Battery Power Supply

[jkeny]

Nige, have you found if one cell is lower in voltage in a series pack that is being float charged does this cell's voltage become more out of line over time?

[nige2000]

In theory if you matched the impedance of the cells in the pack you could charge them in series

I'd be happier with cells in series at over 3.3 each an there not on the downward slope

Like a 5v pack could end up been 3v and 2v which I wouldn't get super excited about or even 4v and 1v not good
I'm not sure it's always the most negative v cell
But I did leave the gb amp prototype on for a fortnight and most of the dead cells but not all were in one side of the voltage rail I'll check which one later
Could be just coincidence?

[jkeny]

Not sure if that's a yes or no to my question - have you noticed a weak cell in a pack of series cells getting weaker (lower voltage) over time when on float charge?

[nige2000]

Not sure if that's a yes or no to my question - have you noticed a weak cell in a pack of series cells getting weaker (lower voltage) over time when on float charge?

no issues with cells getting weaker as such, they just drift a bit, they kinda bias themselves between cell voltage and impedance in a float charge situation
the 12 packs i have have cells +/-0.5v or 2.5-3.5v nothing to worry about as float charged, not float charged the cells that are 2.5v would drop v first

lifepo4 cells take loads of abuse to be fair, i could say if there kept between 1.5v and 4.5v they'd probably be ok but im certainly not gonna recommend it

[jkeny]

What I'm trying to get at is that over time I believe that the weaker cell in a pack will eventually die when there's no balanced charging.

I agree that both rails in a bipolar supply, do usually not draw the same current - there is usually one rail drawing more current than another & it can be a different rail, depending on what device is drawing current - in other words it's not always the negative rail that draws most current.

[nige2000]

What I'm trying to get at is that over time I believe that the weaker cell in a pack will eventually die when there's no balanced charging.

dont think it will die unless the impedance difference is huge and the current draw is large or there is a period of usage without been float charged

you can charge them in series, ive several packs done like that for three years without issue, but balanced is just a far better way to do it
certainly provides more confidence

I agree that both rails in a bipolar supply, do usually not draw the same current - there is usually one rail drawing more current than another & it can be a different rail, depending on what device is drawing current - in other words it's not always the negative rail that draws most current.

turns out it was the negative rail on the gb amp i lost 4-5 cells, think i lost one cell on the pos side

[sima66]

Thanks guys!
Again, not as simple as I thought.....or hoped for! :(

Anyone found one piece, "good" quality 12v battery?

[nige2000]

Whats it for?

[sima66]

Whats it for?

For this:
http://www.stereotimes.com/acc091812.shtml

At the moment I run with 12v lithium battery and it takes 2-3 months to discharge the battery. Probably most of the discharge is because of the time and age of the battery!
This units will be away form my stereo and from each other, that is why i want something "movable"!

[tony]

Ah yes I came across this stuff on another forum. This is in the fairy dust air space world. Like the Stein harmonizers it either lightens your pocket by a large amount and delivers the emperors new clothes or it indeed does all it advertises. I think our new battery amp thingies should all come with a free one of these products for evaluation