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View Full Version : Li-on Modification : placing 2 batts in parallel for more juice!



sprockett
01-25-2005, 03:01 PM
Hi everyone, im intending to join a couple of Li-on batt packs in parallel for extra juice. I will be custom making an external enclosure for the extra packs and mount it on my camera.

Anyways, I noticed that there is a third contact on li-on batt packs. I was wondering what this was for, but have found out that its basically a battery fuel gauge that allows the camera to know how much juice there is left.

How did i find this out?
I have a cellphone li-on pack that also has this 3rd contact. I covered it and connected it back to the cell phone, and thats when i realized i lost my "smart battery gauge" the one that predicts how many hours left etc. It also lost the 1/8 battery increment meter. The meter just stated 0, 1/2 or Full.


Anyway, my question is does anyone noe how Li-on batts are configured? I know the base voltage of Li-on cells is 3.7v. so that means for batt packs that have 7.2v, they use 2x3.7 v in series, and so on.

In the series configuration, the overcharging / discharging circuit keeps track of each "cell" in the batt pack, so it won't allow uneven charging/discharging of the cells (for example, one cell being used up, while another remains full)

My question is if this applies in a parallel configuration as well. In a 2x850mah 3.7v configuration, are the 2x850mahs even considered "separate" cells? Or can i just lump them together and consider them ONE cell? One could think of it as just twice the amount of chemicals right? Because if i can make this assumption, i can manually solder 2x850mahs together in parallel.


Appreciate any answers! Thanks!

Robert Besen
01-25-2005, 06:27 PM
You should consider using a diode in series with each cell if you are going to parallel them, to keep one from charging the other. Paralleling Li-Ion cells without diodes can be dangerous since they have fairly low impedance and fairly high energy density. This will lower your effective capacity noticeably, and make charging more complicated.

gary_hendricks
02-20-2005, 02:13 AM
You should consider using a diode in series with each cell if you are going to parallel them, to keep one from charging the other. Paralleling Li-Ion cells without diodes can be dangerous since they have fairly low impedance and fairly high energy density. This will lower your effective capacity noticeably, and make charging more complicated.

Wow very technical stuff. Do you guys have pictures of what you're doing? I'll like to see ...