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How to check external USB power supplies etc

Last response: in Computer Peripherals
December 27, 2010 7:10:37 AM


I have had some HD's fall over and I was wondering how I can check the power supplies that come with the USB's.
Some of them are so similar in looks and plugs but I am not sure what belongs to what and I have about 12 of them.

I wopuld okie to check to see that the voltage etc., is right. Also

Is there a way to check the actual components inside a USB box, other than to try it out with a good drive and hope it doesn't trash it.

I have IDE and Sata boxes and because I had so many HD crashes caused by a bad mobo and power supply, I am not sure which usb boxes still work.



a b ) Power supply
December 27, 2010 7:55:03 AM

I assume you are not talking about devices which are self powered via the USB socket -- that's always 5 volts but is quite limited amperage so most HDs have external PSU units.

Hard to check which PSU cube goes with which external drive -- best to mark them when you buy them.

There may be a statement in the specs or on a label on a drive which mentions voltage (usually 12v dc + 5v dc) and amperage and you should be able to at least establish that any cube with a lower stated amperage or the wrong voltage is not for that drive.

Most have standard looking sockets but there can be size and polarity differences
-- try fitting them with the power off and then disconnect and test with a multimeter with the power on.

Test the integrity of the drives from the boxes by removing them and connecting them directly to a motherboard via IDE or SATA connectors. But bear in mind some external HDs may exceed the size accepted by the motherboard and some large externals use RAID spanning to utilise two drives to appear as one to the computer.
December 27, 2010 8:07:01 AM

Yes , it is a bit messy isn't it? I bought 3 external drives once, all looked the same but found out later that one power supply was different although it looked the same. I plugged it into the other two at different times and they stopped working. Guess it was polarity as they all fitted each other.

I will do the multi check of the power supply units, but how do I find the polarity and amperage?

Haven't used multi-tester for much really.

Thanks for the assist.

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a b ) Power supply
December 27, 2010 11:10:55 AM

Polarity of the power cube you can check with a meter on volts dc -- the needle will deflect negatively or positively -- or a digital meter will state neg, pos.

Polarity of the socket -- you can sometimes tell just by looking at what the centre of the socket connects to. Another test is putting the multimeter into continuity or ohms/impedance (the Omega sign on some meters) and checking the socket centre pin against an obvious earth point on the device like the metal chassis -- no or little reaction suggests centre positive.
December 27, 2010 8:51:59 PM

Hey guys many thanks for the help.

Will get to checking asap and hopefully for once and for all, know which ones work with what and which don't.

BTW: Is it true some external boxes do not take large drives over 100GB? I use XP SP2 and 3

a b ) Power supply
December 28, 2010 8:08:25 AM

No, external boxes are frequently supplied with 2x 500g = 1 terrabyte via RAID spanning.