Q2686 Li-ion Battery mangement

hi all,
I’d like to use in my project the Li-ion battery management but i’m a little bit confused about what kind of component i have to wired to the CHG_IN input. Indeed the Q2686 seems to be able to control the li-ion battery charging but do i need to use an external battery charger IC (bq24081) like the one specified in the “External battery charging solution” application note (in this case the CHG_IN input can be floating) or is there a better suited solution around a dedicated IC or a simple voltage regulator ?

well, first of all. make sure you thoroughly understand how to treat li-ion cells, how they are charged and how you should handle them.

the choice for an internal or external charging solution depends on the intended use, because the module can’t charge the battery if the battery is discharged too deeply.

the application note describes an external charging solution. In this scenario the module isn’t controlling the charging process.
for how to connect a battery to the module for use with the internal charge management, look to the sdk schematics.

But seeing that you mention the use of a simple voltage regulator i strongly suggest you take a good look at how to charge (end not charge) a li-ion cell. because of the simple reason that these things EXPLODE when handled incorrectly.
a good place to start is batteryuniversity.com

Thanks Madouc!

I would like to ask something else and I would be grateful if you could answer my question. Supposing that I use a Li-ion battery connected to the VBATT pin of the Q2686. With the AT commands, I have to declare to the module the specifications of the battery (as well as the type). But when I want to charge the battery, is this process controlled by the module or do I have to tell the Q2686 when to start the charging, how long to keep it and when to end it?

Thanks in advance!

no, the module takes care of all the details after you told it to start the charging process. you just plug in power and the module restarts, stops and changes charging mode based on batterylevel and battery temperature.

btw. all this information is also available in the at-documentation

Thanks Madouc, but the thing is that you say that I have to tell the modem to start charging but in p.94 of the AT COMMANDS USER GUIDE it says that as soon as we get the unsolicited response +WBCI:0, if a charger is plugged in, then the charging process starts AUTOMATICALLY! Isn’t this correct?

Thanks again for your response!


First, which version of firmware are you running?

+WBCI: 0 indicates the battery is fully discharged (as per parameters from AT+WBCM=3,…) and that the Q26 module will be turned off if no charger connected. Automatic charging only begins if it has been previously enabled.

The charging process will not start automatically until you have told the module to enable the charger (i.e. AT+WBCM=6,1 to enable the charger module, and AT+WBCM=1 to start the charger. Now if you have configured the charger correctly, battery charging will restart automatically after a power cycle or reboot; and when the charger detects that the external power supply is reconnected (CHG-IN).

Note that the onboard charger electronics DO NOT CURRENT LIMIT the charge being applied to the battery. It is the responsibility of the external power supply (CHG-IN) to limit the current to the battery. Get this wrong, and you WILL have problems. Especially with a Li-Ion battery. As Madouc said, understand your battery characteristics before starting work - or at least keep a video camera running so we can see the results on You-Tube!

My sequence for managing a Li-Ion battery is as follows:

AT+WBCM=0                                // disable charging if running (clean start)
AT+WBCM=6,1                             // enable battery charge management
AT+WBCM=4,1                             // set up for Li-Ion battery charging
AT+WBCM=3,......................   // set Li-Ion battery parameters
AT+WBCM=5                                // test if charger is plugged.
AT+WBCM=1,1                             // enable battery charging with +WBCI indications

All this is in the documentation - both the AT manual and the hardware design specs.

BTW, the hardware specs indicate that the Q2686 can pre-charge charge the Li-Ion battery if it is between 2.8V & 3.2V. See Q2686 Wireless CPU Technical Specification Rev 008, section 3.13.3 for further info on pre-charging. I have tried this on a dev board and it did seem to work OK.

ciao, Dave

So do you actually use Li-Ion batteries in your project? Do you charge em constantly or you usually have your charger unplugged?


Yep. I’m using a 18650 format cell that has a (nominal) capacity of 2400mAh. It has a PCM built into one end, but unfortunately doesn’t have an built-in NTC temperature sensor. I’ve placed a NTC sensor and resistor on the PCB underneath the battery and am currently testing this set-up.

I run the Q2686 off the battery continuously, and leave the charger plugged in constantly and charge the battery via the Q2686 module. This solved two issues for me:

  1. I didn’t have to design a PSU to supply the large peak currents required by the Q2686 while transmitting (I have a long data upload cycle, so there is enough capacity in the battery to do the transmissions, and the battery is re-charged/topped up during the off period). My power supply can supply around 1.2A @ 4.2V which is enough to re-charge the battery reasonably quickly and provide the quiescent operating current for the Q2686.
  2. Monitoring the presence of mains supply (important for my design) was easy - I just subscribed to the +WBCI: 5 unsolicited message which indicates the charger has been unplugged.

I’m currently in the middle of trialing how my batteries stand up to this treatment. I haven’t found them getting hot under this regime - but I am still testing how they go when they have been fully flattened a few times.

Also, battery management is another area that could do with a proper ADL API. Currently, you have to do everything through multiple adlCmdCreate() calls - which is a pain, and can be messy to follow the program flow.

ciao, Dave

Current monitor? Is it possible to do charging without external monitor?

Did you connect it to BAT-TEMP?

We are afraid of such schema. It seem pretty dirty way to charge battery. But if it will go well, I’d like to hear about it from someone with such an experience.

