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Registered Member #1565
Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159
You can get a IC that monitor all cell voltages, control the FET's to switch the resistors on/off and monitor temp/under/over voltage and maybe even current.
In addition it will only need a external charger circuit.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Erlend^SE wrote ...
You can get a IC that monitor all cell voltages, control the FET's to switch the resistors on/off and monitor temp/under/over voltage and maybe even current.
In addition it will only need a external charger circuit.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
Something like an MC34063 for each cell connected to a dedicated Li+ charger Ic would also work, and guarantee isolation. Also this approach is a bit safer and gentler on the cells if a low current IC is used such as the MAX1555, L6924D or Intersil 9220
Registered Member #941
Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497
Aint the point of balance charging to get all cells in the series pack to the exact same voltage ?
Charge voltage can be changed by changing the full charge constant voltage regulation loop but should be kept at 4.1V or 4.2V depending on which is specced in the datasheet for the cells.
Charge current is limited by sesing the primary side current.
My charger idea is intended for a pack of six 18650 cells out of a laptop battery pack rewired to all in series.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Experimentonomen wrote ...
Aint the point of balance charging to get all cells in the series pack to the exact same voltage ?
Charge voltage can be changed by changing the full charge constant voltage regulation loop but should be kept at 4.1V or 4.2V depending on which is specced in the datasheet for the cells.
Charge current is limited by sesing the primary side current.
My charger idea is intended for a pack of six 18650 cells out of a laptop battery pack rewired to all in series.
yes I suppose when some cells reach 4.2V they go to low current, while other cells below 4.2 continue to draw greater current. but my charger is working on 10mA and 0.05V increments, I don't know if you can get precise regulation with an unmonitored channel system as you suggest. But your not demending super jolts of power output either so it may be fine.
Registered Member #941
Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497
Now that i think about it, the voltage over each winding can rise well above 4.2V as the voltage feedback only activates when the full pack voltage reaches 4.1-4.2V x6 which is 24-25V and only then the duty cycle will back off to 4.1-4.2V per winding.
I'll tinker around with a circuit to measure the voltage of each cell individually.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Is constant current, switching to constant voltage per cell, good enough?
Then consider charging the string in series, with a simple shunt voltage regulator in parallel with each cell.
Each shunt could be instrumented with LED[s] or a little meter to indicate how much of the string current is being diverted around that cell to maintain e.g. 4.2 volts.
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18650 lithium battery pack charging
