DiVER: efficient low voltage grid

DiVER / EiS:
Direct Current low Voltage Electric Grid for Renewable energies / Electrical InfraStructure

  • Any voltage over about 60VDC is not safe to the touch
  • Any voltage over 60VDC needs a special license to operate in Germany, e.g. you may not build and connect a grid over 60V, unless a proper Electrician checks everything (VDE)
  • Small permanent magnet alternators used in a generator at a wind turbine or a water turbine usually operate at below 100V
  • It is very expensive to generate a true sine wave alternating current out of low voltage DC from the renewable energies
  • Solar panels output low voltage DC
  • TEG (thermo electric generators) output low voltage DC

Only a few systems really do need the high voltage AC of 230V or 110V.

  • Desktop Computers (although terribly inefficient compared to laptops and smartphones) do need 12 VDC, 5 VDC and 3,3 VDC.
  • Laptops need about 12-20 VDC
  • TFT Flatscreens run on DC, especially if they have an LED backlight.
  • Mobile phones, smartphones, tablet PCs etc are all charged and run with 5VDC

Difficulties and negative points about a low voltage DC grid:

  • Grid size is smaller with a lower voltage or:
  • available Power is lower at the same AWG / cable dimensions
  • special connectors have to be chosen

I am thinking of a 230 VAC + DiVER infrastructure for OSEG/FeFG: 230VAC for high power appliances like some machines, DiVER for any consumer electronics (wherever possible) and efficient lighting.

Household circuit breakers may be re-used for a DiVER grid, e.g. anything from 8-63A per phase.

System voltage:

N: 0V, GND
l1: 12VDC, 10-15VDC (one lead acid battery)
l2: 36VDC, 24-48VDC (three lead acid batteries)

A cheap NYM-J 3x2.5mm² cabling may be used for low power branches of the grid.

Nominal voltage could be 3x12V = 36V, which equals three lead acid batteries connected in series. If fully charged, grid voltage at the source would be 3*14V = 42V, at empty batteries about 32V.

The grid voltage (only the voltage!) may be compatible with PoE, Power over Ethernet 802.3af (802.3at Type 1) and 802.3at Type 2, if the grid voltage is above 40 V.

At 36V and 63A, there are 2268W available in the grid, if we assume proper cables and connectors. It depends on the application, but I would have switched over to 230 VAC already at this power rating.

One could make the 12V phase on/off grid redundant with one efficient ATX power supply+two Schottky diodes.

+1 totally makes sense.

I already thought about the same concept but not so detailed.

Another Con:

  • We need a special transformer for connecting consumer HW like a laptop directly to the DIVER grid because any consumer device comes bundeled with a power cable + transformer made for 110V/230V and a Schuko / US power connector and transforming from low DC to 230AC back to low DC really would be a special type of stupidity :smiley:

Some consumer electronics are equipped with standard co-axial or USB connectors, which could easily be used. As in almost any other case, the proprietary ones are the worst case: Apple uses a proprietary protocol for their MagSafe chargers and they won’t start charging if one would just apply the voltage. iPhones, iPads, iPods, … are USB compatible though. And there are third-party MagSafe chargers for 12V :slight_smile:


Star topology with multiple energy sources: a BMS (battery monitoring system) will help here, it will also be possible to charge battery banks and match their voltage automatically:


Battery → fuse → ZVD (Zero Volt Diode) → cable → appliances ← cable ← ZVD (Zero Voltage Diode) ← fuse ← Battery

and with automatic equalizing + anypoint™ charging :smiley: :

Battery → fuse → ZVD (Zero Volt Diode) || anti parallel (ZVD with offset or Schottky diode) + charging circuit, current limiter → cable → appliances ← cable ← any power source in the nominal voltage range.

In addition to the hardwired fuses, I would implement a controller who monitors and logs the currents and voltages which has a built in over current protection and gives general feedback, how much energy is available and used. Hint: Energy monitoring with DC is a lot easier than AC. Plus we would not need any galvanic isolation.

If the 230V cable is hardwired and the device has an internal transformer, I would modify the device for low voltage use.

FYI Chrono von Apollo NG arbeitet im Rahmen seiner PDU an genau so etwas. Und da ist Monitoring etc schon fertig. Er ist sehr weit wenn ich ihn richtig versanden habe.

Sein System wäre sogar in der Lage auf Basis von Metriken weniger wichtige Systeme bei Engpässen zeitweise abzuschalten etc.

Echt cooles Zeug. Sollten wir mit ihm abstimmen.


Ja die PDU kenne ich, gefällt mir auch super gut und so etwas werden wir auch verwenden: So einen PDU node braucht man an einem Zweig vor den Verbrauchern, falls diese über 12/5/3.3V versorgt werden. In einem Auto klappt das die PDU zentral einzusetzen, aber bei einem DIVER grid nicht möglich: Vdrop von Kabeln ist nicht konstant und auch recht hoch je nach Last. Ein DIVER.Wilssen wandelt keine Spannungen an der Quelle (also auch keine Verluste, und das grid funktioniert auch ohne Wilssen), die Spezifikationen vom DIVER grid erlauben eine voltage range anstatt eine fixe Spannung am Eingang. Nur so kommen wir um die Wandlung herum. Ein feedback loop vom node zur source bringt hier auch nichts, denn wir wollen ja ein grid mit mehreren branches, also ring mit stern.

Which voltage should be used for the grid?

12V (10-14V): high losses, high currents, large connectors needed, but well suited for any small appliances.

24V (21-28V): easy to achieve with two lead acid batteries, industrial standard, solar panels, motors are often 24V.

36V (32-42V): three lead-acid batteries. about 30% less infrastructure losses in the cables, less current, longer cable distances vs 24V, I don’t know any commercial 36V sources and appliances.

48V (42-56V): four lead-acid batteries. about 50% less infrastructure losses in the cables, less current, longer cable distances vs 24V, there are industrial inverters and off-grid systems which run on 48V. One draw-back is the maximum voltage of about 56V when the batteries are fully charged: Most components are rated for 50V max, like small DC/DC power supplies and electrolytic capacitors on SMPS PCBs.

I would go for a two phase system with 12V (mandatory) and 24V.