Using a USB thumb drive for backups?
isw
week.
Pros/cons?
Isaac
Jolly Roger
isw <i...@witzend.com> wrote:
What if you lose it? Perhaps <https://www.ironkey.com> is the answer.
--
Send responses to the relevant news group rather than email to me.
E-mail sent to this address may be devoured by my very hungry SPAM
filter. Due to Google's refusal to prevent spammers from posting
messages through their servers, I often ignore posts from Google
Groups. Use a real news client if you want me to see your posts.
JR
nospam
<i...@witzend.com> wrote:
maybe for a few files, but when i think of backups, i think of where to
put several hundred gigabytes.
Fred Moore
isw <i...@witzend.com> wrote:
NO! NO! NO! NO! NO! NO! NO! NO! NO! NO! NO! NO! NO! NO! NO! NO! NO!...
...if by 'backup' you mean a REAL backup in the sense that we usually
use it here (secure copy of data from which the data can be recovered
_uncorrupted_ at some time months or even years in the future), and not
just an extra convenience copy or a copy to sneakernet to another
machine.
RAM chips are FRAGILE! Static electricity either by a single jolt or
through accumulated smaller zaps will KILL integrated circuits. The
microscopic connections on integrated circuits are TINY (think
nanometers). Every exposure to high voltage (and the voltage doesn't
have to be that high) vaporizes a small amount of the metal in one or
more of the connections. Sooner or later the last molecule of gold or
copper escapes into the cosmos from which it came, and the RAM chip is
hosed. Some of the better constructed thumb drives claim to have
electrical circuit buffering to extend their lives, but they are still
vulnerable.
Strong magnetic fields and x-rays can also corrupt/destroy integrated
circuits.
Why aren't the RAM chips inside your computer just as fragile? THEY ARE!
except that the computer manufacturers take a number of steps to protect
all of the semiconductors inside the machine.
And none of the above addresses losing a thumb drive because it falls
out of your pocket when you go for your car keys, or other numerous and
mundane accidents.
For more info on semiconductors and static electricity, Google can be
your guide.
nospam
Fred Moore <fmo...@gcfn.org> wrote:
> RAM chips are FRAGILE!
not really.
> Static electricity either by a single jolt or
> through accumulated smaller zaps will KILL integrated circuits.
a large zap might kill it, smaller ones probably not.
> The
> microscopic connections on integrated circuits are TINY (think
> nanometers). Every exposure to high voltage (and the voltage doesn't
> have to be that high) vaporizes a small amount of the metal in one or
> more of the connections. Sooner or later the last molecule of gold or
> copper escapes into the cosmos from which it came, and the RAM chip is
> hosed. Some of the better constructed thumb drives claim to have
> electrical circuit buffering to extend their lives, but they are still
> vulnerable.
no
> Strong magnetic fields and x-rays can also corrupt/destroy integrated
> circuits.
no
> Why aren't the RAM chips inside your computer just as fragile? THEY ARE!
> except that the computer manufacturers take a number of steps to protect
> all of the semiconductors inside the machine.
as does anyone else who uses them
> And none of the above addresses losing a thumb drive because it falls
> out of your pocket when you go for your car keys, or other numerous and
> mundane accidents.
there is that
> For more info on semiconductors and static electricity, Google can be
> your guide.
and hopefully will result in more accurate information.
isw
Jolly Roger <jolly...@pobox.com> wrote:
> In article <isw-AC315E.10332418122009@[216.168.3.50]>,
> isw <i...@witzend.com> wrote:
>
> > Not with Time Machine, but with "backuplist+", which does them once a
> > week.
> >
> > Pros/cons?
>
> What if you lose it? Perhaps <https://www.ironkey.com> is the answer.
Same as if I lose the hard drive I'd be replacing it with...
Isaac
isw
Probably a good place to visit for accurate information on thumb drives,
too...
Isaac
Tim Murray
Flash memory, the kind used on thumb drives, is not the same as the chips
used inside the computer. Flash memory wears out: It is the "flash" -- the
signal that causes the bit to be locked in -- that eventually wears out the
chip. Some thumb drives can detect a bad bit and compensate, but this only
postpones the inevitable (see http://en.wikipedia.org/wiki/Wear_levelling).
