« Return to Thread: Re: Lithium battery charger with balancer proof of concept
Re: Lithium battery charger with balancer proof of concept
by RussellMc
::
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> Or you could just buy a Turnigy 3S balancer and charger for $4.50,
> does pretty-much exactly this. Back-order at the moment though.
> http://www.hobbyking.com/hobbyking/store/__7637__Turnigy_balancer_Charger_2S_3S.html
looks good.
Appears to use special magic.
It says it is a balancer.How do you balance 3S LiIon with no centre
taps? That's not to say you can't do it - just that the lead acid
method would be unwise.
With some battery chemistries you can bring up a low cell by charging
the overall battery at a higher than usual voltage so that fully
charge cells are driven into the steep upper tail of the charge curve
while the low cell ramps up to meet them.
LiIon frowns extremely severely on such practices. Normally, when a
cell reaches its upper voltage limit the cell is put in a constant
voltage mode and accepts whatever current it wishes and the current
"tails off". The tail current is controlled by the most charged cells.
There is no way to apply a higher current that this without pushing
the cell out of CV mode and back into voltage increasing mode - magic
smoke may follow.
What MAY be done is to rely on the fact that charging is less
efficient as the end of CC mode is approached and then also as CV is
initiated. ie for a given number of amp-seconds of charge a cell will
accept a greater percentage of charge if it is more discharged. By
charging the good cells up into the edge of CV and then discharging
and repeating the lowest charged cells are operated in a higher charge
efficiency region and so their stat of charge asymptotes towards that
of the more charge cells. Maybe.
Russell
> [1]
> > I suggested a module made up of a lithium charger IC, a switching
> > mechanism that could isolate those batteries in the chain
> (envisaging no
> > more than 3) once they've charged and some form of electronic load
> > (probably a FET). It has been proposed that each battery could have
> its
> > own switch controller and thinking about this a small Pic or Atmel
> chip
> > could be used to provide the intelligent switching per battery with
> the
> > charger/battery gauge chip providing the correct charging
> algorithm, the
> > controller chip would either switch it out of the pack chain or
> > alternatively switch in the active load to maintain that particular
> battery
> > charge state.
> >
> > Does this seem workable in theory?
> -------------------------
> Msg sent via Webmail - http://hosting.myob.com/
>
> Links:
> ------
> [1]
> http://www.hobbyking.com/hobbyking/store/__7637__Turnigy_balancer_Charger_2S_3S.html
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
> does pretty-much exactly this. Back-order at the moment though.
> http://www.hobbyking.com/hobbyking/store/__7637__Turnigy_balancer_Charger_2S_3S.html
looks good.
Appears to use special magic.
It says it is a balancer.How do you balance 3S LiIon with no centre
taps? That's not to say you can't do it - just that the lead acid
method would be unwise.
With some battery chemistries you can bring up a low cell by charging
the overall battery at a higher than usual voltage so that fully
charge cells are driven into the steep upper tail of the charge curve
while the low cell ramps up to meet them.
LiIon frowns extremely severely on such practices. Normally, when a
cell reaches its upper voltage limit the cell is put in a constant
voltage mode and accepts whatever current it wishes and the current
"tails off". The tail current is controlled by the most charged cells.
There is no way to apply a higher current that this without pushing
the cell out of CV mode and back into voltage increasing mode - magic
smoke may follow.
What MAY be done is to rely on the fact that charging is less
efficient as the end of CC mode is approached and then also as CV is
initiated. ie for a given number of amp-seconds of charge a cell will
accept a greater percentage of charge if it is more discharged. By
charging the good cells up into the edge of CV and then discharging
and repeating the lowest charged cells are operated in a higher charge
efficiency region and so their stat of charge asymptotes towards that
of the more charge cells. Maybe.
Russell
> [1]
> > I suggested a module made up of a lithium charger IC, a switching
> > mechanism that could isolate those batteries in the chain
> (envisaging no
> > more than 3) once they've charged and some form of electronic load
> > (probably a FET). It has been proposed that each battery could have
> its
> > own switch controller and thinking about this a small Pic or Atmel
> chip
> > could be used to provide the intelligent switching per battery with
> the
> > charger/battery gauge chip providing the correct charging
> algorithm, the
> > controller chip would either switch it out of the pack chain or
> > alternatively switch in the active load to maintain that particular
> battery
> > charge state.
> >
> > Does this seem workable in theory?
> -------------------------
> Msg sent via Webmail - http://hosting.myob.com/
>
> Links:
> ------
> [1]
> http://www.hobbyking.com/hobbyking/store/__7637__Turnigy_balancer_Charger_2S_3S.html
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
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