My tablet needs 5v, 2A to charge via the micro usb but all I have is a
700ma walwart (which does not work) so I was thinking I could use my ATX
power supply. There are 2 rails on the ATX for 5v, one for 30a and one for
2a. Is there any reason I cannot use either rail? The tablet will only
draw the current it needs, right?

mark wrote:
My tablet needs 5v, 2A to charge via the micro usb but all I have is a
700ma walwart (which does not work) so I was thinking I could use my ATX
power supply. There are 2 rails on the ATX for 5v, one for 30a and one for
2a. Is there any reason I cannot use either rail? The tablet will only
draw the current it needs, right?

Yes, your supply can have infinite current and as long as the load only
draws 2 amps then the supply just happily idles along.

Now, some switching supplies require a minimum load to boot, but most of
the ATXs will power up (even with a tiny load) if you short the correct
control lines.

John :-#)#

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On 12/3/2012 9:51 PM, mark wrote:
My tablet needs 5v, 2A to charge via the micro usb but all I have is a
700ma walwart (which does not work) so I was thinking I could use my ATX
power supply. There are 2 rails on the ATX for 5v, one for 30a and one for
2a. Is there any reason I cannot use either rail? The tablet will only
draw the current it needs, right?

Don't do it!!!
There are several reasons that this is risky.
And none of them have anything to do with the numbers printed
on the labels.
Yes, you'll find 100 people who say it's ok.
And maybe 10 who say they've done it successfully.
But not likely any who used your exact supply on your exact tablet.
99% probability that it will work fine is of little
solace if you're the 1%.
If you knew what you were doing, you wouldn't be here asking.
Bottom line:
Get a supply designed for this kind of application.

On Tue, 4 Dec 2012 05:51:50 +0000 (UTC), mark
wrote:

My tablet needs 5v, 2A to charge via the micro usb but all I have is a
700ma walwart (which does not work) so I was thinking I could use my ATX
power supply. There are 2 rails on the ATX for 5v, one for 30a and one for
2a. Is there any reason I cannot use either rail? The tablet will only
draw the current it needs, right?

Is it worth the risk of damaging the tablet? Micro USB has 2 wires
that determines the charger capabilities. If they're not present or
used, a 5V supply is only allowed to operate the device, not charge
the battery. Chances are good that your creative wiring isn't going
to work.

Since you didn't bother to mention the Thinkpad tablet model, I can't
offer a specific supplier.
http://www.ebay.com/sch/i.html?_trksid=p5197.m570.l1313&_nkw=thinkpad+tabl et+charger
There should also be plenty of iPad 2 and Kindle chargers, which also
require 5v 2A power. Count the number of pins are there are different
flavors of microUSB.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558