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I want to make a multiple voltage regulator, the goal was to make a variable power supply and make it as compact as possible. I know there are many other voltage regulator projects out there, but I wanted to make mine to suit my needs.
My material includes dual 9v battery terminal, mini digital voltmeter, a potentiometer,1000ohm resistor, LM350 3A voltage, Regulator, toggle switch, small alligator clips, Some wire. After soldering some wire to the Ground terminal of the potentiometer and the other wire (copper) to the output of the voltage regulator and soldering the wire to the alligator clips, the test failed, I think whether I need to redo the heat shrink if I already did that earlier, but through several adjustments, the result is the same, I don't know where the key problem is.
Is anyone know it?

How much is load current? Output voltage range needed? Is 9V battery the primary supply? What is resistance of poteniometer?

dual 9V battery is the primary supply, and the Output voltage range is 35, 4.2 V, the resistance of potentiometer is 10k. Maybe I missed something when I connected the components with wires.

What is the "35"? The max and 4.2V the min?

With two 9V in series the max available with "near the end" batteries is 12V. 18V fresh. And LM350 needs about 2V difference between supply in and regulated out; so max out is 10V to 16V depending on freshness.

With 9V batteries the max "sustainable" (a dozen hours ... maybe) current is like 50mA.

Have you checked the sample schematic on a LM350 spec sheet?

Cheers,

Thanks a lot for helping me, I made it for my interest, whatever temporary holding it, but I want to try because I am a complete newcomer to the electronic field. And now to be serious, for the circuit, I have checked the datasheet of whatever electronic component I used, I chose the LM350 because it has higher current output, but I've used LM317 in the past. If I plan to drive something with higher current needs, shall I need a heat sink?

... shall I need a heat sink?

Maybe.

Need input (supply) voltage, regulated output voltage, max current to be drawn, which part number regulator and package. For example, an LM350 in TO-3 may handle more power than TO-220.

A variable regulator like LM317 will work but it will be inefficient when you run it at low voltage and higher current, that's when you maximize the voltage drop across the device and maximize and so is the power, this is when it will become hottest. The regulator is best used for known loads if battery life and stability are of concern.

If your current setup is failing, then you may have a miswire or you didn't pit the part on a heatsink and it burned up before you got much results out of it. you are going to have to post photos if you need help debugging. it may be a construction error as much as a design error

yea, I want to pose some pictures before, but I don't how to do here, I am not good at using this tool now, or maybe it can't do that.

Hi Leo Hathaway, direct uploading of attachments was not working previously but as of around 12:15am PST I believe the problem is fixed. Try again normally under the attachment tab when making a post.