Many more expensive SLC-type thumb drives are rated for 300,000 cycles, but
cheaper MLCs are only around 10,000.
Flash has a problem disks don't, in that flash drives move your data around
with every update. Every time a flash drive writes a page, it has to erase
the entire block that page is in.
What happens to the data in the block? It gets read and rewritten along with
the new page to a new location. The map that keeps track of where your data
is rapidly gets very complex and itself is regularly read and rewritten.
If the drive's physical to virtual block map gets corrupted there is no way
to recover data. And that critical map is getting read, updated and rewritten
with every file update.
While I would recommend an external disk for a backup, statistically you're
probably okay with a USB as a backup, but not as a "working" drive. The
reason is that if your computer goes south the chance that your thumb drive
is also bad is small, unless what killed your computer was, say, a lightening
strike that happened while your thumb drive was installed.
Tim Murray
>> The microscopic connections on integrated circuits are TINY (think
>> nanometers). Every exposure to high voltage (and the voltage doesn't have
>> to be that high) vaporizes a small amount of the metal in one or more of
>> the connections. Sooner or later the last molecule of gold or copper
>> escapes into the cosmos from which it came, and the RAM chip is hosed.
>> Some of the better constructed thumb drives claim to have electrical
>> circuit buffering to extend their lives, but they are still vulnerable.
>
> no
Every connection causes a spark. Some metal is lost in vaporization (the
metal sputters and is carried away in an aerosol) and some to excitation. The
melting point of the metal is a major factor. Gold has great conductive
properties but a low melting point and a low life-span.
The flashing circuit in a thumb drive is destructive, only for a different
reason.
nospam
Murray <no-...@thankyou.com> wrote:
um, no.
> The flashing circuit in a thumb drive is destructive, only for a different
> reason.
flash memory does have a limited life but it's far higher than what
someone is realistically going to reach. they'll probably want a larger
capacity device before it fails (or lose it).
Tim Murray
>> Every connection causes a spark. Some metal is lost in vaporization (the
>> metal sputters and is carried away in an aerosol) and some to excitation.
>> The melting point of the metal is a major factor. Gold has great
>> conductive properties but a low melting point and a low life-span.
>
> um, no.
What wrong?
JF Mezei
Tom Harrington
isw <i...@witzend.com> wrote:
Others have discussed the potential cons. I'll just suggest that most
of these can be avoided by using multiple drives for redundant backups.
It's unlikely they'd all fail at once, so even if one was to wear out or
get zapped or go through the laundry or something you'd still have
others to fall back on. Get 2 or 3 (they're cheap these days) and
rotate them.
--
Tom "Tom" Harrington
Independent Mac OS X developer since 2002
http://www.atomicbird.com/
Nick Naym
nos...@nospam.invalid wrote on 12/18/09 2:22 PM:
I wonder why no one has addressed this. And if one is only talking about a
handful of files (especially infrequently), what's the advantage of using
"backup" software over simply drag-and-dropping copies?
--
iMac (24", 2.8 GHz Intel Core 2 Duo, 2GB RAM, 320 GB HDD) � OS X (10.5.8)
Tim Murray
> I wonder why no one has addressed this. And if one is only talking about a
> handful of files (especially infrequently), what's the advantage of using
> "backup" software over simply drag-and-dropping copies?
Actually there is an advantage in the most backup apps have an option to
verify that the backup had no errors, more than the OS will do.
isw
Nick Naym <nicknaym@[remove_this].gmail.com> wrote:
> In article 181220091422276843%nos...@nospam.invalid, nospam at
> nos...@nospam.invalid wrote on 12/18/09 2:22 PM:
>
> > In article <isw-AC315E.10332418122009@[216.168.3.50]>, isw
> > <i...@witzend.com> wrote:
> >
> >> Not with Time Machine, but with "backuplist+", which does them once a
> >> week.
> >>
> >> Pros/cons?
> >
> > maybe for a few files, but when i think of backups, i think of where to
> > put several hundred gigabytes.
>
>
> I wonder why no one has addressed this. And if one is only talking about a
> handful of files (especially infrequently), what's the advantage of using
> "backup" software over simply drag-and-dropping copies?
