But it makes sense to balance at a Low Rate, Its not like Im going to throw two vastly out of proportionally charged batteries into this thing. Im actually going to Precharge them both to a full charge using a single Charger. Once both cells are at 4.2V, THEN I'll plug them into the final circuit. Im under the assumption that there will never be a vast difference in voltage, However, Assumptions are a Bad thing. So The Jury is still out for deliberation, Balance at 1C or Some Fractional Number of C?
My engineering instinct tells me to go with a 1C Balance, Just In case Some where along the lines one of the cell's do malfunction, But the BQ2057 has a temp sensor which I will be using, so there shouldnt be any issues other than ageing. Since the end Application will be a LED flashlight, Its also possible the Boost Converter can malfunction, and short out (On the input side of things that is). A Fuse should be able to handle that sort of malfunction, shouldnt it?
Add (off topic warning): I seem to need a bit of help calculating the resistors needed for the temp sensing portion of the BQ2057 Charger (page 12) . Li-Ions have a max temp of around 45C when charging (well should be below that). I dont need a lower temp as its going to be inside. Heres the
datasheet for said thermistor. Its rated 10k @25C, Part Number NTCLE100E3103JT2. Itsa NTC thermistor.
Now the Formula For the resistors for temp monitoring need Two resistances from the Thermistor, Rth and Rtc (hot and cold). So luckily theres a table of values. Im going to be using 45C and 0C (Even though I dont need the lower temp). For those looking, the values are on page 10. For 45C its 4372, and for 0C its 32,554 Ohms. Now my Issue here is, for the denominator on the formula given by the BQ2057 Data sheet, Are negative, thus giving negative resistances.
But heres my answers for those who want to plug and chug: Rt1 = -8.41k and Rt2 = -3.24k. Do I just drop the negative?