Why Electric Bike Motor Cuts Out Under Load?

You may find numerous trolls and memes about e-bikers in bicycling forums. But, the truth is e-bike is the most convenient transportation in terms of pace and comfort.

Yeah, you can’t get the feel of cycling with an e-bike. But, you will get the max level’s performance; it is possible until the electric bike motor cuts.

However, a motor cut is an error that mainly occurs for electrical faults or battery problems. Since an e-bike has a complex mechanism, it’s difficult to explain the problem in a few words.

That’s why I will explain the problem in detail and suggest a possible solution for them. So, stay with me to know about the DIY solution that can help you save some money.

Why does an electric bike motor cuts out under load? (Most 3 Common Reasons)

It can happen because of the limitation of the battery capacity or error on the battery management system.

Also, it occurs for faulty electrical systems like a loose connection or sensor failure. So let’s discuss them in detail so that you can understand the problem well.

1. Battery Limitation/Error

battery

A battery management system on an e-bike is featured to supply power to the motor and run the bike. In most electric bicycles, there is a power cutout system to prevent battery damage under load.

So, when you are riding the bike under load, it’s pretty normal to cut out. It’s not a technical fault. So, where is the problem?

You can’t say the battery is the culprit here. But, honestly speaking, the problem is that the battery capacity is not enough to fulfill your expected performance.

The thing is if you got a cheap e-bike, the low quality of the cells will be pretty apparent. So, not getting a too cheap electric bike is the only solution here.

However, excluding capacity, sudden voltage jump often causes motor cut. So, again, a high-capacity battery is recommended to avoid the problem.

Also, be careful when switching the assist level. Higher assist levels consume more power, so the voltage gets higher. Oppositely, the lower assist level consumes less energy, so the voltage reaches lower here. 

So, when switching the assist level from highest to lowest or lowest to highest all of a sudden, there is a significant voltage jump.

That’s why I suggest changing the assist level successively to minimize the voltage jump and prevent the bike from the motor cutout.

2. Loose Connection

electric bike loose connection

It’s the common reason for motor cut out on an electric bike. This is because there are too many wires and connections to the electrical system.

So it is possible to have one or more loose connections on the system. And, when there appear loose connections, the motor will definitely cut out. But how do the connections get loosen?

Mostly it happens generally for the time being. This is because the wire tears out or disconnects at some joint like the motor, battery, or throttle when you use the bike frequently.

Also, when riding the bike under load, the wire can get frayed or melted because of overheating. Thus the connection can get loosened.

However, in that case, you can fix the problem by minor repair work or by replacing the damaged wire. So, my suggestion is to use good quality wiring. Thus, the cables will last longer and get damaged less frequently.

3. Sensor Failure

Another reason for the motor cut is the failure of the sensor in the hub. Sometimes the battery is charged, and everything is okay, but when you turn the bike on, the throttle is not working.

Again, it occurs because the sensor associated with the pedal-assist system is not functioning well. To fix this problem, you have to readjust, reconnect or replace the sensors.

4 Maintenance checklist to avoid motor cut under load

Taking care of motor and batteries

A quick check before every ride is good to avoid motor cuts. But, checking it thoroughly once a week is a must to identify and rectify the problem that causes motor cuts.

So, what should you check on your weekly maintenance routine? 

1. Taking care of the battery

As the battery supplies power to the whole bike, it’s good to start with the battery. If the battery is not okay, it will be a waste to check the entire bicycle.

So, check the battery if it is appropriately charged or not. When turning the bike on, if the display or LEDs light up, the battery should be okay.

Most batteries come with a charging level indicator. So, it’s easy to determine if it is fully charged or not.

Otherwise, use a Voltmeter to measure the battery voltage. For example, if a 45V cell shows 45V reading on display, then it is fully charged.

Anyways, the way you charge the battery has a significant influence on battery life. So, you must do it correctly to ensure a healthy battery management system.

The best way to charge an e-bike battery is to plug it with less than 40% charge and keep it plugged in until full charge. However, don’t overcharge it. Thus, you can expand the battery life use it for a long time.

2. Checking electrical faults

Electrical faults mainly refer to loose/cross-connections of the wires. On your Maintenance routine, check if the wire is engaged with the corresponding components (controller, motor, throttle, sensor, ignition switch, and connectors).

Sometimes the wire gets damaged by stress or overheating. So, check if there is any fused, melted, or torn wire. If insulation coating is damaged severely, it’s better to change the wiring. Otherwise, just fix them.

However, sometimes a bent battery prong causes loose connections. Make sure the prongs stay straight, and they get engaged with the battery correctly.

Anyways, the motor itself can have a problem. When the coil inside the motor is burned out, it stops functioning. You have to take the bike to an e-bike shop.

