T&L Publications

Tired of replacing gel cells in a few 12 VDC projects, so switching to Li-ion.
3 cells (18650- 4 AH) in parallel, and 4 of those banks in series gives the desired 14+ volts.
What is the best way to charge this pack? Have heard each cell needs to be monitored and charged individually, but if I have 3 in parallel, that won't work easily.
Do I just consider the 3-pack a single cell, and charge it by itself, going down the pack, one "cell" at a time?
TIA!
John

Hi
I know that Li-ion computer packs have a 'charge controller' inside the pack but I never saw where each cell was monitored.
Series/parallel batteries could be quite a challenge to watch each cell .
See if this helps...
http://batteryuniversity.com/learn/arti ... _batteries

Hi John.
Consider any amount of Li cells in parallel as a single cell and your life will simplify.
Apply 4.1000 V to each paralleled group for charging. No need to disconnect each.
When there is a series of parallel groups and its use requieres recharging often; then you need a controller. If you find the way to use a laptop pack with its built-in controller, it gets easier, if the pack does not need a clock and thermal and overdischarged condition permission to recharge. Most Li packs want a clock signal produced by a laptop compfuser to run its microcontroller, and permission from the laptop to supply power (Denied if hot or undervoltage)
Another way to consider is individual 'small' DC-DC converters with their outputs connected to each series of cells, like :

(+)cells1 -----A-----cells2------B-----cells3------C------cells4-----(-)

Apply isolated 4.1000V supply(s) to (+)andA ; to AandB ; to BandC ; to Cand(-) sequentially or simoultaneously

Another way, get a controller board; the candy store should have them.
----> http://www.aliexpress.com/wholesale?cat ... ller+board

Be aware chinese do not know the difference between the words 'cell' and 'battery' and may twist your perception of their products.

Miguel

Those are Li Ion not Li Polymer so be sure to charge them properly or you can have a "Hoverboard like Incident" involving fire. More than one have blown up in E Cigarettes, blowing a hole in one guys tongue shortly after finishing charging. These little guys have among the highest power density available

A comparison of brands
https://www.youtube.com/watch?v=7XciiXu5G-4
there are a bunch more similar comparison videos on you tube, worth a look I think

You may find switching to Li-Ion better if this is a frequent discharge high load application. If you have a small load, long time to use or very frequent charging, the SLA may still perform better.

Despite the findings of the you tube videos on the Li Ion battery quality, I have found most SLA batteries to be roughly equivalent. No doubt why they dominate the UPS designs

The single biggest advantage of the SLA (Gell Cells?) is it is far less likely to burn up if abused. If you mean something else than Lead Acid by Gell cell, the advice below is similar but the advantages/disadvantages may vary.

Check the charge discharge curves and long term storage capacity of the two technologies WRT your application before making a final choice.

I've been using a universal charger I got on Ebay for a variety of charging tasks and works fine for 9.6 and 12V most technologies. It has a loose thermocouple, I tuck into the battery jacket (that shrink plastic holding the 3-4 cells together). Its crude and cheap but works on a lot of loads as long as you monitor it.

i always hear....NEVER CHARGE Li Ion or Li Polymer Unattended. there have been some nasty fires. and if you have a Li Ion Li Polymer charging jacket,
( special jacket / pocket for batteries, they help contain any fires ) use it..
never know when a battery will go super nova....

Thanks all! Treating my paralleled 3 cells as one seems the way to go. I have one of these coming:
http://www.ebay.com/itm/151998973264?_t ... EBIDX%3AIT

It also allows one to measure the actual capacity of cells, in Amp Hrs. The popular 18650 Li-ion can be had in 1800 maHr, all the way up to 5000 maHr, but what capacity are they really? This "Cell Balancer" device will let me measure those.