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

autodeskguest over 10 years ago

Hello People,

im 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

(http://www.ebay.com/itm/271660756121?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT)

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

(http://www.ebay.com/itm/121166431897?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT)

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

(http://www.ebay.com/itm/DC12V-Step-Up-to-24V-240W-10A-Car-Power-Converter-Regulator-Adaptor-/161320347784?hash=item258f712888)

any help would greatly be appreciated

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shabaz over 10 years ago in reply to e14 Contributor

Hi Brian, Thanks!
Back when 4Amp-hour D-cell NiCad packs were popular, I saw one burst in a lab. All the cells had overheated (due to accidental prolonged overcharging at a very high rate) and one by one they burst out of the pack, separated by minutes, the first one hitting a wall perhaps 10 meters away! Some got in my eye, but all was ok. The lab was unusable for the rest of the day though!
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e14 Contributor over 10 years ago in reply to shabaz

Thanks, Shabaz.
When I read the post I was calculating just how many Joules would be produced in <5 sec when cheap, eBay, LiCo batteries hit the ground; or ran away during charge/discharge.
Short answer: REALLY BIG FIRE!
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clem57 over 10 years ago in reply to shabaz

Thank you for the fair assessment.
Clem
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shabaz over 10 years ago in reply to clem57

Hi!

I think it is too hard to answer this one given there is a massive risk of damage : (
The original poster is going for a construction that relies on ebay parts, possibly ebay batteries too.
The 24 cells referred to in the post are a huge fire hazard if anything goes wrong. In contrast, buying
traceable, reputable cells will cost around $250-300, and a custom circuit would be needed (there are ICs
designed for multiple cell charging, some offering cell balancing too, but I wouldn't trust an ebay design).
Also, once you have that much energy in a battery pack, you possibly also want to keep track of battery
information (charge level, number of cycles, etc) so then some ADCs, microcontroller circuit+memory is needed too.
So, basically a major undertaking.
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clem57 over 10 years ago

Anyone can help?
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