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It is my understanding that powered USB Type A 3.0, 3.1 and 3.2 switches have over current control and will only output 4.5 watts around 0.900ma unless the output port is a type-c non pd port on the switch that might be able to do up to 15 watts, however actually finding these switches are impossible or at least for me it has been. The only ones I can find are USB hubs that output 900ma unless the port supports PD, or BC 1.2 charging which a NVMe will not trigger either.

So this brings me to my question. When using a NVMe enclosure what watts do you actually get around when the voltage output is reduced from 5v 900ma (4.5watts) to 3.3v (Pcie) in the actual enclosure. I have some drives that simply are too hungry 2A and shopping for NVMe drives. I know when you down voltages and take into a reasonable efficient, it should be more. I know some enclosures will down step better than others but just a safe max would be nice. I.m assuming it's around 1 to 1.2 AMPs

Thanks in advance

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I'm not fully clear on what you're asking, but in electronics terms you can follow this rule of thumb.

Technically, USB-A ports are only legally permitted to supply 5 V, but some smartphone manufacturers have implemented their own non-compliant schemes to provide more power for quick charging (e.g: QC3.0, VOOC, etc...)

  • 5 V @ 900 mA = 4.5 W (5 * 0.9 = 4.5)
  • Assume ~85% efficiency in an SMPS buck, results in ~3.8 W available (4.5 * 0.85 = 3.825)
  • 3.8 W @ 3.3 V = ~1.15 A (3.8 / 3.3 = 1.1515)

So, as a rule of thumb, you might see about 1.15 A available for use by the NVMe storage (not far off your figures). Brief peaks above this may be fine (depends on how twichy the power source is), but sustained will likely trip the Over Current Protection. It's impossible to give you a hard figure - a lower figure will be "safer", but might be unnecessarily pessimistic.

... as you've noted, using a USB-C port with USB PD will give you more headroom, and may be required for higher performance devices.

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  • Thanks for your extended answer. I'd love to go with a 10 port 3.2 Gen 2 10Gbps type C for around 6 Nvmes, even considered using 2 ports to power the one device using what we used to do with USB 1.0/2.0 for 2.5" USB hard drives and DVD writers. The problem I'm finding is they like to use 5v 3amp for 7 ports which is worse than the 12v 5 Gbps versions. I can't find a single hub with 15 watt type C, most of these hubs are high watts and can charge 10 ports at 1.5amp, but these ports only output that when they find a device that supports bc 1
    – Simon Hayter
    Commented Aug 12, 2023 at 21:24

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