Controller: Choosing the right operating voltage (72V, 84V, or 96V)
"72V controller," "84V controller," "96V": these labels often refer to the same family of batteries, viewed from two different perspectives. To make the right choice, the most important question is: what voltage does the battery reach when fully charged, and can the controller handle that voltage with some headroom? Everything else (speed, heat, component selection) depends on this operating voltage.
The essentials
- A battery is characterized by the number of cells connected in series (20S, 22S, 24S, etc.); this is the only figure that is not open to misinterpretation.
- "72V" is generally the average voltage of a 20S battery pack, while "84V" is its fully charged voltage; often, it's the same battery pack.
- The controller must be able to handle the full load voltage, as well as the voltage spikes that occur during electric braking.
- Increasing the voltage causes the motor to spin faster and reduces the current draw for the same amount of power, but it requires components that are designed to handle that voltage.
- On public roads, the speed remains limited to 25 km/h, regardless of the voltage.
Where do these figures come from?
A scooter battery is an assembly of lithium cells. When cells are connected in series, their voltages are added together. Each cell has an average voltage of approximately 3.6V (its nominal voltage) and 4.2V when fully charged. The number of cells connected in series is indicated by the letter "S": a 20S battery has twenty cells (or twenty groups of cells) connected in series.
The sellers then choose to display either the nominal voltage, the full charge voltage, or a rounded figure. This results in different names being used for the same battery.
| Cells in series | Nominal voltage (3.6V per cell) | Full charge voltage (4.2V per cell) |
|---|---|---|
| 16S | 57.6 V, often referred to as "60 V" | 67.2 V |
| 20S | 72 V | 84 V |
| 22S | 79.2 V | 92.4 V |
| 24S | 86.4 V | 100.8 V |
An "84V controller" is almost always a controller designed for a 20S battery pack. It's named based on the voltage it's designed to handle when the battery is fully charged. The term "96V," however, is not standardized: depending on the seller, it can refer to battery packs with different numbers of cells. In such cases, always ask for the number of cells in series and the maximum voltage the controller can accept, and make sure this information is clearly stated.
Why voltage margin matters
A controller contains electronic power switches (transistors, often called MOSFETs) and capacitors. Each component has a maximum voltage rating, exceeding which it can fail. However, the actual voltage within the controller often exceeds the battery voltage:
- During electric braking, the motor becomes a generator and sends current back to the battery, which increases the voltage. When the battery is already full, this voltage increase is the most significant. Our guide on regenerative braking explains the mechanism;
- With each switch, the cables and connections cause brief voltage spikes, which are more pronounced the longer the cables are and the higher the current.
A controller operating close to its limits, with a fully charged battery, has no headroom for those peak demands. This is a common cause of controller failure during braking at the top of a hill, immediately after charging. A controller with a maximum voltage significantly higher than the battery's full charge voltage operates more reliably.
What does a higher voltage change?
Speed
A permanent magnet motor spins faster the higher the voltage applied to it. Its speed constant, Kv, relates the two: at no load, the rotational speed is approximately proportional to the voltage. Switching from a 20S battery to a 22S battery therefore increases the possible top speed, with the same motor. Our guide on Kv, Kt, and the number of poles details this relationship.
Current and heat
The power drawn from the battery is equal to voltage multiplied by current. For the same power output, a higher voltage requires less current. However, power losses due to the Joule effect in cables, connectors, and battery cells increase with the square of the current. Therefore, increasing the voltage while maintaining the same power output reduces the stress on cables and connectors.
Here's what needs to be reviewed:
In return, everything connected to the battery must accept the new voltage: the controller, of course, but also the display, the converter that powers the headlights and the control electronics, the charger, and sometimes the BMS (Battery Management System). The motor, for its part, will spin faster; it's important to verify that it can handle this, and that the brakes are adequate. Our guide "How to increase the voltage of your scooter" covers what might break.
How to choose, in order of priority:
- **Starting with the battery:** The number of cells in series determines the full charge voltage. If you plan to change the battery, use the specifications of the future battery. Our scooter batteries list their voltage on each product page.
- Check the maximum voltage of the controller, not its commercial name. It must exceed the full charge voltage, with a margin for regenerative braking.
- **Check the rest of the system:** display, converter, charger, accessories.
- **Check the motor:** Verify the higher rotational speed and the requested torque.
- Adjust the electric braking so that it doesn't push the voltage too high when the battery is fully charged, if the controller allows it.
Summary:
| Label read | This often refers to.. | To be verified |
|---|---|---|
| "72V" Controller | 20S battery, named for its nominal voltage | Does it support 84V and handle braking surges? |
| "84V Controller" | 20S battery, named for its full charge voltage | Margin above 84V |
| "96V" Controller | Varies depending on the seller | Number of cells in series and maximum writeable voltage |
Workshop tip
When a customer brings us a "72V" scooter, the first thing we measure is the fully charged battery voltage. We've seen machines sold with a certain label but equipped with a battery containing a different number of cells. A voltmeter costs less than a fried controller.
And what about Rage Mechanics?
We are not selling controllers today. Our RageLink range is announced at 100V and is currently available on a waiting list. For increasing the voltage on your existing machine, our workshop can handle the installation and checks with our installation package. For the basics, see our electric scooter controller guide.
Frequently Asked Questions
Are a 72V controller and an 84V controller the same thing?
Often, yes: both systems are designed for a battery pack consisting of 20 cells in series, which is sometimes referred to by its average voltage (72V) and sometimes by its fully charged voltage (84V). Only the maximum voltage specified on the controller's datasheet can definitively determine the correct configuration.
Can a 22S battery be connected to a controller designed for a 20S battery?
Always double-check. A 22S battery reaches 92.4V when fully charged. If the controller's maximum voltage is lower, or too close to that value, it risks overheating, especially during electric braking.
Does increasing the voltage improve battery life?
Not necessarily. The range depends on the amount of energy stored (in watt-hours) and the riding style. A higher voltage reduces cable losses slightly, but it mainly allows for higher speeds, which consume more energy.
Why does my electric scooter brake less forcefully when the battery is fully charged?
Many controllers reduce the electric braking power when the battery voltage is already high, to avoid exceeding their limits. This is a normal safety feature: the mechanical brakes must be able to stop the vehicle on their own.