Re: Power loss thru long cables?

[Tom Baker]

Thanks for the info Jeff. The video converter box is this one: 
http://www.miglia.com/products/video/director2/ and when it dies, it's 
dead. Both times it happened, when I tried to turn the unit on, I got a 
faint flicker from those little lights you see on the front of it, and 
then nothing, it went dead as a doornail. Both times I had to send it 
back to the manufacturer for warranty repair, and the last time they 
told me they replaced the entire circuit board.

Nowhere in the manual or on the website is the power draw stated. There 
are only two FireWire 400 ports on this G-4 tower, and the hard drives 
that are connected to the other one have their own power supplies.

I only needed about an 8 foot FireWire cable to reach the box, but 
CompUSA offered either six feet or fifteen feet, too short or too long, 
nothing in between.

Maybe I just got a lemon, and maybe with its new circuit board the box 
is fixed. Time will tell I guess.

Thanks,
Tom
On Feb 7, 2005, at 9:09 PM, Jeff Drummond wrote:
On Feb 7, 2005, at 6:05 pm, Tom Baker <[EMAIL PROTECTED]> writes:
If you have a peripheral that draws its power from the Mac through a
FireWire cable, can an overly long cable significantly reduce the 
power
getting to the peripheral? I've got an analog-to-digital video
converter box at the end of a fifteen foot FW cable that has died 
twice
on me, and I'm wondering if that's why. This G-4 is also loaded with
internal hard drives and cards that may be straining its power supply
to begin with.
How is the box dying? Does it stop working temporarily or permanently
(requiring replacement)?
The FireWire (400) standard specifies a maximum cable length of 4.5 
meters
(~15 feet), so you should be OK purely on length. Voltage drops for the
the amount of current should be pretty small. A slightly more relevant
question is how much power is your converter box drawing? Apple's 
FireWire
buses typically supply a maximum of 15 watts (that's for towers, 
powerbooks
and ibooks are about half that). This power is shared over all the 
FireWire
buses and all the FireWire devices on all the buses; so lots of 
devices =
not much power. If you're drawing lots of power then a powered FireWire
hub might be in order.

Another possibility, if the box is failing temporarily, might be 
interference.
Longer cables are subject to more interference than short(er) cables.

-Jeff    [EMAIL PROTECTED]

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