I think you’re reading this wrong. The battery isn’t being charged continuously (eg. not directly connected to the adapter). The Q2686 is controlling the charging and stops it as soon as the battery is fully charged. Nothing ‘dirty’ there.

The battery is always connected to module to VBAT pin. And module is always powered from the battery. The main source can be used only for charging the battery so the schema is: stop charging -> use module -> check voltage -> charge battery -> go to step 1. This is the only suitable schema since wavecom modules do not have MAIN POWER input - only BAT POWER, as in cellular phones.

I am using 6.60 firmware.

Yes, but I 'm afraid that my firmware doesn’t not support the AT+WBCI=5 and AT+WBCI=6 commands. This is told by the AT COMMANDS INTERFACE GUIDE…

The battery is always connected to the vbatt (voltageBattery, would be a strange name otherwise), but the charger isn’t connected to vbatt. It is connccted to charge-In(chg-in). The adapter of the development kit is always connected to vBatt, but then again, you can’t charge a battery off that input.

Yes, I told you the same. I think it is OK for cellular phones, when you mostly use batterie’s power and charge it periodically. But it does not seem not OK for standalone devices, which use mostly MAIN power, and need batteries only during power outage.

Hiya All.

I’ve done all my development using R71a & R72 firmware, so I can’t help you with the functionality of the older firmware. If you’re starting out on a new application, it may be worth your time to move up to the R7xx firmware and the Oasis development environment. A lot has changed between the 6.xx firmware and R7xx firmware.

I put a lot of thought into this when beginning my current design. A couple of factors influenced my decision to supply the Q2686 from the Battery continuously, and use the onboard charger:

  1. I need a ‘no break’ logger system that will not reboot when the mains power fails. One of my alarm conditions is that the mains power has failed. By running off the battery and keeping it charged when mains is available means that I can start uploading data/sending SMS etc immediately the mains fails, and the Q2686 will not reboot under these conditions.
  2. The power supply required to drive the Q2686 (i.e. supply Vbat pins) is quite exacting, and requires the capability to provide large current pulses with fast rise times. This means you essentially require a 4.2V, 2A power supply. It was easier for me to use a Li-Ion battery to provide this capacity and keep it charged while mains are available.
  3. As noted in (1) above, I needed to keep the module on-line continuously, so needed a battery. To add external charger components to my hardware design increased overall component count, was an added expense and used up scarce PCB real-estate. So I used the onboard charger hardware and added the appropriate software to run it.

True, I guess - if you want the modules to only use the Li-Ion battery as a backup supply for when the mains is not present. This would require some sort of change-over circuit to detect when the mains is not present and (quickly) switch over to the battery. Problem here is the switch-over time. The delay effectively has to be zero time - otherwise you run the risk of having the CPU reboot and the radio have to re-attach to the network etc. The system used by myself (and, I suspect the cell-phone manufacturers) is to run off the battery continuously (Vbat connections of Q2686) and charge the battery when mains are available (CHG-IN connection & software on Q2686).

Incorrect. Connect the battery to Vbat connections, and your mains power supply to CHG-IN. The Q2686 has the appropriate on-line charger electronics built in, so there is no need to stop the unit to charge the battery and the firmware in the Q2868 continuously monitors the battery voltage and controls the charger appropriately…

PCM is the protection circuit module that is the last-resort safety shutdown if the battery is subject to over or under voltages.
The power supply attached to the CHG-IN pins has to be designed not to deliver more than the maximum rated charge current for your chosen battery. The Q2686 does NOT do any current regulation while charging the battery. There are quite a few notes on this subject - unfortunately scattered though-out the Wavecom technical specs.

Yep. Battery hasn’t gone on fire yet, and it’s been subject to daily temperature cycling between about 15 and 36 degrees for over a month now. Haven’t seen any battery temperature alarms in the logs either…

That’s about it for now.

ciao, Dave

Ok. I got it. Thank you.

Well, I’ve seen such devices. :slight_smile:

So why not use some external micro for charging? I’d not trust wavecom in charging my batteries :slight_smile:

But you did not measure batteries degradation after such treatment. But for this moment your schema seem to be the easiest and cheapest way to go…

Thanks for the advice but I think there is a great difference between the firmaware version you are using and mine. In my datasheet there are no AT commands like AT+WBCM=6,1 and AT+WBCM=5 . And the module does not offer any possibility of setting that the charging shall run automatically. In page 92 it says that as soon as the WBCI:0 appears, if a charger is plugged in then the charging procedure starts automatically and the same happens with WBCI:1 when the charging plase stops. The application note that Awneil suggested to look has to do with the charger device, not with the immediate charging procedure of the module. I just need somebody that uses the same version (firmware 6.61 and ) to confirm the above automatical procedures!

Thanks in advance!

How can you send all the paraemters in (AT+WBCM=3,… // set Li-Ion battery parameters)?


Hi All,
I have some question regarding battery management of Q2686. Can someone share their views in this regards.

  1. A Li-Ion Battery is connected to VBATT pin and a cherger is connected to the CHG-IN Pin. If the module is power off condition and i put the charger on, module starts. Is it nomal?
  2. Whether i have ot issu AT+WBCM=6,1 and AT+WBCM=1 after issuing AT+WBCM=3,… command?
    Thanks & Regards.

i would think so, because else the module can’t control the charging process?
(please note that if the battery is deeply discharged, the module might not start. see app.note about external charging solution)

i don’t know. (i’m using an external charging solution)