Your suggestion in post #8 was good.
That is a, "pulse only" circuit where the transformer provides some voltage higher than 13.8V peak.
Current initially goes through R2 and D4 as the transformer voltage ramps up above the voltage already in the batteries. When the voltage across R2 is enough to fire the SCR through R1, the SCR fires.
R5 is a limiter with dubious purpose. It causes the limiting circuit to consider both the battery voltage and the charging current. F1 is seriously wrong for a 20 amp charger.

So, as the voltage at the top of R3 increases, R7 directs some of it to the base of Q2. When the voltage at the base of Q2 is more than about .6 volts, Q2 shorts out R1 and stops the drive to the SCR.

This is absurd because you can not turn an SCR off until the transformer current drops to zero. If this were a DC power supply, you could NEVER turn the SCR off and the battery would melt.

So, how to fix the absurd? Give Q2 a time delay.
This can be done at the collector or the base.
The collector is already involved in a time sensitive way, so that would need a balancing act to get it right. The base is therefore our suspect.
Add a capacitor between the base and the ground of Q2. It will charge to an average voltage related to the battery voltage plus the voltage across R5. As the battery voltage rises and the charging current decreases, the capacitor voltage will more and more resemble a proportion of the voltage on the battery instead of the current pulses. You want the capacitor to hold the base of Q2 high enough to defeat the firing current in R1 when the next pulse arrives. That's your minimum time limit.

Now add a resistor between the base of Q2 and the voltage on the capacitor to keep the capacitor discharge slowed down. About 75 ohms should work. What capacitor won't lose 1/10th of a volt in 17 milliseconds when being loaded with 750 ohms?

 

Here are the new parts.

 

Re #12's posted circuit: Shouldn't D3 be a ~10V Zener pointing the other way, instead of a power rectifier?

 

D3 assures that C1 can not discharge into the battery.
Assuming the only capacitor in that circuit is C1.

I just noticed it is labeled 1N1615. Have to look that up.
Holy bleep! That's a 16 amp stud rectifier.
Yet another error in the random circuit rendered up by the Internet.

 

wow, really thanks #12 i never expected this.

 

Initial calculations show that 12.24 volts is the minimum adjustable voltage for the output for that circuit, but changing the diode to a zener could be done if the resistor string is adjusted appropriately. Using a zener will reduce the temperature sensitivity of the adjustment and seems like an improvement.

 

wow, really thanks #12 i never expected this.

I'm only a grouch when I have little or nothing to work with.
Answer what I need and help will happen.

 

thanks, so now i can use the circuit in the post #23 ?

 

thanks, so now i can use the circuit in the post #23 ?

No. D3 is the wrong part number, F1 is the wrong size, C1 has not been calculated, R5 has not been explained, and T1 is not defined. I thought post #1 demonstrated that you could work some of this out.
Can you? or do you need every part calculated and handed to you?

 

i think it would be the second option this is embarrassing really.

 

D3 assures that C1 can not discharge into the battery.
Assuming the only capacitor in that circuit is C1.

I just noticed it is labeled 1N1615. Have to look that up.
Holy bleep! That's a 16 amp stud rectifier.
Yet another error in the random circuit rendered up by the Internet.

I think it should be a Zener so that the transistor turns on only when the battery voltage exceeds a "Charged level", like 13.8V?

 

i think it would be the second option this is embarrassing really.

It should be. But even more importantly, think about what you are trying to accomplish. Would YOU be comfortable going to a doctor that you knew took this approach, namely wanting someone else to do all of their work for them on any topic that they didn't see the need for them to actually learn it? Would YOU hire a mechanical engineer that you knew took this approach?

 

I think it should be a Zener so that the transistor turns on only when the battery voltage exceeds a "Charged level", like 13.8V?

I already said a zener would be an improvement, but the circuit still should have some adjustment in it, even if only for the fact that you can't buy a 13.8 volt zener or a 14.2 volt zener.

I'm sure you could modify the adjustment circuit with one simulator tied behind your back.

 

@WBahn after i graduate as mechanical technicien( not engineer) i won't be making battery chargers, so if this was so important for my carreer , i won't be here begging for help.
i am sure that you won't understand my position right now, but i would agree with you if was i studying electricity

 

I already said a zener would be an improvement, but the circuit still should have some adjustment in it, even if only for the fact that you can't buy a 13.8 volt zener or a 14.2 volt zener.

I'm sure you could modify the adjustment circuit with one simulator tied behind your back.

I would opt for ~10V Zener, and then let the adjustment pot take over from there.

 

I would opt for ~10V Zener, and then let the adjustment pot take over from there.

Do you think that's my design? I'm just pimping a circuit that TS got from Google.

 

i found this, can any one give his opinion for this ? and what do i need to change ?

here is the description here :

Charging circuit for lead-acid storage batteries is not damaged by short-circuits or by connecting with wrong battery polarity. Battery provides currentfor charging C1 in PUT relaxation oscillator. When PUT is fired by C1, SCR is turned on and applies charging current to battery. Battery voltage increases slightly during charge, increasing peak point voltage of PUT and making C1 charge to slightly higher voltage. When C1 vo!tage reaches that of zener D1, oscillator stops and charging ceases. R2 sets 12 V maximum battery voltage between 10 and 14 V during charge

 

I found this, can any one give his opinion for this? and what do i need to change ?

Another random circuit even more difficult than the first? You couldn't understand or modify the easy one, even after the function of every single part was explained to you. I just can't see any benefit in using up several more hours doing this.

 

i may be the most stupid person to this date who signed up in this forum,, 3:23am and still reading , but all i read won't get un to my mind.

i am very stressed, and running out of time because i need something to show to my professor in the morning, i had a week but didn't come up with any thing :'(

what about the circuit proposed by dave , the one with the comparator

 

i may be the most stupid person to this date who signed up in this forum,, 3:23am and still reading , but all i read won't get un to my mind.

i am very stressed, and running out of time because i need something to show to my professor in the morning, i had a week but didn't come up with any thing :'(

what about the circuit proposed by dave , the one with the comparator

Since this isn't important to you, take the zero and move on. That way your grade reflects your knowledge. Don't stress about it, just move one.

No one can prevent you from deciding that some particular topic is not important enough to learn it, but we can ask that you not get credit for learning something you didn't.