with a variable output of 0~12v DC, and max 3amps current.
I have a desktop DC power supply now but it is a fixed 15v.

Have you any recommendations as to which kit, plan, or ??? to use ?
thanks

 

What is the current capability of your fixed power supply? Do you really need 0V? How close to 12V do you need?

 

What is the current capability of your fixed power supply? Do you really need 0V? How close to 12V do you need?

0 volts us not necessary, 1.5 will do if possible and my present unit can crank out 30amps, 35 peak.

Whoops, the specs say that it can be variable. Time to read the darn manual. Colour me embarrassed.
============

Jetstream JTPS31MB Small 30 Amp Power Supply w/ Meters

Specifications:

• Variable 4-16VDC
• 30 Amp Surge
• 25 Amp Continuous
• Light Weight, only 3 lbs!
• Compact, only 5" x 2.375" x 6.125"
• High current jacks on the back
• Switchable volt/current meter
• Over voltage protection
• Over current protection
• Switchable AC input voltage, 110 or 220 VAC

 

LM338 will give you a 1.2-12V at up to 5A variable supply. You'll need a huge heatsink for 1.2V @ 5A unless you set the input voltage to something sane.

 

You can use a 4.3V zener diode to cause the LM338 ADJ pin to track the input at 4.3V below the input.
Since the LM338 output stays at 1.25V above the ADJ input, the output will go from 1.2V to over 12V when the input is adjusted from 4V to 16V.
The regulator power dissipation will thus be basically constant with change in voltage for a given output current, whereas otherwise it would go up as the output voltage goes down.

The LTspice simulation of such a circuit is shown below for an input of 4V to 15V.
The output goes from about 1.3V to 12.9V.

R_Bias provides the minimum 50mA output current for the regulator to maintain regulation.
(The circuit shows an LM317 but an LM338 should work the same).

 

You could always add something like these boards...
https://www.ebay.com.au/itm/MP1584-...982584&hash=item2ee12a0db2:g:DeMAAOSw6BtVTIeZ
Take the trim pot off and replace it with a 12K pot and you can get from a bit under a volt to just over 12V out.

 

Boy, these are all terrific options, so being the geek that I am, I am gonna try them all.
I think that I have been infected with a "if you can build it, do it", virus.