Lead-acid batteries are the anchor dragging your golf cart down. Replacing 400lbs of lead with 90lbs of lithium transforms performance, but it requires handling massive inrush currents. In this traction engineering guide, we detail how to bypass the Club Car OBC, size a 300A BMS for hill climbing, and secure prismatic cells against the G-forces of the fairway.
Unleashing the Vehicle Hidden Under the Lead
For decades, the golf cart industry has been shackled to the limitations of flooded lead-acid batteries. A standard 48V Club Car or EZ-GO carries six 8V lead-acid batteries under the seat. These batteries weigh approximately 65 lbs (30 kg) each. That is a total of 390 lbs (175 kg) of dead weight. That is equivalent to carrying two extra adult passengers every time you drive.
Converting to Lithium Iron Phosphate (LiFePO4) is not just a range upgrade; it is a total vehicle transformation. A comparable 48V 100Ah lithium pack weighs roughly 90 lbs. By shedding 300 lbs, you drastically improve acceleration, braking distance, and top speed. However, golf carts are "Traction" applications. They punish batteries with current spikes that would melt a standard solar battery. This guide explores the unique engineering challenges of building a lithium pack that can survive the golf course.
1. The Traction Current Challenge
A solar battery lives a gentle life, discharging at a steady 20-50 Amps. A golf cart is violent.
When you stomp the accelerator from a dead stop, the DC series-wound motor acts as a short circuit until it builds back-EMF.
The Data:
- Cruising Current: 50A - 70A (on flat ground).
- Hill Climb Current: 150A - 200A.
- Locked Rotor / Start Current: 300A - 400A (for 2 seconds).
The BMS Implication:
If you use a standard 100A BMS designed for solar storage, it will trigger "Over-Current Protection" the moment you try to climb a curb. The cart will shut down violently, throwing you against the steering wheel.
Requirement: You need a specialized Traction BMS or a very high-current standard BMS (e.g., JK BMS 200A/350A Peak or Daly 250A). You must also ensure the BMS has a programmable "Surge" delay to allow for that 2-second startup spike.
2. The OBC (On-Board Computer) Bypass
This is the most common stumbling block for Club Car owners (Pre-2014 models).
These carts have a black box called the OBC wired into the negative battery cable. The OBC communicates with the factory charger to tell it when the lead-acid batteries are full.
The Conflict: When you switch to lithium, you use a new lithium-specific charger. The OBC doesn't recognize this charger. In retaliation, the OBC will lock out the controller, preventing the cart from driving.
The Fix: You must bypass the OBC.
1. Trace the black 6-gauge wire from the charge receptacle. It goes through the OBC hole.
2. Cut this wire and connect it directly to the Battery Main Negative (B-).
3. Locate the small "Sense" wire (usually Grey) on the OBC harness and splice it to the fuse assembly to trick the controller into thinking the charger is disconnected. (Consult your specific wiring diagram for the exact pinout).
3. Voltage: 36V vs 48V vs 72V
If you are upgrading, should you stick to the stock voltage?
36V Systems (Older Carts): Obsolete. High amperage means hot cables. Upgrade the controller and solenoid to 48V. The efficiency gain is worth the cost.
48V Systems (Standard): The sweet spot. 16S LiFePO4 (51.2V Nominal). Easy to source components.
72V Systems (Performance): If you want to do wheelies or go 40mph, go 72V (22S or 24S). However, this requires a complete drivetrain swap (Motor, Controller, Solenoid). Do not put 72V into a stock 48V motor; it will arc internally and destroy the commutator.
4. Mechanical Restraint: The G-Force Problem
A solar battery sits on a shelf. A golf cart battery hits bumps at 20mph.
Prismatic Cells: Prismatic cells are heavy blocks. If they are loose inside the battery tray, the G-force of a bump will slide them into each other. This movement puts stress on the rigid busbars. Eventually, the aluminum terminal studs will shear off or the busbars will crack.
The Solution: You must build a Compression Box.
Use High-Density Polyethylene (HDPE) sheets or marine plywood to build a box that fits the cells perfectly. Use EVA foam padding between the cells and the box walls to absorb shock. Strap the entire box down to the cart's frame using metal brackets, not just bungee cords. (See our guide on Compression Fixtures for design tips).
5. Charging and Maintenance
You cannot use the old "Heavy" charger. It uses a charging profile that boils lead acid at 60V.
The Charger: Buy a dedicated 15A - 20A LiFePO4 waterproof onboard charger. Mount it permanently under the seat.
The State of Charge Meter: The old analog needle gauge or the "bar graph" voltage meter on the dash will not work. They are calibrated for the steep voltage drop of lead-acid. LiFePO4 voltage is flat. You will read "Full" until the cart dies.
Upgrade: Install a proper Coulomb Counter (Shunt-based meter) on the dash. This measures Amp-hours consumed and gives you a true "Fuel Gauge" percentage.
Summary
Converting a golf cart is a master-class project. It requires high-current electrical skills, mechanical fabrication for the battery box, and digital logic for the OBC bypass. But the result is a machine that feels 300lbs lighter, climbs hills without slowing down, and never needs water added to the batteries again. Just respect the amps; a 400A short circuit on a golf cart can weld the chassis to the ground.
