Battery pack charging

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

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

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

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

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.

Check out the DIY Electronics forum (Aircraft - General section) at

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.

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That's one of my patents :-P

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HAve a look at

Barry

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:

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

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.