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We were asked to install a power management system and a central heating system into a Mercedes Unimog expedition vehicle.  The vehicle had been converted previously but we received it stripped out for its refit.  The one thing that was left was the old electrical system, this system was so unnecessarily complicated, the decision was made to start again.

The old system was made up of a board of 240v AC relays activated by 24v DC switches, this in itself was not the problem, the problem was every AC power feed in the van was switched, this was not necessary and made the chance of failure far higher due to the number of relays being used.  The other problem was the loom was not colour coded, so if a fault occurred while on the road it would be incredibly difficult to diagnose the issue.

The work began by removing all the old electrical system, simplifying, and building a new loom.  The specification is below.

  • 200 AH Victron 24v Smart Lithium battery
  • 3 KVA Victron Quattro
  • Victron Cerbo and GX touch control system.
  • Victron Cyrix split charge relay
  • Victron MPPT solar charge controller
  • Victron BMS
  • Victron battery protects
  • Blue Sea fuse boards
  • BEP pro installer equipment

The DC wiring loom needed to control the following functions.

  • A deck actuator system to allow a side deck to be lowered using a remote control.
  • A bed actuator to raise and lower a bed
  • A table actuator to raise and lower a table
  • A lighting circuit with numinous functions and locations
  • Wastewater pump
  • 2 x freshwater pumps
  • A lift pump into the filtration system
  • A grey water dump solenoid
  • A gas tank switch to operate the solenoid
  • A diesel water heater
  • A diesel air heater
  • Central heating diverter valves
  • A habitation heating pump
  • An engine heating pump
  • Tank levels for the fresh water, grey water, black water, and gas tank
Mock up switch panel

The AC wiring loom needed to control the following functions. Any AC switching needed to be carried out through a relay, so 24v switching circuit could be used.

  • Air purification system
  • Water heater immersion
  • Macerator toilet
  • Socket ring
  • Feed for induction cooking
  • UV tank lights

The complexity of the loom increased due to ignition interruption being required for the split charge and the side deck actuator.  As we were mixing lead and lithium batteries, it is necessary to force the Victron Cyrix relay to close when the engine is not running.  It would be inconvenient if the deck was accidently activated when the vehicle was in motion, lowering it into oncoming traffic, to stop this we made this system dead while the vehicle engine was running.  Permanent feeds were required for the control and memory system and the master switch circuit.

A bespoke wiring diagram was designed, and the loom included more than 36 different wire colours and sizes.

The AC system also included a Dometic Tec 30 diesel generator, with this assisting the Victron Quattro, there was a 5kw off-grid capability.

The central heating system was another challenge that required a technical drawing to be designed.  The system was run using an Eberspacher Hydronic heater installed in the engine bay.  Unlike a conventional LPG heating system, it will damage a diesel heater if you turn it on and off quickly and regularly, this means you cannot directly thermostatically control the heater.  We created 2 heating loops, a long loop and short loop, the valves connecting these loops could be switched using a thermostat to open and close the central heating radiator loop.  This meant the heater would be able to run its normal cycle in a shorter closed loop that included the header tank and the calorifier water heater.

This also allowed for additional functions.  The engine coolant was passed through a heat exchanger with the habitation heating loop on the other side.  This allowed the habitation area to be heated from the engine coolant while the vehicle engine was running.  It also allowed for the diesel water heater to be used to pre-heat the engine in cold climates. 

Configuring the system in this way allowed for safety redundancies to be put in place.  The vehicle already had a diesel air heater which was installed as a backup in case the diesel water heater failed.  Configuring the system in this way allowed for the habitation area to still be heated if the diesel air and water heater failed, the engine would need to be left running, but if you were in Siberia, this could come in handy.

The Unimog has now left us for fitting out, once this is complete it will be coming back for final commissioning.  I will add to this case study when that happens.

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