>-----Original Message-----
>From: Howard Winter [mailto:HDRW@H2ORG.DEMON.CO.UK]
>Sent: 21 June 2004 14:20
>To: PICLIST@MITVMA.MIT.EDU
>Subject: Re: [EE:] USB powered coffee warmer

>...but in the light of this perhaps a low-cost byproduct is
>the ability to shut down if *either* of the limits is grossly
>exceeded, or only if the 500mA is.  And it allows a bit of
>time-leeway to be given to allow start-up surges for things
>like disk drives while they spin up, hence the shutdown being
>delayed in my experience.  I doubt if it's a thermal trip,
>which would be the other way this might be implemented,
>because they use current themselves, and create heat in what
>is (in this hub) a very small casing.


I suspect they use polyfuses for protection.  As these operate thermaly,
rather than by directly sensing current, I suspect they make take quite some
time to trip if the current overload is marginal. That could explain what
you saw on your hub?

Regards

Mike




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