I'm trying to get to the bottom of why my new bike keeps killing KT controllers within a few minutes of riding. It has a rear Bafang 250w geared hub motor which connects to the KT controller via a 9 pin Julet connector. The controller is a 15a KT. PAS is disconnected. The brake cut-offs are connected and working normally. The battery is 36 10.4AH and working normally. The display used at the time is an 810LED (5 wire digital) which powers up and turns on the controller, but I'm told here that it isn't compatible with KT controllers. The bike rides fine up to 32kph for a minute or so, then power starts to get weaker over the following minute or two, down to a crawl, then goes totally dead. And that's the controller destroyed, never to run again. This has happened twice in a few days. After putting my stock non-KT controller back in, everything works perfectly. So my question is, how exactly can using this display (which works fine on the stock controller) destroy a non-compatible controller? I'm really confused about this and need to know so that I can be certain it is the display killing the controllers before I buy another controller and run it without a display.
KT Controller woes and difficulties
- Thread starter Tezzy
- Start date
To answer your question, you need to identify exactly which version of the 810 you have. Do you have a link?
Here's a guess. You mentioned in your other thread that it's the one with the walk button (there are a couple of those), and that you connected the display and controller based on wire colors. The walk button and mode/power level buttons on the 810 output a DC voltage, like a throttle signal. The KT controller is expecting a digital signal that's used to communicate setup parameters, power levels, etc.; and not a straight DC voltage. I'm curious how it lasted 2 minutes.
I think Kunteng uses UART to communicate between display and controller.
Here's a guess. You mentioned in your other thread that it's the one with the walk button (there are a couple of those), and that you connected the display and controller based on wire colors. The walk button and mode/power level buttons on the 810 output a DC voltage, like a throttle signal. The KT controller is expecting a digital signal that's used to communicate setup parameters, power levels, etc.; and not a straight DC voltage. I'm curious how it lasted 2 minutes.
I think Kunteng uses UART to communicate between display and controller.
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lnanek
10 kW
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Typical ebike on/off wire going from controller to the display is full battery voltage, e.g. 36V, 48V, 52V - whatever your battery runs at. When this is routed correctly by a compatible display it gets fed back into a DC-DC converter in the controller to lower the voltage down to whatever the electronics run at, such as 5V. Routed incorrectly to something expecting 5V I could easily see it destroying something. Most controller to display cables have a TX and RX wire for transmitting and receiving data, for example. Dumping full battery voltage on to that instead of on/off patterns of 0V to 5V could easily destroy some component not spec'ed to take that voltage. Heck, even something simple like the hall sensor in the throttle or motor can easily be destroyed if they are designed for 5V and get fed 36V. Similarly the pin on the controller that reads the result of the hall sensor in the throttle isn't designed for more than 4 or 5 volts. Dumping full battery voltage on there could fry a controller.
Thanks. It looks exactly like this and it has 5 wires. A white circular sticker on the back has "36v" printed on it. There is no other identifying information available for it. It came on a Hyper Jet Fuel electric fat bike. My battery is 10.4AH and has the code xz-3602xl-53-1. I cannot find that exact battery online, but a search brings up this page with potentially similar batteries listed under 'Product Parameters' which seem to be capable of 15amps peak, so the controller I keep trying to use is this one, a KT15A. I have a third arriving tomorrow and will short the display pins and try one last time without a display before I give up on this bike. I really want to get it working. The stock controller is so bad that I do not enjoy riding it, yet I love everything else about the bike. If the third controller blows, even without a display, I can't explain why it's happening.
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Update: I left the display disconnected on the third controller, shorted blue/red and yellow/black and it ran without a display. The controller did not fail this time. However, the bike is 5kph slower and has less torque. The controller is supposed to be 2amps higher maximum than the stock controller, but is weaker none the less. Even down hill I could not reach 33kph, which was the max speed on flat ground of the stock controller. The new constoller also now has delay before the motor kicks in at a stand still, maybe 0.75-1 second. Can anyone offer advice? I almost bought the 17a controller instead of the 15a, but I believe my battery's max discharge is 15a, so I got the 15a one, but it's a weaker bike now.
lnanek
10 kW
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- Sep 26, 2022
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It's pretty common for sellers on AliExpress to flat out lie about the controller max A. I've bought generic controllers labeled 30A before, dug into the advanced settings, and found out it was just a typical 15A max generic controller with a 30A sticker on the outside.
If your battery limit is 15A you can buy a programmable controller like the Grin Baserunner and program the max battery A to 15A.
If your battery limit is 15A you can buy a programmable controller like the Grin Baserunner and program the max battery A to 15A.
docw009
1 MW
The 15A controller is 7A continuous. On 36V. that's around 250W. Not a whole lot of power. KT is pretty accurate on their ratings.
I run my bikes on their 20A and 25A controllers.
I run my bikes on their 20A and 25A controllers.
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I can't find a source for this, that without a display a KT controller is restricted to half current when using throttle only. Someone posted this in another thread:
"Just for fun today, I jumpered one of my KT controller ebikes amd rode around. I would guess that the default PAS level is probably between level 2 and level 3 (out of 5).. Couldn't really tell how fast it was going w/o the speed on the LCD. Throttle seemed to work as it alway did," And apparently the first Sondors bike used a kt controller without a display.
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