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I'm planning on building a device that has the following requirements:

  • 4x devices that are rated as 5v (1.5 amps normal load, however during high loads can require upto 2 amps)
  • 1x raspberry pi

I've sourced a power supply that takes 240 AC mains supply and provides 5v @ 8 Amps.

My plan is to connect all the devices in parallel.

My questions are as follows:

  • Is this power supply a good idea?
  • When the system is idle, will this be an issue, i.e. the devices are not drawing maximum current?

Please advise!

EDIT

This is the kind of power supply I'm planning on using, I don't know if that helps?

http://www.ebay.co.uk/itm/DC-12V-24V-5V-Universal-Regulated-Switching-Power-Supply-for-LED-Strip-CCTV-UK-/291087849273?var=&hash=item43c6301739:m:m6INReCcQQadil-AVWF6qsQ

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    \$\begingroup\$ There is nothing to go on here to work out if the power supply might cause problems. Ripple voltage, minimal load current, sensitivity of devices to ripple. Tolerance of power supply output, maximum and minimum operating voltages of devices etc.. \$\endgroup\$
    – Andy aka
    Jul 14, 2016 at 11:45
  • \$\begingroup\$ so, in theory would this work? all devices are suppose to be 5v. I'm just concerned about the current. \$\endgroup\$
    – Zen Master
    Jul 14, 2016 at 11:48
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    \$\begingroup\$ There is NO theory. \$\endgroup\$
    – Andy aka
    Jul 14, 2016 at 11:52
  • \$\begingroup\$ Sure there is ;-) You only need to solve this equation: preposterousuniverse.com/blog/wp-content/uploads/2013/01/… then when W = 0 it won't work but when W = 1 it will. \$\endgroup\$
    – Bimpelrekkie
    Jul 14, 2016 at 12:16
  • \$\begingroup\$ @FakeMoustache BUT, the Higgs is a Boojum, you see. aND ALSO HERE. \$\endgroup\$
    – Russell McMahon ♦
    Jul 14, 2016 at 15:04

2 Answers 2

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4x devices that are rated as 5v (1.5 amps normal load, however during high loads can require up to 2 amps)
1x raspberry pi
I've sourced a power supply that takes 240 AC mains supply and provides 5v @ 8 Amps.

The RPI can see up to 1 Amp draw, or higher. Some take 0.5A by themselves with nothing plugged in.

So you have a system that takes 6.5 Amps normally, but can jump to 9 Amps during high load.

8 Amps is less than 9 Amps.

So No, that supply isn't a good choice for this.

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Is this power supply a good idea?

It is generally a good idea to design a constant voltage power supply with more current capability than you need. This will generally allow the supply to run cooler, and it also allows for the possibility you underestimated your actual needs.

When the system is idle, will this be an issue, i.e. the devices are not drawing maximum current?

This is entirely down to the design of your power supply circuit. An 8 A supply could be designed that does not lose regulation (meaning the output voltage goes out of spec) under low currents down to a few mA. But if you made a very very bad design, it could possibly lose regulation at 1 A or higher. If you just designed a voltage divider and told your boss it was a voltage regulator, it could lose regulation at 7.9 A load.

As the comments point out, there are numerous other considerations that determine whether your power supply is appropriate. The current capability being 8 A and the actual load being 2-3 A is not going to be a problem if the regulator circuit is at all well designed.

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