Replacing the 4xAAA battery with Li-ions

I’m trying to increase the run time of the 3pi and at the same time reduce the weight. I’d like to replace the 4xAAA battery with a pair of lithium ion cells. I see that the maximum voltage specification is 7 volts. I noticed that this is the same as the “low voltage” version of the power-on switch, Pololu item #751. A pair of lithium cells would average around 7.4 volts, with a peak after charging of 8.4 volts. Would this be too much voltage for the power switch circuit? What about any of the other circuits attached to Vbat?


Dale Wheat


This has already been covered here, buried deep within the extreme line following thread (so I’m not surprised you didn’t find it). The short answer is that the 3pi will not be able to handle this, because certain parts of the power system cannot handle the 8.4 V of a fully charged pack. You could try a single cell, though performance of the motors might be adversely affected.

- Ben


Thanks for the quick reply. Perhaps I’ll just try it with one LiPo cell for the time being. If it works out OK then I’ll post some more details.


Dale Wheat

You might also try to use 2 diodes in series to drop roughly 1.4V. These would have the additional benefit of reverse polarity protection. Test this with a load resistor (maybe 100 ohms, 1/2 watt?) before connecting to 3pi.

The 3pi already has reverse battery protection, and the drop across the diodes won’t be there when the robot is off, so that would not work.

- Jan