> -----Original Message----- > From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf > Of V G > Sent: 12 February 2011 05:57 > To: Microcontroller discussion list - Public. > Subject: Re: [EE] Cell balancing >=20 > On Sat, Feb 12, 2011 at 12:20 AM, Lee Jones > wrote: >=20 > > > Just a question: > > > > > > I know things like laptops are using multiple cells in series > > > in their battery packs. > > > > As do radio control aircraft, particularly helicopters, which > > use multiple cell Li-Po batteries. > > > > > But after repeated use and several charge/discharge cycles, wouldn't > > > one of the cells start to maybe charge/discharge faster than the > > > others? Or have a slightly offset voltage for some reason? In this > > > case, applying voltage back to the battery pack (cells in series), > > > would charge the cells unequally, no? Or perhaps overcharge some > > > cells while undercharging others? > > > > Yes. Yes. Yes. And yes. > > > > > Is this a real problem? And how would one go about solving it? > > > > A balancing charger which charges each cell individually. There > > are also balancers (which just try to even out the cells). The > > requirement is that the battery pack must have a second multiple > > wire connector which brings out a connection to each cell. That > > second wiring harness is what is used by the balancing charger. > > > > The primary harness is the 2-wire one where the series voltage > > of the pack is used to power the electric motor(s) of the air > > vehicle (helicopter, aircraft, etc). > > > > > Thanks. That makes sense. >=20 > however, by bringing out a connection to each cell, doesn't that mean that > the positive end of one cell is connected to the negative end of another, > and when charging those two in parallel, the positive and negative ends of > the charger would short at the junction? > -- There are several options: 1) Buy/build a charger with multiple isolated outputs 2) Use multiple chargers each with an isolated output (i.e. the 0v output is not grounded 3) Use a single charger and charge one cell at a time (obviously takes a lot longer, but is how I balance laptop batteries). 4) Do what most cell balancing chargers do which is to charge the string of cells as a battery, but apply shunts around individual cells once their voltage reaches the maximum permitted level. Either use a constant current shunt (set to the same level as the charging current), or use a much higher current shunt and switch it in and out to provide the same average current. Regards Mike =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .