Watching (ok, listening) to KH 385: "LITHIUM POWERED, UPS RASPBERRY PI CASE " and I have a batte...

[G+_Chris Kurtz]

Watching (ok, listening) to KH 385: "LITHIUM POWERED, UPS RASPBERRY PI CASE" and I have a battery question.

 

Fr. Robert Ballecer, SJ wires the 3x 18650 batteries in parallel to the charger module's B+ and B- pads, as shown below in the screenshot.

 

I'm not sure that's safe. The charger wouldn't know that there are multiple cells, it would just see a nominal 3.7v supply with the combined battery's capacity. What if one cell charges more quickly or more slowly than the others? What if a cell becomes damaged? The charging circuit would cut off charging at 4.2v, but that could mean that a single cell was that charge and the others less (potentially a failed/damaged cell) -- that seems to fall in the It Would Be Bad category.

[G+_Dan Baldwin]

When I came across this I thought the same thing so I used one of these: 3S 12V 10A 18650 Lithium Battery Charger Protection Board Module 11.1V 12.6V With Over-Charge Over-Discharge Over-Current Short Circuit Protection Function. I have never played with lithium batteries before but have seen them explode! Not good. Didn’t want to chance exploding my pi.

[G+_Dan Baldwin]

[G+_Paul Hutchinson]

Went to see if the unit shown above (designed specifically for three LiPo's) was the one used in the project. So I figured I'd search for the episode to get the show notes. I entered Know How 385 in Google and the show page didn't come up but look what Google showed from the Vatican web site :-)

[G+_Chris Kurtz]

Dan Baldwin Yeah, this is far more what I'd expect to be able to safely charge and power.

[G+_Dan Baldwin]

As a second note the ubec is only needed to run the pi and you give the full 12 vdc to the charger board and your battery output is a single 3.7vdc to pi which actually wants 5vdc? Now I’m confused but hey it works!

[G+_John Sullivan]

Dan Baldwin We were discussing that in another post here. We think that the charger board has not only a "buck" converter to drop the 5 v down to about 4.1, but also a "boost" converter to raise the 3. 7 battery voltage back up to 5.0 v

 

Note that the UBEC shown in Padre's parts list outputs 5.0v, and is used in the schematic to feed the battery charger board. The charger board both charges the batteries plus feeds the Pi. The charger board only "sees" 5.0 v, not the 12 v as you were thinking.

[G+_Roy Z]

In regard to the circuit safety and the connectors recommended, I have a problem in that the wires on the connectors - they appear to be only about gauge 30 or 32 - miked at about .20 mm (at least the ones I purchased). A 32 gauge wire is only rated for 500 mA. Yet you are powering the Pi were it is usually recommended to use at least a 2 amp charger. I think better to just wire entire project with 20 or 22 gauge wire.