The voltage question is one of the first decisions you'll make, and it shapes everything that comes after: which motor you can run, how fast your battery drains, what top speed is physically achievable, and how much the whole system costs.
This guide explains exactly what voltage does in an electric drivetrain, where 48V makes sense, where 72V is the right call, and how to make the decision for your specific build.
Voltage is electrical pressure. It's the force that pushes current through your motor. Power — the thing that actually determines performance — is the product of voltage and current:
Power (Watts) = Voltage (V) × Current (A)
This equation has a profound practical consequence. If you want to produce 3000W of power, you have two routes:
Same power output. Very different current requirements. And current is the expensive variable — in terms of heat, wire size, connector ratings, battery discharge requirements, and controller cost. A 72V system producing the same power as a 48V system does it with roughly 33% less current.
That single fact explains most of the practical differences between the two voltage standards.
48V is not the inferior option — it's the right option for a specific range of applications. Understanding where it works well prevents you from over-building for your actual needs.
For builds in the 500W–2000W range, 48V is entirely adequate. The current levels involved — 10A to 42A — are manageable with standard components. Wiring, connectors, and controllers at this current range are widely available, well-understood, and comparatively affordable.
A 48V 1500W motor for a lightweight electric bicycle, a small go-kart for younger riders, or a low-speed utility vehicle is a sensible choice that doesn't require the cost and complexity of a 72V system.
48V components are generally less expensive than their 72V equivalents. The battery in particular — the most expensive single component in most builds — costs meaningfully less at 48V capacity than at equivalent 72V capacity. If budget is the primary constraint and your performance requirements are modest, 48V reduces the total system cost.
48V systems typically produce lower top speeds than 72V systems with comparable motors. For builds intended for younger riders or beginners who need a performance ceiling that doesn't exceed their skill level, 48V is a practical safety consideration. A 48V 1000W motor on a Razor-style build has real performance — but not the kind that requires extensive experience to manage safely.
A 48V battery with equivalent energy capacity weighs less than a 72V battery delivering the same runtime. If the build is weight-sensitive — a lightweight dirt bike where every kilogram affects handling — and the performance requirements can be met at 48V, the weight saving is a genuine advantage.
72V is the standard for serious e-moto and high-performance go-kart builds. Here's why.
Motor top speed is fundamentally constrained by back-EMF — the voltage the spinning motor generates that opposes the battery voltage. When back-EMF equals battery voltage, the motor reaches its speed limit.
A higher battery voltage means a higher back-EMF ceiling, which means the motor can spin faster before it limits out.
The same motor running on 72V will achieve a meaningfully higher top speed than on 48V — not because the motor changed, but because the electrical headroom increased. For the KR5V V2, the difference between 48V and 72V operation is significant: the motor is spec'd and optimized for 72V, and running it below that voltage leaves performance on the table.
Returning to the power equation: to produce 5000W on a 48V system, you need over 100A of continuous current. At 72V, the same 5000W requires approximately 70A. The lower current at 72V means:
For sustained high-power operation — which is exactly what demanding off-road riding involves — the 72V system's lower current requirement at equivalent power is a meaningful thermal and efficiency advantage.
At 48V and 5000W, you need a controller capable of handling over 100A continuously, with wiring and connectors rated to match. At 72V, the same power level requires a 70A-rated system — a lower specification that's easier to source, lighter, and less prone to thermal issues.
The Fardriver NS18 controller paired with the KR5V V2 operates at 72V and 100A. That 100A at 72V represents 7200W of capacity — operating the 5000W KR5V at rated power leaves meaningful headroom in the controller's capacity. On a 48V system attempting the same output, you'd be running the controller at or near its limits continuously.
Lithium battery cells have internal resistance. When you draw high current, that internal resistance causes a voltage drop — called sag — that reduces effective voltage and wastes energy as heat inside the battery pack. Lower current at equivalent power means less sag, better effective voltage, and less wasted energy in the battery itself.
In practice, a 72V system running the KR5V V2 at 70A will have noticeably better battery efficiency than a hypothetical 48V system drawing 104A to produce the same output. The battery lasts longer per charge, and delivers more consistent power as it discharges.
For the KR5V V2 specifically, here's what voltage means for top speed in a typical build with a 6:1 overall gear ratio:
At 48V: The motor's back-EMF limit is reached earlier. With the KR5V's winding spec optimized for 72V, running at 48V significantly reduces the achievable RPM ceiling. Expect top speeds in the range of 30–38 MPH depending on sprocket ratio and rider weight.
At 60V: An intermediate option some builders use. Performance improves substantially over 48V. Top speeds in the 40–48 MPH range are achievable, but you're still leaving performance on the table versus the motor's design voltage.
At 72V: The motor operates as designed. With appropriate sprocket selection and 100A line current, 50–60 MPH is achievable. This is the voltage the KR5V V2 is engineered and rated for.
Important note: Running the KR5V V2 below 72V is technically possible — the motor won't be damaged — but you're using a motor designed and priced for 72V performance while only accessing a fraction of that performance. For a 48V build at lower power targets, a motor designed for 48V at lower wattage is a better value proposition.
The most common reason builders consider 48V over 72V is battery cost. This is legitimate — 72V battery packs cost more than 48V packs of equivalent Ah capacity, and the 72V pack typically needs to be a larger format to source quality cells at that voltage.
However, there's a nuance worth understanding: what matters for runtime is watt-hours (Wh), not voltage or Ah alone.
Same energy storage. The 72V pack has fewer amp-hours but at higher voltage — and delivers that energy more efficiently at high power (less sag, less internal heating). The price difference between these two packs at the same Wh capacity is real but narrower than it appears when comparing Ah ratings at different voltages.
For a high-power build, the 72V pack's lower current draw and better efficiency often justify the price difference in long-term battery health and consistent performance.
This is a factor many first-time builders overlook: what happens when you want more performance later?
A 48V build has a hard ceiling. You can swap sprockets, tune the controller, optimize the wiring — but the fundamental power and speed limit is set by the 48V architecture. To go significantly beyond it, you're replacing the motor, battery, and controller simultaneously.
A 72V build built around a motor like the KR5V V2 has room to grow within the same architecture. You can push current limits higher through controller tuning, experiment with different sprocket ratios, and optimize the system's performance without a complete rebuild. The 72V platform supports more headroom for iteration.
If you think you might want more performance in six months, building at 72V from the start is almost always the right call.
Work through these questions in order:
1. What's your target power output?
2. What's your top speed target?
3. Who is the primary rider?
4. What's your budget for the battery?
5. Do you want to upgrade later?
48V is a legitimate, capable voltage standard for a specific range of applications. It's the right choice when power requirements are modest, budget is constrained, or rider age and experience call for a natural performance ceiling.
72V is the right architecture when performance is the priority. Lower current at equivalent power means less heat, less wiring complexity, higher achievable top speed, better battery efficiency, and more headroom for future tuning. For any build targeting above 2500W or above 40 MPH, 72V is where the serious builds live.
The KR5V V2 is a 72V motor. It's spec'd, wound, and optimized for 72V operation. If you're building around it, you're building a 72V system — and the performance you get from that system is what the motor was designed to deliver.
The KR5V V2 Complete Kit is a 72V system, designed and matched for performance: motor, Fardriver NS18 controller, your choice of sprocket, matched chain and chainring, and throttle — everything you need on the drive side.
