current limiting 3

[kenre]

I once had a circuit diagram for adjustable current limiting using a ua 741 and 2n3055 pass transistors.
No longer to be found. Anyone have a similar one? its to limit up to 30 amp.

http://www.retallickeng.com.au

Was told it couldnt be done, so
i went and did it!

 

[ScottyUK]

ken,

No, refering to my earlier post timestamped 6 Apr 08 0:54. Lionel corrected something for me.


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If we learn from our mistakes I'm getting a great education!

 

[kenre]

operahouse,

im going to try your circuit with the 1.5 v.

you posted,

Te other end of the pot connects to the battery + and to where the common pin of the LM317 used to connect to, the output of the regulator.

Which pin are you referring to as the common pin?

http://www.retallickeng.com.au

Was told it couldnt be done, so
i went and did it!

 

[OperaHouse]

That should be the center pin or case depending on the package. What you are doing is subtracting out the reference voltage of the regulator. The battery should last a year at that current. A weak/dead battery will be indicated by inability to go to zero. A 1K with a 220 ohm would make the pot more linear with a little shorter battery life. The resistor makes the pot useful the full range.

 

[LionelHutz]

I guess I was confused as to your requirements.

You posted you need up to 50V for certain types of anodizing. This means you need more than 50V input to the current regulator to get 50V output. If you build that circuit and short the output while running at this voltage level you'll blow up the typical 40V max input LM317.

It's kind of like the power dissipation levels. Sure, you can say I'll only allow a 10V drop across the current regulator making at most 300W of power losses. But, what happens if you run outside of this design, ie a short occurs or you forget?

I would try to design a circuit that can handle a short circuit at the highest voltage myself, but that's just me I guess.

 

[kenre]

I think i have had a short circuit in my brain!

I have rewound the transformer so i have 38V DC output, to protect the 317.

This lower voltage will fine for my mostly small jobs, anything larger will just take much longer.

Any opinions on this circuit ive found?

http://www.retallickeng.com.au

Was told it couldnt be done, so
i went and did it!

 

[LionelHutz]

The voltage and current don't meet your requirements???

I'm not really sure what you'd want to know.

 

[kenre]

Is this a good design? The current can be increased easily, maybe the voltage also with a Lm317 in place of the 7812.

What does have me interetsed is the single FET, i cant see how it could be a PWM circuit, so can the single FET handle it?

http://www.retallickeng.com.au

Was told it couldnt be done, so
i went and did it!

 

[OperaHouse]

I know it is tempting. I look at those adds that tell me I can increase my gas mileage by 70%. But, you haven't been listening. Single devices have power limits and if you get anywhere near to half the rating, your design is often in real trouble. The variable current part of that design has no current sense and that fet would easily turn to toast under certain operating conditions.

 

[kenre]

Im listening! but i cant learn without asking.
So the design has major flaws, i wasnt too far off, asking how one Fet could handle all that current. It Cant.

http://www.retallickeng.com.au

Was told it couldnt be done, so
i went and did it!

 

[OperaHouse]

It doesn't appear that you have read any of the application notes of the devices you are using. None of the questions have been technical in nature or show a basic understanding of of the application. Your interest has been more in having someone supply a complete design. Given that you intend to sell this as a kit, you should be reading all you can. There are a lot of questions that you should be asking that you are not.

 

[kenre]

"Given that you intend to sell this as a kit..."

Where have i mentioned this? It is for my personal use only.
I manufacture and sell metal and fibreglass products, i understand these.

http://www.retallickeng.com.au

Was told it couldnt be done, so
i went and did it!