Electronics > Beginners

DIY power supply

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MarkF:
DO NOT TAKE THE ATX CASE APART.
The extra space is needed for air flow.

Just use the wires on the connector for the motherboard.
Cut out the wires you want to use from the connector and leave the rest.
You may wish to use the leftover wires in a future mod. Or power your function generator.
Leave the disk drive connectors alone.

You said you have polyfuses. 
I would recommend them for the low current outputs and the variable output.
They reset after the load is removed.

I would save your breakout boards for something else. 
They don't have any special current limiting.
You're not going to gain anything over using the ATX outputs with some polyfuses.

The slow-blow fuses will react slower and will take a little more current.
I would suggest 0.5A for the low current outputs and 5A for the high current output.

Something in the 0.5A to 1A range for the variable output.
Put the fuse on the output of the variable supply. Also, you will need a heat sink and cooling.
You will need to carefully consider the grounds for this if you drive the input from something other than the +12V of the ATX supply.

You are probably okay not having fuses for the internal things you power from the ATX.  Just for lines leaving the box.

You also need to be careful how you wire those volt/amp panel meters. 
You especially need to check the low sides of the input power, volt meter and amp meter. 
Some have the low sides tied together and will short what you're trying to measure if connected wrong.

Like I said before, I would not get overly ambitious for a first project with unknown needs.  Just the basics for now.

Pirateguy:
lol i already cut off the connectors, but no worries, i may be a noob but this isn't the first time i heat up a soldering iron.
(and i have several half finished robots to show for it :P)
and don't worry, i know all about discharging the caps n stuff. u could safely shower with this thing right now.
i intend to desolder the wires i don't need instead of cutting them, and will have no trouble adding new ones if needed.
and the case, once i find a larger enclosure for it all, i will ditch entirely.

with the room i have available, and some reworking of the wiring, changing yuge connectors for solder connections,
i think there is more then enough room for air flow and the circuit for the regulator for the variable output
shouldn't take up too much space.
only the interface will take up space, and it's not too terrible (again after taking care of some unnecessarily bulky plugs n stuff.)
also there will be a thermometer on the thing, so if i run into trouble i should get fair warning, and i can always drill some holes and add another fan if needed.

also i think right now i will just do the fixed outputs in the ATX box, and make the variable a separate unit for now until i find
a proper housing for it all. i have a nice looking HP 32V 1.550A linear psu with what looks like ample protection.

also there is a yuge heatsink already in the atx and i was thinking of making use of that. though i do have other heatsinks if needed, incl specific to220 ones.

once my brain gets done booting up ill post some pics.

Pirateguy:







MarkF:
The 32V HP Supply and a LM317 would make a very nice variable supply.
However at low output voltages and a 1A load, the LM317 would need to dissipate 30W. 
You could use a bypass transistor to handle the load. There is a two transistor configuration in the datasheet if you want to use the 2N3055.

I saw a thread last week discussing a LM317 and a TIP36C PNP bypass transistor.  I would opt for the PNP single transistor.
   https://www.eevblog.com/forum/beginners/lm317hv-and-heatsink/

I would also use a 10-turn potentiometer to adjust the voltage.
   https://www.mouser.com/ProductDetail/Bourns/3590P-2-103L/?qs=sGAEpiMZZMvygUB3GLcD7uCOAMig3YAGHWGOtVZsEa0%3d

Pirateguy:
what about lm338?
i have some of those coming my way.

edit:
that pot is a bit pricey for my budget, how about this one:
https://www.ebay.com/itm/1PCS-3590S-Precision-Wirewound-Potentiometer-Pot-10Turn-500R1K2K5K-10K-20K-50K/302098816720?hash=item46567e1ed0:m:mEC_-G0YRedjCMHo_CI84VQ

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