SparkFun Forums

[Marttyn]

Hi everyone! This is my first post here.
For more than a year ive been serching for a simple, yet effective, 2 cell li-ion/poly balanced charger circuit.
The closest ive been is this: http://www.wattflyer.com/forums/showthread.php?t=20575
But it has TO MANY components! I need something like MAX1555, but for 2 cells, with balancing.
I have 2 ideas that could work:

*A ballancer conected to both cells, and a 2 cell charger connecter to the cells in serie.



Problem?
MAX1665 is not for sale ¿? And i didnt find other IC as simple as this...


*A More simple and cost effective design would be a 12v source, 2 LDO 5v regulators and 2 MAX1555 in this way (inspired on the first link os this post):



The above configuration would be grate, but i dont know if it would work.


Disconecting the batteries from eachother and charging independently could be a "simple" solution, but im trying to avoid this so i could use the balanced connector to charge the batteries without having to cutopen the bat-pack and making a disconnection system

Other way could be a microcontroller, but im not confident building the charging process myself... so many people saying the batteries explode that it should be true!

If anyone has a design of 2 cell balanced charger and wants to share it, you are welcome
If someone has a design of 2 cell balanced charger and wants to SELL IT, contact me via PM.
Thanks!

[VStar650CL]

This is an app note and source code for a 16HV PIC microcontroller design. It's fairly simple but pretty smart, you basically fill-in the blanks for your own battery when programming the code:

http://www.microchip.com/stellent/idcpl ... e=en025788

This is a complete reference design with gerbers and BOM using the MCP1630 from Microchip's analog division:

http://www.microchip.com/stellent/idcpl ... e=en023108

[olivier_p]

That design with 2 MAX1555 will probably not work. Your grounds are not on the same levels, their will be more current passing through BAT1 than BAT2.
To use 2 MAX1555 you would need to separate your cells so that they are not in series when you charge them.

MAX1665 does not charge the batteries, it simply monitors the voltages to prevent over or under charging.

Some solutions to your problem are mentionned in this thread:
viewtopic.php?t=13140
I use the BQ2057WSN from TI.

[Marttyn]

The grounds are not in the same level because i want the refference of the regulator1 to be the same as the voltage of the cell2. that way the regulator will supply 5v above the voltaje of cell2, and max1 will charge in this limits.
Max1 should charge cell1, and max2 should charge cell2, the grounds are at different levels, and each has its own, so the batteries should charge indepently...
or not
thanks for the thread, ill check it

[Marttyn]

Although the BQ2057WSN doesnt balance charge 2 cells, it performs ok? any sign of unbalancing?
I didnt see the post with the appnot, ill read it carefuly
Thanks!

[MrPotatoHead]

I have been researching cell balancing some lately. My plan is to build a capacitor array. The concerns are basically the same.

I should really ask someone at work this question, but have not gotten around to it yet. Why not connect the cells is parallel and use a boost convetor to achieve the desired output voltage?

[Marttyn]

charging the batteries in parallel does not balance the cells i think...
also, you need to open the battery pack so you can connect the cells in parallel... bad
a boost convertes may be the solution for some projects.... but many of my projects use servos, witch drains more than 1A... not many dc-dc converters can output that

[peterpan]

I realize this is an old thread, but I like your Max1555 idea, and am curious how it worked. I thought of doing something like this years ago, but after discussing with a MAXIM engineer, he seemed to "poo-poo" the idea, so i didn't pursue it. I also had looked into the MAX1665, and you can still buy it from Rochester https://buy.rocelec.com/buy/search?q=ma ... artasc&p=1, and it is about $6. If I'm going to design price is a concern, but i need a three cell charge and balance. The 1665 still needs at least two more FETs. I imagine if I add another leg to your MAX1555 solution, it might cost me more, and I won't have the added overcharge and over discharge protection. But anyway, I'd still like to know if you tried the MAX 1555 solution and whether it worked, or held any unforeseen bad surprises.

[Marttyn]

I never tried.
All my projects now work with only one LiPo cell, and if needed i use a stepup converter module based on XL6009, that you can buy from eBay for about $1-2 and can output up to 2-3A.
Im happy with this solution, although its not what i was looking for.