Wiring Your EV Conversion: Centralized vs. Decentralized Architectures (The Route Phase of SPARK)

You’ve come a long way. You’ve picked your donor vehicle, worked through energy calculations, chosen your motor and batteries, and figured out your charging setup. Now what do you do with all these components? They don’t work on their own, they have to somehow work in unison to make the vehicle move the way you expect it, or designed it, to. It’s now time to Route energy and information through them, and we do this with our Integration Map.

The Integration Map will aid us in understanding how energy flows, and how information flows. Energy flow is relatively straightforward, it flows from the battery to the components that consume electricity, or from the motor back to the battery (regenerative braking). Information, though, is a different story. In this particular context, information is anything that the contorl modules might need in order to act: for example, the BMS requires temperature, voltage and current readings to determine the State of Charge. The motor controller needs to know the accelerator pedal position to determine how much torque the motor needs to make. You get the point, we need to get these components talking.

Now, there are different methods by which components could talk, mainly Decentralized and Centralized architectures. One is simpler, the other one is more powerful.

Decentralized Architecture: Simpler is Sometimes Better

Let’s start with what’s simple. Imagine throwing a small gathering. You don’t need a strict schedule or an appointed host—everyone just mingles and interacts naturally. No agenda, no coordination, everyone doing their own thing, either on their own or in small groups. A decentralized architecture works similarly: individual components communicate directly with each other without a central coordinator. This direct communication makes decentralized setups perfect for simpler, beginner-friendly EV conversions.

High Voltage (HV) Power Flow in a Decentralized Setup

Here’s what this typically looks like:

• Battery Pack → Main HV Contactor → HV Fuse → Main HV Junction Box
• From the junction box, the power splits off neatly:
  • To your motor controller and motor (for propulsion)
  • To your DC/DC converter, stepping down High Voltage to Low Voltage for your vehicle’s 12V accessories
  • To your HVAC components—cabin heater and A/C compressor

In a decentralized system, every component manages itself, simplifying the wiring significantly.

Low Voltage (LV – 12V) Power Routing

This setup remains straightforward:

12V Battery & DC/DC Converter work in tandem to power the 12V systems. The easiest way to think of this interactions is like this: the 12V battery feeds all 12V systems in the vehicle, mostly the same systems the donor vehicle had, and the DC/DC converter makes sure the 12V battery is topped off, so to speak. So to illustrate: if you were to disconnect the DC/DC converter from the 12V battery, the 12V system would still run until the 12V battery runs out. 

• Fuse & Relay Box splits power to:
  • Dashboard displays
  • Electric power steering
  • Brake vacuum pump
  • HVAC blower fan
  • Standard vehicle accessories (lights, stereo, etc.)

Communication in Decentralized Architectures

Communication is also straightforward, typically analog. The accelerator pedal sends a basic 0-5V signal directly to the motor controller. The BMS communicates battery status directly to the charger and the dash display, eliminating complexity. Charging the HV battery might be activated through manual switches. 

Pros:

• Cost-effective and beginner-friendly
• Simpler wiring, making troubleshooting easier

Cons:

• Limited expansion and advanced features
• Less precise control and diagnostics

Centralized Architecture: The VCU – Your Conversion’s Brain

Now let’s talk about centralized systems. Going back to the previous analogy, imagine this time you host a more formal and elaborate event, like a panel of experts to discuss a complex topic with a huge audience. Every expert is eager to elaborate on their point of view, every attendee is eager to bombard the panel with questions. Without an articulate, experienced host, such an event would be a mess. The facilitator needs to conduct the orchestra, so to speak, allow an expert to talk, pose a question to the audience, guide who answers the questions, etcetera. 

In EV conversions, this facilitator is called the Vehicle Control Unit (VCU). A centralized architecture introduces a VCU to manage and coordinate every aspect of your conversion, greatly enhancing your control, functionality, and safety.

High Voltage (HV) Power Flow in a Centralized Setup

The physical power routing closely mirrors the decentralized model, but each HV component now communicates its status and needs to the VCU. The VCU acts like an orchestra conductor, directing the timing and intensity of energy flow:

• The battery sends energy through a VCU-controlled HV contactor and fuse.
• The VCU instructs the inverter/controller precisely how much power the motor receives.
• The charger, DC/DC converter, and HVAC components all report their status back to the VCU, creating a comprehensive energy management system.

Low Voltage (LV – 12V) Power Routing with a VCU

The VCU oversees even the LV power flow, monitoring battery health and managing power distribution:

• DC/DC converter and 12V battery status are constantly monitored.
• Accessories and systems are intelligently managed by the VCU to optimize efficiency and reliability.

Advanced Communication in Centralized Architectures

Communication here primarily runs on a CAN bus network, a digital protocol well-suited for automotive environments:

• Accelerator pedal input first goes to the VCU, allowing intelligent interpretation of driver intentions. This allows for variable pedal maps to change vehicle behavior (like sport mode), it allows for one-pedal driving, smoother torque control, among many other things.
• The motor controller and BMS continuously relay status and health data back to the VCU in order to better manage thermal loads, durability, or safety. The battery will only allow certain amount of power to be discharged at a certain temperature and State of Charge to avoid damaging the cells long term, for example.
• Dashboard displays present centralized, comprehensive diagnostic and operational data which facilitates decision-making by the driver, or even gives insight into what to change in the VCU to improve performance or behavior.

