USB Hub Question

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USB Hub Question

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AlanS17:
Different devices require different amounts of power. Plus how many people use all 4 at once?

My question is why do they make a 4-port laptop USB hub. Wouldn't having all those devices defeat the purpose of being mobile?

grafixmonkey:
USB ports are supposed to be able to supply like 500 mA or something (not sure if that's exactly the number but there's a standard limit) but if you have a hub that's not powered, all four devices draw from one port that can supply a max. of 500 mA. So if you have gamepads with vibration feedback, those probably draw a good deal of power... if they draw 200 mA each, then you can plug in two for 400 mA total, but plugging the third would be 600 mA and the port can't supply that. Just a bank of 4 or 5 bright LEDs would bring you close to or above the 100 mA mark, so it's pretty easy to break the 500 mA limit with four devices.

If you power the hub, then each port on the hub can supply 500 mA again.

Looked at my hardware - my Microsoft optical mouse has '100 mA' marked on it. Same with my keyboard. My graphics tablet says 40mA, an old Logitech joystick (analog) says 25mA. So I could plug all four of those in with no problems. 74XX chips and lots of off-the-shelf logic components (like the IPAC has on it) often draw more power than optimized commercial products.

Brax:
Hmmm, the Dual Strike os only 20ma..... in wonder if the IPac and OptiPAC would take me over the limit? I wonder what 1UP has. Powered or non-powered? He has the same stuff hooked up AFAIK.

u_rebelscum:

--- Quote from: Brax on July 12, 2003, 08:32:48 pm ---Hmmm, the Dual Strike os only 20ma..... in wonder if the IPac and OptiPAC would take me over the limit? I wonder what 1UP has. Powered or non-powered? He has the same stuff hooked up AFAIK.

--- End quote ---

The amount of power needed by the optipac depends on the power needed by the trackballs and spinners attached to it. Happ TBs are said to need quite a bit of power.

FWIW, I can run a optipac with two trackballs (one a happs) off my computer port fine. However I usually hook them through a powered hub since I have too many USB stuff, and try to give them all enough power.

You see, my (former) boss broke one computer USB port and a digital camera hooked up to it when he tried to download images without enough power. :o The manual even said don't try to run it straight off the computer port because of the lack of power, but did that stop him? Nope. (The camera was repaired, and he only lost the memory card in the camera + the port.)

grafixmonkey:
burned out a port and a camera? that sucks! I thought those things had some kinda protection on them... guess not.

I just remembered, the USB hub itself contains logic. So the hub itself will consume some power. (so 490 mA of stuff might still not work if it doesn't have a power supply to itself.)

Oh yeah and I think usb hubs, or at least good ones, have "protected" ports, so if something like that happens or you accidentally cross something on your ipac, you'd probably just kill the usb hub's port and not something on your computer's motherboard. Might be worth it to all the tinkerers out there.

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