Boosting performance (speed) by mounting a more powerful battery?

[LongeLance]

Hi all,
I'm completely new to the World of e-bike so please forgive me if I ask some stupid questions. Or questions that have been asked before.... Anyway I've recently taken up commuting on a Trek Allant+ 9s. I'm very happy happy with the bike and the energy boost commuting in this way gives me. But the bike has a hard time reaching 45 km/h or even 40 km/h even in moderate wind conditions. I'm big and bulky from many years of physical activity so I understand and accept I represent a lot of wind resistance. But I'm still thinking of ways to improve the performance. One way might be replace the current 625 Wh battery with a more powerful one. I can mount a 750Wh on the bike. Might that be a solution? Will I have to do something with the bike electronics as well? Another ideas is to replace the crank with one that allows me to use a bigger sprocket. If I can find one sturdy enough. I cannot replace the cassette as the bike has internal gears in the rear hub. The sprocket there is the smallest one available. Any ideas and suggestions will be welcome..

 

[LongeLance]

Well, I found out myself. It won't help with another battery as the intended battery will simply not fit into the frame. Found out by referring to various data sheets.

 

[wheelbender6]

I think you may need replace batteries and controller to achieve higher speeds.
For example, if your battery pack is 48v, get a 52v battery pack.
Higher voltage normally requires that you buy a new controller too.
Speed is expensive.

On the other hand, replacing the the controller, alone, may help by removing the stock speed limiters.

Improving acceleration is do-able.
Increasing top speed involves more factors, like gearing and electronic speed limiters in the stock controller.

 

[LongeLance]

Thank you. I'll have to think about that. Yes, speed is expensive

 

[Calsun]

Adding a second gas tank to your car does not increase the power of the engine and the same applies to your bike. It is the motor that is the primary driver and a given motor needs a battery able to provide it with sufficient current for a sufficient amount of time.

 

[Hoggdoc]

Thank you. I'll have to think about that. Yes, speed is expensive

Ok I think you are confusing battery capacity with power. What determines speed when encountering head winds or hills is the torque your motor creates. Torque is controlled the controller and the batteries ability to discharge [output] the motor needs at that time. This is referred to as Watts in electric motor jargon that is calculated by volts x amps.

Controllers can be programmed to limit the amount of amps passed to the motor but there is also a BMS [battery management system] that can limit the maximum amount of amps the pack can output to protect the battery pack. in most battery packs.

Not to confuse you even more the is a limit that a brushless motor can spin [RPM] based on how the windings are in the motor. This is generally call KV on the motor which means how many RPM will the more spin per volt provided to the motor. For instance a motor with a KV rating of 1000 would develop a maximum RPM of 4800 when being powered by a 48 V battery. This RPM along with other factors like the watts of the motor, weight of bike and rider as well wheel diameter would be what determines the maximum speed of the bike.

I hope thats not too much information for you but it helps to know these things to determine what any given e bike is really capable of. Unfortunately most mfgs only tell you part of the story in their advertising.

I think you're issue maybe you are not using the gearing provided with the design of your bike to benefit you in situations like you described in your first post. All brushless motors like to spin at higher RPM to produce their maximum power. With that in mind I suggest you gear down let the motor spin faster in those circumstance and see how that works for you.

You might also check with your dealer and see if anyone there has the ability to reprogram the motor to maximize it power.

Hope this helps you a bit.

 

[Hoggdoc]

I think you may need replace batteries and controller to achieve higher speeds.
For example, if your battery pack is 48v, get a 52v battery pack.
Higher voltage normally requires that you buy a new controller too.
Speed is expensive.

On the other hand, replacing the the controller, alone, may help by removing the stock speed limiters.

Improving acceleration is do-able.
Increasing top speed involves more factors, like gearing and electronic speed limiters in the stock controller.

His bike has a Bosch mid drive motor changing that out would be a real problem.

 

[wheelbender6]

Good to know, Hoggdoc. I guess its not as easy as "swapping the box" on some systems.

 

[spinnanz]

Wh/ah is range, amps is torque and volts are speed.

Generally for more speed, however its not really linier. The kids elec scooter gets 25kph on 36v, 30kph on 48v, 54kph on 72v (37v x2) , and 61kph on 84v.