3 1 cell Lithium chargers in parallel to charge 3 cell

[nickolae]

Hi everyone,

I have been looking everywhere for some info on using lithium ion batteries in a bluetoothe speaker I am building. I watched Dave's video on the topic but the main question I had wasn't answered in that video.

If I have a 3 cell lithium ion battery pack that has the necessary protection circuitry in my speakers and I have a charger that can be connected using a dc jack (for example this charger http://www.powerstream.com/lithium-ion-charger-3-cell-3a.htm) can I safely use the speakers whilst they are charging. I am unsure how the batteries would deal with being charged and powering the speakers or would the amplifier in the speakers just draw its power directly from the mains charger and bypass the batteries?

Alternatively does anyone have any suggestions of a cheaper method for charging lithium ion batteries (3s 2200mah)? I found this online which is good for me in the UK: https://www.7dayshop.com/products/7dayshop-18650-twin-battery-charger-with-2-high-capacity-2200mah-18650-batteries-DS-046
would there be some way of modifying the charger to charge 3 cell if I bought two?

 many thanks in advance!

My blog where I post all my projects: http://makealittlemore.co.uk

[Rager]

Hello,
First of all, there is no problem in using the device while charging. The Charger is, simly said, a constant current source and it can not tell if the current is beeing sucked by the battery or the speaker. What kind of pack are you using exactly? Do you have a link?

I found this online which is good for me in the UK: https://www.7dayshop.com/products/7dayshop-18650-twin-battery-charger-with-2-high-capacity-2200mah-18650-batteries-DS-046
would there be some way of modifying the charger to charge 3 cell if I bought two?

This charger does ONLY charge single cells. in this case there are two one cell chargers. There is no easy way to charge a 3SPack.

Here is a cheap charger that might work, but it is a switchmode charger and could induce some noice if you run the speaker while charging.
just type "b3 charger" into google

The one you linked might has better quality BUT it is a 3.3A charger. http://www.powerstream.com/lithium-ion-charger-3-cell-3a.htm
This is not good for the life of a 2.2Ah battery.

Hope I could help,
Florian

[nickolae]

Thanks for the help, I have been delving more into this and I now have a battery pack (I stripped out an old laptop battery and wired the 6 18650s in series-parallel so I have a 4000mah 3s pack now)

I'm still struggling with charging though... I had a though about using 3 of these ( http://www.ebay.co.uk/itm/5V-Micro-USB-1A-18650-Lithium-Battery-Charging-Board-Charger-Module/161922506085?_trksid=p2045573.c100033.m2042&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20131017132637%26meid%3D79de2fe766064124a34db4c740e9242d%26pid%3D100033%26rk%3D2%26rkt%3D4%26mehot%3Dag%26sd%3D400665522246)

I thought I could wire their inputs in in parallel and use a 5v 5amp supply to power them and then split the battery pack up that I made and connect two cells in parallel to each charger pcb and then connect the outputs of the charging pcb in series to power my project. Would this work?

[Rager]

I thought I could wire their inputs in in parallel and use a 5v 5amp supply to power them and then split the battery pack up that I made and connect two cells in parallel to each charger pcb and then connect the outputs of the charging pcb in series to power my project. Would this work?

What will happen is that it will go wrong You can not do that. Paralell input yes, please don't do that with the output. What voltage and current do you need for your system?
I would say you use just on cell and a boost converter that steps up the voltage, that makes many things easier. You also NEED a cell protection.

[michaeliv]

I thought I could wire their inputs in in parallel and use a 5v 5amp supply to power them and then split the battery pack up that I made and connect two cells in parallel to each charger pcb and then connect the outputs of the charging pcb in series to power my project. Would this work?

That will not work. It will work if you use 3 separate chargers, each one connected to a module.
If I were you I would just get a boost converter with CC limit, set the voltage to 12.4V, set the current to 2A and power it from 5V.
Hook it up directly to the output of the battery pack. The physics should take care of everything.
I'm curious if this would be a bad idea long term, do LI-ION cells get damaged if continuously trickle-charged ?

http://www.ebay.com/itm/-/371279559525

[nickolae]

Okay thank you!

[Rager]

Yes, this can be used as a charger but the output voltage is not very precise. If you want to use this, then set the voltage to 12V and not the limit of the cells. Also if you use used batteries, a balancer and protection will be a very good idea so that your cells don't blow up. I can be that they charge otherwise like that:

--------12V-----------
--5V-----3V-----4V--
  Burn
  Burn
  Burn


or if you discarge them

--------9V-----------
--1V-----4V-----4V--
 Dead

here is a protectior agains over/under charge and over current. It will not balance, but keeps your li-ions safe.
http://www.ebay.de/itm/3s-4A-5A-PCB-BMS-Battery-Protection-Board-for-18650-Li-ion-lithium-Batterie-Cell-/221996193934?hash=item33b001188e:g:3i4AAOSw-zxWmXOW

[nickolae]

but if I use 3 of the charging circuits (http://www.ebay.co.uk/itm/5V-Micro-USB-1A-18650-Lithium-Battery-Charging-Board-Charger-Module/161922506085?_trksid=p2045573.c100033.m2042&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20131017132637%26meid%3D79de2fe766064124a34db4c740e9242d%26pid%3D100033%26rk%3D2%26rkt%3D4%26mehot%3Dag%26sd%3D400665522246)

one for each lithium cell, then they will be individually balanced when charging so I don't see the problem?
sorry for the crappy diagram!

