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'[EE:] USB powered coffee warmer'
2004\06\16@090436 by Russell McMahon

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USB powered coffee warmer.
Technical travesty continues.

       http://www.trademe.co.nz/Computers/Other/auction-12466151.htm

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2004\06\16@142718 by Bob Barr

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On Thu, 17 Jun 2004 00:37:40 +1200, Russell McMahon wrote:

>USB powered coffee warmer.
>Technical travesty continues.
>
>        http://www.trademe.co.nz/Computers/Other/auction-12466151.htm


What a hoot!

I wonder if it's USB 2.0 compatible. Low, full or high speed?


Regards, Bob

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2004\06\16@151255 by hilip Stortz

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another fine example of the misuse of technology.  just because it can
be done doesn't mean it should be, usually it shouldn't be done just
because it's possible.  besides, there is only something like 2.5 watts
available, hardly enough to provide proper warming i would think.

Russell McMahon wrote:
>
> USB powered coffee warmer.
> Technical travesty continues.
>
>         http://www.trademe.co.nz/Computers/Other/auction-12466151.htm
>
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2004\06\16@164843 by Bob Ammerman

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But, IIRC, they actually have to have some electronic hardware in there!

If a USB device tries to draw 500ma directly on plug in, that is a violation
of the standard, and IIRC the HUB should shut it down.

The device has to enumerate first, and tell the hub its wants the 500ma
before cranking up the juice.

This, of course, just makes the whole think a little bit sicker.

Bob Ammerman
RAm Systems



{Original Message removed}

2004\06\16@170958 by Spehro Pefhany

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At 04:44 PM 6/16/2004 -0400, you wrote:
>But, IIRC, they actually have to have some electronic hardware in there!
>
>If a USB device tries to draw 500ma directly on plug in, that is a violation
>of the standard, and IIRC the HUB should shut it down.
>
>The device has to enumerate first, and tell the hub its wants the 500ma
>before cranking up the juice.
>
>This, of course, just makes the whole think a little bit sicker.
>
>Bob Ammerman
>RAm Systems

I'll bet you a buck they don't bother with that...

Best regards,

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2004\06\16@181754 by llile

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Need 5 volts?

Strip a USB cable and plug it into your PC.  Interrogate the wires with a
meter until you find the ones with 5V on them.  Then fire up your project
on 5 volts!  No emnumeration, no hassles, always on, I've sucked up nearly
an amp this way without issues.  The USB spec may say that a device must
negotiate before sucking up 500mA out of the USB port, and real USB
devices may do so before sucking up juice, but the 5 volts is there
constantly regardless without any grief or BS and no limits.

For a device to be sold commercially, it must pass a USB plugfest, and
specific tests about enumeration and negotiation for power.  But for the
lab - Mwo-Ha-Ha-Ha!  Every laptop is a 5 volt power supply.  I doubt the
USB map lights and USB toothbrushes and USB nose hair trimmers even bother
with USB certification, just add the connector and sell em!

What happens if you short it out?  I dunno yet.   Prolly fry your laptop.
Be safe, add a fuse.

-- Lawrence Lile





Bob Ammerman <.....rammermanKILLspamspam@spam@VERIZON.NET>
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06/16/2004 03:44 PM
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       cc:
       Subject:        Re: [EE:] USB powered coffee warmer


But, IIRC, they actually have to have some electronic hardware in there!

If a USB device tries to draw 500ma directly on plug in, that is a
violation
of the standard, and IIRC the HUB should shut it down.

The device has to enumerate first, and tell the hub its wants the 500ma
before cranking up the juice.

This, of course, just makes the whole think a little bit sicker.

Bob Ammerman
RAm Systems



{Original Message removed}

2004\06\16@183243 by David VanHorn

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At 05:17 PM 6/16/2004 -0500, EraseMEllilespam_OUTspamTakeThisOuTSALTONUSA.COM wrote:

>Need 5 volts?
>
>Strip a USB cable and plug it into your PC.  Interrogate the wires with a meter until you find the ones with 5V on them.  Then fire up your project on 5 volts!

My palm IIIc charges at 5.0V input.  Guess how I charge it from my laptop? :)


>What happens if you short it out?  I dunno yet.   Prolly fry your laptop.
>Be safe, add a fuse.

They have overcurrent protection, it's in the spec.

