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Power from usb ports - macbook pro vs macbook

14996 Views 11 Replies 10 Participants Last post by  kaiako
I was wondering if anyone else has had this problem... I have an external harddrive - oem 2.5" 80gig in a nexstar3 case - running off usb power only. I've never had a problem with this setup on my macbook - using only usb power. However, when using it on my macbook pro the drive freezes and refuses to show up some times. It looks like it has something to do with how much power comes out of the usb ports - but why would the macbook pro have less... Anyone else ever have this problem - or problems using an external usb powered drive? Is it just my macbook pro? There are also no other drives plugged in at the same time. I also use the drive where there is no other power available..
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Are you running off of AC or battery. In the PPC days it could make a difference, especially if the battery was getting old or just needed charging.
tried both ac and battery power. works fine for the macbook but not the macbook pro - on either...
me too!

I have the same problem. Any ideas.
MBP is phiniky with their USB power. I could never run my M-Audio Trigger finder with MBP.. I had to use an external powered USB hub.. utterly useles..
I have no clue if it still applies to the Macbook Pro's but some Powerbook's USB ports were underpowered (I don't know if this was a design issue or a defect). There were some very specific drive compatibility issues that I came across (one involving an 80GB WD passport). I wonder if the issue is the same for the Pro, I've never encountered a problem like it on my macbook.

Sorry if it doesn't answer the problem, but just a bit of info.
I had the same problem with my Powerbook with a USB drive. The drive came with a 2-into-1 USB cable. It wasn't long enough, but, with an extension, I was able to use the 2 usb ports to power it. Not sure if that was recommended, but it did work for the several times I needed it.
I think the problem is more with the drive manufacturers than the Mac.
The standard for USB IIRC is 500mA available at 5V.

I think drive and enclosure manufacturers assume - "well, if it can do 500 mA it should be able to do 600 mA" and go ahead and design their drives around drawing 600 mA. Then everyone is surprised when Apple actually enforces the 500 mA standard, and some drives don't work.
I have a Seagate FreeAgent 2.5" USB 2.0 (80GB) that comes with the 2-into-1 USB cable. With my MBP I only need to connect 1 of the two usb cables but with my iBook G4 1.2 the drive will not work until I connect the 2 USB cable's end. Why ?? Must be a different voltage in the USB ports of the two laptop models ???
I have a little Meritline 2.5" USB/sata case for my original MacBook drive, and it too came with a 2 into 1 USB cable. I find that I only need one USB port to power and run the drive, but if I want it to BOOT, I must use both USB ports.

So the data point here is that some drives need more power, particularly at startup, than the 500mA Apple provides to those ports. This also explains a wealth of USB hub issues.

Bottom line: this one is not Apple's fault. It's PC-world mentality ie lack of adherence to published standards.
Not sure if this applies to MacBook vs MacBookPro, but I have read this now a few times:
In a nutshell:
...Sophisticated designe, ie MBP - Each port has a totally power feed of minimum 500ma at 5 volts. So external laptop hard drives which require 600ma worst case may not work unless you pick up power from two USB ports.
...Simple design, ie MB - Only one power supply for the two USB ports rated at 1000 ma at 5 volts. So each port can supply 500ma and meet the USB spec. However, if one port requires more current than 500ma, this simple design will supply that if the other USB port requires proportionally less - so drawing 600ma from one port is fine as long as the other port only requires 400ma or less.

I have seen this also with powered USB hubs - the cheap one sometimes work better because of the more simplistic power feed arrangement.

On this subject - does anyone know of a 2.5-inch drive that is spec'd at 500ma or less? All the ones I have seen so far are spec'd at 600ma.
but wait, there's more

:eek: Ha! my 2.5 drive also has Y cable. After a week of trying everything to get it to function on the mpb (works fine on one of those other pcs), I had to place the drive on the other side of the table ('cos it was easier than cleaning up), which meant swapping which end of the Y cable went into which port. It now works!!

BUT if I swap them back to the other side it doesn't.

So, to all with similar, stop being creatures of habit - swap he cables over and see if it works.

YES, i know it makes no sense - but it works.:confused:
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