Just curious if anyone knows of a good source for power supplies.
I am looking for a 5v around 70W supply. So probably some kind of a switching supply like a computer power supply.
Would I need to modify an ATX computer supply to use only the 5V outputs?
I will be running 3W LED’s off this as well as I hope the arduino? Is the 5V from these regulated enough for an arduino?
ATX power supplies are switching types with some basic requirements that need to be met before they operate reliably.
One of those requirements is that SOME form of load must exist on each output for proper voltage regulation to occur. Usually the 5V line is the most important source to have a constant load on. This is usually done with a BIG power resistor of low value.
If not there, you can get oscillations in voltage or it won’t stay “on” and that won’t be much fun for your projects.
Here are some examples:
Normally PC supplies normally do around 30 something amps at 5V, maybe a bit more for really big power supplies.
[edit]Server supplies would give you enough, someone was offering some on here a bit ago for the price of shipping but that wasn’t cheap.[/edit]
A supply for that current at 5v will be hard to get. I think you will need to split up to a few supplies for that.
Mowcius
One of those requirements is that SOME form of load must exist on each output for proper voltage regulation to occur. Usually the 5V line is the most important source to have a constant load on. This is usually done with a BIG power resistor of low value.
I get 5.12V on most of my pc supplies just measuring with my mulitmeter which is well within the range of most 5v components (5.5v max standard)
Mowcius
70W is like 15amps… right?
If you don’t mind surplus –
The Vicor 5V/40A supplies at Electronic Goldmine are
9.25"L x 2.5"W x 1.37"High and are selling for $40 each. See
This supply is trimmable. For LEDs adjust the voltage just above the Vf(max)
spec. You will have a very efficient solution.
(* jcl *)
www: http://www.wiblocks.com
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A supply for that current at 5v will be hard to get.
Not in the U.S.
Several 60-100W supplies at $15-35 (Mail order from Florida)
And those are just a couple of my favorites from among the dozens of surplus dealers across the country.
They’re a little harder to find than the 5-10W wall wart variety, but there are lots of them out there.
One of those requirements is that SOME form of load must exist on each output for proper voltage regulation to occur.
That’s generally true, but ATX supplies in particular have to be designed so they stay stable even under the very minimal “sleep mode” loads. I’m guessing they’re doing that with more-sophisticated circuits that the older supplies that absolutely would get squirrelly if you didn’t load them with some minimum percentage of their rating.
I share your caution, but I keep seeing reports online from people who use ATX supplies on the bench without blowing up their projects, and can’t recall any about 100V “surprises” on the 5V bus.
There are lots of choices for 60 watts. For 70, you may have to pay more.
One choice is:
http://www.mpja.com/prodinfo.asp?number=16011+PS
but it seems to be out of stock.
Thanks for all the replys! Im actually only going to be using about 11A max @5V which is 55Watt I was just throwing in a little safety factor which is why I said 70Watt. So 60Watt would probably work fine.
I have no problems using surplus parts, maybe I should look around my area for some…
With all of the switching power supplies what kind of a load would I need to maintain? I am not too familiar with these types of supplies.
The min load specification varies by supply. Some may have a looser regulation spec
others may require a load.
IIRC there is no minimum load for the Vicor supply I suggested.
(* jcl *)
Yeah that VICOR supply looks like a great deal. Its a little overkill for me currently as im only using 11A however… I could tripple the number of LED’s im using. ;D
If the VIcor supplies are new and in new condition it is a great price. The DC-DC
converter is about 80% efficient at 75% load.
Since you need much lower currents you should use a fuse or a current
limiting circuit. I do not recall if those foldback or not. If they straight line
current limit you will get 40A into a short!
(* jcl *)
70W is like 15amps… right?
Something like that. Sorry, I misread the W bit…
Yeah I use an old PC power supply as my bench supply which pumps out 35A at 5V. I also fitted someone else up with an old supply which is providing 12v for the LED light circuit in their ‘train shed’ (they have a lot of LEDs).
As I said, all of the ATX supplies I have tested give voltages very close to the ‘intended voltage’.
My current supply (with no load) gives:
5.19 on the 5V and 5V standby (1.5A for the standby - used for most things)
3.31 on the 3.3V line
12.11 on the 12V line.
I have not had any issues with my supply or any others that I have converted 
Mowcius
Thanks guys, I just read the two walkthroughs pwillard linked to above. Sounds like an old PC power supply could work nicely, especially as just a bench supply.
A supply like this one that Ran linked to might make more sense for a permanent solution for this project. Would I need a load like a power resistor on it or would you think it already has something built in?
http://www.mpja.com/prodinfo.asp?number=17425+PS
Would I need a load like a power resistor on it or would you think it already has something built in?
Well it states that it is regulated and it doesn’t say it needs to be under load so it should have something built in.
Mowcius
I wouldn’t assume that there’s no load requirement, but I found the datasheet, and it specifies a minimum load of 0A.
Thanks for looking into that Ran!
I’ve got a big stack of high-capacity power supplies that I’ll send to anyone for just the cost of shipping.
See this thread for the full story:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1254460064