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Does using the usb on Macbooks degrade life of the power unit?

Message #1 - Posted 2011/08/29 - dorayme

So far I have managed without any powered usb hubs, but now that usb powered hds and speakers etc are around, I am wondering if their use can somehow strain the power unit in a little Macbook (I never gave it a thought with desktop - "underdesk"?) towers.

For example, say you have a 500 usb powered hd, and you also have two usb sticks in and an external keyboard, to take an example, is the load unlikely to stress a 13" Macbook (charging power tether on).

dorayme

Message #2 - Posted 2011/08/29 - David Empson

dorayme wrote:

So far I have managed without any powered usb hubs, but now that usb powered hds and speakers etc are around, I am wondering if their use can somehow strain the power unit in a little Macbook (I never gave it a thought with desktop - "underdesk"?) towers.

For example, say you have a 500 usb powered hd, and you also have two usb sticks in and an external keyboard, to take an example, is the load unlikely to stress a 13" Macbook (charging power tether on).

No. Each USB port on the computer has a maximum output current rating, and has circuitry to limit current or shut down peripherals which try to draw more power than they have negotiated to use.

The standard supply current limit on a USB 2.0 port is 500 mA. If you connect a bus-powered hub, it typically draws 100 mA itself and can supply up to 100 mA to each of the connected peripherals. You cannot connect a peripheral to the hub if the peripheral requires 500 mA, unless you use a separately powered hub.

Recent Mac models (some from mid 2007 and all introduced in 2008 or later) support higher output current from the USB ports, as long as the peripheral complies with the USB Battery Charging Specification. This allows the computer to supply up to 900 mA to the peripheral. (Apple exceeds this limit and can supply up to 1100 mA in some cases when the computer recognises an Apple peripheral such as an iOS device or aluminium USB keyboard.)

USB is rated at 5V, so a standard USB port can supply up to 2.5W and a port which supports battery charging can go up to about 5W.

Firewire and Thunderbolt ports have even higher power output: typically in the order of 8W or a little higher.

Whichever Mac model you have, its power supply and battery are designed to cope with the maximum power being output via all ports.

A Mac Pro has a much bigger power supply because it needs to cope with the worst case for power hungry peripherals in the internal PCI Express slots, additional internal storage devices, as well as the CPU, RAM, etc.

David Empson
dempson@actrix.gen.nz

Message #3 - Posted 2011/08/29 - dorayme

Previously, David Empson wrote:

dorayme wrote:

So far I have managed without any powered usb hubs, but now that usb powered hds and speakers etc are around, I am wondering if their use can somehow strain the power unit in a little Macbook (I never gave it a thought with desktop - "underdesk"?) towers.

For example, say you have a 500 usb powered hd, and you also have two usb sticks in and an external keyboard, to take an example, is the load unlikely to stress a 13" Macbook (charging power tether on).

No. Each USB port on the computer has a maximum output current rating, and has circuitry to limit current or shut down peripherals which try to draw more power than they have negotiated to use.

The standard supply current limit on a USB 2.0 port is 500 mA. If you connect a bus-powered hub, it typically draws 100 mA itself and can supply up to 100 mA to each of the connected peripherals. You cannot connect a peripheral to the hub if the peripheral requires 500 mA, unless you use a separately powered hub.

...

Thanks, so I guess there is no need to worry too much, if there is not enough power, a peripheral won't work. I now remember I even charge my remote control helicopters from the MB now and then. Still, I suppose I will buy a powered hub next time I see one at a reasonable price.

dorayme

Message #4 - Posted 2011/08/29 - Jeff Gaines

On 29/08/2011 in message dorayme wrote:

Thanks, so I guess there is no need to worry too much, if there is not enough power, a peripheral won't work. I now remember I even charge my remote control helicopters from the MB now and then. Still, I suppose I will buy a powered hub next time I see one at a reasonable price.

I bought one recently that allows me to slot hard disks into, bit like a 1TB floppy.
As David said the machine will disconnect the hub and pop up a message telling you what it has done if you try and draw too much power. The trick with the disk hub is to turn its own power on BEFORE connecting it to the Mac.

