hahah thank you very much the reason i get different voltages is that my breadboard and jumper cables have too much resistance and my power supply is old desktop computer power supply which can give me 5,1 v and upto 15 Amps i think the reason that i get voltage drop on load is because also the cables that coming from my power supply i think they have high resistance so what i did is i remove the comparator (just for testing current draw for now ) i take the components from breadboard and i just soldered all like this (picture down below) and i get 450 mA charging current to the cell )) so tomorrow i will play with it and see whats going on thank you very much guys i will ask you later on another questions about this curcuit . i loved this website and people that makes this website awesome here is the curcuitYou've got it, grasshopper.
Looking at all the voltages often make it clear what's happening in the circuit.
The op amps positive input voltage is slightly lower than the negative input so its output is low, and there is thus no voltage to turn Q2 on.
It would appear that your supply voltage is only 4.85V, not 5.1V as you earlier stated.
But how did you measure 4.85V, 4.83V, and 4.81V for the same supply voltage?
(Which brings up the point that all those nodes are at the same voltage so only one measurement would have been required.)
Is the source a battery that was nearly discharged?
So you should use a reference voltage source, (such as the cheap TL431) to provide the voltage for IC1a's (-) input so that any supply voltage change doesn't affect its trip point.