Need help trying to buy a USB hub!

CrackedButter

macrumors 68040
Original poster
Jan 15, 2003
3,221
0
51st State of America
AND... it isn't what you think.

I am eyeing up a certain USB hub and it is telling me it is USB 2. Plus I don't need a power adapter if I don't use more than 100 mA for any single port. This is fine until I check out the details of my scanner, it reports 2.5 watts. :confused:

How do I make sure the hub will handle the scanner and for that matter 2 ipod shuffles?

Now I was told a formula to figure this out.

Volts x amps = watts

or

Watts x Volts = amps

This isn't my field of knowledge, so i'm hoping somebody here knows the answer to this.

Now i know the amps, and basically I need to know if the 2.5 watts is higher than 100mA, if its under, I can buy the hub without an external power supply. Btw, I don't want the power supply to begin with, hence the issue here.

I live in the UK and the electrical current is AC.
 

strider42

macrumors 65816
Feb 1, 2002
1,460
6
Bus powered hubs cause problems. Get a self powered one, that is, one with its own power supply. I don't care what devices you are using it with, a self powered hub just works better.
 
Comment

Mechcozmo

macrumors 603
Jul 17, 2004
5,215
2
Scanner has its own power supply so it doesn't matter.
Shuffles will draw off of the hub. So they need to draw less than 500 mA combined (USB 2.0 standard and what Mac's dump out per port).
But get a powered one. That way you do not have any issues. Because trust me, it is a pain. I had a USB 1.1 hub that when I first set it up for my dad gave errors that the devices weren't getting enough power. After a bit, that was fixed thankfully.... but still a pain.
 
Comment

Mechcozmo

macrumors 603
Jul 17, 2004
5,215
2
CrackedButter said:
My scanner doesn't have a power adapter. It uses the USB port only.

If the answer is to get a powered usb hub then I won't bother. Thanks for the help.
What kind of a scanner do you have that doesn't use an A/C adaptor?
 
Comment

johan_tanying

macrumors member
Nov 28, 2004
38
0
Gothenburg
CrackedButter said:
My scanner doesn't have a power adapter. It uses the USB port only.

If the answer is to get a powered usb hub then I won't bother. Thanks for the help.
First: if the device is usb-powered you will most likely need a powered hub. A scanner is more often than not using some kind of light source, electric motors and so on.

Second: is it possible to buy a hub that does NOT include a power brick/adapter? Sometimes they say it is optional to use them but do not count on it (I agree with the above poster - non-powered hubs are likely to be a pain in the a__...
 
Comment

Mechcozmo

macrumors 603
Jul 17, 2004
5,215
2
CrackedButter said:
This is the great scanner that I have:

http://www.canon.co.uk/for_home/product_finder/scanners/flatbed_with_film_scanning/lide_80/index.asp

If the scanner I have operates under 100mA, I shouldn't have a problem with the hub should I?
The other devices on the hub cannot draw more than 400 mA then. Good luck trying to do that. You may be able to do it by having each one plugged in at different times, and then plugging/unplugging and turning off what ones draw the most power. And add like a USB mouse or something to that circuit, those don't draw a lot.
 
Comment

mkrishnan

Moderator emeritus
Jan 9, 2004
29,777
12
Grand Rapids, MI, USA
The scanner draws 2.5W off the 5V power bus on the USB? Doesn't that mean that it uses 500 mA (by itself), or have I been out of engineering for that long? :eek: Even in the 1.5W standby mode, it's going to draw 300 mA. Where did you get the 100 mA figure from, CrackedButter?
 
Comment

CrackedButter

macrumors 68040
Original poster
Jan 15, 2003
3,221
0
51st State of America
mkrishnan said:
The scanner draws 2.5W off the 5V power bus on the USB? Doesn't that mean that it uses 500 mA (by itself), or have I been out of engineering for that long? :eek: Even in the 1.5W standby mode, it's going to draw 300 mA. Where did you get the 100 mA figure from, CrackedButter?
The 100mA figure is from the website that is selling the usb hub.
It seems you have found the voltage, and it proves that the scanner isn't right for the hub.

Thanks for the calculation.
 
Comment

CrackedButter

macrumors 68040
Original poster
Jan 15, 2003
3,221
0
51st State of America
mkrishnan said:
Any time, although it probably wasn't the answer you wanted to hear. :( I hate having sixty power supplies connected. ;)
I'm still going to buy it though. There are other devices which will benefit from the extra ports. With my devices I have; 2 ipod shuffles, pen drive, (the scanner) mouse and a usb card reader because of my digital camera using 2 types of memory card.

All I have is the 2 USB ports on the iBook.

This new usb hub is also a 19 in 1 card reader, it will help consolidate my afforementioned list of stuff. So it was helpful simply by knowing the power usage.
 
Comment
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.