It's on the Mac of a barely-capable user who works with critical
(financial) data (she understands the finances; just not the computer),
and so absolutely cannot be trusted to do any backing up in a reliable
fashion. The backup app launches at login, and runs continuously, waking
up once a week to copy the folders I told it to copy.
To be clear, her method for dealing with technology is just like her
method for dealing with children: shake a finger and sternly say "you'd
better not do that!"
Which, of course, works just as well for one as for the other.
Isaac
isw
Tom Harrington <t...@pcisys.no.spam.dammit.net> wrote:
> In article <isw-AC315E.10332418122009@[216.168.3.50]>,
> isw <i...@witzend.com> wrote:
>
> > Not with Time Machine, but with "backuplist+", which does them once a
> > week.
> >
> > Pros/cons?
>
> Others have discussed the potential cons. I'll just suggest that most
> of these can be avoided by using multiple drives for redundant backups.
> It's unlikely they'd all fail at once, so even if one was to wear out or
> get zapped or go through the laundry or something you'd still have
> others to fall back on. Get 2 or 3 (they're cheap these days) and
> rotate them.
It goes on a mini, so it has to be external (the mini is replacing a
blue & white, where the B/U drive was internal). I'm trying to avoid an
external disk that needs a separate power cord and all that stuff.
Isaac
isw
JF Mezei <jfmezei...@vaxination.ca> wrote:
> For a real backup solution, rent the movie Johnny Mnemonic. :-) :-) :-)
Best idea yet...
Isaac
nospam
<i...@witzend.com> wrote:
> > I wonder why no one has addressed this. And if one is only talking about a
> > handful of files (especially infrequently), what's the advantage of using
> > "backup" software over simply drag-and-dropping copies?
>
> It's on the Mac of a barely-capable user who works with critical
> (financial) data (she understands the finances; just not the computer),
> and so absolutely cannot be trusted to do any backing up in a reliable
> fashion. The backup app launches at login, and runs continuously, waking
> up once a week to copy the folders I told it to copy.
the perfect candidate for time machine.
Tom Harrington
isw <i...@witzend.com> wrote:
> It's on the Mac of a barely-capable user who works with critical
> (financial) data (she understands the finances; just not the computer),
> and so absolutely cannot be trusted to do any backing up in a reliable
> fashion. The backup app launches at login, and runs continuously, waking
> up once a week to copy the folders I told it to copy.
Sounds like a candidate for Dropbox, <http://www.dropbox.com/>.
Have her put the files in the Dropbox folder, and the software will
silently mirror it to a Dropbox account (and optionally to other
computers) whenever it changes. She doesn't need to "do" backups,
they'll just happen, and if/when disaster strikes the files are easily
recoverable.
BreadW...@fractious.net
> It goes on a mini, so it has to be external (the mini is replacing a
> blue & white, where the B/U drive was internal). I'm trying to avoid an
> external disk that needs a separate power cord and all that stuff.
There are plenty of USB-powered 2.5" external drives in enclosures.
I had a problem with such a drive on an old powerbook, but I use
a current-generation one with my MBP and it works just fine.
--
Plain Bread alone for e-mail, thanks. The rest gets trashed.
Are you posting responses that are easy for others to follow?
http://www.greenend.org.uk/rjk/2000/06/14/quoting
Nick Naym
wrote on 12/19/09 12:28 AM:
Been watching too many old Henny Youngman routines? ;)
Nick Naym
wrote on 12/18/09 1:33 PM:
BTW...I never heard of backuplist+. Upon perusing its manual, I got the
impression that it's a nifty little program. And being a freebie certainly
adds to its attraction. Any idea how it compares to other shareware backup
apps (e.g., ChronoSync, SuperDuper!, etc.)?
Warren Oates
Michael Vilain <vil...@NOspamcop.net> wrote:
> For someone who's not so sensitive to such things, Dropbox might be OK.
> If this technically unsophisticated user can't be trained to take care
> of themselves and their data, they need to hire someone to make sure it
> gets done. It would be irresponsible to do anything else.
... and anyway, her machine can be set up with rsync and cron to back
stuff up every couple of hours. Dropbox actually sounds scary. All your
stuff are belong to us.
--
Very old woody beets will never cook tender.
