Power supply question I am just starting to collect all the bits for a Mendel and I have a question about the power supply. I will probably want to add a heated bed fairly soon after building it. Will a 400w ATX power supply run the machine and still have enough left over to run a 12v heater for the bed? I haven't even done any planning on the heater so I don't have any estimated power consumption figures. I don't even know what temp I would want the bed at. I am just looking for a gut feel from some of the more experienced builders. If I should be buying a 650w power supply it's cheaper and easier to do it now. Any thoughts on this? https://reprap.org/forum/read.php?14,35176,35176#msg-35176 Fri, 04 Sep 2026 17:04:32 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?14,35176,35356#msg-35356 Re: Power supply question https://reprap.org/forum/read.php?14,35176,35356#msg-35356 nophead Mechanics Sun, 07 Feb 2010 10:36:56 -0500 https://reprap.org/forum/read.php?14,35176,35350#msg-35350 Re: Power supply question https://reprap.org/forum/read.php?14,35176,35350#msg-35350 -------------------------------------------------------
> Yes but safety regulations require the maximum
> load to be stated correctly, so these are
> fraudulent. They rely on the fact that PC's don't
> take the load they state under normal
> circumstances.
>
> If it is a 450W PSU you should be able to load it
> up to 450W, keeping each rail within its current
> limits and run it continuously. In fact most cheap
> ones blow up if you do.

The main problem with cheap PC PSU's is temperature, they are correct in stating it can handle 450w, but it's usually 450w at 20degC, but under continuous load they warm up and due to impedances varying the capacity of the power supply invariably drops, so if the user is still pulling peak current as always the system fails at the weakest point.]]> annodomini2 Mechanics Sun, 07 Feb 2010 09:39:32 -0500 https://reprap.org/forum/read.php?14,35176,35343#msg-35343 Re: Power supply question https://reprap.org/forum/read.php?14,35176,35343#msg-35343
If it is a 450W PSU you should be able to load it up to 450W, keeping each rail within its current limits and run it continuously. In fact most cheap ones blow up if you do.]]> nophead Mechanics Sun, 07 Feb 2010 08:28:29 -0500 https://reprap.org/forum/read.php?14,35176,35341#msg-35341 Re: Power supply question https://reprap.org/forum/read.php?14,35176,35341#msg-35341 Triffid_Hunter Mechanics Sun, 07 Feb 2010 08:12:12 -0500 https://reprap.org/forum/read.php?14,35176,35338#msg-35338 Re: Power supply question https://reprap.org/forum/read.php?14,35176,35338#msg-35338 nophead Mechanics Sun, 07 Feb 2010 06:54:29 -0500 https://reprap.org/forum/read.php?14,35176,35318#msg-35318 Re: Power supply question https://reprap.org/forum/read.php?14,35176,35318#msg-35318 Triffid_Hunter Mechanics Sun, 07 Feb 2010 02:14:15 -0500 https://reprap.org/forum/read.php?14,35176,35306#msg-35306 Re: Power supply question https://reprap.org/forum/read.php?14,35176,35306#msg-35306
Quote

So the important PSU spec would be a 12V rail with more than 14.3A.

So all you really need is 172W? Plus whatever you run off the 5V rail.]]> kitep Mechanics Sat, 06 Feb 2010 22:47:27 -0500 https://reprap.org/forum/read.php?14,35176,35219#msg-35219 Re: Power supply question https://reprap.org/forum/read.php?14,35176,35219#msg-35219
It's exactly the same principle as attaching a high power light or heater to a generator so it doesn't choke when the fridge or other inductive load kicks in.

As far as I know, the 3.3v rail undergoes secondary regulation and is sourced from 5v or 12v so it's basically out of this part of the equation.]]> Triffid_Hunter Mechanics Fri, 05 Feb 2010 21:11:59 -0500 https://reprap.org/forum/read.php?14,35176,35208#msg-35208 Re: Power supply question https://reprap.org/forum/read.php?14,35176,35208#msg-35208
So we have 4 motors @ 1A and a heater @ ~ 2A, so 6A @ 12V to run the basic Mendel.

A heated bed needs about 1kW / m^2 to maintain 100C for ABS. The Mendel build area is 200 x 200 I think, which is 0.04m^2 so 40W. I would use at least twice that to get a reasonable warm up time, so 80W, call it 100W for some margin = 8.3A.

So the important PSU spec would be a 12V rail with more than 14.3A. The other rails have negligible loads so as TH says you need to load them otherwise the PSU is totally out of balance and will give a 12V rail that is a few volts lower than it should be.

The more power you can spare for the heater, the faster the warm-up time will be.]]> nophead Mechanics Fri, 05 Feb 2010 19:15:03 -0500 https://reprap.org/forum/read.php?14,35176,35193#msg-35193 Re: Power supply question https://reprap.org/forum/read.php?14,35176,35193#msg-35193
It's the electronics part of this that worries me the most. I will buy the boards from Makerbot but if I have any problems getting them to work I have no idea how to troubleshoot them. I guess I will figure it out as I go!]]> ksmith5135 Mechanics Fri, 05 Feb 2010 16:58:36 -0500 https://reprap.org/forum/read.php?14,35176,35191#msg-35191 Re: Power supply question https://reprap.org/forum/read.php?14,35176,35191#msg-35191 Triffid_Hunter Mechanics Fri, 05 Feb 2010 16:33:44 -0500 https://reprap.org/forum/read.php?14,35176,35176#msg-35176 Power supply question https://reprap.org/forum/read.php?14,35176,35176#msg-35176
I haven't even done any planning on the heater so I don't have any estimated power consumption figures. I don't even know what temp I would want the bed at. I am just looking for a gut feel from some of the more experienced builders. If I should be buying a 650w power supply it's cheaper and easier to do it now.

Any thoughts on this?]]> ksmith5135 Mechanics Fri, 05 Feb 2010 15:57:34 -0500