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2004\06\16@184733 by Bob Barr

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On Wed, 16 Jun 2004 17:17:05 -0500, llile@ wrote:

<snip>>

>For a device to be sold commercially, it must pass a USB plugfest, and
>specific tests about enumeration and negotiation for power.

That's not exactly the case. Passing a plugfest (or an independent
testing lab) is only a requirement for using the USB logo. Passing the
tests isn't required to sell a product as long as you don't use their
(USBIF's) copyrighted logo.

<snip>


Regards, Bob

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2004\06\18@143931 by Andrew Warren

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Philip Stortz <PICLISTspamspam_OUTmitvma.mit.edu> wrote:

> there is only something like 2.5 watts available, hardly enough to
> provide proper warming i would think.

   The intent isn't to heat up a cold cup of coffee or keep it hot
   indefinitely.  The advertisements that I've seen usually include
   a graph showing that the cupwarmer extends the time that your
   coffee remains above a "drinkable" temperature... They usually
   claim about an hour of additional time above 40 degrees C.

   I've got ads for USB-port-powered cupwarmers, cellphone battery
   chargers, fans, lamps, therapeutic heating pads, a talking
   wing-flapping plastic parrot, an electric toothbrush... There's
   a lot you can do with 5V at 500mA, I guess.

   I'm still waiting for the cable that lets you charge your
   laptop's battery from its own USB port.

   -Andy

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2004\06\18@144340 by Robert B.

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I'll sell you a cable that does it for a large fee.  (externally powered hub
required)


----- Original Message -----
From: "Andrew Warren" <RemoveMEaiwTakeThisOuTspamCYPRESS.COM>

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2004\06\18@150110 by Wouter van Ooijen

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>     I'm still waiting for the cable that lets you charge your
>     laptop's battery from its own USB port.

I think Microsoft will have patented that idea..

Wouter van Ooijen

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2004\06\19@080644 by Howard Winter

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On Wed, 16 Jun 2004 17:17:05 -0500, EraseMEllilespamSALTONUSA.COM wrote:

> Need 5 volts?
>
> Strip a USB cable and plug it into your PC.  Interrogate the wires with a
> meter until you find the ones with 5V on them.  Then fire up your project
> on 5 volts!  No emnumeration, no hassles, always on, I've sucked up nearly
> an amp this way without issues.  The USB spec may say that a device must
> negotiate before sucking up 500mA out of the USB port, and real USB
> devices may do so before sucking up juice, but the 5 volts is there
> constantly regardless without any grief or BS and no limits.

Arrgghh!  It may work, but it might also destroy the USB port by overloading.  Or the USB port may shut down
because your "device" isn't complying.  As I remember, you can draw 100mA without enumerating, and 500mA when
you've "asked nicely".  Anything outside of this is outside the ratings.

I have an external 2.5" drive housing with USB 2 connection and no power supply, and because the drive itself
is rated at 500mA and there's the USB circuitry on top, it has two USB plugs fitted, so you can draw an Amp.
I tried it in my ThinkPad T23 with just one plug connected, and it shut down without warning after a few
minutes.  Plugging them both in means it runs as long as you like...

You may get away with it on your particular machine, but as a "handy tip" it's not a good thing to suggest,
IMHO.

Cheers,

Howard Winter
St.Albans, England

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2004\06\20@140258 by Peter L. Peres

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Howard Winter <RemoveMEHDRWspam_OUTspamKILLspamH2ORG.DEMON.CO.UK> wrote:
>I have an external 2.5" drive housing with USB 2 connection and no power
>supply, and because the drive itself is rated at 500mA and there's the
>USB circuitry on top, it has two USB plugs fitted, so you can draw an
>Amp. I tried it in my ThinkPad T23 with just one plug connected, and it
>shut down without warning after a few minutes.  Plugging them both in
>means it runs as long as you like...

This is a good point. I was just looking at external USB2.0 ide drives and
cdrom writers and was seriously intrigued by the power problem. One I saw
was a 2.5" external HDD enclosure with USB. There was no spec on the size
of disk one can put in it. Most HDDs for laptops draw well over 1A at
least part-time. I would really hate to burn a backup on a drive that is
bound to shutdown about midway into it. Is there a spec for the current
draw and shutdown delay (besides the USB defined limit of 0.1/0.5A) ?