Jeff Gaines Wiltshire UK
It may be that your sole purpose in life is to serve as a warning to others.

Message #5 - Posted 2011/08/29 - dorayme

Previously, Jeff Gaines wrote:

...

The trick with the disk hub is to turn its own power on BEFORE connecting it to the Mac.

Good point.

dorayme

Message #6 - Posted 2011/08/29 - Alan Browne

On 2011-08-29 00:09 , dorayme wrote:

In article, dempson@actrix.gen.nz (David Empson) wrote:

dorayme wrote:

So far I have managed without any powered usb hubs, but now that usb powered hds and speakers etc are around, I am wondering if their use can somehow strain the power unit in a little Macbook (I never gave it a thought with desktop - "underdesk"?) towers.

For example, say you have a 500 usb powered hd, and you also have two usb sticks in and an external keyboard, to take an example, is the load unlikely to stress a 13" Macbook (charging power tether on).

No. Each USB port on the computer has a maximum output current rating, and has circuitry to limit current or shut down peripherals which try to draw more power than they have negotiated to use.

The standard supply current limit on a USB 2.0 port is 500 mA. If you connect a bus-powered hub, it typically draws 100 mA itself and can supply up to 100 mA to each of the connected peripherals. You cannot connect a peripheral to the hub if the peripheral requires 500 mA, unless you use a separately powered hub.

...

Thanks, so I guess there is no need to worry too much, if there is not enough power, a peripheral won't work. I now remember I even charge my remote control helicopters from the MB now and then. Still, I suppose I will buy a powered hub next time I see one at a reasonable price.

I bought a 7 port externally powered USB hub a few months back for about $15 in an electronics supply store. (same thing would sell for 2 or 3x that in a brand name store like Staples or Best Buy).

gmail originated posts filtered due to spam.

Message #7 - Posted 2011/08/30 - David Empson

Alan Browne wrote:

On 2011-08-29 00:09 , dorayme wrote:

In article, dempson@actrix.gen.nz (David Empson) wrote:

dorayme wrote:

So far I have managed without any powered usb hubs, but now that usb powered hds and speakers etc are around, I am wondering if their use can somehow strain the power unit in a little Macbook (I never gave it a thought with desktop - "underdesk"?) towers.

For example, say you have a 500 usb powered hd, and you also have two usb sticks in and an external keyboard, to take an example, is the load unlikely to stress a 13" Macbook (charging power tether on).

No. Each USB port on the computer has a maximum output current rating, and has circuitry to limit current or shut down peripherals which try to draw more power than they have negotiated to use.

The standard supply current limit on a USB 2.0 port is 500 mA. If you connect a bus-powered hub, it typically draws 100 mA itself and can supply up to 100 mA to each of the connected peripherals. You cannot connect a peripheral to the hub if the peripheral requires 500 mA, unless you use a separately powered hub.

...

Thanks, so I guess there is no need to worry too much, if there is not enough power, a peripheral won't work. I now remember I even charge my remote control helicopters from the MB now and then. Still, I suppose I will buy a powered hub next time I see one at a reasonable price.

I bought a 7 port externally powered USB hub a few months back for about $15 in an electronics supply store. (same thing would sell for 2 or 3x that in a brand name store like Staples or Best Buy).

Interestingly, all the 7 port externally powered USB hubs I've seen in local retailers have a power supply which is not rated high enough to be able to supply 500 mA to all downstream ports. Something in the order of 2A output rating. Assuming it can also get 500 mA from the host and needs 200 mA for the hub itself, that enough to allow 500 mA for four ports and 100 mA for the other three. That's probably good enough for most uses.

David Empson
dempson@actrix.gen.nz

Message #8 - Posted 2011/08/30 - dorayme

Previously, Alan Browne wrote:

I bought a 7 port externally powered USB hub a few months back for about $15 in an electronics supply store. (same thing would sell for 2 or 3x that in a brand name store like Staples or Best Buy).

You mean, of course, Dick Smith or Jaycar.

dorayme

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