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### Topic: Li-ion battery voltage measuring (Read 1 time)previous topic - next topic

##### Mar 29, 2011, 04:23 amLast Edit: Mar 29, 2011, 04:53 am by SadiaV Reason: 1

Hello guys,

I have a little problem with a li-ion battery pack. I would like to measure each cells' voltage to avoid over-discharging them. In the image above you can see what I came up with. The thing is that it is basically impossible to measure G3 and G6 voltages separately.

The way I would do it is to measure GND to V1 for G1, then GND to G2 minus V1 for G2, etc. But what to do with G3 and G6?

Another idea would be to separate each bank of batteries and then somehow switch between them when one gets low, or, maybe put a large capacitor and constantly switch between banks... Hmm.

The max current I have to draw from these is ~2A.

My second idea:

http://vsshs.com

#### RuggedCircuits

#1
##### Mar 29, 2011, 04:32 am

Linear Technology just came out with a neat chip for measuring battery stacks -- up to 12 cells:

http://www.linear.com/product/LTC6803-1

Granted, at 44 pins it is a little intimidating.

While you fix your image link, perhaps this circuit suggestion will get you thinking of a possible solution:

http://ruggedcircuits.com/html/circuit__5.html

--
The Rugged Motor Driver: two H-bridges, more power than an L298, fully protected

#2
##### Mar 29, 2011, 04:56 am
In both of the links it is used for measuring only one bank. My problem is that I need to do it with two connected in parallel.
http://vsshs.com

#### RuggedCircuits

#3
##### Mar 29, 2011, 04:58 am
I'm not really seeing the problem. Why not just measure V1, V2, V4, and V5, then take a measurement of V6. The G3 voltage is V6-V2, and the G6 voltage is V6-V5.

--
The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons

#4
##### Mar 29, 2011, 05:02 am
Thanks RuggedCircuits, I guess I got lost with the parallel connection (panicked a little)
http://vsshs.com

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