Getting 4.5 watts from laptop USB2 ports

Avoriaz

Hi, I have an Acer 8935g laptop with 4 x USB2 ports.

USB2 spec is up to 0.5 Amps x 5 Volts = 2.5 Watts.

Can I get 5 watts by connecting to 2 ports or will that overload the motherboard or something else?

I need about 4.4 watts and want to avoid buying a separate power supply.

I want to power a 3.5 inch 2tb WD20EURS disk and that requires up to 4.4 watts. I am doing a lengthy Sky+ backup that will take maybe 18 hours to complete.

I can do that by using external caddies connected via USB2 but it will be faster if I can use the spare second internal 2.5 inch drive bay in my laptop with a short extension cable. I have tested this method and a 2.5 inch drive works fine when connected with a short extension cable. Write speeds are significantly faster than using external caddies.

However it is obviously important that I don't overload or overheat my laptop and kill it by using a 3.5 inch disk connected to 2 x USB2 ports for power.

Thanks

espresso

Yes you can increase the current capability by using a USB Y cable e.g.



These are commonly supplied with portable drives.

kwikbreaks

As above. It is pretty common for external USB hdd enclosures to use a cable that connects to two ports with one being data+power and the other just power. I've used plenty of different ones in the past with no problems.

almillar

Hmm, 3.5 inch drives really aren't meant to be powered like this. I also don't quite understand how you are going to power a 3.5 inch drive with a USB plug - surely it should have a molex, SATA power connector, or a combined USB3 one?
I'd rather buy a cheap powered USB caddy off ebay than risk blowing USB ports on my laptop, or make do with the USB transfer.
When using these Y cables for anything, remember, connect both computer ends to the computer first, THEN connect the one end to the device, otherwise, you'll be trying to power the device off one port, exactly the thing you're trying to avoid, however briefly...

espresso

I answered your USB question assuming that you knew what you were doing regarding powering your drive, however your WD20EURS 2TB 3.5" actually requires much more than 4.4W - it requires 12V @ almost 1.6A.

patman99

Actually, a 3.5" HDD requires 1x 12v+, 1x 5+ & 1x 5- feed.
Your best bet is to buy an external case which will already have a mains powered PSU in so will power the HDD. I would also invest in the 'Y' USB leads. From personal trial I can say that the ones that came with my HDD actually split the DATA across both lines. I found this out by accident.

The lead fitted my DSLR, so I decided to use it to transfer some images off the camera. I was surprised just how quickly they transferred across, so did a time experiment. The speed difference between a single USB 2 cable connection and the 'Y' lead was very noticeable indeed.

kwikbreaks

Yes I'm also guilty of stopping reading at the "Can I get 5 watts by connecting to 2 ports" point.

I don't think there is any way you can power a 3.5" drive from USB ports.

I also don't believe the post above about the data going through two USB ports. With all the Y cables I've ever used only one leg carried the data plus only one device ever shows up in windows when such cables are in use.

Quiet_Spark

patman99 wrote: »

Actually, a 3.5" HDD requires 1x 12v+, 1x 5+ & 1x 5- feed.

There is no requirement for a -5V feed, it's +12V and +5V with each supply having it's own return.
Some S-ATA power connectors provide an additional +3.3V feed, although not all drives will need it.

Avoriaz

Thanks for all the replies.

I had overlooked the voltage difference of the 3.5 inch disk.

I'll use a proper caddy and put up with the extended time.

Thanks again.