Pros:

• Superior flexibility, scalability, and advanced diagnostic capabilities: you can start with the most basic components and then scale up, add more components or improve your calibrations to achieve the ideal vehicle behavior.
• Ability to add features like traction control, sophisticated regenerative braking, and advanced thermal management to improve safety, control and overall driving experience.

Cons:

• Higher upfront complexity and costs: in-depth knowledge of the whole system, as well as the specific VCU controls is required to achieve decent results. This is an advanced architecture that requires knowledge, time, and effort, besides it’s economic investment up front.
• Requires more initial setup time. Think of a VCU architecture like an investment: you put effort and time upfront, but you reap the benefits in the long run through a more precise, safe and tailored driving experience.

Which One Should You Choose?

To help you visualize, here’s a quick guide:

Conversion Complexity	Recommended Architecture	Typical Scenario
Basic, Low-budget	Decentralized	Your first DIY EV conversion
Intermediate, Moderate complexity	Either option	Upgrading an existing build
Advanced, High performance	Centralized	Racing, performance-oriented EV conversions

If this is your first conversion, decentralized might be your friend. This is the easiest and cheapest way to start if budget and simplicity are top priority. It will work, plain and simple. Many vehicles have been converted to EV throughout the years with a decentralized architecture, and, just like everything with EV conversions, you need to decide if it works for you based on your vehicle’s purpose. Is it the weekend cruiser for a few miles? Is it your daily? You get the point.

On the other side, VCUs are what OEMs use for a reason: they are scalable and deeply customizable. You can do almost anything you want with a proper VCU; some VCUs allow for custom code to be run, so you know your system will do exactly what you’re envisioning. 

I would not recommend a centralized architecture to a beginner due to its complexity, though. The Torque Academy’s vision of an EV Conversion is a project that is enjoyed. If the challenge is too much, it gets overwhelming.

However, if you have experience with engine tuning, car modifications, motorsports, engineering or are just deeply technical and curious, this is the way to do it. You can start with a simple battery pack, BMS and motor, adjust for them, and later on swap to a bigger motor, or bigger batteries, and adjust your VCU to match these new components. 

Wiring Best Practices (No Matter the Architecture)

Wiring is an art just as much as it is a science. In the OEM world, wiring engineers are one of the most interesting characters you can find given the nature of their craft. Everything in a modern vehicle needs to be connected to many other things, and designing these harnesses, connectors, jumpers, etcetera, is not an easy feat. For this particular reason, we will not get into details about how to design wiring harnesses or generate detailed wiring diagrams; we would need to know the specific of your design in order to properly do so. However, we can touch some of the basic points that will hopefully give you a better understanding of what wiring entails for the purpose of an EV conversion.

Regardless of your chosen architecture, here are some key best practices:

• Clearly label every wire and harness. Your future self will thank you.
• Make critical components easily accessible—think fuses, contactors, and emergency disconnects.
• Always include a High Voltage Interlock Loop (HVIL) for safety. This ensures the system won’t energize until all HV connections are safely made.
• Document your wiring clearly and thoroughly. A clear diagram is invaluable for troubleshooting and future upgrades. Which pin of module 1 goes to which pin of module 2? Which wire of sensor A goes into which pin of module 4? All of these details need to be clearly labeled and documented for future reference!

Common Pitfalls (and How to Avoid Them)

• Poor grounding: Always ensure proper chassis grounds. Bad grounds cause strange, elusive issues. It’s better to get grounding right at the beginning. Clean terminals, ensure contact between metal is sufficient, confirm continuity to ground, etcetera.
• Mixing analog and digital signals improperly: Separate or shield wiring to avoid interference. Keep in mind that analog signals are low voltage low current signals, and any high voltage or high current wiring nearby could induce a current. Shielding is key: look for industry specifications and follow them. Someone has already gone through this and documented it, use those specifications!
• Undersizing wires or fuses: When in doubt, go one size bigger. You wouldn’t want a fuse, let alone a wire, melting during normal vehicle operation due to normal current. Research and use industry specifications.
• Inaccessible wiring or fuses: Make serviceability a design priority. Imagine you keep blowing a fuse and the only way to get to it is to remove the HV battery pack from the vehicle. Not our definition of serviceability. 

Bringing it All Together

Your choice between centralized and decentralized wiring architectures comes down to your project’s complexity, your comfort level with technology, and your future ambitions. The decentralized architecture is beginner-friendly, cost-effective, and simpler overall. Centralized architecture, with a VCU, offers more sophisticated management, flexibility, and advanced diagnostic capabilities.

Remember, neither choice is inherently superior—they simply fit different scenarios. Understanding your needs clearly is the most important step. We sound like broken records, but keep going back to your Engineering Decisions, make sure what you decide to use for your conversion matches your vehicles design intentions, budget, and interest. 

The SPARK methodology’s Route phase is about clarity and confidence. Whether you choose decentralized simplicity or centralized sophistication, make your decisions deliberate. Soon enough, you’ll be ready to move into the Kickoff phase, turning your carefully planned wiring into a live, working EV.

Feel ready to start wiring your conversion? Have any lingering questions or insights from your projects? Share them—we’d love to hear your stories and challenges, and we’re sure the community will too. Let’s keep the conversation going and our projects moving forward!