View Full Version : Lipo question

08-13-2005, 07:14 AM
I picked up a couple of 2 cell 750 Mah Lipos off ebay for $8 and $12 shipped respectively.
Wasn't happy with the preformance at 7.4v so I split both open and made one 3 cell pack and now I'm VERY happy. Followed online instructions, I know how to solder so no firey explosions and I've got a 3rd on the way for $10 so I have a total of $30 in two 11.1v packs.:D

OK here's my question, during de/re-construction of the packs I noticed a small circuit board ontop of each cell with an IC chip and a row of small doiodes.
I'm new to lipos and I've checked places that sell loose cells but none I've seen come with these circuits so I removed them and soldered directly to the tabs but does anyone know what they're for?
I'm going under the assumption that they were charge memory chips like laptop batteries have for whatever these batteries were originally intended to be used in and whoever assembled these packs just left them on.
Am I correct???:confused:

Slent thndr
08-13-2005, 01:18 PM
Those were probably the circuit protection chips. I might be wrong but i think Lipos have them to make sure the batts don't run under voltage, or blow up. You might be fine without them though if your esc has a programmable voltage cutoff. In the future i would just leave them on.

www.batteryuniversity.com (http://www.batteryuniversity.com)
This site has all the answers about batteries.

Matt Kirsch
08-13-2005, 10:58 PM
Typically, the protection circuits disconnect when the current draw on the cells exceed a particular limit, or drop below a particular voltage. The actual values depend on the designer of the circuit, and the application of the circuit. They prevent many of the conditions under which a cell could catch fire, or sustain permanent damage, but not all conditions.

Frankly, I don't know if I'd leave them on, unless I knew exactly what the circuits were designed for. If they're designed for the few tenths of an Amp that a cell phone draws, they're not going to work so well on an R/C airplane drawing several Amps.

Just be careful soldering cells. Your main risk of fire is if you create a short circuit in your soldering. It's far far more likely that you'll overheat the tab and destroy the seal between the tab and casing, which renders the cell useless.