Custom Electric Racing Go-Kart Build (Bons V1) - Wiring & Safety Review (72V / 340A)

[BonsDNB]

Hello everyone!

I’m moving into the final assembly and wiring phase of my custom electric racing go-kart build ("Bons V1") and I’ve put together a detailed wiring schematic. Before I start crimping and final assembly, I’d like to run my plan by the community to ensure everything is safe and optimized.

Core Specs:

• Motor: QS180 90H 8kW Encoder Mid-Drive
• Controller: Fardriver ND721800B
• Battery: 72V Custom pack (Molicel P50B)
• BMS: ANT Smart BMS (340A Continuous / 850A Peak)
• Protection/Control: 400A MEGA Fuse, Main Contactor (with 100Ω 25W pre-charge resistor), E-Stop (NC), LANBOO Key Switch, 5A Inline fuse for the logic loop.
• Telemetry: DKD LCD Display, TF03K Coulomb Counter (with shunt).

My Wiring Schematic:

Segment 1: High Voltage Path (Main Power)Battery (+) -> 400A MEGA Fuse -> Main Contactor (with pre-charge resistor) -> Fardriver (B+)Battery (-) -> TF03K Shunt (B-) -> Shunt (P-) -> Fardriver (B-)

Segment 2: Ignition & Control Loop (72V Logic)Tap from MEGA Fuse output -> 5A Inline Fuse -> E-Stop (NC) -> LANBOO Key Switch (NO) -> Distribution point:

1. Contactor Coil (+)
2. Fardriver Ignition (E-lock) pin
3. DC-DC Converter (72V->12V)
4. DKD Display (72V in)

Segment 3: 12V NetworkDC-DC 12V output -> 10-Way Blade Fuse Box (with warning indicator). From here, I am distributing power to lights, TPMS, USB, etc., with all 12V grounds returning to the DC-DC 12V GND. (Isolation maintained: no 12V grounds touch the main battery ground).

Segment 4: SensorsSiaecosys ATV Hall Throttle and 0-5V Brake Pressure Sensor wired directly to Fardriver signal pins.

The Goals & Questions:

1. Current Limiting: I've decided to set the Fardriver Max Line Curr to 340A (matching the BMS continuous rating). I'm leaving the BMS 850A peak as safety headroom for transients. Does this align with best practices for the ANT BMS?
2. Grounding/Shunt: Is my approach of running all negatives through the TF03K shunt P- side correct, or should logic grounds return directly to the battery/Fardriver to avoid potential interference?
3. Contactor Control: Is it safe to trigger the Main Contactor coil directly from the ignition switch split, or should I use the ignition to trigger a smaller auxiliary relay for the contactor coil to take the load off the key switch?
4. Any Red Flags? I’ve carefully separated the thick HV cables (rear zone) from the signal/logic harness (front zone) to avoid EMI. Given the high phase currents (planning 700-850A phase), are there any specific precautions I should take to protect the encoder sensor signal?

I’m really aiming for "track-ready" reliability here. Any tips, critiques, or "I wish I knew that before I built mine" advice would be incredibly helpful!

Thanks in advance,
Bons

 

[ohv_]

Have you made any progress on this build?

 

[BonsDNB]

Hi @ohv_

Thanks for checking in! The planning phase is officially done, and right now I'm just playing the waiting game with international shipping. All the major components (including the custom P50B battery pack and the heavy-duty wiring) are scheduled to arrive in about two weeks.

As soon as everything is on my workbench, I’ll be diving straight into the final assembly and wiring. I'll make sure to post a proper update with some photos here once the real work begins.

 

[ohv_]

I'm building off a ev van battery at 60v

Today I was looking at the key and Contactor Solenoid. My key is rated for 32v so it should be okay.

 

[dominik h]

You can set your max battery current higher, the QS180 can take more and the BMS can take more for acceleration.
It will be safe to draw 400-500A for up to 10seconds. Enough to get from a standstill to top speed.
You only needs to reduce your top speed power recommendation to a BMS safe level when you have a track with a very long straight part.
You can set and reduce currents in the ratios of speed table at and over max speed.

I would not directly trigger the big contactor coil from the key switch, the inductance from the bigger coil will kill smaller switches fast.

About grounding, I'm not shure what you mean. I would take the logic ground after the current measurement device.

 

[ohv_]

If your running a diode and resistor on the contactor coil, should help with that no?