Kt controller power drops at 35km/h

[Ineocla]

Hello everyone !
I have an OEM ebike i bought a few months ago and i have just swapped its generic display and controller with a KT combo so i could remove the speed limit off of it.

However, when i got it and configured it i saw that the bike still has a speed limit cap where the power stops increasing at approximatly 35km/h which i have verified as accurate with Google maps. (both when riding it and without load).

My system is a 48v 750W motor and the new controller is a 25A sin wave (the original one was 22A) so it seems a little low for a speed limit. Does anybody have a solution for this problem ? Thank you all in advance !

Here are my current settings:

Lim : 60km/h
DIM: 20"
UNT:0
P1: 100
P2: 0
P3: 1
P4: 0
P5: 16
C1: 2
C2: 0
C3: 1
C4: 0
C5: 10
C6: 5
C7: 0
C8: 0
C9: 0
C10: N
C11: 0
C12: 4
C13: 0
C14: 2
C15 : 6
L1: 0
L2: 0
L3: 1
L4: 5

 

[docw009]

That could be physics rather than speed limiiter. I have 25A KT sine wave controllers in several 48V hub motor bikes. Their highest speeds on throttle only, no pedalling, sitting upright is about the same as your bike's 24 mph. Wind resistance can be as high as 700 watts according to Chat GP at this speed, depending on tires and width of the rider.

 

[Alex12345]

Hello everyone !
I have an OEM ebike i bought a few months ago and i have just swapped its generic display and controller with a KT combo so i could remove the speed limit off of it.

However, when i got it and configured it i saw that the bike still has a speed limit cap where the power stops increasing at approximatly 35km/h which i have verified as accurate with Google maps. (both when riding it and without load).

My system is a 48v 750W motor and the new controller is a 25A sin wave (the original one was 22A) so it seems a little low for a speed limit. Does anybody have a solution for this problem ? Thank you all in advance !

Here are my current settings:

Lim : 60km/h
DIM: 20"
UNT:0
P1: 100
P2: 0
P3: 1
P4: 0
P5: 16
C1: 2
C2: 0
C3: 1
C4: 0
C5: 10
C6: 5
C7: 0
C8: 0
C9: 0
C10: N
C11: 0
C12: 4
C13: 0
C14: 2
C15 : 6
L1: 0
L2: 0
L3: 1
L4: 5

Strange that P2 is set to 0, is this a 750w direct drive motor? As far as I know for geared hubs P2 is set to some other value such that speed sensor pulses rather than hall pulses are used for speed. Does the display still show correct speed when coasting?

What happens if you slightly like 10% increase or decrease 60km/h limit, does the wheel speed change?

Maybe the motor hits its RPM limit at 48v in a 20 inch wheel.

 

[Ineocla]

That could be physics rather than speed limiiter. I have 25A KT sine wave controllers in several hub motor bikes, Their highest speeds on throttle only, no pedalling, sitting upright is about the same as your bike's 24 mph. Wind resistance can be as high as 700 watts according to Chat GP at this speed, depending on tires and width of the rider.

It would be coherent if the speed limit didn't persist when the wheel is lifted off ground. But when i try it, the power surges to 100W then drops until it stagnates at ~50W. Same behavior when i'm riding it but with higher powers (1100W peak, drops to 600/700W when peak speed is achieved)

 

[Ineocla]

Strange that P2 is set to 0, is this a 750w direct drive motor? As far as I know for geared hubs P2 is set to some other value such that speed sensor pulses rather than hall pulses are used for speed. Does the display still show correct speed when coasting?

What happens if you slightly like 10% increase or decrease 60km/h limit, does the wheel speed change?

Maybe the motor hits its RPM limit at 48v in a 20 inch wheel.

