Modified power management (LiOn instead of NiMH)

[Jan Oelbrandt]

I'm wondering if the DC - DC boost module is perhaps not capable of supplying the peak current demand of the servo. On my original auto shift bike I’m using a servo specific buck module called a UBEC rated

Yes, that's my guess as well. The one I've got says 3A input current, so I thought it would deliver at least 2A output current. Maybe I'm too optimistic ;-)

When did you measure the voltage output of the dynamo? Open circuit or with the battery connected?

With battery connected.

My experience of batteries is that they are very good at clamping the voltage unless they have unusually high internal resistance. Obviously lithium based batteries most never be over charged but NiMh is quite tolerant of continuing to receive current once charged. Especially the low current of a dynamo, it will just be converted to heat and from my experience still keep the voltage down.

As posted previously, I'm running the 6V NiMh battery pack straight to the Arduino & servo. The simplicity of the setup, the safety aspect, less electronics that can fail during trips,... make me to still prefer NiMh over Lithium. I carry a connector to charge-while-riding from the dynamo hub. Doing great so far (+300 testmiles since mod)