Safe battery charging?

[keymuu]

When Ingvar replied and your response had this in it

I guess others did not want you telling them they do not have enough experiance to answer you question.

You could search the forum:
http://www.picbasic.co.uk/forum/show...ttery+charging
http://www.picbasic.co.uk/forum/show...ttery+charging
http://www.picbasic.co.uk/forum/show...ttery+charging
http://www.picbasic.co.uk/forum/show...ttery+charging
http://www.picbasic.co.uk/forum/show...ttery+charging
http://www.picbasic.co.uk/forum/show...ttery+charging

Not all of the above talks about your battery arrangement...but you have not told the type of battery you are using, you only told the package size.

But to answer your first question about charging.
Use a constant voltage with an amperage limit for the amount of cells in the system. As the voltage of the battery increases the amperage will naturally drop, giving a taper charge to finish. When the voltage is reached have the system shut off. That simple. All the other methods are just a bunch of hooy.

Dave, thank you so much

I do not know now with what words I have been searching the forum, but obviously with wrong ones

I have been googling around and found for ex. those MAX712 but I do not trust an application note when there seems (to me) to be errors (npn-pnp). Is it really so? Can't believe that such a big company as Maxim Dallas could have such an error. That is why I asked if somebody has any experience with such a charger (around the MAX712).

I read through all the links you kindly provided, thanks again for the links.
In one of the links there was an idea of charging each cell (battery) separately when they are connected in series. That is interesting and sound really safe, but will more complicated to build the more batteries you have, so maybe it is just a good idea to forget in normal cases.

You asked what type of batteries. And you are right, I have forgotten to tell that, sorry
They are NIMH, Sanyo AA (HR6) batteries 2700mAh each.

[Acetronics2]

Hi, Keymuu

I guess others did not want you telling them they do not have enough experiance to answer you question.

Also, consider it's a PBP Forum ... not a general electronics Forum ...



Dave is here "close to the truth" ...

Just add to that all batteries have a Tempco ... and you'll have to trim the end-of-charge voltage depending on temp.

Now ... also remember "slow" charge and reasonnable discharge rates give the max. life duration to your cells.

For the end ... remember each cell has its particular capacity ... so it MIGHT be charged cell per cell. and voltage shouldn't drop below .8v ( for Nixx ) ...

For series assemblies ... a Schottky diode parallelled to each element is a safe precaution not to invert the polarity of one cell while discharging, ... or in use ...

The chargers might be able to recognize a cell voltage inversion ( very quick voltage drop of the assembly ) and , as soon as, turn to slow charge ...

But ... I did not hear about that, during all these years ...

Alain

[mackrackit]

Sometimes the manufacture has some specs for charge and discharge.
http://us.sanyo.com/batteries/specs.cfm

[keymuu]

Sometimes the manufacture has some specs for charge and discharge.
http://us.sanyo.com/batteries/specs.cfm

Thank you Dave and merci Alain!

This conversation about this matter and the the info you can find scattered around has brought myself to to new level of understanding the batteries.

Here is how I now will build it:
My PIC has 6*1.2V NiMH batteries and it measures the voltage of the batteries. A regulator (L4940) convert it to usable 5V.

The charging will work in the following way:
You plug 12V/800mAh to the batteries via a mosfet that will be on because the gate is connected via a resistor to the battery side and from the gate directly to a port of PIC so that it can cut off the charging even that the charger is still connected. How to continue from this point is slightly unclear at this point. There could be a small charge pulse for example 1s charge and 15s not, or measure the batteries all the time and wait them the drop a little and charge then until reached the previous "full" state.

So, during measuring of the battery woltage I will measure the voltage "curve" and wait until it does not grow any more (instead it drops a little) and that is the point to stop. On the other hand I will have two NTCs, one on the battery pack and the other as a reference (not near the batteries), I can so follow the heating up of the batteries and if they heat up too much, say 15 degrees PIC could cut off the charger by pulling the mosfet gate down. And keep on the this "batteries warm" mode until then charger is unplugged.

The only bad thing with this idea is that you can not shut off your PIC and the "battery usage" when your batteries are fully charged, but keep on this "after charging procedure" .

If you happen to have an idea how to plug the charger so that your PIC can notice that and turn off the charge when fully charged, please let me now....

[Acetronics2]

Hi, Keymuuu

I remember, some years ago, digging into Maxim , Micrel , National , and Linear AN's ... I finally got very clear infos about battery charging techniques ...

But you should download :

from µChip
- AN 960
- AN 1015a

From Galaxy Power Inc
- AN 0014 ( ICS 1700-1702 Chips --- Which are Pic's !!! )
- AN 0017

that will save your last Hair ....

Alain

[keymuu]

Hi, Keymuuu

I remember, some years ago, digging into Maxim , Micrel , National , and Linear AN's ... I finally got very clear infos about battery charging techniques ...
But you should download :

from µChip
- AN 960
- AN 1015a

From Galaxy Power Inc
- AN 0014 ( ICS 1700-1702 Chips --- Which are Pic's !!! )
- AN 0017

that will save your last Hair ....
Alain

Merci Alain, vous êtes l'homme, ... qui sais, ... vraiment

AN 960 was really good...
I could find a lot info about Galaxy power but was not able to find those ANs or home page for Galaxy Power, however, I will proceed on the path I described in my previous "mail", hope it is not that bad...

Thank you all who helped me with this matter, thank you indeed

[spikegomez]

Some manufacturer have the user guide for charging and discharging the battery in a right way...
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