2 laptop batteries in series - ok?

[JimWix]

I have a head torch that I made for night mountain biking in the local woods and it works great. It uses 2 luxeon leds and is powered from a 10.8v 3000mAh Li-ION laptop battery pack that I pulled from the skip at work. I also have the laptop that the battery came from, it doesn't work as a laptop but works fine to charge the battery.

I've now aquired a second, identical battery pack and 5 P3 Cree XR-E leds and I'm contemplating a 5 cree light powered by the 2 battery packs running in series.

Are there any risks in connecting the batteries in this way?

Thanks for your help,

Jim.

 

[half-watt]

I have a head torch that I made for night mountain biking in the local woods and it works great. It uses 2 luxeon leds and is powered from a 10.8v 3000mAh Li-ION laptop battery pack that I pulled from the skip at work. I also have the laptop that the battery came from, it doesn't work as a laptop but works fine to charge the battery.

I've now aquired a second, identical battery pack and 5 P3 Cree XR-E leds and I'm contemplating a 5 cree light powered by the 2 battery packs running in series.

Are there any risks in connecting the batteries in this way?

Thanks for your help,

Jim.

Do you really need a 21.6VDC supply to power the 5 P3 Cree XR-E LEDs? Are they in series too?

 

[JimWix]

Yes they're in series, they take about 3.6v each and 1v for the buckpuck so a 5 cree light will need 19v.

 

[FredM]

can you post a pic of what connectors you used to rig it up?

 

[sysadmn]

I would find the battery experts in this forum and PM them before doing this. If the Li-Ion cells are unprotected, isn't what you're doing the equivalent of using unmatched Li-Ion RCR123a in series? It is possible that the battery packs are protected even if the cells are not. If I were you, I'd want an expert's opinion - and I am not an expert. (PS - If they say it's not safe, consider using 2 separate circuits run off a two position switch. Then you'd have OFF-LOW (1 bank lit)-HIGH (both banks lit). With a four position switch, you could switch bank 1 and 2 on independently for longer life.)

 

[SilverFox]

Hello Jim,

Welcome to CPF.

There should be no problems using the packs in series, but you need to make sure you don't drain them to too low a voltage. Hopefully there is a low voltage protection circuit within the packs to help guard against this.

Keep in mind that series packs can run into problems while charging if cell balance is not monitored and adjusted during the charge. You can end up with an overcharge situation which can have safety concerns as well as greatly reducing the life of your packs.

Tom

 

[JimWix]

Fred, the only pics I have of the 2 luxeon headlight are here http://www.jimwicks.fotopic.net/c1127260.html but I don't think that answers your question. The battery connectors are cut out of the back of another skipped laptop and held tight with velcro. The 5 cree light is just an idea at the moment - I have the LEDs and these batteries, so I'd just need to buy the lenses, buckpuck & a pot. The body will be copper plumbing stuff that I have lying about.

Sydadmn, sorry but I don't know who those experts are - everyone here seems like an expert to me, I haven't been around here long enough to know who's who.

Tom, thanks for the welcome. I intend to charge the 2 packs seperately, back in the laptop that they are built to go with. Happy to take advantage of all the power management and protection that Toshiba have already built in.

 

[JimWix]

and Tom, Thanks for answering my querry.

 

[sysadmn]

Sydadmn, sorry but I don't know who those experts are - everyone here seems like an expert to me, I haven't been around here long enough to know who's who.

Fair enough, should have been more specific. Start here:

"MDs Lithium-Ion>Incandecent guide, +compatability/comparison chart"
http://www.candlepowerforums.com/vb/showthread.php?t=161536
The section "Use and safety of Lithium-Ion" was a good overview for me.

In more detail, "greatest danger using li-ion cells occurs during re-charging"
http://www.candlepowerforums.com/vb/showthread.php?t=161549

Hope this helps!