On Dec 4, 2010, at 11:50 PM, Stephen Conrad wrote:
The folks as The Apple Store on the Country Club Plaza (Kansas
City, MO) said I'd be fine using a 6V DC power cord on my USB 4-
Port Hub that says it needs a 5V DC power cord (they said it would
only draw 5V DC). I asked them as the only Universal AC Adaptor I
could find has 3, 4.5, 6, 7.5, 9 and 12V settings (Voltage Selector).
Were they right or do I need to order a cord from Belkin?
First go back to the store and tell them they are quite wrong.
General rules of power supplies in particular, wall warts.
1 Polarity is most important, get it wrong and BAD things happen
faster than you can see.
2 Voltage needs to be right.
In some cases it can be higher or lower than spec'ed but only if you
know what you are doing.
Otherwise it should be as spec'ed. Devices don't "draw" voltage,
they get what you give them.
3 Current needs to be at least what is required but can be more.
Caveat to this rule is that many power supplies are expected to be
loaded down by a certain amount of current.
That is the output voltage drops as the load (current) increases.
This is factored into the design.
So if you use a power supply that has a significantly higher current
rating that the device it may well supply
too much voltage.
4 The connector needs to match. This is last because if it doesn't
match nothing happens.
The typical power supply for a USB hub is a regulated supply. This
means that whether it has no load on it or it's maximum load the
output voltage is regulated to within a few percent of 5V. Your
typical universal wall wart isn't regulated so it's voltage could be
several volts above or below 5V.
An unregulated 6 volt wall wart, especially one rated for 2.5 amps is
likely to put out about 8 volts with just the hub connected. But
even if it's spot on at 6 volts you run the risk of blowing the hub
and everything plugged into it.
You may be able to find a suitable replacement power supply as all 4
port USB powered hubs I've checked use a 5V power supply rated at 2.1
to 2.5A. But do watch out for polarity and the connector.
You are probably better off just going out and buying a new hub. The
latest hubs I've bought were Belkin 4 port at the local Target store
for $15-$20. IF Belkin will sell you a new power supply it may run
nearly that much to buy it, including shipping and handling. If you
buy a replacement locally then you can still use your old one as a
bus powered hub (for light loads only.
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