Electronic Schematic Blueprint
 

I need help building an adjustable power supply! What it will be powered off of is 120v AC power and put to a computer powersupply with some resisters and capasitors and a little magic it will have a knob :) to adjust the current output!

now, here is a link to the diagram!


article describing what I want to do:
http://www.slotside.com/tt/power.html

electronic blueprint
http://www.slotside.com/tt/powera.html

I bought the stuff from radio shack, not sure if I got the write stuff below is a list of the parts that I bought

272-1016 Electrolytic Capacitor 100uf (qty 1)
276-1778 lm317t Postive adjustable volage regulator (qty 1)
271-1311 100 ohm resistors 1/4 watt 5% tolerance (pkg of 5)
271-1321 1k ohm resistors 1/4 watt 5% tolerance (pkg of 5)

from tigerdirect I got a 300watt powersupply for 20$, all in all I spent 40$ on this, I got some misc. stuff like aligator clips and wire and all that stuff, to so it would look like one of those NICE 400$ units talked about on the website.

My questions are as follows, where it says ampmeter and voltmeter are those digital (analog) read outs with a knob, or are they without knobs and do I have to add my own knob to control the voltage going them? Where do I add the knob and does anyone know what I need to do without blowing up a 200$ electric motor? I would be using this to power not just small slot car motors, but big stuff also, so I might be adding female power end to it so I can plug stuff in. This would be used for breaking in slot car motors primarly.

Please I really need help..

Thanks,
~PCT

Hello PCTech,

I don't work as a cinema service technician anymore, but I checked the "blueprint" and from my memory and common sense working together the output is as follows:

1: The circuit is made for allowing an adjustable voltage, not current. Otoh I guess it is the voltage you are interested in?
2: The meters are reading the current voltage and current respectively. They can be analog or digital, with knobe or with push controls or nothing at all, just read what they say. Basically they are optional but you want to be able to check what you are doing, at least until you have made a calibrated scale to accompaigne The Knob:
3: which is one only and not in the list of stuff you have bought. You see the arrow at R2? That indicates an adjustable resistor, in this case between 0 Ohm and 1000 Ohms. The output voltage depends upon what value you adjust this resistor to. I think you need to buy an extra component here.
4: Finally: A LM317T... what do you mean "big stuff", I think max current may be something like 1 or 2 Ampere here.

All those little electronic devices are small. I guess you have figured out you'll need to attach them to something? Like a little test board or something. Also, when draining some current from this circuit and having the Lm317t keeping the voltage down you'll have some energy in the regulator needing to leave it. Do you have some way to cool it? For example: You get 12 volts from the power supply, adjust R2 to let the circuit give 8 volts to an electric device that needs 1 Ampere... Now you reduce 12 volts to 8, that is 4 volts that needs to go, at 1 Ampere that is 4 Watt (P=UxI) and yo'll find that your little voltage regulator gets hot.

Good luck!
and watch out for the mains!

I was thinking, that the lm317t has a max voltage of 40v and 15watt, so thats like .375amps and i'm trying to get 8 amps, out of something that will push max .375amp. so i guess #1 i need a bigger voltage regulator AND another one to control the power output to the amp and volt meters. Also will this EVEN WORK? I told the friend of mine that it would be pointless to have this even after it worked! but hey he wanted to try it so he spent his money and I'm trying to help!

~PCT