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I am a computer programmer and after a project with Image processing which runs on ARM Embedded system board. Specification says it needs 12V 1 Amp Supply. I have a computer SMPS which gives me 5v and 12v constant supply and rated as 450 watt. Also it is written it can draw upto 24A current so here I cam confused. Can this heavy amount of current burn my board ? Also I recall Ohm Law that if the v is constant then current will vary according to load. Please give me some right direction whether I can use PC PSU for my embedded works.

Thanks

Dave
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  • all that means is that it will supply up to 24 of your system boards before the output voltage starts dropping. ... think about it like this ... if your computer runs with 8 hard drives, and you disconnect 7 of them, does the 8th remaining drive blow up? – jsotola Dec 29 '17 at 07:40
  • i should have mentioned ... if you accidentally short something out on your system board, you will most likely get bigger fireworks, unless the power supply detects shorts and shuts down – jsotola Dec 29 '17 at 07:45

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The PSU rating just means that up to 24 A is available to be drawn from the 12 V supply. Your board will draw what it needs from the 12 V rail, up to 1 A from what you've said.

However, that means that the PSU will supply up to 24 A into an overload or short circuit from your board or 12 V connections coming out of it. The PSU protection will kick in shortly (something like 10's ms) after the overload is detected and either limit the output current to 24 A or most likely put the PSU into 'hiccup' mode, which you'll find details of on the interweb. This burst/ongoing 300+ W of power is quite likely to burn out tracks on your PCB.

So, in short, if you use it, be very careful not to let your board short-circuit the 12 V supply, otherwise you are very likely to damage that board.

TonyM
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  • Great! I appreciate the explanation. I am thinking to use an intermediate power unit which will have some fuse and current divider circuit with. Is there anything which can blow up the fuse so fast if any short circuit ? – Dave Dec 29 '17 at 09:22
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    A "current divider"? What's that, exactly? – Finbarr Dec 29 '17 at 09:35
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Yes. But you shouldn't. An ATX power supply is for finished and tested products.

This supply is 24 times more powerful than your requirements. It also does not have any protections for prototype work. It only has protections for itself.
If you accidentally make a short, you will see sparks, flames and/or smoke. And you'll be replacing chips or getting new boards.

A much safer way to do this would be to use a lab power supply. With configurable voltage, current limit and even over current trip if you are feeling fancy.

Or, just the appropriate size wall wart if you're feeling cheap. But not an 2000% overrated ATX power supply.

Jeroen3
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  • I have a configurable voltage module with me already which takes 12V as input and output as per I adjust the POT and it displays the output voltage in 7 segment display. How about connecting this module with the ATX PSU ? Does it sound good ? – Dave Dec 29 '17 at 10:18
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The current is completely based on your load, so if you have a voltage source with maximum 24A current, it means based on the load that you are using it can provide currents from miliamps to maximum 24 amps. therefore if you need 24V and 1A there is no difference using a 24V-1A power supply or 24V-100A power supply. But, if for any reason, like mechanical or electronic problems if you get short circuit on your board, with higher currents your board is definitely going to burn up, tracks on your PCB will be burned or even it might cause the board and wires to get in fire. It is highly recommend to use a fuses when you are using high amperage power supply. you can use the wire fuses easily in the input voltage. enter image description here

Majid khalili
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