Power Supply Loading

[davelectronic]

What i meant is ive fixed voltages, and varied voltages, but 18 volts rectified then filtered is way above 12 volts. Something like 23 volts top end, i cant think of a way to close the gap and stay variable with the 18 volt transformer, then pushed up by capacitor filtering. lower the transformers secondary to 12 volts AC then the final out put will be closer to your 12 volts needed, about 16 volts, but will drop some under load to closer to 12 volts.
Dave.

 

[davenn]

Sorry. Should have clarified. Limit the maximum to 12 v.

ok no problem, choose a trimpot that will adjust from whatever minimum to a max of 12V for a given input voltage. try a 2k2 trimpot
You may find you have to just play a little with the values, you may end up with a small value series resistor with the trimpot. check your datasheet for the LM388 it will give you the formula for R1 and R2 for a given output voltage.

cheers
Dave N

 

[Lejoy]

OK. Thanks Dave & Dave! Here are a few pictures of my completed power supply. I left the xfmr in it's original case and use a project box with pc board for all the rest. I plan on putting a computer fan (40 mm) on the right side of the box to pull air through the heatsink that is on the left. The bridge rect and the LM338 are mounted on the heatsink. I drilled several small diameter holes in the heatsink to facilitate are flow over it.

 

[davelectronic]

psu loading

Hi there. glad its come together. I am on my modest phone at the moment, cant view your pic's properly on this, but fire up the pc later, look forward to having a look. until later.
Dave.

 

[davenn]

well done enjoy and have fun experimenting

Dave N

 

[davelectronic]

Hi Lejoy.
A well modded power supply for alternative use, yes the project box is just the job, and the 40mm axial fan will improve regulator performance.
Nice work there.
Enjoy that racing, have fun.
Dave.