There are other options to consider for the complete off-grid system because this could eventually be extended to cover position A lighting and desktop computing, in which case a 48V battery with local 48V to 12V converters may be appropriate. This could then use a rack-mount 5kWh 48V battery, which could be cost effective.

Off-grid 12V system

Currently several systems at Oak House run off 12V:

• Lighting centred on 3 positions
• Server rackmount
• Desktop computer

Historically lighting has been run off 12V leisure batteries, but these now have very reduced capacity and have been replaced by mains ATX power supplies. In one case the original batteries serve as a backup. It was decided not to replace the leisure batteries. This means that the house's base load is higher than it needs to be.

Since the situation was last reviewed prices for LifePO4 batteries and PV panels have dropped substantially, meaning that it could be practical to build a small off-grid system to run these systems. Since we have cheap overnight electricity this could be used in winter to charge batteries. A further advantage of running computers from a battery based system is that the need for a UPS is avoided.

A staged project is being considered:

• Stage 1 - power server cabinet from battery and charger
• Stage 2 - Solar system to charge server battery
• Stage 3 - Expand/replicate for desktop computer OR move desktop to server cabinet
• Stage 4 - Expand to position A lighting

Options for server and desktop

This has been considered further, but since first considered upgrading the server to ubuntu 22.04 and subsequently to 24.04 has proved problematic(mongodb eol). As the desktop is on at least 12 hours a day consolidating the server into either the desktop or desktop + pi should be considered. The rationale for this is that the desktop uses about 30W when idle, the screen uses an additional 23W. The server probably uses about 15W so the total daily use can be compared in the following table.

From a power consumption point of view these options are broadly similar, but the desktop only option would be simpler to power from a single battery, and as it is in the study routing a cable from a solar panel would be simpler.

It might be possible to use a Pi at night if only basic home automation functions were needed. This would then reduce power requirement. The pi would:

• Run mosquitto mqqt hub
• Run tvheadend
• Run some low level nodejs services.
• Run an intermediate lightweight database, which uploads daily to mongodb.

Stage 1 - battery power supply

This will consist of at least one 100Ah LifePO4 battery and charger. The charger will be controlled by a Raspberry PI.

Components:

State of Charge (SOC) from Voltage

Unfortunately the EcoWorthy battery doesn't include a monitoring system, so this needs to be determined from voltage across the terminals when not charging or under load. The following table gives a conversion from voltage to soc.

Server Cabinet Battery Loads

This needs revision as the PicoPSU is no longer in use as is the server it drives, it has been replaced by a RPi 5 with 0.5Tb disk the likely battery use is for the desktop.

Should have simple meters for:

• Total 12V load on battery and battery voltage
• Server supply voltage and current

Battery charging with Victron Charger

Server - 12V DC Stable power supply

Need to analyse use of ethernet ports and group into:

• Core high speed ports between hub positions - desktop, server, main router
• Home automation - low speed (10 or 100mbps) connections
• Entertainment - Main TV, etc.
• Cabinet hosted ethernet - Raspberry PIs, etc.

This should result in a low speed majority spread across several hubs. These to be distributed between 12V and 5V stable supplies.

Server - 5V DC Stable power supply

PI4 measured idle at 0.41A @5.2V = 2.6W, starting code rises to 0.67A @ 5.18 = 3.4W, drops to 0.20A when shutdown.

PI3B is known to use less at idle, contention is that it will mainly be idle.

Server - 230V AC supplied

Questions

• What is 12V bus for battery, all things 12V to connect to?
• What is 12V DC supply from battery?

Installation

• Flash Raspberry Pi with Venus OS
• Install 5V USB Supply with temporary feed from amplifier 12V
• Install Raspberry Pi
• Temporarily mount charger and battery to test
• Make case for battery
• Charge battery
• Connect 12V regulated loads to 12V regulator
• Disconnect mains PSUs from server
• Connect PicoPSU and amplifiers directly to battery
• Test

Stage 3 - Desktop to server rack

INSTEAD ELIMINITATE SERVER RACK AND MOVE SERVER FUNCTIONS TO PI(s) AND DESKTOP

Desktop to be powered by 12V DC supply fed from battery

Have now ordered HDPlex

ATX Adapter

Experimented with plugging 12V into the jack of this device, which appears to drive +12V and USB QC Circuits and puts an incorrect (low) voltage on some others

Connecting charger via UART

This article describes how to interface using UART to victron charger, so no need to use bluetooth. Several versions were encountered, including the latest which has 5 header pins towards the output end of the board. Our charger has serial number HQ2405UU674, which is greater than the critical number HQ2024nnnnn . See also here github

This requires a USB to UART convertor FT232R