Adding head, brake, and tail lights to a KT controller

[MattZ]

I have a headlight that works off battery voltage using a switch, and a separate, rechargeable brake / tail light / alarm that uses an accelerometer to activate the brake light. But I'd prefer brake lever operated battery voltage brake and tail lights, and I'd like those tail lights and the headlight to get turned on by the controller because I'm a glutton for punishment. Truth be told, this is my wife's bike and that rechargeable brake / tail light isn't very bright and has to be set a certain way for the brake light capability to work. She has a knack for mashing on her brakes for mysterious reasons so I want her to have a very bright brake light that works as soon as the bike is turned on so that I don't run her over.

I've read all I can find on hooking lights up but I'm a bit mystified. I got one of these 2-channel 5vdc relays https://www.ebay.com/itm/221962380923 and don't think the brake light will be an issue, I'll tie into the brake lever circuit. What I'm struggling with is the head / tail light signal.
This new controller has a light connection. I've read of people regularly cooking this circuit and they're told this circuit is only meant to send a signal to a relay to power on the lights, not to power lights directly. When the light connection on this particular controller is turned on by holding the up button on the handlebar, that light connector from the controller has 52v across the 2 pins. I was expecting 5v or even 12, but not 52v.
My question is: Is that 52v a sign that this controller is meant to power lights directly without a relay? This controller took over a month to get here so I really don't want to use it as kindling.
As always, any advice is greatly appreciated.

 

[ccihon]

The KT light circuit is 52v, but you can only pull around 100mA through that before you will smoke it... Most lights, even leds will easily pull more than that... Use a solid state relay. I wired my lights separately through a discrete fuse and switch rather than using the controller to switch because of this.

 

[AHicks]

Somebody posted this link not too long ago, and I thought enough of it to save it. It appears to be a nice clean way to add a set of lights to a bike that doesn't have any, or one does have lights that has issues. Simple, and pretty reasonable. That's all I know.

https://www.conhismotor.com/products/unique-design-led-headlight-tail-rear-lights-brake-light-turning-light-for-bafang-mid-drive-motor-kits

It would appear that it avoids that super lightweight KT power supply for their display switched light? Maybe even room for a tiny fuse in the switch housing?

 

[MattZ]

The KT light circuit is 52v, but you can only pull around 100mA through that before you will smoke it... Most lights, even leds will easily pull more than that... Use a solid state relay. I wired my lights separately through a discrete fuse and switch rather than using the controller to switch because of this.

That's what I was wondering - whether 52v on the light circuit was a trick to lead one to think it could power a light directly. It would be so nice if there was some consistency to controllers from the same manufacturer. I thought I'd test it last night with the square wave controller I'm replacing, but it doesn't have a light connection. Both are KT 30A controllers.
I have a headlight working now, through a fuse and switch, but it's a good time to tinker while it's pulled apart.
I've looked everywhere for a solid state relay, the only one I can find is $33 which seems unrealistic, and is out of stock with a long lead time. So I'm trying to make it with non-solid state relays (analog?) and step down buck converters but I'm very space-limited so it's a struggle.
Edit to add: Looking again for solid state relays I remembered the problem with them - For the brake light I need one that is normally closed, and that seems impossible to find.

Somebody posted this link not too long ago, and I thought enough of it to save it. It appears to be a nice clean way to add a set of lights to a bike that doesn't have any, or one does have lights that has issues. Simple, and pretty reasonable. That's all I know.

https://www.conhismotor.com/products/unique-design-led-headlight-tail-rear-lights-brake-light-turning-light-for-bafang-mid-drive-motor-kits

It would appear that it avoids that super lightweight KT power supply for their display switched light? Maybe even room for a tiny fuse in the switch housing?

I have all those as discrete parts, but I don't have a Bafang mid drive or Julet connectors, so I'm trying to recreate it, and I would like to use the controller, no more handlebar room. I'd get wider handlebars but can't find suitable ones, they're all so narrow and it's a quill stem which limits choices. Plus it's a woman's bike so color coordination is unusually important, further limiting choices.

 

[AHicks]

The reason I like the kit is because it taps the required power at the base of the 1-4 cable connector. Though they say Bafang mid drive, unless I'm mistaken that's the same pretty common format used on the waterproof KT and quite a few other controllers.

I get the convenience of the display switched lights though. Would be neat if you could combine that feature with a kit like the one in the link. Lights turned on/off with the "up" button are not that unusual.

 

[MattZ]

The reason I like the kit is because it taps the required power at the base of the 1-4 cable connector. Though they say Bafang mid drive, unless I'm mistaken that's the same pretty common format used on the waterproof KT and quite a few other controllers.

