How do you convert a 3.7 kW wallbox to 22 kW?

The two topics to get from 3.7 kW to 22 kW

Basically, there are two things that you have to deal with in order to upgrade a 3.7 kW wallbox to 22 kW:

  • convert from 3.7 kW to 11 kW (from 1-phase to 3-phase)
  • switch from 11 kW to 22 kW (from 16 A to 32 A)

A 3.7 kW wallbox is connected to the grid with just one phase, meaning with 230 V like a normal household appliance. If you upgrade to 3-phase operation, you add two more phases so that it supplies 400 V three-phase current, like a three-phase AC socket. As with three-phase AC sockets, there is still a distinction between 16 A and 32 A. If you only convert it to three-phase current, you have already tripled the output from 3.7 kW to 11 kW, but to get to 22 kW , you also have to change the box from 16 A to 32 A. This then achieves the full 22 kW.

But as some people will already notice from this explanation: You don't have to do both, you can also do one or the other. You can also leave the power as it is and upgrade it from 3.7 kW to 11 kW. This means you can charge 80% of all electric cars with their full power on Type 2. You could also leave it 1-phase and go from 16 A up to 32 A. Then you would be able to provide the car with 7.2 kW, provided it can accommodate this over 1-phase.

However, due to unbalanced load rules in Europe, this is rarely legally permitted. More about this in the smart EMOTION Wiki under the keyword “unbalanced load”. Also a general note here is that you are working with dangerous voltages and should only do this if you know how to work safely with them. This is not a project that you should tackle without prior knowledge. There is danger to life.

In the following explanation I will now cover both topics, but since the most popular will be how to get from 3.7 kW to 11 kW, this will be the first:

Conversion from 3.7 kW to 11 kW

The easiest and most universally feasible option is to convert from 3.7 kW to 11 kW. Practically any 3.7 kW wallbox that has enough space in the housing for a few additional cables and a 3-phase contactor can be used for this. In my case, a very simple wallbox from a Dutch manufacturer was used, but the procedure can be transferred to many other wallboxes too.

You can also use an old Type 1 wallbox and convert it to Type 2. The protocol of Type 1 and Type 3 is the same, the only difference is that the Type 2 plug also supports three-phase current, while the Type 1 plug does not.

Since this wallbox does not have any complex features such as load management or the like, its inner workings are very manageable and easy to understand. But even more complex wallboxes follow the same principle. In the past I have already shown in detail what kind of things there are in a modern 22 kW wallbox: Teardown - What's in the Tesla Wallbox and how does it work?

Wie rüstet man eine 3,7 kW Wallbox auf 22 kW um?

Three conductors are led into the wallbox: earth, neutral and L1. These are connected to luster terminals in the wallbox to give the local electrician as many options as possible as to how he can connect the wallbox in the garage. From the luster terminals the power goes to the main board. On the one hand, it is supplied with the 230 V itself in order to be able to establish communication with the car and, on the other hand, it also passes on the power directly to the car. You can find out how the Type 2 protocol works below when it comes to switching from 16 A to 32 A.

At this point it is only important to know that the wallbox only connects the 230 V to the car with a relay when communication with the car is established and the car requests the power. In the case of this wallbox, the relay is between the input and output terminals on the motherboard.

A communication line goes from the main board to another board. This allows you to adjust the current, has status LEDs for the charging process and a coil for RFID cards.

In reality the whole thing looks like this, I unplugged the communication line for the photo:

However, in order to convert the wallbox from 3.7 kW to 11 kW, we need a 3-phase contactor, which will replace the 1-phase contactor on the motherboard. With its help we can then switch not only L1, but also L2 and L3. So that we can switch 400 V three-phase current on and off instead of just 230 V alternating current. We don't have to change anything about the Type 2 protocol.

The car and the wallbox only talk about the current, but not the number of phases. If the car gets 3 phases from the wallbox, it charges with 3 phases. If it only gets one phase, it can only charge with one. However, it is important not to switch phases on or off during the charging process; not all cars can tolerate this and you should only do this if you are deeper into the topic.

It is important to pay attention to dada sheet and cross-sections when purchasing individual components. If you don't change the current, you can stick with the cross sections used by the wallbox manufacturer. This is usually 2.5 mm² per conductor for 3.7 & 11 kW. I will go into the selection of the contactor in more detail when switching from 11 kW to 22 kW.

When converting here, I connected the three phases and neutral from the luster terminal to the three-phase contactor. I also placed the supply cable (L1 and N) on the motherboard into the cable lugs. So that it continues to be supplied with its 230 V. Because we still need them for communication between the car and the wallbox. We also still need its relay.

