Sizing the electrical installation for our König KHC303630 Trailer

Once, someone told me the perfect vehicle for a mobile home would be a tri-fold:

1. a 20m truck when stationary;
2. a Unimog when off-road;
3. and a Porsche when on roads.

As it seems hard to get hands on such a vehicle we have tried different combinations over the years – with a few “failed” attempts such as our VW California T6 or the Hymer B-MC I WhiteLine.

So, recently we took a different tac and went for a trailer. A “König KHC303630” to be precise; which is a 2m high, 2m wide, 3.66m long sandwich cabin on a twin-axle trailer (with an overall length of under 5m). The idea was to have something more comfortable and spacious than our Hilux with the roof-top tent. If you want to get an impression of how this looks have a look at one of these videos.

Before we actually made the decision to purchase the trailer, we went to Trochtelfingen to see for ourselves. It was then when we decided to have the main battery system voltage different from the 12V standard.

Originally, I thought to have a 16s 48V system with Eve 3.2V 280Ah cells. However, the resulting weight would be over 80kg – without BMS, case or inverter. So, I thought about installing an 8s 24V system with a resulting nominal power of 7168W. And it seemed that such a system would still satisfy our requirements.

1. The mximum single load would be 2000W for a duration of up to 35min.
2. The sum of all 12V loads would not exceed 360W.
3. The total load would not exceed 2300W.

The Eve cells support 0.5C, meaning I could constantly draw up to 2800W (at 2.5V) and 4088W (at 3.65V) at 140A. However, as my largest DC MCB is only rated for 125A I could only use between 2500W and 2650W. But that would be still more than sufficient. And the Victron EasySolar-II GX 24/3000/70-32, the inverter which I had in mind for this installation, supports sustained loads only up to 2400W anyway.

So first determine, how many 24V connections do we need?

1. 8s 24V battery, via SmartShunt 500A (in/out)
2. inverter/charger (in/out, interally fused)
3. 24V/12V DC-DC converter (out, interally fused)
4. 12V/24V DC-DC converter charger (in)
5. 2* 24V USB-C sockets (out, interally fused)

With 125A as the maximum expected current the use of the Victron Lynx Distributor bus bar seemed a bit oversized. So, I decided to use a pair of (way cheaper) 6P 150A Victron Busbars.

For the 12V system, I expect to use a 12 port Plus/Minus distribution:

1. Refridgerator
2. Bed
3. 5* lights
4. 12V socket for shower
5. 4* 12V sockets

To convert the battery voltage to 12V, I opted for a Victron isolated Orion-Tr 24/12-30 converter. The whole 24V/12V converter will be able to be by-passed and directly connected to the 12V of the trailer, as well.

For minimum chargin on the road, I plan for a Victron Buck-Boost DC-DC Converter 50A. But as this would take more than 6 hours of driving to fully charge, the idea is to mainly charge via AC. However, the EasySolar can only charge with up to 70A. And in order to get closer to the maximum of 125A, I would add a Skylla-24/50 TG . Why I chose the Skylla-TG over the Skylla-I? I only need it for sporadic AC charging and the TG model is lighter and cheaper.

So, with the EasySolar and the Skylla the total amount of charge current adds up to 70A + 50A = 120A, which totals in a theoretic 3072W (just over 13A at 230V). So, any standard 16A cable would do to charge the battery.

A quick overview of the AC connections/RCDs in the trailer (all sockets will be Neutrik powerCON TRUE1 TOP NAC3FPX-TOP):

1. Inverter/charger (out)
2. Bath Immersion Heater
3. Kitchen Microwave
4. Kitchen Coffee Machine
5. Kitchen Kettle
6. Kitchen Stove/Oven
7. Kitchen Spare
8. Entrance AC-DC USB-C Charger
9. Entrance Spare
10. Back Left Spare1
11. Back Left Spare2
12. Back Right Spare1
13. Back Right Spare2

For external AC input, I plan for a Neutrik powerCON TRUE1 TOP NAC3PX-TOP input with a pass-through and a separate 16A RCD.

Anything that I forgot? We will find out, once the trailer is delivered and we begin with the installation.