-section to the inverter:

We have to generate the required 2000W from 12.8V voltage. This means we have a current of (2000/12.8) approx. 160A. To be on the safe side, we put the cable with 200A and use a 35mm² cable to connect our battery to the inverter. Don't forget to protect the whole thing directly after the battery ! Here we would also use a 200A fuse.

3. How long can I cook?

We have calculated that we need around 160A to operate the hotplate. We could therefore operate our fully charged battery with 200Ah for around 1 hour. (200Ah/160A = 1.25h) Here we assume that we only want to discharge the battery to 80% in order to have a longer cycle life. Now let's assume that we only want to cook for around 20 minutes. Is induction really an alternative again now?
(In the chapter Charging Booster and Solar you will find the calculations on charging times.)

Mains priority circuit

A mains priority switch is used to switch to shore power as soon as it is available. This separates the 230V system from the inverter and the energy is no longer drawn from the battery. At the same time, a charger can be switched on to charge the battery.

Let's do another example calculation: let's assume that we have installed solar modules with an output of 200W - that would be an area of ​​about 1 square meter. To calculate how much energy you can charge the battery in one day, you can use solar energy yield calculators. There you can use the coordinates to calculate the average yield over the year (don't forget to enter the inclination of 0°). With a 200W system you should therefore get about 22-25kWh in the summer months. That corresponds to a daily yield of about 750Wh or about 60Ah. However, this is the ideal case. In addition, there are shadows that are not taken into account, losses in the charging control and soiling of the solar modules. A realistic yield is probably more like 400-500Wh.

What is the electricity we generate in summer enough for?

Roughly speaking, the calculated power is enough to run a compressor cooler for around 15 hours. Longer periods of autonomous operation are therefore only possible in conjunction with a large battery. This is because other consumers such as lights or charging cell phones and laptops continue to discharge the battery. The cooler is often turned off at night, but 200W is usually not enough to generate a positive charge in the battery. However, with a suitable charging booster (more on this below), for example, the missing power can be quickly recharged by the alternator.

Wiring and charge controller

Let's start with the charge controllers. MPPT (Maximum Power Point Tracking) has become established on the market and is more efficient than the outdated PWM technology.

What do I need to look for in an MPPT charge controller?

The charge controllers always have two important parameters: the PV (photovoltaic voltage) and the maximum charging current. Using the example of the Victron Smart Solar 75/15, this means: the voltage of the solar system can be a maximum of 75V and the controller can then achieve a maximum charging current of 15A. This controller can therefore be used for 220W solar systems. 15a (14.4V*15A).

How should I design the solar panels?

Solar panels come in a variety of dimensions and circuits. The most important thing here is the PV (or open circuit voltage) and the rated current. If we now design a solar system for the solar controller mentioned above, we can use solar modules with a maximum voltage of 75V. This voltage seems very high, but you could connect three solar modules with 100W and an open circuit voltage of 20V in series and have an open circuit voltage of 60V.

But we can only achieve a maximum of 220W with the solar controller (75/15), so why 300W solar on the roof?

The solar panels reach 300W at peak power, i.e. with optimal alignment and a bright blue sky. However, since we install the modules flat on the vehicles and not at an angle, experience has shown that only 50% of the peak power is achieved - in this case 150W. It therefore makes sense to dimension the solar system somewhat above the solar controller.

What is the most effective way to switch on the solar modules?

The advantage of connecting solar panels in series is the low currents. The voltage is added, but the current remains the same. This means that thinner and lighter cables can be used. But there are also other controllers that cannot handle as much voltage. Or combination devices that are charging boosters and solar controllers in one, such as the Renogy DCC50s. This can only be operated with a maximum PV voltage of 25V. Here the solar modules would have to be connected in parallel. This means that the voltage remains the same and the currents add up.

Regardless of whether it is connected in parallel or in series, the solar system must be connected with appropriate cables and the fuse must not be forgotten under any circumstances!

If you want to be on the road on cold days, you can't avoid having an auxiliary heater. Auxiliary heaters are available with different energy sources, with diesel and gas being the most common.
Gas is mainly used in many mobile homes and trailers. Diesel heaters are often used in vans and self-built systems. However, we will only be looking at diesel heaters from Webasto, Autoterm, LF Bros, Vevor etc.

All of these heaters use energy from the battery to burn diesel. However, this energy from the battery is much less than the heat we ultimately have available (approx. 35W from the battery produces up to 5000W of heating power).

Required performance?

Many people assume that the more power a heater has, the better it can heat a vehicle. What is often not taken into account is that restarting the device too often is not good for its lifespan. This is because combustion does not run optimally during the start-up process, which leads to soot and wear. If we have a very powerful heater that produces too much heat even at the lowest setting, the only way to counteract this is to open windows or temporarily switch the heater off. The latter, as described, shortens the lifespan of the heater. Experience has shown that a 2kW heater is more than sufficient for a normal VAN (long version).

Permanent installation or heating in a box?

Mobile diesel heaters are increasingly found in a small box with a battery and a diesel tank. The cheaper models from the Far East are often used for this purpose. This is because they often do not have approval to be permanently installed in a vehicle. This is not a problem with the more expensive devices.

Which heating modes?

The different heaters can be put into different operating modes; here are a few common methods which are used.

"Power mode": The heater runs at a fixed power level regardless of the temperature.

"Temperature mode": The heater attempts to maintain a certain target temperature by changing the power level.

"Hysteresis mode": The heater has an upper temperature limit at which it switches off and a certain switch-on temperature at which it starts again. The difference between the high and low values ​​is called hysteresis. However, one should not forget that a heater that is starting is very loud and its service life is reduced by starting it several times.

CO detector

No matter what type of heating is installed, it is always advisable to install a CO detector in the vehicle. Even if the probability of something happening is very low, the consequences can be very dramatic. That is why we always recommend installing a CO detector in the vehicle. In an emergency, this will sound an alarm if carbon monoxide enters.