A couple questions about wiring up USB.

gthing · 05-15-2007, 01:41 AM

Hey I just have a couple of questions about USB device considerations. I am using a Carnetix P1900 Power supply which provides a +5V/3A output for power a USB hub/etc.

My question is how do I take advantage of this output - I mean, specifically.

Right now I have a 3 inch USB extender that I have spliced into. I found the pinout on pinouts.ru for USB, cut the 5V (red) wire, and wired in the 5V from my power supply. I left the computer side of the red wire disconnected so that 5V from the power supply does not feed back into the computer (I don't know if this is necessary but it seemed like a good idea).

I have kept the USB ground connected to the computer, even though my power supply provides an extra ground wire as well. Is that okay?

As it stands, my USB hub seems to work for mouse and external sound card (cheapo 5.1 thing), but it will not spin up an external hard drive which can normally run off of USB - this I have to connect to the computer.

So is there a better way to power this? On 3 amps, how many USB devices can that little hub be expected to handle?

What are the problems/issues with simply leaving a bunch of USB devices plugged into the back of the computer. I seem to have problems waking from sleep and am guessing that they are due to USB device issues.

Thanks in advance for any help.

almera · 05-15-2007, 03:19 AM

you will have to power hd through either a external powered usb hub or through the power cord in the back.

2k1Toaster · 05-15-2007, 03:41 AM

Quote: Originally Posted by gthing

Hey I just have a couple of questions about USB device considerations. I am using a Carnetix P1900 Power supply which provides a +5V/3A output for power a USB hub/etc.

My question is how do I take advantage of this output - I mean, specifically.

Right now I have a 3 inch USB extender that I have spliced into. I found the pinout on pinouts.ru for USB, cut the 5V (red) wire, and wired in the 5V from my power supply. I left the computer side of the red wire disconnected so that 5V from the power supply does not feed back into the computer (I don't know if this is necessary but it seemed like a good idea).

I have kept the USB ground connected to the computer, even though my power supply provides an extra ground wire as well. Is that okay?

As it stands, my USB hub seems to work for mouse and external sound card (cheapo 5.1 thing), but it will not spin up an external hard drive which can normally run off of USB - this I have to connect to the computer.

So is there a better way to power this? On 3 amps, how many USB devices can that little hub be expected to handle?

What are the problems/issues with simply leaving a bunch of USB devices plugged into the back of the computer. I seem to have problems waking from sleep and am guessing that they are due to USB device issues.

Thanks in advance for any help.

Quote: Originally Posted by almera

you will have to power hd through either a external powered usb hub or through the power cord in the back.

What you ended up doing was taking a non-powered hub which draws a maximum of 500mA and gave it a maximum potential current draw of 3A. The circuitry inside still will only draw 500mA at most.

So if you get an externally powered hub, then you can connect the carnetix to that. And that is how it is done usually. Also instead of splicing into the USB connector, you will need to splice into the adapter socket going into the hub. If you splice into the usb line, it will still only draw 500mA because that is all USB can draw ever. It is a physical design limitation (intentional).

gthing · 05-15-2007, 10:53 AM

I see. My USB hub does have a power connector port, so basically I just need to splice into that. Cool.

So with USB devices taking 500mA, does that mean I could reasonably expect to be able to hook up 6 standard USB devices without a problem?

mwmcginn · 05-15-2007, 12:35 PM

should be able to attach 6 items, if they are bus powered.

gthing · 05-15-2007, 04:22 PM

Excellent. I really appreciate your help everyone. I have one last question.

I got a hub that has an independent power supply. I'm going to cut off the transformer and splice into the existing wiring.

The transformer says that it outputs 5V at 2.5A. I guess with 500mA coming off the USB connection, this makes a total of 3A available to the hub. I'm not sure if this assumption is correct.

So if I wire in a 3A connection from my power supply, and hook it up to USB, the hub will have a total of 3.5A available to it, meaning I am pushing ~500mA more than it is designed for.

I don't think this would be a problem, but if I know one thing it is to be careful with USB power as I've fried many-a-expensive electronic item through the USB ports.

So if it IS a problem, maybe I should continue to use that USB extension cable I cut the 5V out of, to bring things back down under control. That might work.... Or do I even need to worry about it?

2k1Toaster · 05-15-2007, 04:44 PM

Quote: Originally Posted by gthing

Excellent. I really appreciate your help everyone. I have one last question.

I got a hub that has an independent power supply. I'm going to cut off the transformer and splice into the existing wiring.

The transformer says that it outputs 5V at 2.5A. I guess with 500mA coming off the USB connection, this makes a total of 3A available to the hub. I'm not sure if this assumption is correct.

