Lipo charging question

[prebs]

I have made a charging circuit using the famous MCP73831T-2ACI/OT.

I does work (it seems) , but stops charging once it hits 3.6v. When the battery was new, I would start off at 3.8v. Is this normal, or should it charge it up again to 3.7/3.8?
Im using a 2k resistor, so I should charge 500mAH (i think).

Any advice would be appreciated

Thanks

[amyk]

What is the voltage of the power supply? This a linear charger and requires at least the termination voltage (4.2V) to fully the battery. The datasheet gives 6V as the recommended maximum input voltage.

[Zbig]

Proper Li-Po charging cycle is Constant Current phase until the cell voltage reaches 4.2V then Constant Voltage phase (so the voltage doesn't exceed 4.2V) while the current gradually lowers until it reaches termination value. If the cell voltages you posted are across open terminals, that doesn't tell you much as it drops quickly once disconnected from charger.

[ovnr]

If the cell voltages you posted are across open terminals, that doesn't tell you much as it drops quickly once disconnected from charger.

LiPos don't drop to 3.6V, even when they've been disconnected for a long time. I've got ones that have been sitting in a box for a couple years, and even they are above 4V.

[olsenn]

I got a lipo charger at MacDonald's today; it was delicious!

[Zbig]

LiPos don't drop to 3.6V, even when they've been disconnected for a long time. I've got ones that have been sitting in a box for a couple years, and even they are above 4V.

You're right it shouldn't drop that much but still the measurements should be performed during the charging. By the way, it's not a good practice to store the Li-Pos in fully charged state for prolonged periods. Optimal storage voltage is around 3.8V/cell.

[Jibby]

 Single NiCd, NiMh or Lion batteries are 1.2 volts .So 3 numbers in series makes it 3.6V. It can get charged to n3.7 or 3.8 developing no problem on the batteries but once the charge is removed it goes back to 3.6 volt in.

[dr_p]

Single [...] Lion batteries are 1.2 volts .So 3 numbers in series makes it 3.6V.

   You got this all wrong. A single Lithium-xx cell has 3.2-3.7V and charges at 3.7-4.2V. Depends on the chemistry (ion, po, Fe).

[Zbig]

Single NiCd, NiMh or Lion batteries are 1.2 volts .So 3 numbers in series makes it 3.6V. It can get charged to n3.7 or 3.8 developing no problem on the batteries but once the charge is removed it goes back to 3.6 volt in.

Sorry Jibby, but that's not the case at all. Lithium-based secondary cells are very differrent to Nickel-based chemistry ones in almost all respects. Li-Ion/Po cells require very strictly controlled charging process, otherwise that's what happens:



I found this website a very good resource on everything battery related: http://batteryuniversity.com/

[amyk]

Li-Ion/Po cells require very strictly controlled charging process, otherwise that's what happens:

Anyone who considers putting 10A(!!!) through a 1.2Ah cell deserves a Darwin Award... yes lion chemistry does have a really high energy density and require good voltage regulation at termination but charging them is less involved than the algorithms for nickel-based chemistries. Fireworks tend to occur only if you seriously act like an idiot with them.

[peter.mitchell]

Lithium-Ion Polymer cells can be charged somewhat safely with a 4.2v power supply and a current limiting resistor of appropriate power rating and resistance.

With that said, Lithium-Ion Polymer cells should probably not be charged with a 4.2v power supply and a current limiting resistor of appropriate power rating and resistance.