Li-battery balance connector

[ilufa]

What you can do with the Li-battery balance connector ?

Here is an idea,
Just plug the device into "balance connector" of battery pack, When cells run below 3.0V, the LED on and sound beep to indicate which cell is low.

http://www.geocities.com/ilufa/BM3_E.htm

[Acetronics]

Hi,Ilufa

Nice Gadget ... but don't you think It would have been a better choice to beep for the Weakest element ( a 3.0 v alarm will still be nice, here )... to avoid misbalance and make you correct it in the quickest delay ...

Alain

[ilufa]

Hi,Ilufa

Nice Gadget ... but don't you think It would have been a better choice to beep for the Weakest element ( a 3.0 v alarm will still be nice, here )... to avoid misbalance and make you correct it in the quickest delay ...

Alain

good idea, may be I can rewrite the program, to beep for weakest, without turn on the LED, if the cell still > 3.0 V, but misbalance > 0.2 V

do you think 0.2 V is a good choice ?

[Chippie]

do you think 0.2 V is a good choice ?

My understanding is that lipos should be within 20mV of each other...in which case your 0.2v is a long way off...That said,how many DVMs can guarantee good accuracy?

As a compromise I'd go for 50mV or if thats not achievable then 0.1v

[ilufa]

I had rewrite the program V2.0, added the "unbalance detection" function.

The nominal voltage is 0.2V, actually 0.1~0.15V. not good enough. :mad:

for more precise resolution, got to use 10 bits ADC instead of 8 bits (Ya! 12F675 has 10 bits ADC) :D

[Acetronics]

Hi, Philip

The real problem is not to overcharge a cell, if no balancer used ...

So, if you have a look to Kokam's Data ... tolerance at end of charge is really very small !!!

BUT FMA/Kockam says unbalance is not really important at end of discharge !!!

So, here, unbalance value will just give us an "end of life " info, showing there's a noticeable capacity difference between the elements.

If you look at the end-of-discharge curves ... 0.2v seems to be more than enough !!! ... not to beep for Factory capacity differences between cells.

I'm saying here : your instrument is just intended to check ... not to protect from overcharge ... let's do it what it has been planned for.

Alain

[ilufa]

Thank you, Alain
I got it,

Elements precision is another issue
The ref.V from 7805L has 1~2% variation, the resistors are 1%,
For ADC range from 0 to 5V, 1% means 0.05V variation.

I don't want to make the project too hard for DIY

[ilufa]

BM4 release

for 3S / 4S battery