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Modified power management (LiOn instead of NiMH)
Hi Jan,

very interesting project I found today in the German "Heise-online" article and congratulations for this great idea and the complete instructionss and more...

Since I´m also doing some Arduino programming and 3D printing I have read everything to understand in detail what is done here. :-)
Currently I do not have abike but waiting for my dream bike is back in production. Seems that a lot of parts from China are missing and production in Germany is on hold.

However I developed an Arduino Mini based anti-thief alarm circuit with 105dB sirene based on a acceleration sensor.

And here comes my idea for an improvement of your electronic design. I used a LiOn single cell 18650 (3450mA), a DC StepUp converter (3A) and a LiOn charge / protect module.

The cell has a an output of 3.7 - 4.2V nominale and can be discharged until 2.9 safely. The output voltage can be adjusted via the DC Buck-converter to 6V for the Arduino and servo. So there is no need for 2 batteries. Additionlly I would not use NiMH cells due there is still a little memory effect but also I would say that your charging concept with 2 cells packets in row with different voltages and different discharge current is not very healthy for them. All cells placed in row should have the same dischrage level before charging them.

Here I have attached some links to cells and the modules. maybe you think about this for a future design.
Thanks for your thoughts on the battery arrangement. Indeed, my original design is not really TopNotch... I settled for that because of the economics - LiOn chargers are usually a lot more expensive than NiMh. But with that module you posted here, that's another story... Are you sure that single cell battery will perform well under 3A discharge peaks?
Quote:2 cells packets in row with different voltages and different discharge current is not very healthy for them
Everything has been tested for a lot of kilometers before releasing. The batteries are still doing fine. I always use the discharge function on the charger before I begin to charge.
Well, I did not measure the voltage under such high current but I recommend to perform a practical test on your side. The components are cheap (the 2 moduls an da single cell) should not cost more than 12-15Euro/$.

I searched for the maximum current of a servo and found only a 13kg servo with 1.4A at 13kg maximum at 6V. So I think a 17kg or 20kg servo will stay below 2.5A. However here is a 4A module:

Regarding the NiMH cells... ok if the praxis shows it is working, it´s fine but theoretically you will stress the 2 cell packets since they always have different capacity when starting to recharge them.
Another power delivery option I'm testing is a USB Powerbank, powering both the Arduino and the servo with 5V. Advantages: cheap, self-protecting, easy chargeable, and you can carry a spare one while on the road. Disadvantages: USB cable connection may be vulnerable while mounted on a bike, would require an extra housing or pouch to fix it to the bike. Good results so far on the workbench test-setup, using a 7500mAh powerbank

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