[Rager]

The minus of the carger input and output are connected, they are not isolated, that means that if you connect the chargers in series, you short the negative rail over the three batteries.
One option could be ( I have never tried it)to use three isolated usb power supplies each 500mA and connect to each of them one of the lipo charger+protection http://www.ebay.co.uk/itm/5V-Micro-USB-1A-18650-Lithium-Battery-Charging-Board-Charger-Module/161922506085?_trksid=p2045573.c100033.m2042&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20131017132637%26meid%3D79de2fe766064124a34db4c740e9242d%26pid%3D100033%26rk%3D2%26rkt%3D4%26mehot%3Dag%26sd%3D400665522246 and then like on your sketch. That would work. and would be cheap.

[nickolae]

Ah I see now, could I cut the track so they are not connected? cut it in a place that wouldn't affect the rest of the circuit?

[Rager]

No you can sadly not just cut the track. It is not that easy ^^

[michaeliv]

Ah I see now, could I cut the track so they are not connected? cut it in a place that wouldn't affect the rest of the circuit?

What you could do is not use it while it's charging and just connect all cells in parallel and charge them.

[djQUAN]

Buy the charger shown here:
http://www.belza.cz/charge/battr.htm

It does what you are trying to do. It uses a DC-DC converter with three isolated outputs to power three individual charge control ICs.

[nickolae]

hmmm..okay... the reason I am quie desperate to use these chargers is that I have them left over from an other project!

could I power them in series form a 15v supply? this would eliminate the negative pole of the cells shorting?!

[ion]

...
If I were you I would just get a boost converter with CC limit, set the voltage to 12.4V, set the current to 2A and power it from 5V.
...
...
I'm curious if this would be a bad idea long term, do LI-ION cells get damaged if continuously trickle-charged ?

Yes, trickle charging Li-ion cells will wear them out faster.

Also, I wouldn't push more than 1.5A in a 2200mAh Lithium cell unless there's a datasheet saying it's OK.

Edit:  Here's a couple of papers with data that shows trickle charging is bad:
http://www.che.sc.edu/faculty/popov/drbnp/WebSite/MSA-calendar.pdf
http://ramasamy.uga.edu/pdf/2005%20-%20JPS%20-%20Calendar%20Life.pdf

[michaeliv]

hmmm..okay... the reason I am quie desperate to use these chargers is that I have them left over from an other project!

could I power them in series form a 15v supply? this would eliminate the negative pole of the cells shorting?!

No that won't work... the charger has limit of 5v and now you'll get same scenario as with batteries in series, voltage is not distributed equally and you will fry the charger.
Save yourself the trouble and power your Bluetooth thingy from a boost converter connected to parallel LI-ION cells.

[Rager]

If you allready have the 500mA lipo chargers with protection, then use them in combination with three of those: http://www.ebay.de/itm/3-3V-5V-9V-12V-AC-DC-DC-DC-Power-Supply-Buck-Converter-Step-Down-Module-1A-600mA-/371178736104?var=&hash=item566bfa09e8:m:mALnbRvtGYa6qLrINFUHh6g This is a cheap solution that will balance, protect and charge three cells in series, without problems. Just add enought insulation arround the three AC/DC converters so that no body touches them. 6,90€ is quite a good price for a isolated balanced 3S battery charger I would say ^^

Or use a single cell and a boost converter, as I said earlier.

[nickolae]

okay thanks for your help!

[arunvijaykg]

You can use this board that's available in ebay for cheap. I have used them in a 4P 3S configuration before. It works well.

http://www.ebay.com/itm/4A-5A-BMS-Protection-Board-For-3-Packs-18650-Li-ion-lithium-Battery-Cell-3S-NEW-/161873424944?hash=item25b0687230:g:FgUAAOSwA4dWMewM

[amyk]

...
If I were you I would just get a boost converter with CC limit, set the voltage to 12.4V, set the current to 2A and power it from 5V.
...
...
I'm curious if this would be a bad idea long term, do LI-ION cells get damaged if continuously trickle-charged ?

Yes, trickle charging Li-ion cells will wear them out faster.

Also, I wouldn't push more than 1.5A in a 2200mAh Lithium cell unless there's a datasheet saying it's OK.

Edit:  Here's a couple of papers with data that shows trickle charging is bad:
http://www.che.sc.edu/faculty/popov/drbnp/WebSite/MSA-calendar.pdf
http://ramasamy.uga.edu/pdf/2005%20-%20JPS%20-%20Calendar%20Life.pdf

There is no such thing as "trickle charging" li-ion at a constant current, unless you're referring to charging non-full cells at a tiny current (which AFAIK doesn't hurt the cell at all); you're referring to "float charge", i.e. maintaining a constant voltage on the cells. The papers you linked show that the effects of storage voltage are tiny, the difference between float/open-circuit is similarly tiny (single-digit percentages) and temperature has a much greater effect on cell life. But when you're charging, the lower the current the better; a 1C charge is reasonably fast. 0.5C or below is better for cell life.

The posts in this thread are worth reading too: https://www.eevblog.com/forum/projects/diagnosing-lithium-cells/