PSU for Prusa i3

[ZorAxe]

Hi there guys,

I'm looking for a power supply for my Prusa i3 that I'm building. Is it possible to use a PSU from a desktop computer? If so, how many watts do you need?

Thanks

[zx81]

its quite common to use a computer power supply my first I3 used one. 400W should be the minimum .. you should also use load resistors to increase and stabilize the maximum output of the power supply also allegedly some PSU's will shut down if there is a high load on the 12v rail's and no load on the 5v rails.

[Roxy]

Hi there guys,

I'm looking for a power supply for my Prusa i3 that I'm building. Is it possible to use a PSU from a desktop computer? If so, how many watts do you need?

Thanks

Probably... It would be worth while to search for Prusa I3 and ATX power supply. A lot... If not most of the Prusa's use ATX power supplies. That is the combination I have. Probably, you can get a high wattage ATX supply on eBay for $25 including shipping. Most of the high current is on the 12 volt supply. Make sure you have sufficient wattage on that supply. But still, having multiple supplies on the 5 volt is good too because the Auto Bed Leveling servo's tend to need its share of current from the +5 volt supply and it is just easier to isolate it and keep all of the power clean by using separate supplies for the current pigs.

I'm sure somebody that knows what they are talking about will jump in if something crazy gets said.

[ZorAxe]

its quite common to use a computer power supply my first I3 used one. 400W should be the minimum .. you should also use load resistors to increase and stabilize the maximum output of the power supply also allegedly some PSU's will shut down if there is a high load on the 12v rail's and no load on the 5v rails.

What do you mean by load resistors?

[printbus]

What do you mean by load resistors?

As a result of the switching power supply design, some ATX power supplies require a load of some sort to be connected to the +5V output in order for the other outputs (like 12V) to work properly. Rather than go into details, I'll repeat Roxy's suggestion to search on the terms "prusa i3 and ATX power supply", or "rep rap printer and ATX power supply", etc. It doesn't take long to find people who discussed problems with using an ATX power supply and how adding a power resistor to the 5v output got them working.

[ZorAxe]

So basically you make the PSU think there is a load connected to the 5v rails?

[Roxy]

So basically you make the PSU think there is a load connected to the 5v rails?

Yes. But a better way to look at it is this: Because it is a switching power supply, it turns its output transistors all the way on. Then all the way off. It feeds this into a capacitor to smooth out the power. This is efficient because it isn't dropping a lot of voltage across the output transistors. But... One of the rubs is you need to have some amount of a load on it. Without the load, it can't regulate the output voltage. And if it can't detect a load, it shuts down.
Maybe that isn't quite true. But that is close to the truth and one of the electrical engineer types can jump in and correct this thought.

[ZorAxe]

Oh ok it's making alot more sense now. Thanks