Electric Bikes Conversion Kits EMTBS eRoad/Commuting What's New?

15MPH Limit

jerrysimon

jerrysimon

Esteemed Pedelecer
Aug 27, 2009
3,292
112
Cambridge, UK
It does not limit your bike at all. Legal ebikes are set to only power/assist up to 15mph.

You can pedal faster than that but the motor is then effectively not providing any assistance.

Regards

Jerry
 
flecc

flecc

Member
Oct 25, 2006
52,846
30,401
There are different methods Davie. One way is that the motor controller sets a limit to the rate of current pulses fed to the motor, limiting the turn rate of the wheel or the drive to the chain to 15 mph road speed equivalent. In some other cases the motor gearing is set so that at it's maximum revs on the supply voltage the road speed is roughly 15 mph. This type varies that top speed very slightly according to the state of battery charge.

Yet another way on some bikes is that there's a magnetic sensor on a wheel which signals the turn rate to the controller, that then cutting out at 15 mph.

A small number of crank drive bikes have a magnetic sensor within the motor unit doing the same thing as a wheel sensor.
 
kitchenman

kitchenman

Esteemed Pedelecer
Jul 9, 2010
1,309
7
Aberaeron, West Wales
Hi Davie, Welcome to the forum. I don't think its a daft question and even if it was then it really doesn't matter. I can tell you about my experience and see where that leads. I bought a front hub electric bike and sure enough when I reached about 15 mph the assistance would stop. Then I took the motor out of the wheel, attached a sprocket to it and installed it on my recumbent. Now the assistance does not stop at 15 mph. I posted this on the forum and my understanding from the replies I got is that it is to do with the voltage. I have a 36 volt system. There are TWO voltages. The voltage provided by the battery and the voltage that is generated when the hub rotates. When these voltages are equal then the assistance stops. When my hub was in the wheel this used to happen at about 15 mph. Now its not in the wheel its more like 25 mph.

ps - I think this is the second method as described by flecc.
 
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neptune

Esteemed Pedelecer
Jan 30, 2012
1,743
353
Boston lincs
As I have said before , I am new to electric bikes . My ancient Powabyke has a pedal sensor built inside the bottom bracket ,and also a wheel sensor mounted on the left side of the rear hub . This looks a bit like the band brake you see on kids electric scooters . So presumably this is what controls the speed at which motor assistance is switched off . It just occurred to me that if you wanted , you could increase this speed in the following way . Disconnect the sensor , which I am assuming is a magnets and hall effect affair , and replace it with a simple pulse generating circuit based on a 555 timer chip . A potentiometer could control the pulse rate , and fool the bike controller into thinking that the bike was travelling a lot slower than it really was . You could use the same idea to replace your pedal sensor if you did not want to peddle .As it happens I am quite happy with speed of my bike . Incidentally , my bike has a "power only " option on the ignition switch . So is this still legal ?
 
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flecc

flecc

Member
Oct 25, 2006
52,846
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kitchenman said:
the voltage provided by the battery and the voltage that is generated when the hub rotates. When these voltages are equal then the assistance stops. When my hub was in the wheel this used to happen at about 15 mph. Now its not in the wheel its more like 25 mph.

ps - I think this is the second method as described by flecc.
Click to expand...
Yes, that's the one.
 
flecc

flecc

Member
Oct 25, 2006
52,846
30,401
neptune said:
It just occurred to me that if you wanted , you could increase this speed in the following way . Disconnect the sensor , which I am assuming is a magnets and hall effect affair , and replace it with a simple pulse generating circuit based on a 555 timer chip . Incidentally , my bike has a "power only " option on the ignition switch . So is this still legal ?
Click to expand...
A simpler way with wheel speed sensors is to shift the sensor to the frame by the chainwheel and mount the magnet on the chainwheel. Since the chainwheel turns much slower than the wheel in top gear, the cutoff speed is multiplied.

Power only without pedalling is legal with a 200 watt motor, but not with a 250 watt motor. This is because the two types are depending on different laws, British and EU.
 
D

Deleted member 4366

Guest
neptune said:
As I have said before , I am new to electric bikes . My ancient Powabyke has a pedal sensor built inside the bottom bracket ,and also a wheel sensor mounted on the left side of the rear hub . This looks a bit like the band brake you see on kids electric scooters . So presumably this is what controls the speed at which motor assistance is switched off . It just occurred to me that if you wanted , you could increase this speed in the following way . Disconnect the sensor , which I am assuming is a magnets and hall effect affair , and replace it with a simple pulse generating circuit based on a 555 timer chip . A potentiometer could control the pulse rate , and fool the bike controller into thinking that the bike was traveling a lot slower than it really was . You could use the same idea to replace your pedal sensor if you did not want to peddle .As it happens I am quite happy with speed of my bike . Incidentally , my bike has a "power only " option on the ignition switch . So is this still legal ?
Click to expand...
If you're lucky, you can just remove the magnet. Some controllers, like the Tonaro's one, only limit the speed when the maximum number of pulses is reached. Zero pulses is less than max, so that's OK.

On more sophisticated bikes like the Bosch motored ones, the controller doesn't allow zero pulses, so what you do is to remove the sensor from its location; make a bracket that holds it close to the back of a pedal; and glue a magnet to the back of the pedal. It therefore receives a pulse, but much slower than the wheel. this apparently increases the speed to over 40kph. There's a video on Youtube how to do it.
 
flecc

flecc

Member
Oct 25, 2006
52,846
30,401
DavieH said:
How do you know what type of sensor your bike has.
Davie
Click to expand...
If it's a wheel sensor and magnet like the one I described above, you'll see it of course, they're usually on the back wheel. If not and your bike always has exactly the same cutoff speed as the battery content declines, it's limiting set by the controller. If the maximum speed cutoff reduces as the battery charge declines, say from 16.5 mph to 14.5 mph for example, it's the second type I mentioned which works as kitchenman described.

If you let us know your bike make and model, we may have the answer for you.
 
flecc

flecc

Member
Oct 25, 2006
52,846
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I don't know that one Davie, but it sounds like the one limited by battery voltage and motor feedback. However, UM usually use controller limiting to legal speeds so it's still possible that's the method. If another owner/member doesn't know, UM may confirm for you. Contact page
 
flecc

flecc

Member
Oct 25, 2006
52,846
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Davie's UM doesn't have that motor type like their A2B Dave, it's an SB style geared hub motor by the look of it, with controller below the battery:

 
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