Re: Need USB card with enough power for external hard drive
- From: Carl <carl33@xxxxxxxxxxxxxx>
- Date: Sun, 23 May 2010 15:25:16 -0700 (PDT)
On May 23, 3:05 pm, mike <spam...@xxxxxx> wrote:
On May 23, 12:37 pm, Roger Mills <watt.ty...@xxxxxxxxx> wrote:
On 23/05/2010 16:58, Carl wrote:
I have an HT-Link Cardbus/PCMCIA USB 2.0 2-port card (NEC / 32-bit).The cardbus card probably *can't* supply enough power unless there's a
My external hard drive w/USB adapter won't work with it, and it will
work plugged directly into a USB port on a different laptop. (My USB
ports got fried.) I got the card off E-Bay. My MP3 player works
plugged into that card. The drivers for the card say "Known
limitations: High Speed Isochronus, USB Composite Devices." (No other
details provided.) I don't know if the hard drive adapter is
"isochronous" or "composite." I've read there are problems with too
little power being supplied to the drive. The cable to the drive has
two USB plugs on one end, and it doesn't make any difference if I plug
both of them into the Cardbus card.
What card should I get? I see many different brands on E-Bay. I need
one that supplies sufficient power for an external hard drive, and
doesn't have any "known limitations" in the way.
way of getting power to it from another source. I have a 4 x USB2 port
cardbus card made by Pluscom which has a little power socket on the
front in addition to the USB ports. It comes with a lead which plugs
into a normal USB port just for the purpose of supplying power to the card.
Do you have any other source of power for USB devices, such as a
USB-based mobile phone charger? If so, you could try plugging one of the
drive's plugs into *that* - which may solve the problem.
Please reply to Newsgroup. Whilst email address is valid, it is seldom
The card has a hole in between the two USB port for a plug, but the
card didn't come with a cable. I checked E-bay. I could get a new
card that comes with a cable for the same price as just a cable.
A USB1 port is limited to about 100mA. A usb2 port is limited to about
500mA. Actual computer implementations vary all over the map.
Some just current limit and recover gracefully. I had one laptop that
plain shut off the usb ports until I rebooted.
An external hard drive can pull upwards of 1AMP depending on the model.
Plugging an external hard drive into a laptop is a good way to FRY the
The reason they give you two usb connectors is so you can plug them in
and get an amp total. But this can force one of the ports to current
limit. That overstresses the current limit device and causes it to fail
Cardbus usb cards come in many variants. Some will run a hard drive
even though they EXCEED the design limits of your laptp and can cause
problems. Others just won't run the drive. I have one card that has
ZERO 5V output until you run a cable from the hole in the card to
a usb port or mouse port for power.
External hard drive enclosures come in many variants. Many of the newer
ones have no capability to add external power. Depending on the hard
drive inside, you may or may not be able to run if from a laptop.
They'll usually run from a desktop usb2 port. Or better yet, a powered hub.
Older drive enclosures have a 5V power input so you can plug in a wall
wart and they work fine. But they also have problems. The designers
saved money by hooking the external 5V directly to the 5V usb line.
Although it's bad, bad, bad practice, it works most of the time.
Problem is when you turn off the laptop and the external drive
tries to supply 5V back thru the usb port. This can cause significant
destruction of the usb port, the hard drive as it thrashes trying to
power up, etc.
Another thing they do is use two diodes to isolate the two power
supplies. That fixes the power problem, but now, you have less than
5V and the hard drive may have trouble running.
I've addressed the problem three ways.
Use a powered hub. That works, but depending on your OS and the hub,
there may be problems with some software or hardware.
I took a usb extension cable, cut the power wire and spliced in 5V
from a regulated wall wart to power the drive. I'm very careful to
start the laptop before plugging in the drive and removing the drive
before shutting down the laptop. If your drive enclosure has
an external power input, you don't need the modified wire.
I had a laptop that I used as a permanent mp3 player. I modified the
docking station by rewiring power for one usb port thru a fuse to the
keyboard/mouse power socket. Risky in general, but ok for a dedicated
So, why do you need the external drive anyway. Internal hard drives
are huge these days. USB flash drives are BIG. If you blew the ports,
you can get a flash reader that plugs into the cardbus slot. You can
transfer files via the network connection.
The backup problem is solved by having a small 8-16GB C partitoin
and backing it up to the D partition. Then move the files to archive
storage via the network of flash memory.
The USB cable has two USB plugs on one end, and one of those is on a
thinner cable (after the "Y"). Someone told me that other plug was
for attaching another USB device (so you can attach two devices to one
USB port on your computer), but I thought it was for more power, like
you are saying. I might be interested in cutting that 2nd one off,
and wiring it to a 5 volt/500MA wall plug (do you know a good
source?). I'm not an electrician - I want to use the right wires and
get the polarity right. Do you have any additional tips? Which wires
in the USB cable to use? BTW - I ALWAYS plug in the external hard
drive AFTER the computer is on, and I ALWAYS use "safely remove
hardware" before unplugging it, and I NEVER turn the computer off with
it plugged in.
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