3. Checking sensors and throttle

A  magnetic sensor is mounted to the crankset or sprocket. It determines the movement or speed of the pedal and assists it accordingly.

If the throttle is not working, there is a chance that the sensor is not aligned correctly. However,  the sensor should be parallel and close enough to the bottom bracket or chain.

4. Go to the bike shop

If the job seems complicated and you don’t want this hassle, take help from a professional. However, it’s good to give the bike to a bike shop twice a year for maintenance.

But, e-bike maintenance service won’t be good at a regular shop. Because most regular bike shops don’t have the expertise of fixing e-bikes.

So, go to a specialized e-bike shop for repair work. Even if you need a common fix like fine-tuning or adjustment, don’t take the e-bike to a regular shop. Otherwise, they can mess up things.

How to fix electric bike motor that keeps cutting out

Though it’s a bit complicated, you can fix most e-bike problems that cause motor cuts. Before starting the maintenance job, remove the battery first. Otherwise, the battery can fall and get damaged.

It is pretty expensive to get a new one, so I don’t think you will like it. However, you can use a Repair Stand for your ease or just stand it on the plain ground.

Rectifying electrical faults

Rectifying electrical faults

Before you start fixing loose connections, keep a Soldering Iron Kit and a Screwdriver Set ready.

However, there is a controller which connects all the components to coordinates and supplies power to them.

But, it’s really impossible to explain the e-bike wiring in short. Actually, you don’t need to understand it. Just click some photos to remember which connects with whose.

Now, look for loose connections and mark which wires are causing it. Check the joints and tighten the holder screws if they are loose. If you find disconnected wires, then connect them by soldering.

If you need to replace a wire, loosen the holding screw, remove the old one, and get a new wire of the same capacity.

Then, soldier its ends and connect it accordingly. Finally, use these photos to check is there everything okay. If the job still seems complicated, then take help from experts.

Fixing the Sensors

electric bike sensor

It sounds the most complicated when I am talking about sensors and stuff. But trust me, it’s the most accessible component to fix.

Just to adjust the position of the sensor and magnet ring, that’s it. If the magnet ring is too far from the hub/bottom bracket, try to bring it closer (about 3 mm).

Also, make sure it is parallel to the hub/bottom bracket. Then, adjust the sensor position. The sensor is usually mounted to the frame.

Use a screwdriver to loosen the sensor, then align it straight and close to the magnet ring. Finally, tighten it. It’s all set.

Anyways, after adjusting the sensor, check if it is working properly or not. If there is no effect chance that the sensor gets exhausted.

Get a new Sensor that is compatible with your bike. Take your time to do the research. Meanwhile, I am explaining the installation process.

Firstly, remove the left crankarm with a Crankwrench. Now, set the magnet ring as per the alignment described above and reinstall the crankarm.

After that, mount the sensor with the frame where it fits. But make sure it is faced with the magnet ring and aligned straight and close to it.

Finally, check if the LED blinks while rotating the pedal. If it is blinking, then you are all set. Otherwise, adjust the sensor again.

Take help from professionals.

Sometimes things get too complicated that if you try to fix them, you can mess it up. For example, fused coil, motor replacement, or fine-tuning need advanced troubleshooting to resolve.

In that case, it’s better to take help from a professional instead of DIY. Again, don’t take it to a regular bike shop mechanic. Contact someone who has the specialty to fix electric bikes.

Frequently Asked Questions

How often should I give the e-bike for maintenance?

Well, it depends on your need. When the bike breaks, you have to go to a bike shop. Otherwise, it depends on how frequently you ride the bike. If you ride it more regularly, it’s enough to give the bike twice a year for maintenance.

How much does it cost to repair an e-bike?

It will cost around 50 to 100 USD for a minor fix or adjustment. But, if you want an expert to do the job, it will cost about 300 to 400 USD to troubleshoot the whole bike.

How does an e-bike battery get damaged?

An electric bike battery can get damaged by heat or moisture. So, keep it away from the sun or rain. You can also cover it with protective clothing while it is on the bike. However, the battery can also get damaged by falling. So, make sure the lock is working well. It’s best to remove the battery and keep it in a safe place when not riding.

Conclusion

Since an e-bike has the most complicated mechanism, it’s not easy to maintain or repair an e-bike.

But, once you understand how things work on an e-bike, it will be easy to identify and rectify any kind of error.

For example, the electrical system, including the battery, motor, throttle, and sensors, is involved when I talk about motor cuts. So, you must know the functionality of these components and identify when they malfunction.

However, motor cuts on e-bike spoil the riding experience where the risk of accident/injuries come after it. So, identifying the problem is not enough. You have to rectify it. For that, learn how to fix or take help from professionals. Also, don’t forget to perform regular maintenance to avoid motor cuts while riding.

Hope you can ride without any stoppage.

Cheers!

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