Lifepo4 Cell Balancing

[dumbass]

This question is not intended to be another thread about running with or without a BMS.

With that said I have a question for those in the know. I run 8s lifepo4 Thunder Sky 20ah packs without a BMS. I use a CellLog8 attached to a 100db alarm while riding/charging that warns me of a low/high cell or pack. For charging I ether use a 24v 6a lifepo4 smart charger and bulk charge the pack. Or I also have a 9 pin balance plug setup. With the balance plug I use 8 individual (isolated) 3.65v 2a lifepo4 chargers.

The problem is for some crazy reason the packs (2) will not balance even with the individual cell chargers. Don't jump to the conclusion that one of the chargers are bad because I've got 2 sets of 8 charges with the problem. Please remember I am using 9 pins and wires both inside the packs and from the chargers (connecting the positive from one cell/charge to the negative of the next and so on) the same as done for a CellLog8. Any thoughts???

What I would like is to attach 8 of these balance bleeders to my balance plug and use the smart charger to bulk charge the pack. I called the supplier this morning and was told I had to connect each cell to each balancer individually with 2 wires (no jumping from the positive to negative between bleeders). I reminded him the packs were wired in series of 8 cells. He said "that's ok, you still need to wire each cell individually to balancing. So I need 16 tap wires for this? I would think because I am not actually connecting to any power other then the cells being bled I would be able to use just 9 wires/pins just like a CEllLog8. But is this the same problem with the individual chargers?

http://www.batteryspace.com/Balance-Module-for-3.2V-LiFePO4-Battery-Pack.aspx

Bob

 

[Matt Gruber]

Bob
when someone says cells won't balance, to me, this means some cell(s) run out of juice before the others. ending the ride early. right?

 

[dumbass]

Bob
when someone says cells won't balance, to me, this means some cell(s) run out of juice before the others. ending the ride early. right?

Actually, what I was referring to is "all" cells are not charging to the 3.65v mark and some cells are what I call run-away cells during the charge. Meaning they will go over 4v which is a big no-no with life cells. Because my pack is much larger then I actually normally need for my casual rides I've had a rare low cell warning. I have my low cell alarm set at 2.7v.......actually I recently raised it to 2.8v.

I have tried those cute little cell bleeders that connect across the terminals of a prismatic cell. They can't bleed the cells fast enough to prevent over charging. That's why I liked these balance bleeders because they could be set to bleed up to 1.4a per cell. And their not really that large to install in a small box with a fan and then use a smart charger to bulk charge.

Bob

 

[dogman dan]

Time to sort by capacity. Your lowest capacity cells will fill first.

 

[dumbass]

Time to sort by capacity. Your lowest capacity cells will fill first.

And I agree. But how can any cell charge to a higher voltage then the charger that is charging it? I've checked all 16 individual chargers and they are all 3.65v +/- .01v. So how can a cell climb to a higher (3.8 to over 4.0v) if no charger produces more then 3.66v? While the charger manufacture claims the mini chargers can be linked + to - so as to use only 9 wires because the are isolated I think this linking is causing the problem. But as I said I do agree there are weaker cells in each pack. But sooner or later most packs have this problem.

Bob

 

[Matt Gruber]

ive seen this several times. i had an sla float charger that NEW said 13.8v.
then one day it reads 11.8v!
YET once hooked up it charged to 13.8! another was low, and another was high VERY HIGH when hooked up.
this is what they do when they are failing.