KT48V 45A Controller stuck at 25 km/h – Reset made regen turn on (No e-brakes installed)

[Kxmi1206]

Hi everyone,


I'm dealing with a very weird issue with my KT 48V 45A controller (block-wave/square-wave). It is completely stuck at 25 km/h unloaded (wheel in the air) and drops to 21 km/h under load on every single PAS/throttle level.


Here is what I've already done and observed:

• Reset & Settings: I performed a factory reset on the LCD display. All speed-related parameters (P8 set to 0/off, max speed, C14) are configured for unlocked/unlimited speed.
• Power Drain: Completely disconnected the controller from the battery and motor, left it powered off to fully drain the caps, but the behavior remains unchanged upon reconnecting.
• Sudden Regen Behavior: Regenerative braking (regen) never worked before, but right after this issue started / after the reset, regen randomly activated and is now functioning, even though I do NOT have any e-brake sensors / brake cut-off switches installed.

Since the speed is capped strictly at 25 km/h and regen suddenly kicked in on its own, I'm wondering:

1. Is it possible the controller entered a permanent EU/legal limit safe-mode or recovery loop?
2. Could a short-circuit inside the e-brake connector (or C13 regen setting conflict) force both the regen function and the hard 25 km/h speed cap?
3. Is there a hardware jumper wire on the 45A KT board that hard-locks this, or is the internal MCU EEPROM corrupted?

Any insights from KT controller experts would be awesome. Thanks!

 

[Alex12345]

It may help to state what all parameters like speed limit, wheel size, and all P and C are set to.

Also unclear the circumstances when the speed got capped to 25kmh. From the thread title I assume before the reset. Knowing what preceded the event frequently helps.

Unclear what you mean by regen kicked in if you are able to make the motor accelerate to speed, and you have no brake switches. Normally KT have a slip regen (when you mildly let off the throttle it would slow down accordingly) and a brake-induced regen. The first one shouldn't bother you if you let off the throttle abruptly, unless the controller malfunctions. The second one would need the brake lines connected, you would see the brake indicator (on LCD8 at least), and it would not let you accelerate if the brake signal was intermittent or stuck in ON. My opinion

 

[Kxmi1206]

Thanks for the reply. Here are my exact parameters for my KT-LCD3


P1: 46


P2: 0


P3: 1


P4: 0


P5: 15


C1: 2


C2: 0


C3: 0


C4: 0


C5: 10


C6: 3


C7: 0


C8: 0


C9: 0


C10: n


C11: 0


C12: 4


C13: 0


C14: 3


C15: 6


Max speed limit on screen: 72km/h


About the circumstances:


First I washed the bike and flooded my KT-LCD8H. I swapped it to an old KT-LCD3. Right after, the screen was showing constant 1800W even without touched throttle. I opened the controller, dried it out and 1800W bug went away.


Then I started changing C13 regen settings and the problem started. Max speed capped at 25km/h and regen turned on by itself. It now kicks in over 25km/h and when I slowly release throttle. Sometimes it turns on randomly. Did playing with C13 mess up controller internal MCU memory?

 

[Alex12345]

Okay, water damage. I think anything is possible after that. Flooding the display may have shorted the serial wires which may have damaged something in the controller's MCU. If you had to open up the controller itself to dry and fix some bugs, it means it was also flooded in addition to the display. So it's also possible something was fried in the MCU just from water in the controller. The settings seem correct. Even if brake switch lines got corroded due to water, with C13 = 0 it shouldn't engage the regen. And it shouldn't limit the speed to 25.

So I suspect the MCU is damaged somehow, because no amount of play with settings would introduce such bugs. A KT display continuously sends settings to the controller and any update should get received if the communication packets go through successfully. I guess I would try to change some setting that you can easily verify and see if the bike responds. If so, it means the packets get received and something inside the MCU is toast, if not, it means the packets aren't received, maybe due to damage to the serial input of the controller.

 

[glennb]

Might be worth trying it headless, without display

 

[Kxmi1206]

Okay, water damage. I think anything is possible after that. Flooding the display may have shorted the serial wires which may have damaged something in the controller's MCU. If you had to open up the controller itself to dry and fix some bugs, it means it was also flooded in addition to the display. So it's also possible something was fried in the MCU just from water in the controller. The settings seem correct. Even if brake switch lines got corroded due to water, with C13 = 0 it shouldn't engage the regen. And it shouldn't limit the speed to 25.

So I suspect the MCU is damaged somehow, because no amount of play with settings would introduce such bugs. A KT display continuously sends settings to the controller and any update should get received if the communication packets go through successfully. I guess I would try to change some setting that you can easily verify and see if the bike responds. If so, it means the packets get received and something inside the MCU is toast, if not, it means the packets aren't received, maybe due to damage to the serial input of the controller.

Thanks for the advice. I've tested other settings and they definitely work, so the communication is fine. I also tried to fully discharge the capacitors to reset the controller's memory, but the issue persists after turning it back on. I just bought a new controller, so I'll check if that solves the problem shortly. Thanks again for your help

 

[E-HP]

Thanks for the advice. I've tested other settings and they definitely work, so the communication is fine. I also tried to fully discharge the capacitors to reset the controller's memory, but the issue persists after turning it back on. I just bought a new controller, so I'll check if that solves the problem shortly. Thanks again for your help

Water in the controller is probably the issue, but it would be worthwhile testing your throttle, and what range it's outputting.

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When I was using a KT controller I discovered some odd behavior. The valid throttle range for your controller is written on the label, for KT's usually it's 1v-4V

What I noticed is that below 1V there was a range where the controller would regen, separate from the brake lever regen, then below a certain point, the controller would "disconnect" from the motor and the motor would coast (as much as a DD motor can coast). I made a little circuit with a pushbutton and resistors to keep the throttle voltage minimum above that cutoff point and was able to use that voltage range below 1V and the cutoff for variable regen. It would regen to a lower speed than the brake lever regen would, since the brake lever regen would "freewheel"/coast once the speed dropped below 7mph, while the throttle mod would regen down to 4mph. Anyway, I used this for a little while, mainly for experimenting, but it occurs to me that if your throttle is not going to zero and outputting in this weird range, it could be causing regen.