Kalkhoff durban G9 Ebike - Display mod

By Philipp Schönberger

E-bike buying decision

Last year in October I bought a Kalkhoff durban G9. It is a 28" bike with a mix between a load and a touring bicycle.

It wasn't my first choice but for my usage it is enough and fulfilled all requirements.

I wanted to have a normal size bicycle with a lot of storage space for groceries. Also, the range does not have to be super huge with about 30-40km but I shall be extendable if need more at a later time for some tours or the battery capacity drops on aging.

Therefor I found the Tern GSD and the Kalkhoff durban G9 pretty appealing. The GSD costed about 4000€ and the Durban 1200€

First I wanted to have a Tern GSD, since it would more fit to me from point of driving and loadable storage. Also, the lower mass centre and the fact that I would not have to steer against the front rack are the real benefits.

However one big drawback would be the price. I could have bought nearly 3.5 times the Durban G9 for the same price as one GSD.

Another con was that this is a Bosch bike. Bosch Ebikes have for each battery one CanOpen controller inside, which results in the fact that only Bosch batteries can be used. If you would connect a third party battery the motor drive would not support you even though it gets power.

Also, I got the information from a former working college that self replacing the 18650 cells is on some bosh batteries nearly impossible, since they lose the configuration if power gets lost and therefore do no longer work with the closed source CanOpen bus protocol of bosch. So instead of replacing just the 40 cells for routhly 5€ each (in case of good LG cells with 3500mAh) and 200€ in total, you would have to buy the 700€ official Bosch battery.

So I boughth the Kalkhoff Durban G9 since it is much cheaper and the storage room would be enought for me at the current possion. I would however change to the Tern GSD if I would need a bigger storage room or need Kid seats. Then I could sell my Kalkhoff and buy a maybe a used GSD much cheaper than the 4000€.

Kalkhoff durban G9

The Kalkhoff has a rear hub motor SWX02 36V 250W from the chinese company Bafang.

The con I could not lay aside was the fact that this bike system is missing the display for battery values and choosing the support levels. With the official system only 3 steps of support are possible: 0%, 70% and 100% This support levels are choosable via a button on the Battery. This is not even close to comfortable while riding.

Also the battery indicator leds are hard read, since the frame pipe is blocking the view and they are not that bright in sunlight. The angle of the leds are directed more towards the rear crack and not towards the driver.

This issue I wanted to address and disassembled the controller and battery of the durban and did take a closer look.

On the bottom connector plate there exists a bafang typical port for debugging and configuring. This port is the same interface as the Bafang Displays are using to send over a serial bus the support level. After some research I found the pinout and connected my logic level analyser and I saw the protocol of the "display", which in this case coming from the controller within the battery housing.

Therefor I ordered a display from aliexpress which should replace the "display" within the battery. There are several display options available. In order to save space on the handlebars I've chosen the "500C".

For connecting the 500C the 2 serial wires have to be disconnected from the battery controller and only the new 500c is connected to the debug port of the motor controller at the bottom.

There was one problem remaining. The battery is including a display which auto turns off in case it could not communicate with the controller or no moving was detected.

So after 10 min the battery turns off and the motor support is gone.

To solve this issue the Rx cable for the battery has to stay plugged in. With this "hack" the battery reads the feedback of the motor controller but can not transmit its own commands. The Rx cable you can see in the pics below with a XXX isolation.

With this configuration you can choose the support level and limit by the 500c (yes also the speed limit :))

With this the range of the battery can be optimiced so turn off support on easy tracks and add additional support for steep hills if fully loaded. I really wonder why Kalkhoff did no add this kind of display from the start since this display costs about 50€. The only reason I could think of is to have a con or attractive selling points for more expensive bosch ebikes.