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I want to use a Yamaha PW-X mid-drive motor for a new Maxun One Solarbike. However, this motor only works together with a Yamaha battery, which I cannot use: The Yamaha battery will explode with the large charging current coming from the solar panels, which is sometimes 8A.

For my solar bike are very strong batteries required, such as the LiFePO4 from A123. But as with other e-bike motor manufacturers, it is not possible to use other batteries than of the same brand. The Yamaha motor can see via a serial data line whether the battery is from Yamaha or not.

Note that this is forbidden product tying, see my article HERE.

On the Pedelec forum is a hack described (which I will call a dongle from now on) by which another battery can be used:
https://www.pedelecforum.de/forum/index.php?threads/yamaha-reverse-engineering.39480/page-4
https://www.pedelecforum.de/forum/index.php?threads/yamaha-reverse-engineering.39480/post-728001

However, in my case the dongle doesn’t work, the motor stops after some time. Then I tried to match the dongle-data as much as possible with the Yamaha data, with no results so far.

To find the problem, I have built the following circuit:

I can switch the serial data with a switch between the Yamaha battery (A) and the dongle (B). The data from the Yamaha battery is read by the use of an Arduino Mega board, see the code HERE:

https://www.pedelecforum.de/forum/index.php?threads/yamaha-reverse-engineering.39480/post-728001

The serial data contains 19 integers, the last is the CRC. Integer b18 represents the current. I wondered if the Yamaha system checks if b18 changes.  When the motor starts (unloaded), b18 goes from 80 to 150 ... 170. That is why I have changed the dongle code so that b18 randomly varies between 150 and 170 if the motor is on, but also without result. The serial data of the dongle is almost the same now as that of the Yamaha battery but the dongle still does not work. See here the serial data in Excel:

I have done the measurement as follow:

Switch in position A

After 3s press the walk assist button (row 13)

After 2s switch from A to B (row 23)

After 5s the motor stops (row 45)

This is another procedure:

If the switch is in position B and I press the walk assist button, the motor stops after 1s.

This is the code on my Yamaha PW-SE motor:

X0S10 / 000 8881

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