KT LCD3 headlight won't stay on, does have power

Mashed Potato

10 µW
Joined
Dec 1, 2022
Messages
5
Hi all,

Hoping someone might be able to shed some light on this one, I recently purchased an ebike which is all working fine except for the headlight, I'll bullet point it below so it's clearer:

- Turn ebike on, headlight flashes on briefly. LCD panel shows headlight & LCD backlight are off.
- Hold UP for 3 seconds to turn headlight & LCD backlight on.
- LCD backlight is now on, headlight is not on.

It's weird, because it flashes on when the bike is switched on, so it clearly has power, even weirder is when I go into the settings (UP and DOWN within 5 sec of switching bike on), and navigate to C6 (backlight settings), any changes I make immediately make the headlight come on and stay on, until I leave the settings (saving as I leave) where it goes back off again and the initial behaviour resumes.

Any ideas? I have uploaded two short YT videos for clarity on what I mean.

Bike light flickers once when bike is switched on:
https://www.youtube.com/shorts/HLE7syfY1kM

The C6 settings enabling bike light:
https://www.youtube.com/shorts/TJThdpi3_Io

Thanks for your time, any assistance welcomed :)
Mash.
 
Mashed Potato said:
Hi all,

Hoping someone might be able to shed some light on this one, I recently purchased an ebike which is all working fine except for the headlight, I'll bullet point it below so it's clearer:

- Turn ebike on, headlight flashes on briefly. LCD panel shows headlight & LCD backlight are off.
- Hold UP for 3 seconds to turn headlight & LCD backlight on.
- LCD backlight is now on, headlight is not on.

It's weird, because it flashes on when the bike is switched on, so it clearly has power, even weirder is when I go into the settings (UP and DOWN within 5 sec of switching bike on), and navigate to C6 (backlight settings), any changes I make immediately make the headlight come on and stay on, until I leave the settings (saving as I leave) where it goes back off again and the initial behaviour resumes.

Any ideas? I have uploaded two short YT videos for clarity on what I mean.

Bike light flickers once when bike is switched on:
https://www.youtube.com/shorts/HLE7syfY1kM

The C6 settings enabling bike light:
https://www.youtube.com/shorts/TJThdpi3_Io

Thanks for your time, any assistance welcomed :)
Mash.

The lighting output of the kt controller doesn't provide enough power to supply most lights, or only very low powered ones. It can only reliably supply enough to trigger a relay that would control the lights, so powering light directly usually fries that circuit. Based on your description, it's possible that your circuit isn't fried, yet, so you may still be able to use it. I would stop testing it without the lights, check the voltage output when turning the circuit on and off to make sure it's still functioning, and go from there.
 
Hi E-HP, thanks for the super speedy response!

E-HP said:
The lighting output of the kt controller doesn't provide enough power to supply most lights, or only very low powered ones.

This is interesting, I would've expected it to have quite a high output so that is good to know, thanks. Regarding this particular light, it's the one that comes stock with the bike, so I'd assume is designed to work with this controller.

E-HP said:
I would stop testing it without the lights, check the voltage output when turning the circuit on and off to make sure it's still functioning, and go from there.

Apologies for the further questions, I'm very new to this ebike stuff. How best would I be able to test the voltage output without removing the light? Or by stop testing without the lights do you mean I should remove them to test? I'd plan on just sticking a voltmeter into 2 pins of the 3-pin connector where the light would be plugged in, though I'm not sure which 2 of the 3.

What surprises me is that the light works fine when I'm in the settings.

Thanks again for your response.
 
Mashed Potato said:
Hi E-HP, thanks for the super speedy response!

E-HP said:
The lighting output of the kt controller doesn't provide enough power to supply most lights, or only very low powered ones.

This is interesting, I would've expected it to have quite a high output so that is good to know, thanks. Regarding this particular light, it's the one that comes stock with the bike, so I'd assume is designed to work with this controller.

E-HP said:
I would stop testing it without the lights, check the voltage output when turning the circuit on and off to make sure it's still functioning, and go from there.

Apologies for the further questions, I'm very new to this ebike stuff. How best would I be able to test the voltage output without removing the light? Or by stop testing without the lights do you mean I should remove them to test? I'd plan on just sticking a voltmeter into 2 pins of the 3-pin connector where the light would be plugged in, though I'm not sure which 2 of the 3.

What surprises me is that the light works fine when I'm in the settings.

Thanks again for your response.

I didn't catch the part about it working when in the settings which is interesting/odd.

You can unplug the lights and test the output at the connector while turning the circuit on and off to see if you get a steady voltage out, or just a momentary spike. If it's steady, the circuit should still be good, but if it' doesn't work with the light hooked up, it could be drawing too much power. If you only get a momentary spike on the meter, then something else is glitching.
 
Okay so I did some testing. The 3-pin going to the headlight is hardwired into the KT unit, and goes to a female 3-pin connector, the headlight itself being the 3-pin male counterpart, which made testing it a bit harder, had to cram some really thin gauge wire into the holes. That aside, I discovered that the output voltage is determined by the TK's backlight brightness, which I guess confirms what you said about it not being intended to run anything more than a relay.

Backlight brightness 1 (dimmest option): 0.5volts
Backlight brightness 5 (brightest option): 2.5volts

I left the backlight at 5, and plugged the headlight in and it worked right away. A bit disappointing that they wired the bike in this fashion as while it works, I'd like to have the backlight at its dimmest setting so it isn't dazzling at night. I'm amazed the dual-LEDs can even run off 2.5v, and it has a USB port which also somehow works...

Either way, I guess I'll get in touch with the manufacturer and leave it there for DIy tinkering, since it's working now at least.

Thanks a ton for your help E-HP.
 
Mashed Potato said:
Okay so I did some testing. The 3-pin going to the headlight is hardwired into the KT unit, and goes to a female 3-pin connector, the headlight itself being the 3-pin male counterpart, which made testing it a bit harder, had to cram some really thin gauge wire into the holes. That aside, I discovered that the output voltage is determined by the TK's backlight brightness, which I guess confirms what you said about it not being intended to run anything more than a relay.

Backlight brightness 1 (dimmest option): 0.5volts
Backlight brightness 5 (brightest option): 2.5volts

I left the backlight at 5, and plugged the headlight in and it worked right away. A bit disappointing that they wired the bike in this fashion as while it works, I'd like to have the backlight at its dimmest setting so it isn't dazzling at night. I'm amazed the dual-LEDs can even run off 2.5v, and it has a USB port which also somehow works...

Either way, I guess I'll get in touch with the manufacturer and leave it there for DIy tinkering, since it's working now at least.

Thanks a ton for your help E-HP.
Good analysis. I haven't seen anything discussing the backlight setting impacts, so I'm sure this thread may be useful in the future for folks that encounter a similar issue. :thumb:
 
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