Yet another Lipo charging/balancing question

[BrianG]

One of these days, I'll get all this straight! In the meantime, I hope you all can bear with me?

I was looking around at the various chargers and balancers and thought of something. Let's say I am charging a 5s pack and the battery is almost charged so the charger is in constant voltage mode. Then one cell goes out of balance. The balancer is supposed to disconnect the one cell to keep from overcharging, right? But what happens to that extra voltage from the charger? It was charging 5 cells, but if one is disconnected by the balancer, now it's charging 4 cells. So, does that mean that ~20v now gets split across 4 cells instead of 5 (resulting in "bad" things)? Of course, this is not an issue for the TP 1010 due to the feedback link, but what about the other brands out there?

[MetalMan]

The only time a cell is disconnected from charging is when you are using "active balancing", also known as parallel charging. To charge/balance like this you need a charger that charges through taps - a balancer built into the charger.

Conventional balancers discharge the cell(s) that is (are) at a higher voltage than the other(s). So, the charger (conventional) will still be putting out the same current, but the voltage might drop a little on the charger side due to the the balancer sinking some of the charge current (to bring down the voltage on the higher cell(s)).

[BrianG]

Well, I understand how that would work in constant current mode. If a cell is removed during charging in this mode, the voltage will simply go down.

But I was talking about when the charger was in constant voltage mode. If the charger was at 20v on 5 batteries, that's 4v per battery. However, if one of those batteries was disconnected by the balancer, that's 5v per battery.

Specifically, I was looking at the LBA6 hi current balancer.

By the way, is Bishop Power Products good (meaning; customer service)? They are having a 4th of July sale!

[MetalMan]

Convential balancers don't disconnect the cells that are at a higher voltage. They merely drain current from them to lower the voltage of that cell. The voltage difference cause by this small (120ma) drain is very small, maybe 0.002v (depending on the capacity of the battery). The LBA6 is a convential balancer. The only disconnecting it can do is to disconnect the whole battery when any cell reaches 4.30v when it used between the charger and battery. The way the ICE deals with this is by immediately detecting an open circuit. Other chargers act differently, but usually it isn't a problem.

I haven't heard anything bad about BPP.