How to Reverse a Brushed Motor for Electric Bike

Quick Answer

• Swap the two primary power wires connecting the brushed motor to the electric bike’s controller.
• This is a common modification to correct rotation direction or for custom builds.
• Always ensure the battery is disconnected before touching any wiring.

Who This Is For

• Electric bike owners who need to change their motor’s spinning direction.
• DIY enthusiasts building or modifying electric bikes.

What to Check First

• Power Disconnection: Verify the electric bike’s battery is completely disconnected.
• Motor Type: Confirm you have a brushed DC motor, not a brushless one, as the reversal process differs.
• Wiring Identification: Locate the two main power wires from the controller to the motor.
• Controller Manual: If available, check your controller’s documentation for any specific instructions or limitations.

How to Reverse a Brushed Motor for Electric Bike

Reversing the direction of a brushed DC motor on an electric bike is a common and relatively simple electrical modification. This is often necessary if a motor is spinning the wrong way for your intended application, such as a front-drive motor being installed as a rear-drive, or if it was wired incorrectly during assembly. The core principle is to alter the current flow through the motor’s armature relative to its field magnets, thereby changing the direction of the generated torque.

Understanding Brushed Motor Polarity

A brushed DC motor relies on the interaction between stationary magnetic fields (stator) and an electromagnet (rotor or armature) that spins. Brushes and a commutator act as a switch, reversing the current direction in the armature coils as it rotates. This continuous switching creates the torque that drives the bike. The direction of rotation is determined by the magnetic polarities. By reversing the polarity of the current going to either the armature or the field coils (but not both), you reverse the motor’s direction of rotation. On most e-bike brushed motors, the field is created by permanent magnets, so you reverse the armature’s current by swapping the motor’s main power leads.

The Wire-Swapping Method

The most practical way to reverse a brushed motor on an electric bike is by swapping the two main wires that carry power from the motor controller to the motor itself. These are typically the thickest wires coming from the controller, often red and black, or blue and yellow, depending on the manufacturer. Swapping these two wires effectively reverses the polarity of the current supplied to the motor’s armature, causing it to spin in the opposite direction.

Step-by-Step Plan: How to Reverse a Brushed Motor for Electric Bike

Follow these steps precisely to safely and correctly reverse your electric bike’s brushed motor.

1. Disconnect All Power:

• Action: Locate the electric bike’s battery and disconnect it completely. Ensure no power is flowing to the controller or motor.
• What to Look For: Visually confirm that the battery leads are separated from the battery terminals.
• Mistake: Leaving the battery connected, which poses a significant risk of electrical shock and can damage components.

2. Identify Motor Power Wires:

• Action: Trace the wires originating from the motor and leading to the motor controller. You are looking for the two thickest wires, which are the primary motor power leads.
• What to Look For: These wires are usually distinct from thinner wires that might be for Hall sensors or other auxiliary functions. Common colors include red and black, or blue and yellow.
• Mistake: Mistaking battery input wires or sensor wires for the main motor power wires.

3. Access the Wire Connections:

• Action: Depending on your bike’s design, you may need to open a motor cover, a controller housing, or a waterproof connector.
• What to Look For: Clear, unobstructed access to the terminals or connectors where the motor wires attach to the controller.
• Mistake: Forcing open covers or connectors, which can lead to breakage or damage to seals.

4. Swap the Motor Power Wires:

• Action: Carefully disconnect the two identified motor power wires from their current positions on the controller. Then, reconnect them in the opposite positions. For example, if wire A was in terminal 1 and wire B in terminal 2, connect wire A to terminal 2 and wire B to terminal 1.
• What to Look For: Ensure each wire is firmly seated in its new connector or terminal. The connection should feel secure and not pull out easily.
• Mistake: Reconnecting the wires incorrectly, or not ensuring a solid electrical connection, which can result in the motor not spinning, spinning erratically, or not reversing.

5. Secure and Insulate Connections:

• Action: Double-check that both swapped wires are firmly connected. Use electrical tape or heat shrink tubing to insulate any exposed metal connectors.
• What to Look For: No bare wire or metal showing. Connections should be snug and protected from moisture and abrasion.
• Mistake: Leaving connections exposed or loose, which can lead to short circuits or physical damage during riding.

6. Reconnect Power and Test:

• Action: Reconnect the battery securely. Turn on the electric bike’s power system and test the motor’s rotation.
• What to Look For: The motor should now spin in the opposite direction compared to before the wire swap. Listen for any unusual noises.
• Mistake: Testing the motor before ensuring all connections are secure and insulated, risking damage.

