Li-Poly Charging Circuit - Page 1
Forum section: electronics / beginners

author: coldreactor
author_rank: Contributor
timestamp: February 13, 2016, 03:21:15 pm
content: I had a laptop break down on me a few months ago and today I was thinking of using its battery to make a massive capacity 5v charge bank. I take it apart and find the strangest charging circuit I have seen. I have attached below what I found based off the world's cheapest battery polarity finder(a led and a resistor). The top of the battery is in series and the bottom is separated. Could anyone explain how this works and the best way to charge such a thing? Thank you.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: February 13, 2016, 03:45:18 pm
content: I can not match your text with your drawing ?I have to make some assumptions , 1 2 3 & 4 are battery cells , making up a battery bank .When cells are arranged in series you are adding the voltage of each , when they are in parallel you adding add the current capacity of each .A battery bank can have a combination of both series & parallel to get what ever combination of voltage & current you need .Can not tell from your drawing how the battery bank is connected .Most Lithium chemistries have a charge controller in the package , this will look like a circuit board populated with a number of components , the porpoise being that extremes of charge & discharge can create fire hazards .

author: amyk
author_rank: Super Contributor
timestamp: February 13, 2016, 04:07:24 pm
content: That could be a 2S2P or 4S pack, check the voltage with a multimeter to be sure. A 2S will be 8.4V fully charged and around 6V dead, a 4S is 16.8V full and 12V dead. The intermediate taps are for balancing and the controller on the board monitors the cells to ensure that their voltages are equal.As for charging, supply current-limited voltage, 1/2 the capacity of the cells or less and the voltage of the pack, e.g. a 3000mAh cell can be charged with 1.5A at 4.2V, a 2S2P of those with 3A at 8.4V, and a 4S with 1.5A at 16.8V) and wait until the voltage rises to 4.2V/cell and current drops to near 0. Make sure the cells are balanced.

author: coldreactor
author_rank: Contributor
timestamp: February 13, 2016, 04:09:00 pm
content: Ya, The top of the cells 1 and 2 and then 3 and 4 are connected in series yet the bottom is not which is a strange arrangement. (That board in the middle is the charge controller) and this is a 15.2V Pack

author: Teledog
author_rank: Regular Contributor
timestamp: February 15, 2016, 06:43:38 am
content: Fire waiting to happen?Do you not have a cheap volt meter?Don't mean to rain on your parade..but Li-Ioncanstart scary fires when you least expect it.Most (dead?) laptop battery packs I've seen typically only have 1-3 dead cells..the rest are OK..but you have to be careful dissecting them.Lots of YouTube vids how to test/open them..Read up on Li-ion cellshttps://en.wikipedia.org/wiki/Lithium-ion_batterysome nifty geek/cool stuff there & do a search for more..They have dirt cheap (single) chargers on eBay;http://www.ebay.ca/itm/221533778016?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AITand also 2S/3S/etc..G'luck!

author: ion
author_rank: Regular Contributor
timestamp: February 15, 2016, 08:29:40 am
content: From the diagram it looks like cells 1 and 2 are in series with a tap between them (top of controller board) and cells 3 and 4 are in series with a tap between them.As you say this is a 15.2V pack then the 2 strings are also connected in series through the board using a pair of the 4 contacts on the bottom - hard to tell which from such a simple diagram. And there is almost certainly another tap at that point.The taps between the cells are for balance charging the pack.With one or more of the cells dead you should definately not try to charge the assembled pack.