Long time no post. Been busy with several things. Summer is coming, had to do a bit of whipper snipping around the property. Took several days to clear all the knee high grass and weeds in the main areas. Computer work and kiting reduces time for the van. Nevertheless I have been working on the Network Of Things as it is called in modern terminology. At this stage it is important to define where things go to make sure all the required connections are in. Despite the bus system there are still a fair few connections to be made to all the loads and all connections are fused.
There are a few design rules for the network. One major aspect is to minimise power use. With around 35 components even idle current can be 3 – 5 Amps, which can add up to 1.5 kW per day worst case. This is the capacity of a 120 Ah battery discharged to 100%. I use standard components which are not really optimised for the application resulting in higher power consumption than purpose built hardware. Despite having enough battery capacity it is not really clever to burn so much energy just to keep the network idling.
The concept is to create groups of components by time of use and duration of use and only supply power to the components when required. This requires additional switching relays but they will be only engaged when loads are in use. I could use latching relays for all supply lines, but this would require that I build all components myself because the standard ones I use are built with standard mono stable relays, however the main 12V supply lines are switched with latching relays. The larger contacts would require more current to engage while the latching relays only require current when switching. I have 8 groups of supply lines which are controlled by latching relays. These are the relays pictured above. Two coil 12V 100A relays order from Czech Republic. Took 5 days to get here. Could not find anything like this here, at least not on easy to find websites. Maybe some commercial distributors, but experience is that their prices are just totally over the top. With this concept only those sections of the network are powered on when needed. This also requires a bit on the software side. Each component needs a status freeze before shutdown and a restart to previous status. Also important is that relays connected to micro controllers are not engaging unless intended. This requires a two stage init routine. All relays are 12V so is the supply to the Arduinos, but stabelised to 7V to reduce heat build up in the Arduino boards. Digital outputs of the Arduinos are undefined until initialised. I use two separate power supply lines, one for the processor and shields and one for the relay boards. I also use relay boards as power booster to loads requiring higher currents (30A), for example lights, motors etc. The relays on the general supply boards are lower current with maximum 10A per contact.
With two supply lines I can run the whole network for diagnostics without actual loads. Circuits are only powered when required, for example tank senders or ball valve controllers only need power when required and only need it for a short time. The central system determines the policy for use of each component.
Using the concept I can minimise power use for the network. Will take me a while until this is all connected but this is the only way for me within a reasonable period of time without creating all custom hardware and the off the shell system I have seen from Lippert is very expensive and far below the functionality I require for my van.