DIY self-powered USB hub... is it possible?

**PaulF** · 10-12-2010, 06:11 PM

Read the wikipedia USB page's power section at: http://en.wikipedia.org/wiki/Universal_Serial_Bus#Power

In a nutshell:
A USB port in standard mode is allowed to output 500mA.
A USB port in charging mode is allowed to output 1.5 A.
A completely dedicated USB charging device is allowed to output 1.8 A.
Standard USB connectors are rates at 1.5 A.

Relevant portions:

Originally Posted by wikipedia

The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire from which connected USB devices may draw power. The specification provides for no more than 5.25 V and no less than 4.75 V (5 V±5%) between the positive and negative bus power lines. For USB 2.0 the voltage supplied by low-powered hub ports is 4.4 V to 5.25 V.

A unit load is defined as 100 mA in USB 2.0, and was raised to 150 mA in USB 3.0. A maximum of 5 unit loads (500 mA) can be drawn from a port in USB 2.0, which was raised to 6 (900 mA) in USB 3.0. There are two types of devices: low-power and high-power. Low-power devices draw at most 1 unit load, with minimum operating voltage of 4.4 V in USB 2.0, and 4 V in USB 3.0. High-power devices draw the maximum number of unit loads supported by the standard. All devices default as low-power but the device's software may request high-power as long as the power is available on the providing bus.

Originally Posted by wikipedia

In Battery Charging Specification, new powering modes are added to the USB specification. A host or hub Charging Downstream Port can supply a maximum of 1.5 A when communicating at low-bandwidth or full-bandwidth, a maximum of 900 mA when communicating at high-bandwidth, and as much current as the connector will safely handle when no communication is taking place; USB 2.0 standard-A connectors are rated at 1500 mA by default. A Dedicated Charging Port can supply a maximum of 1.8 A of current at 5.25 V. A portable device can draw up to 1.8 A from a Dedicated Charging Port. The Dedicated Charging Port shorts the D+ and D- pins with a resistance of at most 200Ω. The short disables data transfer, but allows devices to detect the Dedicated Charging Port and allows very simple, high current chargers to be manufactured. The increased current (faster, 9 W charging) will occur once both the host/hub and devices support the new charging specification.

So it depends on the device.

**trader007** · 10-12-2010, 07:55 PM

check out jameco for industrial power supplies. we install these on multi million dollar jobs all the time, they are really nice for the cost. i use a 5a, and i just gave a generic $10 7 port hub wired to it. there are some really bad el cheapo usb hubs out there, but theres a lot of decent ones too that wont cause any problems, especially when speed isnt much of an issue (usually not when you are using a hub)

**PaulF** · 10-12-2010, 10:12 PM

I can also vouch for those Jameco power supplies. I'm using them in my install and they work BEAUTIFULLY.

**OldSpark** · 10-13-2010, 05:01 AM

Thanks PaulF for the early new year.
No thanks for causing me to review the link ahead of the new century, but my curiosity for suspected ambiguities won out.

In my earlier reply (lost due to the mp3car "malware" warning) I thought many would probably be confused by "USB ... is allowed to output 1.8 A" (but) "Standard USB connectors are rated at 1.5A". Alas, not me! But I'm used to Specs - others often see them as fabricated and contradictory.

[ Rem: Did I tell of my mate's woe - arguing that Anderson DC connectors were NOT for interrupting current? Alas an Aussie lunchtime-legend argued that he only bought "quality USA-made Andersons"...
LOL - they have the same "no-interruptus" embossing as the others, though they only have it in French and omit the English. Because they provide a Spec for "interruption operations at rated current" does not mean they are suited or intended for interrupting current!
But it was one more stat point for the hypothesis that morons don't read French.
And not many Australians read French. ]

**Enforcer** · 10-13-2010, 10:15 AM

Originally Posted by OldSpark

Thanks PaulF for the early new year.
No thanks for causing me to review the link ahead of the new century, but my curiosity for suspected ambiguities won out.

In my earlier reply (lost due to the mp3car "malware" warning) I thought many would probably be confused by "USB ... is allowed to output 1.8 A" (but) "Standard USB connectors are rated at 1.5A". Alas, not me! But I'm used to Specs - others often see them as fabricated and contradictory.

[ Rem: Did I tell of my mate's woe - arguing that Anderson DC connectors were NOT for interrupting current? Alas an Aussie lunchtime-legend argued that he only bought "quality USA-made Andersons"...
LOL - they have the same "no-interruptus" embossing as the others, though they only have it in French and omit the English. Because they provide a Spec for "interruption operations at rated current" does not mean they are suited or intended for interrupting current!
But it was one more stat point for the hypothesis that morons don't read French.
And not many Australians read French. ]

Is there an English version of this post available?

**OldSpark** · 10-13-2010, 10:47 AM

Certainly.

I'm sure Paul will ask if he wants clarification.

**soundman98** · 10-13-2010, 05:10 PM

Originally Posted by Enforcer

Is there an English version of this post available?

Originally Posted by OldSpark

Thanks PaulF for the early new year.
No thanks for causing me to review the link ahead of the new century, but my curiosity for suspected ambiguities won out.

blah,blah, read a new review, blah, blah.

Originally Posted by OldSpark

In my earlier reply (lost due to the mp3car "malware" warning) I thought many would probably be confused by "USB ... is allowed to output 1.8 A" (but) "Standard USB connectors are rated at 1.5A". Alas, not me! But I'm used to Specs - others often see them as fabricated and contradictory.

replied earlier, but it got lost. usb ports are rated to a max of 1.8A, check the specs!

Originally Posted by OldSpark

[ Rem: Did I tell of my mate's woe - arguing that Anderson DC connectors were NOT for interrupting current? Alas an Aussie lunchtime-legend argued that he only bought "quality USA-made Andersons"...
LOL - they have the same "no-interruptus" embossing as the others, though they only have it in French and omit the English. Because they provide a Spec for "interruption operations at rated current" does not mean they are suited or intended for interrupting current!
But it was one more stat point for the hypothesis that morons don't read French.
And not many Australians read French. ]

a friend argued that a certain type of connector would not work with AC current, and insisted on getting the US MADE versions, that he thought were ac-compatible. they are the same..

morons don't read french..

at least, that is what i got out of it..

**OldSpark** · 10-13-2010, 05:59 PM

Good grief - maybe I do need to translate!

Read ahead of schedule.

Many don't understand specs & will see contradictions (eg: st'd USB connector fails spec ie, 1.5A vs 1.8A).

Anderson Connectors are "not for interrupting current" (eg, SY50A-600V). Aussie moron thought otherwise.
Nothing to do with AC!!!

Although this reply was intended for PaulF as a thanks, shall I drop humour & anecdotes & VAS in future? (The malware-lost original reply was clearer.)

**soundman98** · 10-13-2010, 08:19 PM

i sometimes forget sarcasm doesn't type very well..

**OldSpark** · 10-13-2010, 08:44 PM

That's why I don't direct sarcasm at (this forum's) participants - except when it is VERY obvious. (But I'll separate Swedes from Aussies for the moment.)

If people get confustigated by simple specs, irony & sarcasm have little chance....