So if I wire in a 3A connection from my power supply, and hook it up to USB, the hub will have a total of 3.5A available to it, meaning I am pushing ~500mA more than it is designed for.

I don't think this would be a problem, but if I know one thing it is to be careful with USB power as I've fried many-a-expensive electronic item through the USB ports.

So if it IS a problem, maybe I should continue to use that USB extension cable I cut the 5V out of, to bring things back down under control. That might work.... Or do I even need to worry about it?

If it is externally powered, then it wont draw anything off of the usb bus. So will draw 5 ports x 500mA = 2.5A. It will only draw what it needs. So you will draw 2.5A from the power supply, and you will have another 500mA left over to do whatever. Maybe one of those usb nerf rocket launchers or something.

Beehphy · 05-17-2007, 11:09 AM

Quote: Originally Posted by gthing

Hey I just have a couple of questions about USB device considerations. I am using a Carnetix P1900 Power supply which provides a +5V/3A output for power a USB hub/etc.

My question is how do I take advantage of this output - I mean, specifically.

Right now I have a 3 inch USB extender that I have spliced into. I found the pinout on pinouts.ru for USB, cut the 5V (red) wire, and wired in the 5V from my power supply. I left the computer side of the red wire disconnected so that 5V from the power supply does not feed back into the computer (I don't know if this is necessary but it seemed like a good idea).

VERY good idea. Most power supplies will get mad if they are trying to power the same power rail. very unexpected results can occur.

Quote: Originally Posted by gthing

I have kept the USB ground connected to the computer, even though my power supply provides an extra ground wire as well. Is that okay?

You need to make a ground connection from the power supply into the USB hub, but maintain the ground between the hub and computer. the computer needs a reference to compare the data signal voltages.

Quote: Originally Posted by gthing

As it stands, my USB hub seems to work for mouse and external sound card (cheapo 5.1 thing), but it will not spin up an external hard drive which can normally run off of USB - this I have to connect to the computer.

So is there a better way to power this? On 3 amps, how many USB devices can that little hub be expected to handle?

Like others have said each USB port is good for 500mA, including the one comming from your computer. usually each port has a current sensor to make sure it is within spec.

Without a powered hub it wont work to daisy chain a HD off the hub. HD's usually max's out the USB port. If the HD takes 500mA, the mouse takes 50mA, the 5.1 takes 30mA and the hub it self takes 20mA the power draw from the computer USB is well over the 500mA available. A powered hub is deffinately the way to go.

Quote: Originally Posted by gthing

What are the problems/issues with simply leaving a bunch of USB devices plugged into the back of the computer. I seem to have problems waking from sleep and am guessing that they are due to USB device issues.

Thanks in advance for any help.

I'm designing my system so that 2 powered usb hubs connect to all USB devices. make removing the computer easier and the power draw is signifigantly lower to the computer PSU (extending lifespan and upping stability).

Quote: Originally Posted by gthing

I see. My USB hub does have a power connector port, so basically I just need to splice into that.

Yes. be sure and observe polarity closely. connecting the power backwards will fry the hub and all thats connected.

Quote: Originally Posted by gthing

So if I wire in a 3A connection from my power supply, and hook it up to USB, the hub will have a total of 3.5A available to it, meaning I am pushing ~500mA more than it is designed for.

Current works different from voltage. current draw is scaled based on demand. a 10A PSU with a 2A draw is just fine. Currrent is kinda like horse power of an engine; it may be capable of 150HP but if it only takes 15HP to travel at highway speed on flat ground your not doing the car any damage by not using the other 135HP. the rest of the HP are just waiting in reserve.

So... providing 2.5A will work just fine. If you look at your devices and research them you'll probably find your way under 2.5A.

Hope that helps.

SKiTLz · 09-06-2007, 04:03 PM

To resurrect an old thread. Im trying to wire my USB hub. The power connector has a barrel connector.

So i snip the AC end off. My question is the barrel connector has two wires. How do i determine which to splice with my Opus 5V line? Is one ground?

2k1Toaster · 09-06-2007, 05:32 PM

Quote: Originally Posted by SKiTLz

To resurrect an old thread. Im trying to wire my USB hub. The power connector has a barrel connector.

So i snip the AC end off. My question is the barrel connector has two wires. How do i determine which to splice with my Opus 5V line? Is one ground?

Look at the back of your hub. You should see a symbol of a shaded circle inside a bigger 3/4circle outline. 1 should have a line pointing to it that either says +5v or says ground. Maybe both. The shaded full circle is the inside of the barrel connector. The circle outline is the shield. So wire up the 2 wires off the connector to 5v and ground. Test with a multimeter to make sure the shiled and inside are correct. If not swap wires. Test again to make sure, and plug 'er in. :