Electronic – Battery management circuit for Nokia BL-4C / 5C Li-ION batteries

battery-charginglithium ion

Nokia BL-4C / BL-5C are 3.7V, 700-1000mAh (variants) Lithium-ion batteries, which are available in abundance and at very low cost ($4 – $7 a piece), since these are used in entry level Nokia phones, sold in most developing countries.

These batteries have 3 terminals, as explained here, for battery positive-terminal, ground, and a terminal (BSI) which I believe presents a fixed resistance value, that needs to be measured, to determine battery-type (chemistry, characteristics including capacity etc.)

So here are my questions:-

  1. Is anyone aware of any existing open-source hardware project, that has built battery-management circuit around such batteries ? (PS> In my searches so far, I've not come across any such project).

  2. How exactly, can one accurately measure the resistance offered by BSI terminal of the battery ? A very accurate and stable reference voltage would be required, I believe – but if the battery itself is the source of such reference voltage, it could vary with charge-status and condition of battery, so how could it serve as a good reference ?

  3. Is it necessary to have a temperature sensor in proximity/touching the battery ?

  4. What would be some low-cost battery-management IC's that are not too difficult to source or work with, for hobbyists, which can be used to charge such Li-ION batteries safely ?

Have found this question here related to 'resistance measurement', but the mechanisms described are far too cumbersome, expensive & require manual intervention, to be useful in automated battery-type identification. OTOH, it is possible that I've completely misunderstood the purpose of the BSI terminal.

As for whether "temp sensor" is needed, I think the answer is YES, based on this. However, the question then becomes, without access to proprietary battery characteristics information of this Nokia battery, what can one do with the temp-sensor ?

Best Answer

3rd terminal:

The 3rd terminal on your battery is most likely to be an "on board" thermistor temperature sensor. Try this.
Determine -ve and +ve battery terminals.
Connect ohm meter between -ve and terminal that is not +ve.
Blow warm air over battery (NOT TOO HOT) and determine whether resistance varies with temperature.
Sensor could be comnnected to +ve rather than -ve but -ve connection probably most likely.

Charging:

There are many ICs available for charging LiIon cxells. If you want to build your own Lithium Ion / LiPo charger for up to 500 mA charge rate then using the MCP83831 / MCP83832 charger IC is a very easy and economical way of doing so.
This is eg what Sparkfun use in the LilyPad Simple.
Data sheet here

It can literally be as simple as shown in the circuit diagram below.

enter image description here.

The resistor from Vss to Prog sets maximum charging current.
Several other options are available by selecting variants of the basic device. Unfortunately 3 different options are selected as a group (see datasheet page 21) providing less flexibility , but the device is still useful and well priced.
Options include cell voltage below which charger goes into "precondition" mode,
end point current termination level
and i_condition / i_charge ratio.

My main "complaint" with this IC is that the lowest voltage output level version is 4.2V and higher voltage (and very dangerous) versions are available.
Digikey sell 3 different versions (AC, AT, DC) with the AT mainly stopping charging sooner (longer life, lower capacity), while the DC variant will try to produce 'magic smoke' and 'vent with flame' if a very low voltage battery is charged.

Available in stock from Digikey for $US0.68/1 and $US0.42/100.

Related Topic