Charging two GP Ion-Li Battery packs with only one IC?

Hi Cristian,

as battery packs are equipped with protection circuits (over-charge over-discharge etc. - see datasheet page 6), they should be charged separately. If two packs will be connected in series and will be in different state of charge, when charging protection circuit in one pack will detect overvoltage, it will disconnect this pack, so charging of second pack will be stopped.

If there will be other battery pack without protection circuits, it would be possible to connect packs in series and charge from one charger but blancing circuit should be used. It protects cells from overcharging.

Thank you for your answer RWM,

I was thinking about that... as I fear.

From the two packs I received, only one of them has a third white terminal (cable). Is this a voltage related to the temperature? Can I connect this cable directly to the Thermistor Voltage In (of the IC charger)?

The other pack has only two terminals... so, I don´t know, maybe buy a thermistor and put it inside the second pack? So each IC charger receives the temperature of their associated pack. Is this a normal way you think?

Best Regards,

Cristian.

Interesting, according to product pages on farnell.com and datasheets both modules should have three wires, you have got different model? Anyway, I have not found wires description neither in datasheet nor on gpbatteries web site. I can guess that there is connected 10kohm thermistor between V- and white wire, but you should check this using ohmmeter. If this is not true, you can attach themistor to the pack. It is not necessary to put it inside the pack, it can be attached on outside sleeve but on battery cell (glued for example). Same for second pack. Themistor can be connected to charger NTC input as in datasheet. It is used to determine whether battery temperature is in safe area for charging (usually 0-40 deg C).

I do hope this will help.

Best regards,

Ryszard

Well, about the third terminal it happened with the 14.8V model (with only two terminals)... but anyway it´s more clear now.

This has helped a lot.

Regards,

Cristian

Hi,

I have chosen two IC Chargers for each of the two Li-Ion packs. Now when I´m going to design the circuit I realize that if this two packs are connected in series, the GND of the 24V that powers the two IC chargers must be different on each other.

It´s an automatic charger so I can´t disconnect the packs. So, do I need two source powers? I fear that it will be the only possibility... Anyone has pass through this?

Thanks in advance

Regards,

Cristian

Hi,

as these packs have protection circuits which can disconnect pack, you have some options:

1) use 2 floating power sources (it means GND of both sources not connected, as GND will be connected to negative electrode of power pack),

2) remove protection circuits from power packs, connect them in series and use one charger; however, you should add protection circuit for 5 cells (for example http://www.ti.com/product/bq77pl157a4225 or more advanced

http://es.farnell.com/texas-instruments/bq77pl900dl/ic-battery-protec-li-ion-10cell/dp/1640400).

Regards,

Ryszard

Thanks for the links Ryszard,

I´m considering also buying a 5-cell pack. Is not very usual. But I saw that some companies like "Tenergy" sells chargers and packs of more than 4 cells. Well, packs of 5 cell does not appear in the web, but I think that is probably easy to find this.

Then, the charger could be a LTC008 for example, with adjustable output voltage, so a termination charger IC could be use for specific Ion-Li charge. This termination charger IC should be connected to the LTC008 or similar...

But I can´t understand because here:

http://www.all-battery.com/AT_TenergyLi-Ion18.5V2600mAhRechargeablePackwithPCB-31941.aspx

we see a 5-cell pack from tenergy.

But in the official web site:

http://www.tenergy.com/Site/Li-Ion-Category

It does not appear...

All depends on the difficulty of finding a 5-cell Li-Ion pack... Do you have any recommendation for finding it?

Tenergy company seems not to answer for the request email I sended...

All the best,

Cristian

Hi Cristian,

you have some packs there:

http://www.batteryspace.com/Ultra-High-Energy-Li-Ion-18650-Battery-18.5V-2800mAh-51.8Wh-4.2A-rate.aspx

http://www.batteryspace.com/Li-Ion-18650-Battery-18.5V-2600mAh-48.1Wh-7.0A-rate-Battery-Pack.aspx

If battery pack is available at all-batterycom and not at tenergy.com so perhaps it is intended for OEM customers. If datasheet is available, it can be used.

I don't know LTC008, you can use e.g. LTC4008EGN#PBFLTC4008EGN#PBF, MAX17015B

Best regards,

Ryszard

Hi Christian, by the characteristics of the battery I guess the use to R / C, told him that I had the same problem with Li-Ion batteries are quite sensitive with respect to the overtemperature and overvoltage. In addition, the battery pack that I use are of high capacity (5000mAh) and Vienne linked in series-parallel with no internal protection. I decided to break the pack and reset CI placed a pair of of protection against overload / over temperature and also balances the load of the cell. For the latter decided to take a pair of wires to each cell to the back of the pack and charger by using a load cell by cell in a battery, a load at the end of the cables so that the pack is reinforced parallel series. As an additional point of C.I. also use the download intelligently manage each cell preventing its voltage falls below 3.3V, which were to happen if the cell loses its ability to recharge.

Then I leave the link in the catalog in which the CI search more suitable to my application.

http://www.ti.com/lit/sg/slyt420/slyt420.pdf

Att. Gustavo (sorry my english is bad)

This is the original pack modifying:

__________________________________________________________________________________________________________________________________________

Hola cristian, por las caracteristicas de la bateria me imagino que la utilizarás para R/C, le comento que yo tuve el mismo inconveniente con las baterias Li-Ion, son bastante delicadas con respecto a la sobretemperatura y sobrevoltaje. Además los pack de bateria que utilizo son de alta capacidad (5000mah) y vienne unidas en serie-paralelo sin ninguna proteccion interna. Decidi deshacer el pack y rearmarlo colocandole un par de C.I. de proteccion contra sobrecarga/sobretemperatura y además balancea la carga de la celda. Para esto ultimo decidi sacar un par de cables a cada celda hacia el lado posterior del pack y utilizando un cargador mediante cargar celda por celda en un cargador, al finalizar la carga uno los cables de tal manera que queda armado el pack serie paralelo. Como punto adicional los C.I. que utilice tambien gestionan inteligentemente la descarga de cada celda evitando que su tensión descienda por debajo de 3.3v, que si llegara a pasar la celda pierde su capacidad de recargarse.

A continuación le dejo el link del catalogo en el cual busque los C.I. mas adecuados a mi aplicacion.

http://www.ti.com/lit/sg/slyt420/slyt420.pdf

Atte. Gustavo

Este es el pack original que modifique:

Hi Gustavo,

I´ve also looked for this type of batteries. But I think that packs which are sold in the market that includes protection circuit are also included with a balance charge circuit. The only problem is that they don´t have temperature protection, some of them without even thermistor. (correct me if I´m wrong)

According to the post with RWM, I´ve been speaking with tenergy about prices of pack batteries with temperature protection included (5 cells - 4,400mAH) but prices goes too high. So the best solution I have is to implement temperature protection by myself, (IC or whatever.).

The link of Texas Instruments pdf shows nice ICs for implementation. But I don´t see the difference buying one pack with protection included (5 cells in a pack) than buying a battery without any electronic inside the pack.

Regards,

Cris