The reason is that on my case there is a nice button includs led that i would like to use but it is computer case switch .

If it is complicated to build electronic switch i will not

 

It is a bit complicated to make a latching relay with just a push button.
It is far better to use a rocker switch. Safer better and less of a hassle.

 

The Transformer is ready i did the connections and it is ok


and the connection of secondary...

 

You configured it for 60V/8A.
Or you were thinking to add more Amperage?
Or I'm just wrong since i have no idea about transformers pinout.

PS

OK,I'm wrong didn't realize you wanted negative out.So just ignore what I said....

 

After that i connected everything to test and the test rezualts were very disapointing...

with 4A load in about 30sec the MJ15003 gets very HOT



Very HOT



My load 50W 12V







I am very disappointed an think that this circuit is not good at all
Only the transistors get very hot.
Not the L200 either the emitter resistor.

Except the above problem with a very slight movement of the potensiometer the voltage changes very fast.
Maybe i have made a mistake with connections but i have double checked it

 

With all linear power supplies, the voltage NOT being used, times the load current is the heat the pass transistor will dissipate. So, 4 amp times 18 volts equals 72 watts.

 

When you building a liner power supply, whatever you using 2n3055 or mj15003 to be the power transistors, the heat problem always be there, so you need to in parallel with two more mj15003, when the power transistor pass through 1A current will get a lots of heat, make the transistor continuing working temperature under 60℃ to keep the using life of transistor, you may need a fan to blow the heat sink and reducing the heat.

 

Ok. Understood about heat problems. Maybe i will add 2 more mj15003 but there is one more problem i found while testing
If i turn off the potentiometer for current limit the current go down as expected but if i turn it back on with load connected the current doesn't rise...

 

I Could not understand what exactly must be connected at this point with red circle.
I did only connect R4 bottom and not R2 top since i think it is ok from schematic

Someone could be a big help debugging this one...

 

How is the load(?Ω)?

 

How is the load(?Ω)?

 

You should in series the R2,R3 and connecting them as shown in the circuit.

 

You said when you tested the power with a load, how is the load?
The load was not listed in the parts list.

 

This is my load:




in action...

 

If you want greater reliability, exchange the bridge for 4 diodes, stud mounted. (2 x Anode Stud and 2 x Cathode Stud). Mount each pair on its own isolated heat sink; your case looks big enough. At 30A, the tags on the small bridge have a tendency to overheat.

 

I dont have any problem with the bridge. It dosent get even hot...
Only transistors get very hot

 

....................................
After paralleling them if you measure 30VAC on the secondary winding you are good to go.
Mind you if one winding can handle 8A you can draw max of 16Amps by paralleling them

Not if the transformer is driving a rectifier-capacitor supply. You need to derate the DC output to about 60% of it's maximum ampere value to allow for the high RMS current that the high peak current draw of a rectifier-capacitor supply causes (because the transformer power dissipation is proportional to the square of the instantaneous current draw, not the average). Thus a 16A transformer is good for about 9.6A DC maximum, close to the 10A the OP wants.

 

I dont have any problem with the bridge. It dosent get even hot...
Only transistors get very hot

Sounds like you need a fan blowing on the heatsink, as previously suggested. Mount the fan in the case so it blows outside air directly on the heat sink fins. Use a large muffin fan with a high air capacity.

 

I found out by searching the circuit that i have a mistake with connections of R4
As written from the author R4 and R2 top i thought this must be connected parallel....

Below i have drawn the connection and will make changes this afternoon



Hope this will solve the very short changes of current with very small movement of the potentiometer.

 

Sounds like you need a fan blowing on the heatsink, as previously suggested. Mount the fan in the case so it blows outside air directly on the heat sink fins. Use a large muffin fan with a high air capacity.

I will definitely use a blower and also i am thinking of connecting it with thermal resistor to start at 40 celsius
Or maybe less than 40?


Thanks for your suggestions