USB/DC LiPo battery charger questions
Moderators: adafruit_support_bill, adafruit

USB/DC LiPo battery charger questions

by Mcmoody1472 on Fri Nov 16, 2012 4:47 pm

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.
Mcmoody1472
 
Posts: 9
Joined: Fri Nov 16, 2012 4:42 pm

Re: USB/DC LiPo battery charger questions

by adafruit_support_rick on Fri Jan 18, 2013 4:09 pm

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

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
User avatar
adafruit_support_rick
 
Posts: 11660
Joined: Tue Mar 15, 2011 10:42 am
Location: Buffalo, NY

Re: USB/DC LiPo battery charger questions

by Mcmoody1472 on Fri Jan 18, 2013 4:19 pm

Is there a board that will support this chip?
Mcmoody1472
 
Posts: 9
Joined: Fri Nov 16, 2012 4:42 pm

Re: USB/DC LiPo battery charger questions

by adafruit_support_rick on Fri Jan 18, 2013 4:37 pm

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.
User avatar
adafruit_support_rick
 
Posts: 11660
Joined: Tue Mar 15, 2011 10:42 am
Location: Buffalo, NY

Re: USB/DC LiPo battery charger questions

by adafruit_support_rick on Fri Jan 18, 2013 4:44 pm

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

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...
User avatar
adafruit_support_rick
 
Posts: 11660
Joined: Tue Mar 15, 2011 10:42 am
Location: Buffalo, NY

Re: USB/DC LiPo battery charger questions

by Mcmoody1472 on Fri Jan 18, 2013 4:53 pm

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
 
Posts: 9
Joined: Fri Nov 16, 2012 4:42 pm

Re: USB/DC LiPo battery charger questions

by Mcmoody1472 on Fri Jan 18, 2013 5:06 pm

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.
Mcmoody1472
 
Posts: 9
Joined: Fri Nov 16, 2012 4:42 pm

Re: USB/DC LiPo battery charger questions

by adafruit_support_rick on Fri Jan 18, 2013 5:07 pm

Mcmoody1472 wrote: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)
User avatar
adafruit_support_rick
 
Posts: 11660
Joined: Tue Mar 15, 2011 10:42 am
Location: Buffalo, NY

Re: USB/DC LiPo battery charger questions

by Mcmoody1472 on Fri Jan 18, 2013 5:10 pm

So does that mean you would just solder a wire across the two holes? Sorry, I'm not very proficient with electrical stuff.
Mcmoody1472
 
Posts: 9
Joined: Fri Nov 16, 2012 4:42 pm

Re: USB/DC LiPo battery charger questions

by adafruit_support_rick on Fri Jan 18, 2013 5:18 pm

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.
Last edited by adafruit_support_rick on Fri Jan 18, 2013 5:18 pm, edited 1 time in total.
Reason: typo
User avatar
adafruit_support_rick
 
Posts: 11660
Joined: Tue Mar 15, 2011 10:42 am
Location: Buffalo, NY

Re: USB/DC LiPo battery charger questions

by adafruit on Fri Jan 18, 2013 5:20 pm

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
User avatar
adafruit
 
Posts: 11671
Joined: Thu Apr 06, 2006 3:21 pm
Location: nyc

Re: USB/DC LiPo battery charger questions

by Mcmoody1472 on Fri Jan 18, 2013 5:57 pm

Ok. Thank you for all the information.
Mcmoody1472
 
Posts: 9
Joined: Fri Nov 16, 2012 4:42 pm

Re: USB/DC LiPo battery charger questions

by thinkBig on Sat Aug 03, 2013 1:52 pm

Did this work? I want to charge a 2 cell LiPo battery with item 390.
thinkBig
 
Posts: 1
Joined: Sat Aug 03, 2013 1:49 pm

Re: USB/DC LiPo battery charger questions

by Mcmoody1472 on Sat Aug 03, 2013 6:30 pm

Yes it worked. You just have to make sure to use the dc port to charge and not the USB since the USB has a built in 5V max draw. Dc port is 12V max. Worked great for our 2 cell lipo. We used solar panels to supply the 12V
Mcmoody1472
 
Posts: 9
Joined: Fri Nov 16, 2012 4:42 pm

Re: USB/DC LiPo battery charger questions

by chrisc123 on Sat Oct 26, 2013 10:15 am

Hi,

I'm now working on my senior design as well, and I have a question if you guys happen to see this! I saw that replacing the 4.2 volt chip with the 8.4 volt chip allowed you to charge two LiPo cells. In my case, I need to charge a 2S 7.4 V LiPo battery pack for use in an RC car (using solar power). I have seen two potential solutions to the multi-cell issue on adafruit: either do the chip replacement as you did, or make a simple balance charger and charge the LiPo cells in parallel.

The advantage of the chip replacement is that it seems like I could still charge the battery and simultaneously run the car (maybe I'm wrong), but with the simple balance charger there is a switch and the car is in either run mode or charge mode. So my questions are:
(1) Is it difficult to replace the 4.2 volt chip with the 8.4 volt chip?
(2) Did you run into any problems because of uneven charging of the LiPo cells?
(3) How could you tell when the LiPo battery was fully charged or when the battery was low? Was overcharging of the cells prevented?

Sorry, but I'm in Mechanical Engineering and don't know much about electronics. It seems like the safer route is to go with the balance charger, but it would be really nice to run our car and charge the battery at the same time!

Thanks,
Chris
chrisc123
 
Posts: 9
Joined: Tue Oct 22, 2013 6:53 pm