Intermittent Loss of Power on an Ebike? 8 Reasons and Fixes

It does get very exasperating when you have an e-bike that falls prey to intermittent power losses. This issue can confuse a lot of owners and make them feel like they have wasted money. But why do these happen?

E-bikes can suffer intermittent power losses due to a faulty battery pack, loose wiring, or damage to the internal power train. These issues go away with repairs, replacements, looking after, or upgrading components.

The first step, however, is to identify the root cause.

The following article comes to the aid of all grief-stricken and confused e-bike owners by explaining the causes behind the intermittent power losses your e-bike might be experiencing. I’ll cover the 8 most common reasons why the power will go out on an e-bike, and talk about lots of fixes for these issues.

8 Reasons Behind Intermittent Power Losses (+Fixes!)

Electric vehicles are composed of different components, all of which work in perfect harmony.

Malfunctioning components are the primary cause behind frequent and unexpected power losses.

1) BMS Malfunctions

The BMS or battery management system is a device installed in all-electric vehicles. The BMS acts as a supervisor and monitors the battery pack’s health.

The BMS will:

• Provide a display of the current battery capacity and remaining charge
• Ensure an even discharge between individual cells of the battery during use
• Prevent overcurrent and overheating while the vehicle is in motion
• Drain the battery at an even rate to ensure no cells die  

However, a malfunctioning BMS can provide wrong information and show that your battery is on a full charge, even if it isn’t.

This can cause your power to run out rapidly, leading to power failures. The absence of a supervisor can also cause over-current and burn your e-bike’s battery, or worse, the entire power train.

Moreover, the uneven charging of your cells may give the malfunctioning BMS the impression that the battery is at full capacity and ready to discharge.

Since it isn’t, the e-bike will show intermittent power losses.

Since the BMS also checks the battery pack to prevent overheating, it can malfunction and switch off the battery when it detects high heat, even if the battery is cold.

Fixing the BMS

The BMS usually demands a full-system replacement.

However, if you notice damage to the wires or any particular sensor in the BMS, replacing it might work too. Resolving the BMS issue can be a little tricky since it is quite challenging to figure out whether the fault is in the BMS or the battery pack. 

Therefore, using a multimeter to test the battery’s terminal voltage and taking current readings is always a good idea (source).

You can also test the battery and BMS systems by using them in a different e-bike to discover the problem.

Individual cells inside the battery pack must also be examined for visible signs of damage, leaking electrolytes, or high temperature. This will further help you to identify the problem with the battery pack.

2) Brake Motor Inhibitor Issues

Unlike conventional vehicles that use internal combustion engines, e-bikes have brake motor inhibitors instead of hydraulic brake pads.

The motor inhibitors are essentially electric components that stop the motor from spinning when the brakes are applied.

The BMI system not only helps slow down and stop your e-bike but prevents damage to the driving motors.

However, the motor inhibitors can malfunction and lead to an unpredictable braking system.

The motors are automatically stopped by the inhibitors regardless of whether or not you press the brakes and give you another bout of an annoying power loss. Your e-bike will stop moving until the malfunctioning brake motor inhibitors decide to allow free motion.

Brake Motor Inhibitor Fix

The BMI system in your e-bike is usually a problem caused by a faulty sensor in the inhibitor.

Checking the system by running tests with a small dc motor and a portable power supply can help you discover the issue, although most e-bike owners prefer to replace the entire brake motor inhibitor.

3) Loose Battery Pins

The pins act like the blood vessels of an e-bike. The battery pack transfers power to the entire bike through these pins, which is why they should be snugly attached to the system.

However, if the battery pins are loose, the power transfer can slow down, making your e-bike feel slow and lose power.

The loose connection may cause power to come and leave, making the entire e-bike’s operation highly unpredictable.

The pins may also break due to poor handling, cutting off access points between the battery and the components.

The Fix

This requires quite a bit of skill and DIY knowledge to be honest! I’d almost certainly take it to an ebike repair specialist. There might be a bit of welding required.

Or at least ordering and replacing the pins.

4) A Faulty Velocity Sensor

E-bikes have a velocity sensor that judges how fast you are going and directs the information to your bike’s controller so that it can redirect power to the motors. The velocity sensor also acts as a safety shield and sends information to the e-bike controller when you travel too fast.

The power may be cut-off in such cases for your safety. 

However, a broken or poor-quality velocity sensor may misread your e-bike’s speed and send wrong signals to the controller.

This results in your e-bike cutting off power intermittently since it cannot accurately detect your speed.

You could be moving slowly, but the faulty speed sensor will not be able to tell the difference and will erratically cut off power (source).