Peter

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2004\06\21@051649 by hael Rigby-Jones

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>-----Original Message-----
>From: Howard Winter [RemoveMEHDRWTakeThisOuTspamspamH2ORG.DEMON.CO.UK]
>Sent: 19 June 2004 13:05
>To: EraseMEPICLISTspamspamspamBeGoneMITVMA.MIT.EDU
>Subject: Re: [EE:] USB powered coffee warmer
>
>Arrgghh!  It may work, but it might also destroy the USB port
>by overloading.  Or the USB port may shut down because your
>"device" isn't complying.  As I remember, you can draw 100mA
>without enumerating, and 500mA when you've "asked nicely".
>Anything outside of this is outside the ratings.
>
>I have an external 2.5" drive housing with USB 2 connection
>and no power supply, and because the drive itself is rated at
>500mA and there's the USB circuitry on top, it has two USB
>plugs fitted, so you can draw an Amp. I tried it in my
>ThinkPad T23 with just one plug connected, and it shut down
>without warning after a few minutes.  Plugging them both in
>means it runs as long as you like...

I also have one of these.  Note that the second USB plug has only power and
ground connections, not data.  Therefore it cannot be enumerated as a second
device, yet the port is still able to provide enough power.  Mine will
actually power up with just this secondary connector plugged in, and the
hard drive states a current draw of 0.55 amps.

I don't think that typical USB ports actually do anything to supply the
extra current, it's just to ensure the total maximum current is not exceeded
on e.g. a powered hub.

Note also that USB ports are protected against over-current faults, it's
part of the spec.

Regards

Mike




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2004\06\21@135905 by Howard Winter

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Michael,

On Mon, 21 Jun 2004 07:57:42 +0100, Michael Rigby-Jones wrote:

>...<

External 2.5" drive housing...

> I also have one of these.  Note that the second USB plug has only power and
> ground connections, not data.  Therefore it cannot be enumerated as a second
> device, yet the port is still able to provide enough power.

Yes, but according to the spec in this situation it can draw 500mA from the first plug when it's enumerated,
and 100mA from the second at all times.  In the case of mine the drive is labelled as 500mA and obviously the
USB circuitry takes it over that, but as long as the latter is less than 100mA it's within spec.

>Mine will
> actually power up with just this secondary connector plugged in, and the
> hard drive states a current draw of 0.55 amps.

As far as I know the spec doesn't say the port mustn't supply in excess the 100/500 limits, just that it
doesn't have to!  I had a powered hub that I tried to run my drive from, with just one connector, and it shut
down that port after a few minutes' running.  That port was "dead" until I power-cycled the hub itself -
removing the offending device didn't resurrect it, although the other ports were fine.  I don't know if the
hub firmware did that or something electronic.

> I don't think that typical USB ports actually do anything to supply the
> extra current, it's just to ensure the total maximum current is not exceeded
> on e.g. a powered hub.

In theory they could enforce the 100/500 limit as the spec says, but I suppose it's the designer's decision
whether to or not...

> Note also that USB ports are protected against over-current faults, it's part of the spec.

...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.

If I had some 3-or-so Watt resistors I might conduct some experiments, but it's not high on my priorities!
:-)

Cheers,

Howard Winter
St.Albans, England

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2004\06\21@212535 by Mike Hord

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I don't know what the current limit is, but it must be rather high, as I
made a mini-fan for a friend that runs on USB, and it had to be pulling
at least several tens of mA, if not more than 100.

Another abuse.

Mike H.

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2004\06\22@041735 by hael Rigby-Jones

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>-----Original Message-----
>From: Howard Winter [HDRWSTOPspamspamspam_OUTH2ORG.DEMON.CO.UK]
>Sent: 21 June 2004 14:20
>To: spamBeGonePICLISTSTOPspamspamEraseMEMITVMA.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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2004\06\22@054611 by Howard Winter

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Michael,

On Tue, 22 Jun 2004 09:16:52 +0100, Michael Rigby-Jones
wrote:

>...<
> 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?

Hmmm... I'm not familiar with hos polyfuses work - do
they have to have power removed to reset?  I sort-of
thought they'd reset when the fault current was removed.

Dammit, I'm going to have to dismantle the hub and see
what's in there!  :-)

Cheers,

Howard Winter
St.Albans, England

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2004\06\22@062823 by hael Rigby-Jones

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{Quote hidden}

They are basicaly a type of PTC, they have a low resistance normaly, but
under fault current conditions they heat up and the resitance increases
greatly.  Simply removing whatever is drawing too much current will allow
them to reset.