Even stranger is that the speed becomes wrong when i put any value other than 0. It's a hub motor but i have no idea what are its exact specs since there's no reference on it other than its serial number and rated power

 

[Alex12345]

Even stranger is that the speed becomes wrong when i put any value other than 0. It's a hub motor but i have no idea what are its exact specs since there's no reference on it other than its serial number and rated power

Looks to me like some geared motor perhaps a bafang g062 clone. I saw a bunch of threads on the forum discussing various KT speed setting problems, but I only operated gearless motors with KTs so have no experience of my own with this issue

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Maybe you can get some ideas on appropriate parameters from these threads.

 

[docw009]

If P2 is zero, the display will only show speed when the motor is spinning. It will use P1 and the wheel diameter to calculate speed from the motor phases. The number should decay to zero when coasting, SInce the display speed was confirmed with GPS, ithe P1 number and wheel diameter must be close enough,

KT displays enter pre-set wheel diameters, 20", 24", 26" etc in the displays instead of the actual tire diameters, so the speed calculation can be inaccurate. I once tried setting P1 so that the speeds matched between two identical ebikes with different tire brands. While this worked, the odometer values still were different, off by the 5% difference in tires. It suggests that the odometer was calculated off the wheel size in the display and the P2 signal.

Is the OP saying that the speed with the wheel off the ground is higher than 35 km/hr?

 

[Ineocla]

If P2 is zero, the display will only show speed when the motor is spinning. It will use P1 and the wheel diameter to calculate speed from the motor phases. The number should decay to zero when coasting, SInce the display speed was confirmed with GPS, ithe P1 number and wheel diameter must be close enough,

KT displays enter pre-set wheel diameters, 20", 24", 26" etc in the displays instead of the actual tire diameters, so the speed calculation can be inaccurate. I once tried setting P1 so that the speeds matched between two identical ebikes with different tire brands. While this worked, the odometer values still were different, off by the 5% difference in tires. It suggests that the odometer was calculated off the wheel size in the display and the P2 signal.

Is the OP saying that the speed with the wheel off the ground is higher than 35 km/hr?

I have asked chatgpt and Gemini about this (which aren't really reliable but it's the best i have right now) and they both seem to converge into the faulty hall sensor wiring. And in fact, when i tested the hall sensor using an ebike tester it didn't show up yet i know the sensor is picked up by the controller since unplugging one of the wires gives an error. Could the hall sensor really be the cause of this issue ?

 

[Alex12345]

I have asked chatgpt and Gemini about this (which aren't really reliable but it's the best i have right now) and they both seem to converge into the faulty hall sensor wiring. And in fact, when i tested the hall sensor using an ebike tester it didn't show up yet i know the sensor is picked up by the controller since unplugging one of the wires gives an error. Could the hall sensor really be the cause of this issue ?

I highly doubt that because your motor worked with the previous controller without a problem, a hall fail in general would instantly cause motor start problems, erratic running , a KT display would issue a hall error etc. And I never heard of a Hall fault impacting the top speed value.

I think personally you just have to meticulously follow through the diagnostics, along the lines or what docw009 and I mentioned.

By first probably setting the speed limit to max possible value (99 I believe) so that it doesn't impede the debugging, and then adjusting P1 and P2 and monitoring indicated and actual speed and actual loaded vs actual unloaded speed to determine if speedometer is correct, if you can make it go slower or faster, or faster but never faster than 35km/h which would likely mean RPM max out at your battery voltage...

Also as docw009 mentioned keep in mind, fat tire 20in wheel is more like 22 outer diameter, so you will never be able to set an accurate speed on a KT display for this

 

[Ineocla]

I highly doubt that because your motor worked with the previous controller without a problem, a hall fail in general would instantly cause motor start problems, erratic running , a KT display would issue a hall error etc. And I never heard of a Hall fault impacting the top speed value.

I think personally you just have to meticulously follow through the diagnostics, along the lines or what docw009 and I mentioned.

By first probably setting the speed limit to max possible value (99 I believe) so that it doesn't impede the debugging, and then adjusting P1 and P2 and monitoring indicated and actual speed and actual loaded vs actual unloaded speed to determine if speedometer is correct, if you can make it go slower or faster, or faster but never faster than 35km/h which would likely mean RPM max out at your battery voltage...