I get the convenience of the display switched lights though. Would be neat if you could combine that feature with a kit like the one in the link. Lights turned on/off with the "up" button are not that unusual.

Yeah I don't have the waterproof version though so I'd have to cut it apart and figure out the wiring, or add Julet connectors all over and hope I match it up correctly.
The aspect of this that really rubs me the wrong way is that they provide a light connection from the controller that is essentially useless unless you have what amounts to an electric glow stick for a light. It doesn't provide enough current to run a decent light, and it provides too high a voltage for almost every relay out there so you have to step down the voltage to trigger a relay. If the controller sent out 5v signals for head / tail and brake, and provided 5v supply to power a relay it would be a breeze, or better yet provide connections and enough current to power them directly. It would probably cost KT 10 cents per controller to add that capability.
You're right though, it wouldn't be too hard to design a 'black box' small board that would accept the light, brake and battery voltage as inputs and have head, brake and tail light connections as outputs. Putting it together with separate components is way more trouble than it should be.

 

[ccihon]

I had fried the resistor in the KT controller light circuit that I had and learned this the hard way. Fortunately, this failure only disabled the light circuit and had no effect on the other controller functions. Seems like the only real gain to setting this all up via relay is that you can use the KT display to switch lights on or off, and the light icon will display on the lcd. I don't think the KT controllers I have seen have any built in provision for "brake lights" so that would be a relay add-on also.

The front and rear lights I am using on my trike are rather bright, and work with anything from 12-60v or something. I used a motorcycle-style handlebar mounted rocker switch. One trick with these auto- or motorcycle switches is that while the simple ones seem happy at switching voltages well over 12vdc, the ones that include an indicator led are an issue since that will generally cook also if you try and use the indicator at much over 12.

I have a stepdown buck convertor for 12v but have no current use for that on the trike. Opinions may vary, but I think brake lights - that is, a rear light that is brighter to indicate the application of the brakes, are of limited use for cycling as cars would seem to have no real regard for bikes or trikes, regardless of whether they are slowing or not. I wired both leds in my tail light to be on all the time to maximize basic visibility.

 

[TheBeastie]

I did some research on this and here is the information I found.
This is the post and information I wish I had found when I started looking into adding a front light onto my KT controller based ebike.

And note that everything I type is just theory of what I read elsewhere, as I haven't yet put a light on my KT controller myself, but I have put a volt-meter on my light-out wire on my KT controller and can confirm it is the full voltage of my ebike battery (which for me is S14 ~54volts)

My conclusion is that you can only use very specific and very low watts light on the 2pin out light-wire on the KT controller (if it is a version that even has it). Again, low power light only. I visited a few ebike sites and found such compatible lights listed below, as it is somewhat hard to find a light that can take 36v-60v and ALSO only want to draw a tiny amount of amps/power.
Conversely, there are tons of lights designed for combustion motorcycles that can take high voltage but also expect a lot more amps, and thus if used on the KT controller create a huge drain of power through your controller and burn-out the controllers light circuit.

Even though the light-wire is the actual the full voltage of your ebike battery, it is appears true and logical that it's 100mA max amps so that means about 4.8watts for a 48volt battery pack, if you plug on a light that wants/expects more amps/power then it will kill/burn-out the internal light circuit of the KT controller.

What I found SUPER ANNOYING, is that in Australia it is law that your bicycle/ebike only has flashing/strobing lights, if it is a solid light then in theory you can be fined by the police, unlucky to actually get a fine but it could happen in theory if the police felt like it, just like getting fined for riding on a regular pedestrian only footpath.
I used to only EVER see strobe-flashing lights on bikes, but now due to the flood of china based ebikes they all have solid lights which is just as illegal as the 1000w motor they are using...

I actually ONLY want a strobe/flash only light, as when I do drive a car tend to see ebikers who have a solid light as a street light in my side mirrors and often nearly hit them.. I find it extremely annoying, as strobe light bikers (which is the law in Aus) are 100x easier to spot from all angles when driving..

So what appears to be another goal is to find some kind of circuit (I can't be stuffed making my own) that I could plug in serial of these lights and force it to strobe so I can be road-legal. I can't believe strobe lights only for bicycles isn't a global standard.

