USB/DC LiPo battery charger questions

[Mcmoody1472]

I was wondering if it would be possible to change out the chip on the USB/DC Lithium Polymer
Battery Charger, item 280, to the 8.4v chip instead of the 4.2v chip. I
need the charger to charge a 2 cell LiPo battery. Would this be possible? Is there more to it than just switching the chip? I can tell that the board was designed to be compatible with the 8.4v chip because of the check box on the right side of the board. We
need this for a solar powered UAV for our senior design project. Please let
me know ASAP. Our whole design is riding on this charger.

Also, to be clear, will the charger cut off when the battery is completely
charged so it doesn't overcharge? And what is the maximum input amperage for
the charger? I know the max output is 1.2A, but is there a maximum input
current? And if I am using the second JST port to discharge the battery at
the same time, is there a limit to the output of the battery? One more
question, how do I make it so the charge rate is 1.2A instead of the
default?

Again, I need to know ASAP due to deadlines for this project.

Any other advice you have is appreciated.

[adafruit_support_rick]

Sorry it took so long to respond - your post kind of fell thru the cracks

Anyway, the answer is no. Item 280 can support either an MCP73861 (4.1V) or MCP73863 (4.2V).

The 8.2 and 8.4 V chips are the MCP73862/4. They require a voltage input of 8.7V minimum, which the breakout board cannot supply.

For reference, here's the schematic:
https://www.adafruit.com/datasheets/mcp73861.png

[Mcmoody1472]

Is there a board that will support this chip?

[adafruit_support_rick]

I don't know of one. Maybe Microchip could point you at a manufacturer.

On the other hand, if you are already prepared for surgery to swap out the chip, you might as well also cut out the USB power supply section and splice in a higher voltage supply. According to the datasheet, the 2/4 parts will accept anything between 8.7 and 12V. A regulated 9V wall wart should be all you need.

[adafruit_support_rick]

OH! Duh! Wait a minute - the board already has a barrel jack for an external PS!

Alright - back up. If you swap out the chip, I think that's all you need to do. The datasheet has an application drawing for the 1/3 parts, but it doesn't say that you have to do anything different for the 2/4 parts. The differences seem to be all internal to the chips.

Let me verify that...

[Mcmoody1472]

Okay, well not to be that guy, but we're in a bit of a panic now here. I would really appreciate a definite response and again, thank you so much for your time and effort with regard to this issue. Thanks in advance!

[Mcmoody1472]

And by the way, I still need to know what resistor to solder on to the Rprog to make the charge rate the maximum 1.2A.

[adafruit_support_rick]

And by the way, I still need to know what resistor to solder on to the Rprog to make the charge rate the maximum 1.2A.

That would be a 0 Ohm. (i.e., a short)

[Mcmoody1472]

So does that mean you would just solder a wire across the two holes? Sorry, I'm not very proficient with electrical stuff.

[adafruit_support_rick]

Yes. Just solder a wire (or a cut-off resistor lead).

And you should be good to go on the chip swap. MicroChip has an evaluation board for these chips with essentially the same design as our board. No modifications to their eval board are required when changing chips.

[adafruit]

Hi there, while -in theory- its possible to swap the chip, we have -not- tested the 8.4v chips so we dont know for sure if they work! sorry, we do not carry any 2 cell lipo chargers and we dont know where to get any

[Mcmoody1472]

Ok. Thank you for all the information.