Building a massive Li-ion battery pack

[HenryE]

I'd like to use up to 20 RCR 123 Li-ion rechargeable cells to make a large battery pack capable of powering/charging several items, including flashlights, laptop computer, etc.

The laptop power supply, for instance, provides 19.5V (regulated down to 14.5V), so that's the highest voltage required. 5 cells at 3.7V would provide 18.5V, which works fine. I'm thinking of four rows of 5, in parallel, for total 20.

I'd provide regulated taps for the cellphone, flashlight, radio, DVD, and perhaps other items. 20 cells at $5 is $100, plus misc connectors and a PVC housing plus a charger.

Has anyone here done anything like that? Or, is something like that already available?

Thanks,

Henry

 

[SilverFox]

Hello Henry,

How do you plan on charging this pack?

Laptop battery packs use around 2200 mAh cells and you can get around 2 hours of run time off of them. The R-CR123 cells come in at around 600 mA, so that means you could expect around 30 minutes of run time. Is that adequate?

Tom

 

[Brighteyez]

Don't devices like laptops and MP3 players that use LIon batteries generally have the protection circuitry, and the circuitry for charging the battery built into the device itself?

Hello Henry,

How do you plan on charging this pack?

Laptop battery packs use around 2200 mAh cells and you can get around 2 hours of run time off of them. The R-CR123 cells come in at around 600 mA, so that means you could expect around 30 minutes of run time. Is that adequate?

Tom

 

[HenryE]

I have some 650mAh RCR123 cells that have worked well for me, so would probably use the same ones. Four rows in parallel would provide 2.6A max, which is in excess of the 2A charging rate of the laptop's battery and should be good for more than an hour of laptop use.

That's a superset of all other outputs.

I do not know how I'd charge it, unless I built something.

Henry

 

[VidPro]

whatever you do, your going to have to make sure that the batteries stay BALANCED, if you tap off a few cells in it, its going to effect that drastically.
and your really going to want to charge each parellel cell set seperataly.

everything you said is possible to accomplish, but the FIRST thing you would need to know is, they AINT your average rechargable, and they can NOT be dumb charged, and they are gonna want to stay balanced. otherwise your just going to have an non-fuctional pack.

setting up and using a SERIES pack of li-ion so it lives a long time isnt even being done by manufactures correct, so potentially you could do better than they do, but without lots of knowlege of the caveats of the li-ion , you could make a bloody mess, been there done that

 

[SilverFox]

Hello Henry,

I don't see any problem using the pack, but with small capacity cells you will have to live with reduced run time. You will have to figure out a way to make good connections between the cells.

The problem comes with matching the cells for use and figuring out a way to charge them without blowing the whole pack up. You will need to monitor the voltage of each cell and have the protection circuitry shut things down upon low or high voltages of any cell.

My laptop battery pack uses 8 cells of 2000 mAh capacity. It is rated at 14.8 volts and 4000 mAh. It is a 2P4S configuration, with 8 cells total. I get just over 2 hours of run time with it.

Once you have figured out how to safely charge it and how you can protect it from over discharging, the rest is just mechanically putting it together.

Tom

 

[mdocod]

use 18650 size cells for the highest energy per dollar rather than a huge number of RCR123s... like everyone else is saying- you need to proceed very carefully.. A li-ion pack can't be treated like a NIMH or NICD pack at all. I suggest building in protection cercuitry for each cell(over-charge, over-discharge, and current), (eithor included in cell, or buy the little circuits and install them in the pack)... and solder in connections for every single cell to be monitored individually from a ballancing charger... also keep in mind that li-ion cells start off at 4.2V off the charger, not 3.7V... so a pack with 5 in series will have 21V fresh off the charger.... you could build a 10 cell (using 18650s). (sets of 5 in series) that would be 5200mah (using LG 2600 cells), for probably around $150

 

[TMorita]

Using 20 RCR123 batteries is IMHO a bad idea.

I fly electric helicopters, and we use large battery packs, and use balance chargers to ensure the batteries stay balanced.

Look here:

http://www.thunderpower-batteries.com/Li-PolyBatteries.htm

Toshi

 

[HenryE]

I was planning to regulate each of the required outputs rather than tap cells and drain independently.

But these responses lead me to the idea of just using a second laptop battery, which is easy enough to pull apart and wire for the purpose.

 

[tron3]

I actually re-built an old 12v portable battery pack.

The old pack was ten 4500 mAh D cells in NiCd.
The new is ten 10,000 mAh D cells in NiMH. Twice the power with no memory. A simple power inverter gives me portable house current. :rock:


Tabbed batteries available here. I soldered them together myself.
http://www.zbattery.com/drechargeablebatteries.html

Contact the people at http://www.powerstream.com/
Tell them what you are building, and they probably have a charger for it.

 

[Tronic]

I recommend you to use Li-Ion Manganese cells.

See here

A 4S3P 3,3AH pack is available for about $145

Advantage over "normal" Li-Ion:
- Don't rapid vent with flame or burn
- No balancing required
- No protection PCB required