Battery pack charging

[James Thompson]

I have been thinking of a design for series battery packs and the charging
of them. What I envision is custom wiring of the pack (other then its
series connection) with each cell having additional wire (positive and
negative terminals) feeding to a charge controller circuit. The charge
controller will then charge each cell independent of the pack and stop the
charge current when that cell peaks. Also for each cell in the pack, place a
reversed biased diode to limit and reverse charging to the diode drop
voltage when the pack is discharging or even when each cell gets fully
charged and the others are still charging. Has this scheme been tried or is
in use now?
All comments welcome. JTT

 

[Luhan]

I have been thinking of a design for series battery packs and the charging
of them. What I envision is custom wiring of the pack (other then its
series connection) with each cell having additional wire (positive and
negative terminals) feeding to a charge controller circuit. The charge
controller will then charge each cell independent of the pack and stop the
charge current when that cell peaks. Also for each cell in the pack, place a
reversed biased diode to limit and reverse charging to the diode drop
voltage when the pack is discharging or even when each cell gets fully
charged and the others are still charging. Has this scheme been tried or is
in use now?
All comments welcome. JTT

Currently (no pun), lithium ion rechargable cells have 'built in'
controllers that prevent several problems: overcharging, overdischarge,
rapid dischage, etc.

I guess that the cost of making the type of charger you propose (which
would work), has not been cost effective on a comercial basis. So, a
'less than optimal' compromise is to just charge the whole stack of
cells as a unit and replace them sooner.

Luhan

 

[martin griffith]

I have been thinking of a design for series battery packs and the charging
of them. What I envision is custom wiring of the pack (other then its
series connection) with each cell having additional wire (positive and
negative terminals) feeding to a charge controller circuit. The charge
controller will then charge each cell independent of the pack and stop the
charge current when that cell peaks. Also for each cell in the pack, place a
reversed biased diode to limit and reverse charging to the diode drop
voltage when the pack is discharging or even when each cell gets fully
charged and the others are still charging. Has this scheme been tried or is
in use now?
All comments welcome. JTT

ISTR Micrel doing some battery ics, mainly lion protection(grr, down
Clarence), but it was a few months ago. Try looking at/in the
pro-video mob, they have sophisticated chargers, HDTV camcorders aint
energy efficient, BHphoto maybe ?

Probably not worth the effort unless you need the last mA/hour


martin

 

[Roger Hamlett]

I have been thinking of a design for series battery packs and the
charging of them. What I envision is custom wiring of the pack (other
then its series connection) with each cell having additional wire
(positive and negative terminals) feeding to a charge controller circuit.
The charge controller will then charge each cell independent of the pack
and stop the charge current when that cell peaks. Also for each cell in
the pack, place a reversed biased diode to limit and reverse charging to
the diode drop voltage when the pack is discharging or even when each
cell gets fully charged and the others are still charging. Has this
scheme been tried or is in use now?
All comments welcome. JTT

Multi tag charging is common in some laptops.
Have a look at some, and they have about an 8 terminal strip on the
battery. Two larger terminals at the ends, and a series of smaller ones
between. This allows access to each cell voltage for the charging. Most
are also smart enough to switch off the equipment if a cell gets too low,
removing the need for the diodes.

Best Wishes

 

[legg]

I have been thinking of a design for series battery packs and the charging
of them. What I envision is custom wiring of the pack (other then its
series connection) with each cell having additional wire (positive and
negative terminals) feeding to a charge controller circuit. The charge
controller will then charge each cell independent of the pack and stop the
charge current when that cell peaks. Also for each cell in the pack, place a
reversed biased diode to limit and reverse charging to the diode drop
voltage when the pack is discharging or even when each cell gets fully
charged and the others are still charging. Has this scheme been tried or is
in use now?

I believe there's some emphasis on charge balancing using switched
capacitor voltage equalization techniques, but not in commercial
products.

Regular series strings tend to balance during charge and float, due to
the varying charge efficiency that occurs as full-to-overcharged
conditions are approached.

