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Topic: EMBEDDED CONTROLLED BATTERY CHARGER (Read 4772 times) previous topic - next topic

elico

Hi all

when battery is charged , how the charger knows when to
stop charging ?

I am sking this because the battery is constantly chraged and it's terminal voltage
is charger dependent .
so how the charger controller  knows the real status of the battery to decide if to disconnect
it from charger ?

Elico

CrossRoads

The battery charge profile is predetermined by the battery manufacturer.
The battery charge control chips then implement that profile.
For example, see this datasheet for a LiPo charger
http://datasheets.maximintegrated.com/en/ds/MAX1811.pdf
It tests the charge condition of the battery, then charges at user selected current levels to user selected voltage level.

Not as well spelled out is how it knows when to stop charging:
"The MAX1811 is in current mode when the BATT voltage is below the regulation set point and in voltage mode when the BATT voltage is near the regulation set point."
I can only guess from this document that as the charge voltage is reached, it stops charging and tests to see if the voltage is being maintained.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Docedison

At that point the charger IC 'flips' from CC mode to CV mode to limit the max voltage the battery will see from the charger. Kinda a float charge.

Doc
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Chagrin

I think OP is saying that if you applied (e.g.) 4.2V to a lithium battery that it would always look like the battery was sitting at that same 4.2V as you were charging it. The answer is that the charger either limits the amount of current flowing into the battery (when this is occurring the voltage to the battery will not be seen as a full 4.2V) or limits the voltage being fed to the battery (and measures the amount of current flow into the battery).

All chargers limit the rate of charge using one of the above methods. If this is not done then the battery is at risk of overheating and becoming damaged.

pico

Also note that (safe) recharging of a Li battery usually involves temperature monitoring of the cells, which is why they usually have an extra terminal on the battery (for the built-in thermistor).

Recharging other chemistries is usually more straightforward.
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CrossRoads

Usually, but not always.These 1000mAH LiPo's do not, and the MAX1811 does not monitor battery temp to charge it.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

pico


Usually, but not always.These 1000mAH LiPo's do not, and the MAX1811 does not monitor battery temp to charge it.



Is it just a case that you have to recharge these batteries (relatively) slowly, or is there something inherent to design of these batteries that make them safer to recharge than other Li batteries? 
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elico

Whjat I am trying is to design a wind turbine batteries
charger for suitable batteries , usually used in wind turbines .

So that the chargers charge 24/7 .
I need to know how the embedded based controller
"knows" when the batteru is charged so no more charging curent will
be applied .

i would think that the best wat will
be periocically stopping current to battries and
mesuring battery volyage with some resitive load
connected at measure time .

Elico

CrossRoads

@pico,
I don't really know.
Chip only does 100/500mA charging, and 4.1 or 4.2V.
Asked the battery manufacturer, said to charge using 500mA/4.2V so that's what I used.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

CrossRoads

elico,
I think you need something like this
http://www.reuk.co.uk/Wind-Turbine-Charge-Controller.htm
Search google, there's a lot of wind turbine info available.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

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