Fix – Having the Sensors Repaired or Replaced

Your e-bike is only as intelligent and responsive as its sensors. If you notice that the battery life of your bike has drastically fallen or that your bike keeps switching off even if you’re not going fast, it’s time to replace your velocity sensor.

Your e-bike’s battery can also drain out too fast if it is not fully charged or discharging unevenly.

Therefore, you should have the sensors in your BMS inspected by an expert to see if the system is malfunctioning. This step will ensure steady and even charge-discharge battery cycles to help your e-bike function smoothly.  

5) A Damaged Controller

All e-bikes have a central processing unit in the form of a controller.

This controller receives signals when you want to throttle, speed up, slow down, or break and sends messages to all the other components in the bike. It is also responsible for reading when you want to switch your bike on and off.

The controller can burn out, overheat, and malfunction due to extended use and lead to intermittent power losses. 

Since it is the primary force that communicates with the bike, damage to it can cause poor communication between the battery and the motors, leading to frequent losses in power and other malfunctions.

This can also make the e-bike very unresponsive and slow.

Fixing your E-bike Controller

The controller in your e-bike is the central system of command and can cause intermittent power failures if it is not working normally.

However, the controller may be pointing out other problems in your e-bike that aren’t letting it work effectively. If you correctly pinpoint the problem with your e-bike controller, you may be able to fix other underlying problems with components in the vehicle’s system that could give you problems in the future.

Thus, you should solve this issue by first identifying what the controller issue is as the following table suggests:

Identifying occurence	Problem	Solution
A controller that has discolored, or is hot to the touch.	The controller is overheating. The battery is malfunctioning and causing over-currents or the wiring is faulty.	Check battery health and BMS status. Inspect wiring to identify and repair the damage.
A controller that has a strange smell to it and has burn marks.	The controller has been fried.	Replace the controller since the current one is no longer working.
A controller that has broken or bent pins.	The wire connection terminals have been damaged and must be replaced.	Install new pins and replace terminals. If the terminals of the controller are broken, you may have to remove them and solder them in new pins.

6) Jammed Throttle

Sometimes, the throttle on your e-bike can get stuck in place when you switch off your bike.

The next time you turn it on, the controller could have difficulty connecting with the throttle due to its different position and cause it to miscommunicate with the controller.

This can lead to poor power transmission from the battery pack to the throttle and give your e-bike power losses and a slow speed. 

The system can also overheat as the controller can misread the throttle command and assume full throttle for a little movement of the handles. This can not only be dangerous for the rider but acts as a great drain on the battery and causes it to run out very quickly.

Checking the Throttle to Controller Connection

The throttles are your conduit for communicating with the controller and getting the bike to move.

Therefore, if you notice an unresponsive throttle, having the connections inspected is always a good idea.

You can also have some lubrication done in the throttle system if you notice a jammed and choppy turning system.

Although replacing the entire throttle system is a rare occurrence that is not needed for most throttle issues, it will most definitely remove all throttle-related problems. 

7) Damaged Wires on Rear Driving Motors

The e-bike motors must have high-quality wiring to ensure that an adequate power supply reaches them and they can communicate with the controller.

However, the wire connections can deteriorate over time and use, particularly in rear hub motors. The terminals may burn out or get rusted, and the wires can fray. 

This condition can cause low power output from the motors and, in extreme cases, lead to a full power loss since your e-bike controller simply cannot communicate with the driving force behind your e-bike (source).

Checking the Wiring

Never a bad idea, checking the wiring on your e-bike is of great help, particularly as far as helping with poor throttle power goes.

You can inspect the wire terminals connecting the components, and check for signs of burns or rust.

You can also check to see if any of the wires are loose since that can also lead to intermittent power failures. 

If the wires are losing insulation or looking frayed, replacing them will certainly help your e-bike feel more powerful and solve the motor issue.

8) Damaged Cells In The Battery Pack

Often, due to exposure to high voltage, uneven discharge, overheating, or even blunt force trauma, individual cells in a battery pack can take irreversible damage and cause the power system of the entire e-bike to be badly affected.

The power can drain too quickly, the e-bike may suddenly stop working due to the lack of the required Wattage from the battery pack.

This issue can also damage other components like the motors if surging currents are passed on to them by a damaged cell.

Fix

Take the bike to an e-bike repair shop and let them take a look if you suspect this is the issue.

Conclusion

E-bikes are fun and very versatile since they can take you on joy rides, business meetings, or even road trips by simply charging up wherever you can plug them in.

However, it can be an exasperating experience if your e-bike faces intermittent power losses. 

With the information mentioned above, you can easily identify any problems that your e-bike has been experiencing as far as power losses and poor performance are concerned and make the required changes to help your machine run at its best!