Convert 0-30V 3A PSU to 5A or more

[audioguru2]

This project would need a complete re-design to get its output voltage up to 50V.
It still has nearly the same schematic as the original. The output transistor has an added emitter resistor then two more output transistors and emitter resistors are added in parallel on the heatsink. Many parts values were changed. Someone mentioned adding trimpots in series with the main pots for calibration.

 

[Niksun]

Gah!!  I apologize; I made a mistake.  I meant 0-30V and 0-5A.  Wow, the "5" key is awfully close to the "3" key, eh? 

As an aside, I've been investigating recharging regular, old alkaline batteries (I know, most think this is not a good thing) with this PS.  In any event, I figure that capping the current at ~65mA and setting the voltage to the appropriate value for the cell I wish to charge, it may just work.  What do you think?

 

[audioguru2]

I don't think ordinary alkaline battery cells can be re-charged. I tried it and the "charge" lasts only a couple of hours if it is used or not.
You can only discharge a cell a small amount then you charge its capacitance.

 

[Niksun]

Noted.  I am trying out a circuit now to charge them to see if it will even work.  In any event, does anyone have some sort of current schematic for the 0-30V, 0-5A PS?  Thanks.

 

[ante1]

Hi Niksun,

The PSU is not any good for charging alkalines! The DC is much too good! You should use only a half wave rectifier and no smoothing cap for best results!

 

[Herman the German]

I'll try a completely new way concerning the power stages. 2N3055 is something I have seen in the museum. Two main changes will apply to a power supply with high perfomance. First the transformer will be a ring type (excuse me, my English is not better but may be understood). You can drive a ring type transformer almost to saturation and it will still work. Secon change: through out the dinosaur transistors and replace with N-channel Power MOSFET with no higher restance than 0.04 Ohms, even having the luxory that each individial transistor has a FLAG output to indicate that it is tired of working and give the whole burden to his brother.

Just let me think two or three nights about the theme. I'll come out soon with a good and affordable power supply.

Kind regards to all being busy with the problem.

HtG

 

[audioguru2]

Hi Herman,
Sure the old 2N3055 is in the museum. This entire project is an old design, but it works well when its parts are corrected. 2N3055 transistors are cheap, Mosfets are expensive.

This modified project has a max output current of only 5A, so why use a Mosfet rated at 33A?

The output transistors are linear, not used as switches, so they get hot. The project would  still need 3 Mosfets instead of transistors to dissipate the heat.

Also, the gate voltage of an N-channel Mosfet needs to be much higher that the voltages in this project. 

 

[MP1]

As an aside, I've been investigating recharging regular, old alkaline batteries (I know, most think this is not a good thing) with this PS. In any event, I figure that capping the current at ~65mA and setting the voltage to the appropriate value for the cell I wish to charge, it may just work. What do you think?

I think that this is a different subject and should be discussed in it's own thread - not as an add-on to this thread...

MP

 

[paulo.antunes]

Hi

I dont read all the posts, but I have a link to a project of a power supply that in the specifications that you want.

http://www.uoguelph.ca/~antoon/circ/ps3010/ps3010a.html

bye

Paulo

 

[audioguru2]

Hi Paulo,
Welcome to our forum. ;D
I forgot about the 723 regulator IC. I haven't seen one for nearly 40 years. We have a power supply project that uses it but the current isn't adjustable, it is fixed at a max of 2.5A.

The circuit you attached is adjustable up to 10A. Its automatic fans are good.

 

[Roomi]

I have planned to build the modified power supply unit and almost all the parts got collected.But the problem is here i did not find the huge capacitor like 15000uF 63V.I found a 10000uf but its voltage rating is 25v.now i am planning to manage it from a wasted  elecronic devices like tv,microwave oven etc. Do you know inside where i can find these types of capacitor ?I tried getting sample capacitor from some company but the did not respond.please help me... :'(

 

[audioguru2]

I buy electronic parts online at Digikey or Newarkinone. A 12,000uF/63V capacitor is $8.45US today.

 

[Roomi]

Thanks Audioguru for your comment.But I will not be able to buy on internet from Bangladesh.Is there any alternative ?

 

[Ughadoo]

But I will not be able to buy on internet from Bangladesh.Is there any alternative ?

Yes.

 

[Roomi]

Thnks for uor comment but I heard that it will decrease the quality of filtering... 8)

 

[audioguru2]

I think that smaller-value capacitors in parallel will work exactly the same as a single capacitor with the total of their values, except they will cost more and use more space.
At VHF radio frequencies and higher it will make a difference due to the inductance of a larger capacitor.

 

[indulis]

Thnks for uor comment but I heard that it will decrease the quality of filtering

Actually it is better because the ESR will be lower with parallel caps.

At VHF radio frequencies and higher it will make a difference ...

Who would use a capacitor of that value at those frequencies???

 

[audioguru2]

Hi Indulis,
We have had many questions about radio circuits, "Why is there a small-value capacitor in parallel with a larger-value capacitor? Why not use just one large-value capacitor?" Even a moderator wrongly said to use just one capacitor with the total value.

 

[indulis]

... "Why is there a small-value capacitor in parallel with a larger-value capacitor? Why not use just one large-value capacitor?" Even a moderator wrongly said to use just one capacitor with the total value.

The moderator is not wrong!! There are cases where you do want to do this, but IT IS NOT nessessary everywhere!!

Guru... how exactly do values in the range of 10,000uF and RF go "together"??

 

[audioguru2]

I was explaining that paralleled capacitors also work well and are needed at RF frequencies.
A low-value capacitor is an excellent low-inductance bypass for high frequencies. A higher-value capacitor is inductive so is a poor high frequency bypass but is good at lower frequencies. Both in parallel bypass a wide range of frequencies not possible with just one value.

This original 3A project used only 3300uF as its main filter capacitor. It was reported to produce plenty of ripple at its output.