These power nodes would be used for field use, camping and emergency situations powering DC lighting and communication gear. For emergency preparedness every ham should have a power system they can use when the AC grid is down and many turn to a gasoline generator today. These gas generator are great, however some are very loud or heavy and the good ones can be expensive. Most of the ham gear today runs nicely on 12 volt DC but these generators are setup to make stable 120 v AC and not just DC, some can charge batteries though.
In a ham radio field day situation there is typically several complete radio stations setups, usually the stations are not operated at the same time, so if each station had a power node and were connected together the capacity of one node could be shared with another and each node would not have to be too large. From a standpoint of minimal complexity, each power node would have four 12 v DC power ports (outputs), two 300 v DC ports (input or output) and a solar/wind port (input). Each of the 12 v DC ports can be disconnected under the control of a micro-controller unit (MCU). By providing this control on the 12 v DC ports, a form of load shedding can be done where the loads can be prioritized and if capacity is getting low, loads can be switched off to prevent premature capacity loss. The two 300 v DC ports can be either a input or an output, giving the node the ability to send 300 v DC on one of the ports or receive 300 v DC on one of the two ports, but can not send and receive at the same time even on different ports (more on that later). Finally, the primary method of keeping the battery charged is via the solar/wind input. This port is basically the input to a Pulse Width Modulated (PWM) or Maximum Power Point Tracking MPPT controller. These controllers can take inputs as high a 30 v DC and adjust it for the proper charging of batteries. As long as this input is a few volts higher than the maximum float voltage of the battery array the controller will handle it. In practice there is a difference between a solar controller and a wind controller. Here is a basic block diagram of the proposed system:
This system has been mostly a thought experiment, however a computer simulation has been developed that has helped me explore it deeper that I thought. The current simulation is written in Basic-256 and supports a three node cluster like below:
The simulation abstracts a lot of what will need to be worked out in hardware like the node to node communications and how the power transfers will work. What I found in the three node system is that if one node is giving power to another node then no other transfers can occur in the cluster until that one is finished due to the current design. I have determined that the communication would be easy to implement if it is a master/slave configuration. In the figure above, all the "A" ports are connected to "B" ports. So an "A" port is a master and a "B" port a slave. In the power node detail drawing there is a Power Line Modem (PLM) shown connected to the cross-bar switch. The PLM can communicate over the same 300 v DC line when it is on or off by superimposing a high frequency signal on the line. With a single PLM in the design, it will need to "listen" on port "B" much more than it transmits (masters) on port "A". The cross-bar switch will be responsible for configuring the "A" and "B" ports for either receiving or sending 300 v DC or listening or transmitting with the PLM. Another consideration is if a node "dies" then the cross-bar switch fails in a "bridge mode" where port A and B are bridged so that the cluster is still workable.
I am still testing the simulation under various condition to confirm it is valid for a three node system. When I complete the testing I will post the code.
Next steps are to build up a real charge controller and use it with a battery and instrumentation like Voltage and Current Sensor and a variable load to explore the effects of loading a battery while charging it, etc.
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