Power USB devices

**spdyscotty** · 07-14-2005, 09:35 PM

I need extra power for my USB harddrive and USB DVD player. I've read up on the topic and even made various posts. But, I just stumbled arcross the "CNX-P5V 15 Watt +5V Regulator". Not a bad price. I know I could make it myself, but this seems easier. 15watts is way more than enough. 3 watts would probably be sufficient. Is there a similar option that would be easier / cheaper? Any ideas? Am I being silly? Maybe I should build it?

Scott

**Wiredwrx** · 07-14-2005, 10:28 PM

Originally Posted by spdyscotty

I need extra power for my USB harddrive and USB DVD player. I've read up on the topic and even made various posts. But, I just stumbled arcross the "CNX-P5V 15 Watt +5V Regulator". Not a bad price. I know I could make it myself, but this seems easier. 15watts is way more than enough. 3 watts would probably be sufficient. Is there a similar option that would be easier / cheaper? Any ideas? Am I being silly? Maybe I should build it?

Scott

How do you figure that 15 watts is WAY MORE THEN ENOUGH. That is just 3 amps. And, 3 watts is about .6 of an amp. Are you only powering a single device?

According to some powe supply calculators, each USB device is an amp (5 watts), that means the most you can connect to that PS is 3 USB devices. Perhaps you only have 3 or less, and then you are golden. But, if you have more (My 4 port hub I think is full) that might not be enough.

Now, the last time I responded to a post of yours, some of us discussed a 5 amp 5volt PS, that is 25 watts. That should be enough for 5 USB devices.

Also, Optical drives and Hard drives draw about an amp each, if not more. That is at least 10 watts. You are seriously gonna be getting close to that max. Add a Mouse, or GPS receiver, and your probably done for.

Look here
http://www.jscustompcs.com/power_sup...or.php?cmd=AMD

Michael

**spdyscotty** · 07-14-2005, 10:39 PM

My bad. I confused watts for amps. Not knowing 5 watts = 1 amp, I guess 3 amps is just perfect. I need to power a DVD drive (1.3 amps) and a HD (maybe 1 to 1.5 amps). My other USB devices will be powered directly from the ports. So is the "CNX-P5V 15 Watt +5V Regulator" a good way to go?

**spdyscotty** · 07-14-2005, 10:47 PM

I'm also a little confused about the "hub". I have a 4-port hub in my PCMCIA slot of my laptop. There is a small DC power port on it. Am I supposed to connect that to a 5V power source? I was under the assumption that that port was an output? Anybody know what I'm talking about?

**fromplanetbob** · 07-15-2005, 06:58 AM

Originally Posted by Wiredwrx

According to some powe supply calculators, each USB device is an amp (5 watts),

I could be wrong, but USB Powered Devices can only pull a max of 500 mA (or 1/2 amp).

Personally, I'd run a 5v regulator with a relay (turn the relay on and off with the 12v power of the computer, so it turns the hubs on and off when you turn the computer on an off.)

I have a second power supply to supply my USB devices. I hooked up the ACC line for that power supply to the 12v output of my OPUS 150 that powers my computer, that way it turns on when my computer is on.

**MikeH** · 07-15-2005, 07:17 AM

spdyscotty,

Here are some actual measurements of USB devices in my system. One device not listed is the Audigy 2NX which draws about .8 amps. Hopefully this info will help.

**Wiredwrx** · 07-15-2005, 12:10 PM

Originally Posted by spdyscotty

My bad. I confused watts for amps. Not knowing 5 watts = 1 amp, I guess 3 amps is just perfect. I need to power a DVD drive (1.3 amps) and a HD (maybe 1 to 1.5 amps). My other USB devices will be powered directly from the ports. So is the "CNX-P5V 15 Watt +5V Regulator" a good way to go?

Ya, that will probably work. Watts=Amps*Volts. So, 2 amps at 5 volts is 10 watts, 2 amps at 12 volts is 24 watts.

Michael

**Wiredwrx** · 07-15-2005, 12:14 PM

Originally Posted by MikeH

spdyscotty,

Here are some actual measurements of USB devices in my system. One device not listed is the Audigy 2NX which draws about .8 amps. Hopefully this info will help.

That's cool.

Can you measure some USB HDs or Optical drives.

The other things seem quite "obvious" as they do not include any spining motors. I guess I would figure that Mice (Or is it mouses, I forget

) and the GPS receiver were not that heavy on the amperage load, but if you look above, the DVD and the CD use more then 500ma, and in fact, over an amp during spin up. I wonder if thoe numbers change for a 5 volts device (assuming of course that the DVD and CD ROM you were testing were 12 volt devices)

EDIT: Oh ya, I am wondering how you measured those current draws.

Michael

**MikeH** · 07-15-2005, 12:32 PM

Oh ya, I am wondering how you measured those current draws

Looking back on this chart, there is an error in the calculation of total power. All of the USB devices were measured by inserting a current meter in the USB +5V supply line. So the power associated with these devices should be calculated at +5V, not +12V (the summary at the bottom of the table is wrong). However, the currents shown for the USB devices is correct and directly measured on the USB cable.

Also, the CD/DVD drive was USB attached. So its currents are for a +5V supply. I don't have a USB HDD to measure. Sorry.

**Wiredwrx** · 07-15-2005, 01:41 PM

Originally Posted by MikeH

Looking back on this chart, there is an error in the calculation of total power. All of the USB devices were measured by inserting a current meter in the USB +5V supply line. So the power associated with these devices should be calculated at +5V, not +12V (the summary at the bottom of the table is wrong). However, the currents shown for the USB devices is correct and directly measured on the USB cable.

Also, the CD/DVD drive was USB attached. So its currents are for a +5V supply. I don't have a USB HDD to measure. Sorry.

No problem. Thanx for the information.

Michael