Also as docw009 mentioned keep in mind, fat tire 20in wheel is more like 22 outer diameter, so you will never be able to set an accurate speed on a KT display for this

The speed is already more or less accurate which is not the issue. The issue currently is the top speed which is still capped even without any load with a wheel off ground

What bugs me the me the most is that the ebike i have comes in too batches. The oldest ones which are rated for 50+km/h and the one i have which are limited to 35. That means that the motor should have much more to give then it already outputs. Also if it was an rpm limit i don't think it would perisist when no load is applied

 

[Alex12345]

The speed is already more or less accurate which is not the issue. The issue currently is the top speed which is still capped even without any load with a wheel off ground

What bugs me the me the most is that the ebike i have comes in too batches. The oldest ones which are rated for 50+km/h and the one i have which are limited to 35. That means that the motor should have much more to give then it already outputs. Also if it was an rpm limit i don't think it would perisist when no load is applied

Yeah but then if it is not a physical limit of the system, the controller must calculate your top speed as 60km/h which it's clearly not, so that's why I bring up the accuracy of calculated speed.

How about you crank up the P1 from 100 to like 150? Or increase speed limit from 60km/h to 99km/h? Do you get your GPS estimated bike speed increased?

 

[Ineocla]

Yeah but then if it is not a physical limit of the system, the controller must calculate your top speed as 60km/h which it's clearly not, so that's why I bring up the accuracy of calculated speed.

How about you crank up the P1 from 100 to like 150? Or increase speed limit from 60km/h to 99km/h? Do you get your GPS estimated bike speed increased?

Nope the speed doesn't increase and i really feel like it's hitting it's rpm limit since even lowering the tire size doesn't change anything (the reported speed does get lower but the bike stops accelerating lower too) It's really weird because as it said this ebike comes in batches that have a default speed of up to 55km/h and that version isn't more expansive so the hardware can't have changed that much. And a 750W motor at 48V should be able to push a little harder than 35km/h. If anyone can give their opinion on this matter i'd be very grateful

Another thing is that power wise the bike still has a lot to give with a power of 50W without load on its idiling speed (~35km/h). So unless it does hit rpm limit there's something else making it stop early

 

[Alex12345]

Nope the speed doesn't increase and i really feel like it's hitting it's rpm limit since even lowering the tire size doesn't change anything (the reported speed does get lower but the bike stops accelerating lower too) It's really weird because as it said this ebike comes in batches that have a default speed of up to 55km/h and that version isn't more expansive so the hardware can't have changed that much. And a 750W motor at 48V should be able to push a little harder than 35km/h. If anyone can give their opinion on this matter i'd be very grateful

Another thing is that power wise the bike still has a lot to give with a power of 50W without load on its idiling speed (~35km/h). So unless it does hit rpm limit there's something else making it stop early

Well based on this and everything above, my opinion is then the motor must be topping out its RPM at 48V. Otherwise the vehicle speed should respond loaded or especially unloaded to you increasing the speed limit parameter (since you have room to increase it like 1.5 times but somehow see no change). The displayed power when unloaded is always tiny because it's easy to spin the wheel in the air, so I wouldn't look too much into it.

The thing is if they do make two variants of the bike with different speed classes, they might as well change the motor winding. As far as I know BLDC motors work most efficiently at around 80-90% of their max possible RPM at a given battery voltage. So if the manufacturer makes this model that must be limited to 20mph/32kph they might as well choose the motor winding that does best at that speed, and could easily then top out at 35. In the result they can produce a bike that is more efficient and has more torque compared to using a motor potentially capable of 45km/h, and since presumably the bike would never need to go faster than 32km/h anyway, they don't loose anything. The motor itself can then look identical from outside. Power ratings such as 750W are about voltage and amps, not speed, motors with identical power ratings can have different max RPM due to different windings, that's why manufacturers frequently specify appropriate wheel size for motors in addition to power.

This is all my opinion, maybe others can offer other opinions or advice ...