You'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.

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 curcuit

 

Hi crutschow,
As there is no load on the output it explains why it is working in voltage limiting mode. I am wondering how low the "5.1 volts" will drop if it is attempting to supply 0.7 amps. (The TSs constant current figure.)

psoke0,
Can you load the output of your 5.1 volts source with a 6.8 ohm 5 watt (or larger.) resistor to simulate the load that would be taken by the charging circuit and measure it's voltage under those conditions. (This will draw just over 0.7 amps)

Les.

Les. i will do it tomorrow i think the problem is not the power supply its cables resistance

 

the reason i get different voltages is that my breadboard and jumper cables have too much resistance

But there was no significant current going through those wires according to your circuit, so I don't see how that could be a problem.

 

Here's an LTspice simulation of your circuit with a TL431 reference to make the trip point independent of the supply voltage.
(Note: I see no reason for C1 in your circuit.)
The circuit cuts off the charge current at a nominal battery voltage 4.1V for the resistor values shown.
You can use a 10kΩ pot in place of R4 if you want to make the cutoff point adjustable.

Note that the charging current of 700m is marginally close to the 800mA maximum current rating of Q1.
I suggest you increase the value of R1 to about 1.5Ω to keep the current below 0.5A for that transistor.

 

Here's your circuit with a TL431 reference to make the trip point independent of the supply voltage.
(Note: I see no reason for C1 in your circuit.)
You can use a 10kΩ pot in place of R4 if you want to make the cutoff point adjustable.

View attachment 123756

the C1 is acting like battery just for see it in smulation and your link is not opening i cant see the curcuit you give

EDİT : i see the curcuit now thank you

 

Here's an LTspice simulation of your circuit with a TL431 reference to make the trip point independent of the supply voltage.
(Note: I see no reason for C1 in your circuit.)
The circuit cuts off the charge current at a nominal battery voltage 4.1V for the resistor values shown.
You can use a 10kΩ pot in place of R4 if you want to make the cutoff point adjustable.

Note that the charging current of 700m is marginally close to the 800mA maximum current rating of Q1.

View attachment 123758

and what is the program you are using can you tell me please

 

the C1 is acting like battery just for see it in smulation and your link is not opening i cant see the curcuit you give

EDİT : i see the curcuit now thank you

Good.
Note my edit to post #44.

I'm using LTspice, a free download from Linear Technology.

 

C1 is acting like battery just for see it in smulation

Okay.
I didn't pay attention to the large value of C1.

Here's the simulation with the capacitor.

 

Good.
Note my edit to post #44.

I'm using LTspice, a free download from Linear Technology.

i see the edit im aware of that okay i will look at that program thank you

 

Okay.
I didn't pay attention to the large value of C1.

Here's the simulation with the capacitor.

View attachment 123761

its almost acting the *same right

 

okay i will look at that program thank you

If you want to simulate that in LTspice you will need to add the models for the LM324 op amp and the TL431 regulator, which I can post, if you need them.

 

If you want to simulate that in LTspice you will need to add the models for the LM324 op amp and the TL431 regulator, which I can post, if you need them.

i just downloaded it yes i will need them lm358 is the same as lm324 right because i have 358 one

 

i just downloaded it yes i will need them lm358 is the same as lm324 right because i have 358 one

Yes, they are essentially the same with the LM324 being a quad in a package, and the LM358 being a dual.

The TL431 files are attached below:
The .asy file goes in the C:\Program Files\LTC\LTspiceIV\lib\sym\References directory.
The .lib file goes in the C:\Program Files\LTC\LTspiceIV\lib\sub directory.
(If you are using a newer version of LTspice then you will need to look for the directory locations on your computer)

Be sure and make a backup of both directories before making the addition.

I also attached the sim with the capacitor.

Note that you can't use 10F for the capacitor value since that is interpreted as 10 femto farads by LTspice.
Also 10M is interpreted as 10 milli by LTspice (a common mistake when using Spice); for 10 million you need to write it as 10meg (or 10MEG).
LTspice ignores letter case.

 

Yes, they are essentially the same with the LM324 being a quad in a package, and the LM358 being a dual.

The TL431 files are attached below:
The .asy file goes in the C:\Program Files\LTC\LTspiceIV\lib\sym\References directory.
The .lib file goes in the C:\Program Files\LTC\LTspiceIV\lib\sub directory.

Be sure and make a backup of both directories before making the addition.

I also attached the sim with the capacitor.

Note that you can't use 10F for the capacitor value since that is interpreted as 10 femto farads by LTspice.
Also 10M is interpreted as 10 milli by LTspice (a common mistake when using Spice); for 10 million you need to write it as 10meg (or 10MEG).

okay i need comparator model too

 

okay i need comparator model too

I'm confused.
You previously stated this:

lm358 is the same as lm324 right because i have 358 one

 

I'm confused.
You previously stated this:

i meant in real life i have lm358 sorryy

 

Okay.
Here're the LM324/358 files:

.lib goes in C:\Program Files (x86)\LTC\LTspiceIV\lib\sub
.asy goes in C:\Program Files (x86)\LTC\LTspiceIV\lib\sym\Opamps

 

Okay.
Here're the LM324/358 files:

.lib goes in C:\Program Files (x86)\LTC\LTspiceIV\lib\sub
.asy goes in C:\Program Files (x86)\LTC\LTspiceIV\lib\sym\Opamps

thank you

 

Here's an LTspice simulation of your circuit with a TL431 reference to make the trip point independent of the supply voltage.
(Note: I see no reason for C1 in your circuit.)
The circuit cuts off the charge current at a nominal battery voltage 4.1V for the resistor values shown.
You can use a 10kΩ pot in place of R4 if you want to make the cutoff point adjustable.

Note that the charging current of 700m is marginally close to the 800mA maximum current rating of Q1.
I suggest you increase the value of R1 to about 1.5Ω to keep the current below 0.5A for that transistor.

View attachment 123758

okay i tested the curcuit but without shutt off power section. i tested the current draw i see when i plug the battery the battery draw 450 mA current but when i am not using the battery im shorting the cables the amp draw jumps to 690 mA isnt that supposed to be stay at 450 mA even in short circuit because its constant current curcuit right. what am i missing here educate me please

 

With your 1 ohm sense resistor the current should be about 700 mA. So the 690 mA when the output is shorted is about right. What is the MEASURED voltage input to your circuit when the output is shorted. In other words what is the voltage from your supply that you claim is 5.1 volts when it is providing 690 mA of current ?

Les.