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I'm not an engineer, but I build custom audio equipment and systems as a hobby. My question to you is: from a computer power supply (PSU) which converts AC power into DC of various voltages (12 V-5 V) would it be possible to power a Bluetooth receiver which uses 5 V 1 A power from a wall plug USB socket, directly from the PSU? I've tried using the red (5 V) wire with the ground to a female USB cable which I plug into the Bluetooth receiver, but to no avail. The part I don't know about is the 1 A. What is the relevance of this?

Wasabi
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user6236
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  • 5V 1A means the power supply for the Bluetooth receiver can maintain 5V with currents up to 1 A (when plugged into the wall). The actual current demand may not be exactly 1 A. Question 1 is what is the maximum current the PSU is rated for? Question 2 is are you sure you connected the red/ground wires to the cable correctly? – willpower2727 Apr 28 '16 at 20:05
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    The answer is almost certainly yes. 5V*1A = 5 W of power, while most computer power supplies are rated for hundreds of Watts. This brings you back to willpower's second question: are you sure you wired it correctly? – Chris Mueller Apr 28 '16 at 20:27
  • The psu(this model) is rated for 550 watts. I use any from 350 and up. Wiring it is simply red to red and black to black, I was only twisting the wires together as I didn't want a permanent bond. I'll give it some more work and see if I can make it happen. Thanks guys! – user6236 Apr 28 '16 at 21:21
  • Since your device says it requires 5V 1A, it's a good bet that it requires more than the "base-level" current of 500mA that is available from any USB cable. To protect the complete network of USB devices from malfunction if the power supply is overloaded, probably the Bluetooth device sends some data over the USB link requesting more current, and only switches itself on to accept the current if it gets the appropriate reply from the USB power supply. If that is the case, your concept won't work. I'm no expert in this, but start here: https://en.wikipedia.org/wiki/USB#USB_Power_Delivery – alephzero Apr 29 '16 at 01:13
  • @alephzero, based on the table below for a ATX power supply, 5V supply should be able to source the necessary current. – Mahendra Gunawardena Apr 29 '16 at 10:20

1 Answers1

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I did a quick google search on current rating on a 5V supply on a ATX power supply here is data.

Power Rating

Base on this data your 550W power supply should be able to source sufficient current to power the Bluetooth receiver. Your problem might not be power rating but how you are using the PSU.

As I understand ATX power supplies have a PS_ON which needs to be pulled down to switch on the PSU. When you pull down the PS_On the PWR_OK signal line goes high. After this point you can source current from the other supply lines. The a power supply is connected to the mains the 5VSB is hot. You might be able to power your device using the 5VSB source too. This is the purple wire, you might want check with a multi meter to verify.

Below is the power sequencing diagram for a PSU.

ATX Power supply timing

Below are some notes about PS_ON and PWR_OK

PS_ON description PWR_OK description

Below is the connector pin out that might be of helpful to you.

ATX PSU connector layout

Below are few references with more insight that might be of assistance to you.

HTH

References:

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Mahendra Gunawardena
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