ATX power supply for Gen7
October 13, 2013 04:08PM
Hi, I've built the Gen7 v. 1.5 board and now I'm looking to connect a proper PSU (The one i have now is 226W) but I couldn't find any clues on the wiki page, so my basic question is :

- How big a PSU do I need for a standard Prusa setup ?
- Is a 680 W ATX enough ?

My main concern is how many amps you can draw from a single +12V rail ? since heatbed + hotend alone takes ~ 14 A And i've read on the Gen7 wiki that some PSU's are limited to 10A on each +12V rail.

Or should i Simply just use 2 PSU's, that is use the 680W for the heatbed + hotend and my 226W for my motors ?
Re: ATX power supply for Gen7
October 13, 2013 05:04PM
How much current do they supply (how many Amps)?
Re: ATX power supply for Gen7
October 13, 2013 06:13PM
The 680W PSU is rated at 22 A max on the +12V line, though I think this might be a little too optimistic, because the last couple of times i've tried to have some kind of load on it, the PSU had a 1V voltage drop after ~220 W so the total ampage would have been 20 A. My idea as it seems now, would be to connect my 680 W PSU as the main supply, and let the load be heatbed + hotend, and have a 2nd PSU (the 226W one) delivering the power to the motors, would this be a feasible solution ?
Re: ATX power supply for Gen7
October 13, 2013 06:21PM
I just converted one!

Usually if its a helpful one , it should be found on a label on the unit, if not try and find a website about it. Usually as its computer gear they like to boast the specs.

overall watts does not really tell you the amps per rail as it depends on how efficient the unit is and how the power is distributed. I think 226W might be a little too low, I have a 500W that does 30A 12v

My experience is the wires of the same voltage go to the same spot on the PCB, but this could vary. I have seen ones that say 12v1 12v2 on the box. you can use a multimeter to check which ones are common to eachother.

I use use all the wires ( yellow for 12v ) at once because 10A+ down one thin wire will get warm!

see this [farm1.staticflickr.com]

it is likely you will need a dummy load on the 5v rail.

I power a Raspberry Pi running Octoprint (octopi!) off the 5v too.
Re: ATX power supply for Gen7
October 13, 2013 06:41PM
Thanks ! and how should i connect a dummy load to the +5V rail ? like just a resistor across it down to GND ? (1k, 10 k .. ?)


Anyway I'm going for the dualsetup with both my 680W and 226W that way im in the safe area.
Re: ATX power supply for Gen7
October 13, 2013 06:47PM
Btw.. I just looked through the website of a hardware shop nearby, i can buy a 500W (max 30A load on +12V rail) for 35$ I think I'm going to buy that next month
Re: ATX power supply for Gen7
October 13, 2013 07:09PM
Generally speaking, I try to avoid PSU with fans, Fanless server psu's are the way to go imo


Used plenty of 300-1200 watt psu's with fans, no problems,
Fanless is much better tho, and quiet
Re: ATX power supply for Gen7
October 14, 2013 03:38AM
nechaus Wrote:
-------------------------------------------------------
> Generally speaking, I try to avoid PSU with fans,
> Fanless server psu's are the way to go imo
>
>
> Used plenty of 300-1200 watt psu's with fans, no
> problems,
> Fanless is much better tho, and quiet


True, and to make things worse, the 680W PSU is noisy as hell, so I think i'm going to put a potmeter in series and do some manual control that way.
Re: ATX power supply for Gen7
October 14, 2013 06:02AM
Quote

- How big a PSU do I need for a standard Prusa setup ?

Depends on the equipment. Add 1.5 for each axis + extruder, 3A for the extruder heater and the heated bed, if you have one. Multiply with 1.5 to have a margin against overload.

226W might be sufficient to run without a heated bed. As you already have it, try it! Will just turn off when overloaded.

Quote

and how should i connect a dummy load to the +5V rail ?

[reprap.org]

Quote

Fanless is [...] quiet

Fan'd ones in standby, too, and temperature controlled fans (standard these days) are barely noticeable. Printers tend to be much noisier.

That said, if you know a source for affordable fanless PSUs, please let me know. My PC would need one.


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Re: ATX power supply for Gen7
October 14, 2013 10:36AM
Traumflug Wrote:
-------------------------------------------------------
>
Quote

- How big a PSU do I need for a standard
> Prusa setup ?
>
> Depends on the equipment. Add 1.5 for each axis +
> extruder, 3A for the extruder heater and the
> heated bed, if you have one. Multiply with 1.5 to
> have a margin against overload.
>
> 226W might be sufficient to run without a heated
> bed. As you already have it, try it! Will just
> turn off when overloaded.
>
>
Quote

and how should i connect a dummy load to
> the +5V rail ?
>
> [reprap.org]
>
>
Quote

Fanless is [...] quiet
>
> Fan'd ones in standby, too, and temperature
> controlled fans (standard these days) are barely
> noticeable. Printers tend to be much noisier.
>
> That said, if you know a source for affordable
> fanless PSUs, please let me know. My PC would need
> one.

Update, I think my 680W might be fried... I inserted the PSU into my desktop PC and fired it up again, after 10-15 minutes or so the computer shutoff all of a sudden, after inspecting the 4 pin CPU connector i could see soot, and it was firing hot !

So.. could the PSU be dead ? if not, maybe it can still power, to some degree the Gen7 board :-)
Attachments:
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Re: ATX power supply for Gen7
October 14, 2013 01:01PM
Looks like dirty or oxidized connector pins. Careful cleaning of both sides (board header and connector) is probably a good idea.


P.S.: please quote only the neccessary parts.

Edited 1 time(s). Last edit at 10/14/2013 01:04PM by Traumflug.


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