Very handy devices for this type of application; cheap and resettable with
no user intervention.

Regards

Mike




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2004\06\22@073019 by Alan B. Pearce

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>>Hmmm... I'm not familiar with hos polyfuses work - do
>>they have to have power removed to reset?  I sort-of
>>thought they'd reset when the fault current was removed.
>
>They are basicaly a type of PTC, they have a low resistance normaly,
>but under fault current conditions they heat up and the resitance
>increases greatly.  Simply removing whatever is drawing too much
>current will allow them to reset.

But they do have a thermal time constant, which is why the item would work
for a while before cutting out, and then the power would not come back
immediately after unplugging. They are ideal devices to protect against
massive overcurrent loads as they will heat up quickly, but for a load that
is close to the Polyfuse rating the heating time is quite long. When it came
to needing to power cycle the hub to get the power back, the time taken to
do that was probably long enough for the Polyfuse to cool off and lower the
resistance enough for the power to appear, especially if the power had been
left off for 5 seconds or so.

In the UK farnell and RS have both had polyfuse devices in the past. On the
Farnell CD I have they are called "resettable fuse". Looks like RS may have
them as "thermal fuse".

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2004\06\23@142239 by Andrew Warren

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Peter L. Peres <.....PICLISTspam_OUTspammitvma.mit.edu> wrote:

> > I have an external 2.5" drive housing .... it has two USB plugs
> > fitted, so you can draw an Amp.

   That arrangement, although not explicitly prohibited by the USB
   spec, will not pass USB compliance testing.

> This is a good point. I was just looking at external USB2.0 ide
> drives and cdrom writers and was seriously intrigued by the power
> problem. One I saw was a 2.5" external HDD enclosure with USB.
> There was no spec on the size of disk one can put in it. Most HDDs
> for laptops draw well over 1A at least part-time.

   Yeah, high-speed USB bus-powered hard drives really have to be
   carefully designed in order to meet the USB power spec.  I
   wouldn't expect good results from an empty enclosure into which
   one puts his own off-the-shelf drive.

> Is there a spec for the current draw and shutdown delay (besides
> the USB defined limit of 0.1/0.5A) ?

   There's no spec for USB Vbus power except the USB spec.

   -Andy

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2004\06\26@100715 by Howard Winter

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On Wed, 23 Jun 2004 11:24:53 -0700, Andrew Warren wrote:

> Peter L. Peres <.....PICLISTspamRemoveMEmitvma.mit.edu> wrote:
>
> > > I have an external 2.5" drive housing .... it has two USB plugs
> > > fitted, so you can draw an Amp.
>
>     That arrangement, although not explicitly prohibited by the USB
>     spec, will not pass USB compliance testing.

Maybe so, but it's how a lot of bus-powered external 2.5" disk drive housings, are made...

I just dismantled the powered 4-port USB 2.0 hub that I have (the one that powered-down the external 2.5"
drive connected to just one USB port, after a few minutes).  It'a a RadioShack Cat.No.26-192, shaped like a 3"
diameter flying saucer, and quite nicely made!

Most of the work is done by a big NEC chip, but there are two little "AP1212L" chips, which I looked up: they
are "Dual USB High-Side Power Switch" - designed specifically to supply USB ports with power according to the
specs.  Each port can be turned on and off by a logic signal, and they perform overcurrent, undervoltage, and
thermal shutdown on their own, with a flag pin telling the controller they've done so.

There's no mention of the 100mA pre-enumeration current, so perhaps they are generous with the spec, and
supply 500mA all the time (except during fault conditions)?  The fault current is limited to 1000mA, so it
looks like you can abuse it below this level at the mercy of the thermal shutdown, which is presumably what my
external drive did, hence the few-minutes' grace before it shut down.

I would guess that once the "Fault" flag has siglalled the controller that there's a problem, the latter shuts
down that port for the duration.  That's what seemed to happen in my case, with only a power-cycle restoring
it (several hours powered up but with nothing connected didn't reset it).

Since each chip supplies two USB ports, presumably adjacent, I imagine it's better to use USB ports from each
half, rather than an adjacent pair, if you're getting creative with drawing power from two ports. This would
spread the thermal load (at least) and have more chance of working reliably.  Still out of spec, of course!
:-)

Cheers,

Howard Winter
St.Albans, England

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