Switched Power Distribution & Protection System

Hello and welcome to post # 17 on building a custom car computer. This post is long overdue so I'll get straight into it:

Due to the large amount of 12V DC accessories and devices of all different shapes and current ratings I have installed in my vehicle, there was a large amount of messy wiring taking up the space where many of the power supply and various signal wires run through the firewall (the only two openings on that side were jammed full of wires!) I decided to design and build a safer, more reliable and easier to fix system.

Messy wiring from the computer & various  power circuits.

My solution is the Switched Power Distribution & Protection System, or SPDS for short. It is divided into two modules stacked on top of each other and Its purpose and function is threefold:

1) Provide a high current link directly back to the auxiliary battery for running devices intended for use from that battery. This was done by using industrial grade 1 gauge wire ran directly back to the 100A breaker in my engine bay, which is in turn connected to the battery via a similar cable. The SPDS end runs into a gold plated terminal block (housed in the  distribution & protection module) where it splits into different sized wires to power various areas of the vehicle.

1 Gauge battery cable running into the distribution block.

There is also an additional two wires run out of the PD&PM from the terminal blocks and into two high current fuses. these power the four channel and sub-woofer amplifiers.

2) Provide a high-current and reliable platform for improving switching options on the PC. Two issues arose with the original design, which turned the PC on when the key was set to the accessory position in the ignition barrel, and turned it off after a one minute delay when the key was removed. 

The first was that it posed a security risk in situations where I wanted to leave the computer on but wanted to lock the car, and was forced to leave the car unlocked as the key had to be in the ignition (EG when I use it for music while working on the car and go inside for a break). 

The second was that in situations when I was driving and didn't want the computer to keep automatically turning on (the hard power button kills the computer when held for 3 seconds but it turns on again as its PSU is configured to keep sending an on pulse (the equivalent of someone pressing the power button again) if the key is in the accessory position. The latter function is achieved by simply adding a switch between the accessory wire and PC.

To do this I used three relay switches. The relay labelled illumination is switched by a wire from the park lights. It acts as an isolator between the main and auxiliary batteries so that various devices can be switched on by turning on the park lights without draining the main battery. This is irrelevant for PC functionality however it was installed to run the auxiliary running lights built into my Hella Luminator LED driving lights as it was more convenient to wire them to a relay, switch and then the auxiliary battery then run a power wire across the dash and to a high current park wire and switch.

Relay module

The relay labelled screen (far right) is turned on by a switch in the centre console labelled "Screen Power". it is powered constantly from the distribution module, which turns on when the key is moved to the accessory position. This acts as an isolator between the main and auxiliary batteries so that the turn on signal to the PC (this is a +12V signal which signals the PC to turn on, similar to the remote turn on wires found on automotive amplifiers) can be activated at any time simply by flicking the rocker switch, regardless of key position. If the key is on than this will have no immediate effect.

The relay labelled power is turned on by a wire that is connected to the cigarette lighter socket. It switches on a high current connection from the distribution module to power various devices around the vehicle that only need to be running when the key is in the accessory position, eg extra cigarette lighter plugs.

finally,

3)Put devices and systems on different circuits and protect them with automatic circuit breakers.

These are switches that protect  the wiring by automatically opening when a certain amount of sustained current passes through them, eg if a short circuit occurs. These are vital for redundancy as they do not require changing of single use fuses and can be reset on a whim. The configuration of the circuits and their rating is as follows (from the top down):

Distribution & Protection module

1)

Rating: 30A

Area Powered: Overhead Console

Connected Devices:

• Car Computer
• Roof Console Lights

Additional Affected Devices & Systems on Failure:

• Amplifiers will not turn on (Remote turn on signal runs from this circuit).
• 7 Port USB Hub
• PC Screen

2)

Rating: 30A

Area Powered: Rear Barn Door

Connected Devices:

• Rear panel fuse block

Additional Affected Devices & Systems on Failure:

Reverse/rear lights

Rear cigarette lighter socket (Beware if fridge is connected)

Rear USB Charging sockets X2

Rear table strip lighting

3)

Rating: 15A

Area Powered: Centre Console

Connected Devices:

• CB Radio
• Centre console USB hub Boost power
• Centre console floor light

4)

Rating: 15A

Area Powered: Unsure

Connected Devices: Unsure

To construct the modules I bought two small project boxes that can be disassembled by hand by pulling off the end plates. I drilled holes in the corners of one side of each box, then fitted metal standoffs and screws to hold them together. As an added bonus the spacing keeps the modules held securely in place in the electronics bay without the need for fasteners.

Fastening the two halves together
I mounted the components in the boxes with stainless steel screws, spring washers & nuts then crimped the wiring together.

Adding components

Connecting components with suitably rated wire

. The system took a whole day's work to build but will be worth it for the safe and reliable operation of equipment and systems on my vehicle. Keep an eye out for my next post and as always, thanks for reading.