I'm wanting to use an ATX power supply for a bench power supply. I'm no expert on PC power supplies, so I just want to verify what I've been reading. PC power supplies supply the power you need at what amperage you need. So If I attach my Arduino directly to a 5v line, it will output 5v at whatever mA the Arduino needs? And if I attach an electric motor that is 5v at 3A it will output 5v at 3.xA altogether? I just want to know before I fry my Arduino and/or anything else I try to use on this. I've tried using a multimeter to test amperage but that doesn't work (just draws power I guess).
it will output 5v at whatever mA the Arduino needs?
Yes but and it is a big BUT
If you make an error in your wiring and accidentally get a short that power supply is going to deliver a track melting amount of current. So while it will work it is not very tolerant of errors. A lower capacity power supply would have it's voltage collapse under those sorts of errors and maybe save something.
You are basically correct, however....note that ATX power supplies sometimes require a "minimum load" in order to keep the output voltage regulated properly. If they don't supply at least xxx Amps of current, the output might just not be 5V and then you are going to fry stuff.
ATX power supplies (IMHO) are not good replacements for general-purpose bench power supplies.
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Interesting, this seems like a huge fault that engineers would fix (this refers to the whole frying thing...). I wonder if there is any protection of the internal headers on a motherboard, so something like the USB front panel headers, are they rated at anything specific? Or are they just directly connected to the 5V line of the PSU?
this seems like a huge fault that engineers would fix
No it is not a huge fault, switch mode power supplies often have minimum current values.
Or are they just directly connected to the 5V line of the PSU?
No USB power goes through a switching chip so the current can be monitored and turned off if it exceeds what the USB port is currently set for.
g0bl1n:
Interesting, this seems like a huge fault that engineers would fix (this refers to the whole frying thing...)
You are using the supply for an application other than it was intended. How would engineers know your plan was to throw out all support circuitry and expect the supplyto behave? Maybe the fault isn't theirs, but someone else...
The concern isn't really frying the power supply, it is what is being connected. There is just a lot of current available. The rails can provide 10s of Amps. Your projects may only use 1.
Now, does this mean you can't use it as a bench supply? No. You can, BUT you need to understand the implications. First step would be undertaking what the terms "Power", "Voltage", and "Current" each mean. Next is how they relate to each other.
V=I*R
voltage(volts)=current(amps)*resistance(ohms)
or I=V/R
or R=V/I
At the risk of being totally boring (quote form Billy Elliot musical... SEE IT.. it is on tour, in the US...)...
A fuse would be a good idea if you go that route.
Might not save your Arduino, but will at least limit... not eliminate... the chance of a fire. And it MIGHT save your Arduino!
Would an LM317 be enough to at least die before passing an overload down the line?
http://www.national.com/ds/LM/LM117.pdf
LM117/LM317A/LM317
The LM117 series of adjustable 3-terminal positive voltage
regulators is capable of supplying in excess of 1.5A over a
1.2V to 37V output range.
....
In addition to higher performance than fixed regulators, the
LM117 series offers full overload protection available only in
IC's. Included on the chip are current limit, thermal overload
protection and safe area protection.
....
Allelectronics has them for 70 cents.