Active Balance lipo cells

[Uitgeslapen]

Does anybody know a good way to actively balance lipo cells?

regards
Daan

[Discharger]

By "actively balance" do you mean charging each cell independantly?
I am considering building 3 seperate simple constant current and volt reg. systems to charge through the balance leads on the lipo batteries.

[Uitgeslapen]

By active balancing I mean keeping the cells balanced at every point. While charging and while discharging. One way of doing it is by taking the charge out of a cell with a high voltage and putting it in a cell with a low voltage.

[coro]

By active balancing I mean keeping the cells balanced at every point. While charging and while discharging. One way of doing it is by taking the charge out of a cell with a high voltage and putting it in a cell with a low voltage.
That is not so easy idea, to MOVE charge between series connected cells.
It is possible.. Schulze LipoBal 8 and 14 balancers are moving energy, instead of bleeding higher cells as other balancers do.
Before wasting Your time, You should think twice what You are willing to do.
I am sure that there is no good reson to do it.

[AndyOne]

There systems for balancing series connected cells over the whole cycle but in my opinion having spent 16 years in the battery industry, it's not necessary.
It's only really important to balance cells at the top of charge because this is where the damage can be done if there is any over charge. Out of balance cells at the bottom of discharge can be damaged by over discharge but a much better way of preventing this is to monitor the individual cell voltages to determine when to end the discharge. There is a circuit in this very forum for doing this... http://www.rcgroups.com/forums/showthread.php?t=526862.

Holding cell voltages together over the whole cycle is wasteful by resistive discharge method or requires a big overhead in complex DC/DC converter circuitry.

Andy.

[Uitgeslapen]

I think active balancing would be a good way to keep your cell's balanced when you have not a lot of energy to charge them... for example when you use solarpower... Are there schematics available how the schulze chargers work in theory? Sounds like a good way to go...

[AndyOne]

I think active balancing would be a good way to keep your cell's balanced when you have not a lot of energy to charge them... for example when you use solarpower... Are there schematics available how the schulze chargers work in theory? Sounds like a good way to go...

If there's not a lot of difference between the cells then it's not worth the bother to do it at all since it won't gain you much compared to the circuitry necessary to make it happen.
Far better to use a charger that balances the cells at top of charge.

Andy.

[Uitgeslapen]

I was thinking about your previous posts and think some extra explaination would be usefull:

The balancer should make it possible that:
*all cells can be fully loaded without damaging a cell.
*make it so that the pack can be disharged completely without damaging a cell.

Because the input energy is very limited burning energy over resistors feels like a stupid thing to do. Because this will require a massive amount of A/D conversion and even more fet's I thought to limit the balancing current it would be better to do it constantly so the differences don't get to big. If the technology is there why not use it???

The cells will almost never be fully charged and they will be charged while being used.

[AndyOne]

If you really want to do it this way you will need to compare all the voltages of the cells with each other or preferably with a reference which is a fixed division of the total battery voltage, 1/3 for 3s pack. Then you will need MOSFET switches to discharge selective cells to keep them inline with this ideal voltage level. The problem with any analogue method is that the tolerance of the components has to be extremely tight for it to be accurate enough even 1/2% out on a voltage reference is too much as this would represent about 7% capacity difference at top of charge.

I still think the method of creating a soft cut-off by acting on cell voltages at the end of discharge is the best method as this does not have to be nearly as accurate to be effective.

Andy.

[Acetronics]

Does anybody know a good way to actively balance lipo cells?

regards
Daan

Hi, Uit

Surfing through the IC manufacturers sites could show you tons of specialised circuits "already cooked" for your application ...



i.e. Maxim's, Linear or National ...

Alain

[Uitgeslapen]

Hi, Uit

Surfing through the IC manufacturers sites could show you tons of specialised circuits "already cooked" for your application ...



i.e. Maxim's, Linear or National ...

Alain

? Can you give one example ?