Of course, the motherboard will still be grounded. When it comes to grounding cables, it is always an advantage if they are shorter than the others. Therefore, the grounding for the motherboard comes directly from the luster terminal at the input and also goes directly over to the luster terminal from the output to the type 2 cable.

Wie rüstet man eine 3,7 kW Wallbox auf 22 kW um?

In order to close the new contactor at the right moment and open it again after charging, the old cables from the main board are connected to its control connections. If communication with the car is established and the main board wants to release the power to the car, it closes its relay and thus also the new three-phase contactor. The charging process can then begin.

The finished interior of the wallbox looks something like this in real life:

Of course, it is also important that the three-phase contactor then passes on all three phases and neutral to the car. Not only does the wallbox have to be 3-phase, but also the type 2 cable. It's always a bit of a gamble. If you're lucky, the 3.7 kW wallbox has a 3-phase cable because the manufacturer wanted to have fewer variants.

If it doesn't have it, you can look for one on eBay or something similar and install it. In my case, the plug was prepared for 3-phase, but the cable from the box to the plug was still only 1-phase.

If the wallbox has a Type 2 socket instead of a cable, the procedure is effectively the same. The locking of the cable remains unchanged. The socket should then already be prepared for operation on three-phase current. Otherwise, you can replace it with a damaged Type 2 cable and remove the control cable for the plug lock in the socket from the circuit board without replacing it.

However, it is then advisable to ensure that the missing socket does not leave a hole through which water can get inside the box.

I paid about 40 € for the new three-phase contactor and around 50 € for the used type 2 cable. Plus a few luster terminals, cable lugs and additional cable wires. The wallbox has now been successfully converted from 3.7 kW to 11 kW.

It goes without saying that after such a conversion you also have to redesign the supply line to the wallbox in the garage and the fuses.

Conversion from 11 kW to 22 kW

So far we haven't had to touch the wallbox's control electronics or understand significantly how the communication between the vehicle and the wallbox works. This article gives a rough overview: Type 2 in detail - How does it actually work? I go into more detail about the Type 2 (and Type 1) protocol in the smart EMOTION Wiki: Type 2 and Type 1 in detail - signals, pin assignment and everything else

In general, the wallbox allows the car a certain amount of current and this then results in the power with which the car charges. The following formula applies:

[230 V] • [number of phases] • [current in amps] = [power in watts]

To get from watts (W) to kilowatts (kW), you have to divide by 1,000. For example, 3,700 W corresponds to 3.7 kW. As stated above, the car takes as many phases as it can take. This is not discussed in the protocol.

However, what is discussed is the current and the fact that the wallbox allows the car more, it needs to be convinced of this in some way. This varies from wallbox to wallbox. Some don't allow it at all. In the case of my wallbox, there is a jumper on the control board that allows me to switch from 16 A to 30 A. So it actually can't deliver the full 22 kW, but only just under 21 kW. Unless I want to start tinkering with infinite complexity, in my case it is now 21 kW. All I have to do is change the jumper. Here in the photo it is set to 30 A.

Changing this didn't cost me any money directly. But I still had to make sure that all cables, the type 2 connector and the contactor were designed for this current. At 16 A, 2.5 mm² per conductor is advisable, at 32 A you should use at least 4 mm² per conductor.

You should also make sure that the Type 2 plug is designed for the current. Otherwise the car will only charge with the maximum of what the Type 2 plug can do. The car automatically recognizes how much it can do.

When it comes to the contactor, you should make sure that it is designed for 20 A if you want to charge with 11 kW (16 A) and for 40 A if you want to charge with 32 A (22 kW). The reason for this is that we are talking about continuous current here. It is advisable to design electrical components in a way that they operate at 80% of their maximum power during normal operation.


Converting from 3.7 kW to 11 kW is relatively easy. However, it should only be carried out by someone who is aware of the dangers of 230 V and 400 V. Such a conversion is possible with almost every wallbox, the only physical limitation here is how much space the housing offers.

Upgrading from 11 kW to 22 kW depends on what the wallbox manufacturer allows. Since many manufacturers offer their boxes in different versions, it is quite possible that a switch to 22 kW is planned. But you can also have bad luck here. When converting, you should also make sure to correctly design cables and components.

In general, I would recommend to everyone not buying a 1-phase wallbox when purchasing a wallbox. Even if you can only connect it in 1-phase or the car can only charge in 1-phase. It's better to buy a 3-phase wallbox and then only connect it to 1-phase, instead of having to buy a new one at some point. The surcharge for 1-phase wallboxes over 3-phase wallboxes is negligible when purchasing new ones.

However, if you still have a 1-phase wallbox and know how to work with electricity, converting it to 3 phases is a nice project. If the wallbox also has the option of being converted from 11 kW to 22 kW, it may even be less stressful than having to sell the old box and buy a new one.

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