cell phone battery in series or parallel

[Ichan]

I am thinking to use multiple cellphone battery for a portable device, anyone ever tried it?

What is the effect of internal protection circuit of the battery on charging / discharging if we use it in series, parallel or series-parallel?

-ichan

[peppeviruz]

if U charge them in parallel, with proper charger, only have to wait more time....
if you use them in series, then you need a charge voltage that is the sum of the batteries in series. (or more chargers in series as the batteries are!)

[Ichan]

Have you tried it?

I just examine an opened cellphone battery protection pcb, it is based on DW01 protection IC and S8205 dual n-ch mosfet. Google gave the datasheet, here is the typical application circuit.

I wonder, will it work in series or parallel connection, in both direction charging and discharging?

-ichan

[pushycat]

If you are intending to use mobile batteries externally for other purposes, you may not use the third pin which is a charge controller pin which controls the charging and discharging cycles of the battery, in conjunction with the cellphones internal circuitry. When connected in series or parellel, you need to connect it with thick conductors as the Amphere capacity of single battery is about 2 amps approx, and a good charger which results to the equivalent of the batteries volatage as "peppeviruz " has mentioned.

[eSilviu]

Hello,
You should use li batteries in series ONLY when you need a bigger voltage, and a DC/DC step-up converter can't be used.
1. If you connect batteries in series you will need a special charger, that will charge every battery separately (search on a RC forum for Li-po chargers for examples). You battery pack will have +,- and (n-1) aditional wires, where n=number of batteries. You must connect in series ONLY batteries of the same type and capacity!!!

2. If you connect them in parallel:
 - you can use a simple charger to charge the pack;
 - you must use ONLY batteries of the same type (Li-ion or Li-po);
 - charge batteries to the same voltage before connect them in parallel !!! if one is charged, and other empty, the emply one will absorb a very big current at the connection time;
 - I would give-up the protection circuit from phone batteries if current bigger than 500mA is necessary.


Posted on: June 19, 2010, 08:44:18 20:44 - Automerged

Have you tried it?

I just examine an opened cellphone battery protection pcb, it is based on DW01 protection IC and S8205 dual n-ch mosfet. Google gave the datasheet, here is the typical application circuit.

I wonder, will it work in series or parallel connection, in both direction charging and discharging?

-ichan

Put them in series, and connect the pack to a charger. When first battery will be charged, the OC MOSFET will break the circuit, blocking all other batteries to charge.

Parallel connection is the best option. This way you can use the protection circuit from every battery.

[Ichan]

I would give-up the protection circuit from phone batteries if current bigger than 500mA is necessary.

From the datasheet of DW01. the current limit value depend on the Rds On of the mosfet used. With S8205 mosfet which has 25 mOhm Rds On the current limit is 3A.

Put them in series, and connect the pack to a charger. When first battery will be charged, the OC MOSFET will break the circuit, blocking all other batteries to charge.

Are you sure about this?

-ichan

[pickit2]

Are you sure about this?

If M2 is off then charge of batteries would be blocked by diode in FET. only when M2 is on (low Rson)would the other batteries charge.
one thing is you could use more than one charger if they are not got a earth on the + or - supply pins.
I'm sure you could allow for this.

[eSilviu]

From the datasheet of DW01. the current limit value depend on the Rds On of the mosfet used. With S8205 mosfet which has 25 mOhm Rds On the current limit is 3A.

from my experience, phone batteries have overcurrent protection: shortcircuit + and - for half a second, and for 30sec to 2 min you will get 0V at the supply pins.
(tested on some Nokia 3310 Li-ion, sony-ericson + others)