Common Mistakes When Reversing a Brushed Motor

• Mistake: Failing to disconnect the battery.
• Why it matters: Working on live electrical systems can cause severe electrical shock and damage sensitive electronic components like the controller.
• Fix: Make disconnecting the battery your absolute first step before touching any wires. Always confirm it’s disconnected.

• Mistake: Swapping the wrong wires.
• Why it matters: Incorrectly swapping battery input wires, sensor wires, or other control signals can lead to immediate component failure or unpredictable behavior.
• Fix: Carefully identify the two main motor power wires. If your controller has labeled terminals, use them. If not, consult your controller’s manual or manufacturer.

• Mistake: Poor wire connections.
• Why it matters: Loose or corroded connections can cause intermittent power, overheating, reduced performance, and eventual failure of the motor or controller.
• Fix: Ensure all connections are clean, tight, and properly insulated. Use appropriate connectors, crimps, or solder, and protect them with heat shrink or tape.

• Mistake: Reversing both field and armature polarity.
• Why it matters: In a brushed motor, reversing both the field and armature current simultaneously will result in the motor spinning in its original direction. You must reverse only one relative to the other.
• Fix: Understand that you are changing the polarity of the current supplied to the motor’s armature by swapping the two main power leads.

Expert Tips for Reversing Your Electric Bike Motor

• Tip 1: Document your original wiring.
• Action: Before disconnecting anything, take clear photos or sketch a diagram of how the wires are currently connected.
• Common Mistake to Avoid: Making changes without a reference, making it difficult to revert or troubleshoot if something goes wrong.

• Tip 2: Use a multimeter for verification.
• Action: After reconnecting the wires, use a multimeter set to DC voltage to check the polarity at the motor terminals before applying full power. You should see a voltage reading that corresponds to the direction you expect.
• Common Mistake to Avoid: Relying solely on visual inspection and assuming the wires are correctly swapped without electrical confirmation.

• Tip 3: Consider controller compatibility.
• Action: Ensure your motor controller is designed to drive the motor in both directions. While most brushed controllers are, some specialized controllers might have limitations.
• Common Mistake to Avoid: Assuming all controllers will handle bidirectional operation without issue, potentially leading to controller errors or damage.

Troubleshooting Your Motor Reversal

If your motor doesn’t reverse, spins erratically, or doesn’t run at all after swapping wires:

• Verify Wire Swap: Double-check that the two main motor wires are indeed swapped correctly at the controller.
• Check Connections: Ensure all connections are secure and making good electrical contact. Loose wires are a common culprit.
• Controller Settings: Some advanced controllers might have settings that influence motor direction. Consult your controller’s manual.
• Motor or Controller Damage: If the motor was run incorrectly for a period, or if there was a short circuit, internal damage to the motor or controller might have occurred.

Decision Checklist for Successful Motor Reversal

Before you consider your motor reversal complete and safe, run through this checklist:

• [ ] Battery power was completely disconnected before any wire manipulation.
• [ ] The correct two main power wires to the motor were identified and swapped.
• [ ] All wire connections are secure, with no loose strands or exposed copper.
• [ ] Insulation (e.g., heat shrink tubing, electrical tape) is properly applied to all connections.
• [ ] After reconnecting power, the motor spins in the intended opposite direction.
• [ ] There are no unusual noises, smells, or overheating from the motor or controller during testing.

FAQ

• Q: Will reversing the motor affect my bike’s speed or power?
• A: No, simply reversing the direction of a brushed motor does not inherently change its top speed or power output. It only changes the direction of rotation.

• Q: Can I reverse a brushless motor the same way?
• A: No, brushless motors require a different method. Reversing a brushless motor typically involves swapping two of the three phase wires or reprogramming the controller, depending on the motor and controller type.

• Q: What if my motor has four wires, not just two?
• A: If your motor has four wires, two are likely the main power wires for rotation, and the other two are for Hall effect sensors, which help the controller determine the rotor’s position. You only need to swap the two main power wires.

• Q: How do I know if I have a brushed motor?
• A: Brushed motors typically have brushes that wear out over time and need replacement. They are generally simpler in construction than brushless motors and often have visible brush access points. If your motor has a distinct “whine” at high RPMs and doesn’t have many wires coming out (usually 2-4 for basic function), it’s likely brushed.