I used @crutschow's circuit with his model of battery.
My work was to convert it to pulse charger by adding few parts (U3, R4, C1, D3):
View attachment 294249


I like Escher's works, but unfortunately I am not artist, I found picture for my avatar HERE.

Hi,

Ok, i asked because i think you may need a more detailed battery model in order to test with a pulse charger. That's because a pulse plays with the dynamics of the battery a lot more than a DC constant current source. That would help establish the best on and off (measurement period) times. That's just a suggestion.
Also, are you sure you want to apply 3 amps to the cell, even if for a short period?
It's still an interesting modification though.

I had a feeling you would know about his work. He was so good at expounding the absurdity of using two dimensions to represent three, or should i say he went out of his way to bastardize it (ha ha). I have one of his books i got way back in the 1970's. Lots of illustrations but many are online now.

 

Here's my sim of the circuit with the added current limit transistor.
I modified a couple of the resistor values as needed: and changed the power source for the op amp from the output to the supply voltage.
I also re-arranged the schematic to be in the conventional left-to-right signal/current flow.

The battery is emulated by the 100 Farad capacitor CBat, and resistors RTrickle and Rbat.

Initially the battery charges at the 3A limit (yellow trace) until the battery voltage reaches 54V (green trace), at which point the op amp maintains the voltage at that value, and the current then drops to the 108mA trickle charge current due to RTrickle.

Note that starting at a discharged battery voltage of 44V, the dissipation of Q1 (red trace) is initially 33W, and will require a hefty heat-sink (possibly with a fan) when charging at 3A.
That's why a switching regulator with higher efficiency was suggested for charging.

View attachment 291046

Hello Mr Crutschow.

The Q1 will on to limit the current through R6 when the VBE 0.6-0.7V is achieved? When Q2 is on the current share and flow to the ground as well.

 

The Q1 will on to limit the current through R6 when the VBE 0.6-0.7V is achieved? When Q2 is on the current share and flow to the ground as well.

Yes.
Q2 turns on at about a Vbe of 0.6-0,7V which then bypasses the base current to Q1 so it can't carry more current.