I also attached an image with a red x on it of the typical "motorcycle 60-80v light" that is a total no no, these are easy to find but are going to kill your KT controllers light output circuit, as listed it is 23watts, again and will burn out your controller.
I actually REALLY wanted to use one of these motorcycle lights as they are all metal, I really need an all metal light as I live in an area where they are a lot of "gov/new arrivals" housed people and they simply rip off any plastic lights I have on my ebike (even if it's probably useless to them) even when just having the bike locked up for short times if I lock it up outside the shops and are gone more than 10minutes, so its been double annoying to look at all these nice all metal lights and not be able to use them (and still have another problem to deal with)

Here are some lights that "should" be compatible/work, I also took screenshots in case these URLs die over time, for the greater good of the world...
What you will notice about all these lights is they list in specs that they can take up to 60v or even 80volts but all list mA of about 40-60mA (0.04A-0.06A) which means about 4watts max on average.
Since typing up this post I am spotting more compatible lights on market place sights like ebay/Aliexpress etc, so hopefully everyone can find a compatible light more easily.

Ebike 6V-58V LED 80 Lux Powerful Front Light With Julet 2Pins Waterproof Plug/SM Plug
Listed specs (Voltage:6V-58V, Wattage:2.5W)

Ebike 6V-58V LED 80 Lux Powerful Front Light With Julet 2Pins Waterproof Plug/SM Plug [TBK-C7P Front Light] - $14.00 : Zen Cart!, The Art of E-commerce

Zen Cart! Ebike 6V-58V LED 80 Lux Powerful Front Light With Julet 2Pins Waterproof Plug/SM Plug [TBK-C7P Front Light] - ★★★★★ Ebike 6V-58V Front Light With Julet 2Pins Waterproof Plug/SM Plug 1--Luminous Letensity:80lux 2--Voltage:6V-58V 3--Waterproof:IPX5 4--Material:ABS,PMMA,Aluminum...

www.topbikekit.com

Ebike 6V-58V T13 LED 100 Lux Powerful Front Light With Julet 2Pins Waterproof Plug/SM Plug
Listed specs (Voltage:6V-58V Wattage:4.2W)

Ebike 6V-58V T13 LED 100 Lux Powerful Front Light With Julet 2Pins Waterproof Plug/SM Plug [TBK-T13 Front Light] - $16.00 : Zen Cart!, The Art of E-commerce

Zen Cart! Ebike 6V-58V T13 LED 100 Lux Powerful Front Light With Julet 2Pins Waterproof Plug/SM Plug [TBK-T13 Front Light] - ★★★★★ Ebike 6V-58V T13 LED 100 Lux Powerful Front Light With Julet 2Pins Waterproof Plug 1--Luminous Letensity:100lux 2--Voltage:6V-58V 3--Waterproof:IPX5...

www.topbikekit.com

Searching on AliExpress for "Ebike Front Light 6V-58V" seems to bring up the same type of light as above.

https://vi.aliexpress.com/w/wholesale-Ebike-Front-Light-6V%2525252d58V.html

"Wuxing Headligths QD139"

Wuxing Headligths QD139

Wuxing Headligths QD139

bmsbattery.com

"Wuxing Rear Lights WD113"

Wuxing Rear Lights WD113 Voltage 48V

Wuxing Rear Lights WD113

bmsbattery.com

Here are relevant and useful links I found about this topic.

What lighting current from the KT controller?

My driver KT36/48V 12A (max. 25A) Sinus has an output for lighting. This feature can be enabled on the KT-LCD3 display. I wonder what current can be taken from the controller so as not to burn the elements. How strong the lamp can I connect directly to these wires? I use a 48V battery.

endless-sphere.com

Passion eBike 6 FET Kunteng Controller (S06S)

I bought a Kunteng 6 FET controller and S-LCD3 from Passion eBike recently. The controller is supposed to be sine wave, although I haven't confirmed that yet. The controller shown in their picture as of today is a 9 fet version. The size and everything else in the description are correct though...

endless-sphere.com

Kunteng KT 36/48SVPRK light output

I have the funktion that when I turn on the lights on the LCD3 display, I get an output to the lights on the bike. The problem is, I don´t have any instructions for the controller. How much current can this output handle?

endless-sphere.com

Accessory KT Controller/Lighting trouble-shooting

I've got a bit of an electrical trouble-shooting problem, of my own creation, that I need a hand with (if anyone else has done this): frustrated with the cheap/weak headlight packed with ebike, I retrofitted a 12v LED off-road "light bar" to cast a wider beam. It worked quite well for a short...

forums.electricbikereview.com

Lights compatible with KT controller

Hi all, I’m in the process of installing a KT-22a controller on my Aventon LEVEL and I'm looking to install some lights. The controller has a output for lights (2 pin) and have been looking around for some as I want them to be powered by the battery, I can’t really find anything but to be...

forums.electricbikereview.com