RL

 

[James Thompson]

Currently (no pun), lithium ion rechargable cells have 'built in'
controllers that prevent several problems: overcharging, overdischarge,
rapid dischage, etc.

I guess that the cost of making the type of charger you propose (which
would work), has not been cost effective on a comercial basis. So, a
'less than optimal' compromise is to just charge the whole stack of
cells as a unit and replace them sooner.

Luhan

Thanks for all the replies. Nearly every pack I have had has died via 1 or
2 cells going bad and I figured I would maybe rebuild packs like for my
cordless drills to balance out the cells and extend there useful service. I
was not really thinking about it in a commercial aspect, but for my own use
to test out the idea.

 

[John]

Has this scheme been tried or is in use now?
Check out the DIY Electronics forum (Aircraft - General section) at
http://www.rcgroups.com/forums/index.php. They have several circuits
for you to use and, I believe, circuit boards are available for some
of the designs. This includes chargers and balancers.

Check out the Batteries and Chargers forum too. Tons of info there.

-- remove SPAMMENOT for e-mail responses --

 

[Mochuelo]

I believe there's some emphasis on charge balancing using switched
capacitor voltage equalization techniques, but not in commercial
products.

That's one of my patents

 

[Barry Drodge]

I have been thinking of a design for series battery packs and the
charging of them. What I envision is custom wiring of the pack (other
then its series connection) with each cell having additional wire
(positive and negative terminals) feeding to a charge controller
circuit. The charge controller will then charge each cell independent
of the pack and stop the charge current when that cell peaks. Also for
each cell in the pack, place a reversed biased diode to limit and
reverse charging to the diode drop voltage when the pack is
discharging or even when each cell gets fully charged and the others
are still charging. Has this scheme been tried or is in use now?
All comments welcome. JTT

HAve a look at
http://members.shaw.ca/Botgoodies2/LithBatt/LithBatt.htm
http://shdesigns.org/lionchg.html

Barry

 

[Martine Riddle]

I have been thinking of a design for series battery packs and the charging
of them. What I envision is custom wiring of the pack (other then its
series connection) with each cell having additional wire (positive and
negative terminals) feeding to a charge controller circuit. The charge
controller will then charge each cell independent of the pack and stop the
charge current when that cell peaks. Also for each cell in the pack, place
a reversed biased diode to limit and reverse charging to the diode drop
voltage when the pack is discharging or even when each cell gets fully
charged and the others are still charging. Has this scheme been tried or
is in use now?
All comments welcome. JTT

A belated Yes/kinda, Check out the Hobby Sites. The switch to Li batteries
has spurred battery pasks with IDC connectors for monitoring cell volatges
and controllers.

eg: http://www2.towerhobbies.com/cgi-bin/wti0093p?&C=ANC

Cheers

 

[PeteS]

A belated Yes/kinda, Check out the Hobby Sites. The switch to Li batteries
has spurred battery pasks with IDC connectors for monitoring cell volatges
and controllers.

eg: http://www2.towerhobbies.com/cgi-bin/wti0093p?&C=ANC

Cheers

TI makes some multicell chargers/monitors designed for charge balancing
etc. by bringing out the pos/neg connections of each cell.

Interestingly, they seem to use a technique I used a long time ago
(well, 15 years ago) to clabrate the remaining charge state.

Cheers

PeteS

 

[[email protected]]

Thanks for all the replies. Nearly every pack I have had has died via 1 or
2 cells going bad and I figured I would maybe rebuild packs like for my
cordless drills to balance out the cells and extend there useful service. I
was not really thinking about it in a commercial aspect, but for my own use
to test out the idea.

I think for such a design to really fly, you would need to both charge
and discharge (i.e. use) the batteries in a manner where the cells are
employed individually. You have now forced the design to have a charger
per cell. Maybe the charger cicuit, which would be modeled around a
DC/DC, can deliver an output current per cell that can then be mixed
and feed to the load. Or the load, say a motor, has a winding for each
battery.