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What's the best way to make a dual voltage 18650 battery pack

penta-designs

Hello People,

 

I'm working on a project that needs 12 and 24 volts from a modular battery pack. and i'm hoping that its possible to make a battery pack that will do just that.

 

what i was thinking of using is

 

24 x  LGDBMJ1 li ion 3.7 v, 3.5 A cells

 

individually charge / discharge protection pcb in series               ( is this possible?? )

2pcs New 5V Micro USB 1A 18650 Lithium Battery Charging Board Charger Module | eBay

 

4 cells in series going into a stepdown converter to 12 volt 5 amps

DC DC 4 5V 30V to 0 8V 30V 5A Step Down Power Apply for Arduino Raspberry Pi | eBay

 

and then some how to create a efficient circuit to also have a 24 volt 3 / 6 amp output

 

so the questions i have are

 

1 - can a li ion charge / discharge protection pcb be placed in series?

  - and if so thus it affect the discharge protection?

 

2 - is there a way to place the step down converter in series?

 

or should i just make a 12 volt battery pack with an 24 volt step up converter

DC12V Step Up to 24V 240W 10A Car Power Converter Regulator Adaptor | eBay

 

 

any help would greatly be appreciated

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  • 0

    This is not a task to undertake unless you are sure you know what you are doing. 24 x 18650 cells is a lot of lithium.

     

    My initial approach would be to go for at least 28V battery voltage minimum and use step down converters for both outputs.

    You could use 3p10s (30 cells) for a battery voltage range 25 - 42V.

    You MUST use cell balancing which means lots of complicated cell monitoring and charge pumping - Linear technology (and others) sell suitable chips.

    (You can get away with putting three cells in series with just monitoring (but can expect to lose quite  a lot of battery life as they age) but 8 or 10 cells is too many in series without the ability to pump between them - the controller is complicated )

     

    If you use a 12V battery (4 cells in series is really a 10 - 16V battery) you can get away without charge pumping but you'll need an up/down converter for the 12V and an up converter for the 24V. Less efficient but simpler to do.

     

    The little charging board could only work if you removed the cells and charged them one at a time. I expect chargers for 4 cells in series exist.

     

    I suggest you read up on Lithium cells and recommend that you look at data sheets and app notes form TI and Linear Technology, these two sell chips but not batteries so tend not to gloss over the problems with the batteries.

     

    If you can stand the size and weight a sealed lead acid battery is cheaper, more reliable and much more forgiving if you make a mistake.

     

    MK

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  • 0

    This is not a task to undertake unless you are sure you know what you are doing. 24 x 18650 cells is a lot of lithium.

     

    My initial approach would be to go for at least 28V battery voltage minimum and use step down converters for both outputs.

    You could use 3p10s (30 cells) for a battery voltage range 25 - 42V.

    You MUST use cell balancing which means lots of complicated cell monitoring and charge pumping - Linear technology (and others) sell suitable chips.

    (You can get away with putting three cells in series with just monitoring (but can expect to lose quite  a lot of battery life as they age) but 8 or 10 cells is too many in series without the ability to pump between them - the controller is complicated )

     

    If you use a 12V battery (4 cells in series is really a 10 - 16V battery) you can get away without charge pumping but you'll need an up/down converter for the 12V and an up converter for the 24V. Less efficient but simpler to do.

     

    The little charging board could only work if you removed the cells and charged them one at a time. I expect chargers for 4 cells in series exist.

     

    I suggest you read up on Lithium cells and recommend that you look at data sheets and app notes form TI and Linear Technology, these two sell chips but not batteries so tend not to gloss over the problems with the batteries.

     

    If you can stand the size and weight a sealed lead acid battery is cheaper, more reliable and much more forgiving if you make a mistake.

     

    MK

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