Tuesday, 10 January 2017

Using a 3 Speed Switch on an EBike

Using a 3 Speed Switch on an EBike - Intro


When using an EBike normally the speed is controlled by:
  • Pedaling (with assistance from the motor)
  • Use of Throttle
So why would you require a 3 speed switch to control the speed as well? 

Using a 3 Speed Switch on an EBike - Types of 3 Speed Switch


There are lots of different types of 3 speed switch available, the most simple is shown below. 


Some are slightly more complex . . . 

The above model incorporates a "walk" mode and also  power level indicator for batteries. 

Using a 3 Speed Switch on an EBike - Why Use One?


When using pedal sensors the speed switch can be used to control the amount of exertion put in by the rider, over a certain speed you will have to do the work . . so you:
  1. Get more exercise
  2. Use less battery
On a bike with a throttle, the reasons are a little more complex. There are two main reasons for having one . . . 

1 - Helps control speed.


If you have ever tried to travel across rough ground whilst holding a throttle in a half open position, you will know that generally your hand wiggles around, cause the throttle to move and the bike to surge forward occasionally, because your wobbly hand is moving the throttle. 

By using a three speed switch you can set the speed at a low speed, and fully open the throttle. This makes for a smoother low speed experience on rough ground. 

This is also useful for kids, as you can limit the maximum speed they can use. 
If you find that the motor pulls the bike along at a speed which is too fast for you to pedal, then a switch can be used to slow the bike down to a speed where you can provide useful pedal assistance. Installing a cheap switch is easier and cheaper than changing the gearing of a bike. 

2 - May limit peak wattage and protect motor in steep climbs.


This reason depends on the controller you have installed, but the premise holds true for most controllers that allow for connection of a 3 speed switch. 

When you choose a lower speed, you are selecting a lower voltage, for example a 48v controller in low speed may deliver 24v.

All controllers have a maximum current that is supported. My controller for example has a 15 amp upper limit. So in low speed I have restricted my motor to 360w. And so in a steep climb using maximum amps, and therefore maintaining maximum torque there is a reduced chance of overheating the motor. 

This is of use when non technically minded people are riding an e bike in a hilly area. "You need to be on speed setting 1" for example is a lot easier than saying "third throttle ".

Questions I do not know the answer to:

When normally entering a steep hill at full speed, the bike will slow down as it climbs the hill. Without using a speed controller what is happening inside the motor? 

Are 48 volts and up to 720w trying to turn the motor, with non movement resulting in buildup of heat?

or

Does the controller adjust the voltage according to speed, ignoring throttle position, so as to reduce wattage, and reduce chance of overheating?

If you would like to learn more about the relationship between torque, amps and wattage < read this. 


Using a 3 Speed Switch on an EBike - Do they work on any ebike.

It is not the bike, that is important, but the controller. Look at the controller's wiring diagram. . . is there a connector labelled for "3 speed switch" or "speed switch"? If yes there is a good chance you will be able to use one.

The 3 speed switch that I purchased, worked fine with one controller but not with another.  

Using a 3 Speed Switch on an EBike - Notes 

It is worth noting that is you have an e bike that goes 15mph, the 3 speed settings will result in the following speeds:
  1. 17.5mph
  2. 15.0mph
  3. 12.0mph
So you have to be careful that installing a switch pushes you over your max allowable speed for road use. In my case I uninstalled my switch because in the high speed setting it made the bike illegal.

Using a 3 Speed Switch on an EBike - Conclusion


Part of me thinks that these switches are surplus to requirements, they serve no real purpose because the bikes speed can be controlled via the throttle.

BUT they do add in a extra option for controllability of the bike at a very low cost. 





1 comment:

  1. Thanks for this post - I have often seen and wondered about three-speed switches and you have given me a much better idea of when I might need one.

    Keep up the great work!

    ReplyDelete