Hi again Ron,
If you look at the sense resistor in that circuit is it only 0.005 ohms, so it would take about 100 amps through the mosfet to get that transistor to start to turn on. With 0.05 ohms, it would take about 10 amps. With the original circuit and same sense resistor values it would be about 10 amps and 1 amp respectively which unfortunately is still not right because the circuit will not function as balancer as is anyway.
It is actually a good thing you posted a different circuit because now i think that makes us take another look at what exactly the OP was trying to do in the first place, which if i understand this project right, does not look right at all.
In a battery balancing circuit, we have two main concerns:
1. The current through ALL the cells, which should be the same for all cells that are not too close to full charge yet, and with medium accuracy.
2. The voltage across EACH individual cell, which should be limited to 4.20 volts for a normal Li-ion cell for example and with good accuracy.
The usual way to get this is to provide a current limited power source (say 1 amp) that has enough voltage to reach the total series combination of all the cells that are to be charged in the same string, and to limit each cell's voltage on an individual basis by shunting any unwanted current around the cell (shunt regulator).
So for example if we connect four cells in series and provide at least 4.2*4=17.2v and current limited to 1 amp, then conenct a shunt regulator to each cell, as each cell gets near full charge the shunt regulator for each cell starts to bypass some of the current to that cell and keeps it from over charging.
As it is right now, all the mosfet does is limit the current through the mosfet itself, which is not what we want.
If we want to limit current on a cell by cell basis, that would be harder to do because we definitely need to limit voltage on a cell by cell basis. It is easier to limit the current to the whole series string, then limit only the voltage on a cell by cell basis.
This means that we need a single circuit that can limit current, then each shunt regulator needs to measure the voltage across it's respective cell and shunt current around the cell when the voltage starts to get near 4.2 volts.
The only difference between the shunt regulators and the normal single cell series regulator is that the shunt regulator draws more current as the cell voltage rises while the series regulator cuts back (lowers) the current as the cell voltage rises near to 4.20 volts.
BTW i like to charge my cells to 4.15v which supposedly allows them to age better.
So for 8 cells in one series string, we need one current limiter circuit and 8 shunt voltage regulators, and the shunt regulators need to have good accuracy. I would not try to obtain the reference from a forward biased diode but use a voltage reference diode or something like that.
I think modern day NiMH cell 15 minute fast chargers use PWM as they have to handle 10 amps charge current for each cell. That might get complicated for the OP here though. I think other slightly slower chargers might use PWM too these days.