-- Fannie Farmer
Jolly Roger
BreadW...@fractious.net wrote:
> isw <i...@witzend.com> writes:
>
> > It goes on a mini, so it has to be external (the mini is replacing a
> > blue & white, where the B/U drive was internal). I'm trying to avoid an
> > external disk that needs a separate power cord and all that stuff.
>
> There are plenty of USB-powered 2.5" external drives in enclosures.
> I had a problem with such a drive on an old powerbook, but I use
> a current-generation one with my MBP and it works just fine.
USB bus-powered enclosures have a design flaw: the power supplied by the
USB bus is barely enough for todays faster, more power-hungry drives. To
make matters worse, at certain times, the power delivered by USB ports
can fluctuate. When a hard drive does not receive enough power during a
write, unpredictable things may occur, including data corruption on the
drive. Laptops are especially prone to USB bus power fluctuations. I
have experienced data corruption several times with a USB bus-powered
enclosure connected to my MacBook Pro used for Time Machine backups. I
can tell you from experience that finding out your Time Machine backup
is corrupt when you most need it is not a pleasant experience. I refuse
to use a USB bus-powered enclosure anymore. For me it's Firewire-only,
and no USB unless absolutely necessary - and then only with an external
power source for backups.
Fred Moore
nospam <nos...@nospam.invalid> wrote:
>
> no
Care to back your opinions up with facts? A Google search supports
everything Tim and I said.
nospam
Jolly Roger <jolly...@pobox.com> wrote:
> USB bus-powered enclosures have a design flaw: the power supplied by the
> USB bus is barely enough for todays faster, more power-hungry drives.
actually, recent drives use less power than older drives. usb is
sufficient for normal operation, but not enough to spin it up.
> To make matters worse, at certain times, the power delivered by USB ports
> can fluctuate.
only if the host is defective.
> When a hard drive does not receive enough power during a
> write, unpredictable things may occur, including data corruption on the
> drive. Laptops are especially prone to USB bus power fluctuations.
no, they're prone to not being overspeced. desktop computers have a
much higher power budget and can easily overspec the usb ports.
all usb hosts are required to supply 500ma, and most drives need about
1a to spin up the drive, but can run fine once spinning on 500ma. since
usb hard drives are common, some computers provide more than required
500ma.
> I have experienced data corruption several times with a USB bus-powered
> enclosure connected to my MacBook Pro used for Time Machine backups. I
> can tell you from experience that finding out your Time Machine backup
> is corrupt when you most need it is not a pleasant experience. I refuse
> to use a USB bus-powered enclosure anymore. For me it's Firewire-only,
> and no USB unless absolutely necessary - and then only with an external
> power source for backups.
that could be due to any number of things. i had a time machine archive
with a desktop drive get corrupted. time machine is not all that
reliable.
nospam
Fred Moore <fmo...@gcfn.org> wrote:
> Care to back your opinions up with facts? A Google search supports
> everything Tim and I said.
cites?
memory circuits don't spark and nothing is vaporized.
JF Mezei
Is the user's machine connected to a netork ? Are there any servers (mac
or otherwise) on the netowrk ?
If so, you could setup either appleshare or NFS automounts on the users
machine, and have time machine automatically run in the backgound to
copy data over the net to an NFS or appleshare store.
isw
Tom Harrington <t...@pcisys.no.spam.dammit.net> wrote:
> In article <isw-C0CD34.21281918122009@[216.168.3.50]>,
> isw <i...@witzend.com> wrote:
>
> > It's on the Mac of a barely-capable user who works with critical
> > (financial) data (she understands the finances; just not the computer),
> > and so absolutely cannot be trusted to do any backing up in a reliable
> > fashion. The backup app launches at login, and runs continuously, waking
> > up once a week to copy the folders I told it to copy.
>
> Sounds like a candidate for Dropbox, <http://www.dropbox.com/>.
>
> Have her put the files in the Dropbox folder, and the software will
> silently mirror it to a Dropbox account (and optionally to other
> computers) whenever it changes. She doesn't need to "do" backups,
> they'll just happen, and if/when disaster strikes the files are easily
> recoverable.
backuplist+ works without intervention (once I set it up); I'm just
looking for the best option for external storage. I'm leaning heavily
towards a 2 or 4 Gig USB Thumbdrive at this time.
Isaac
isw
Warren Oates <warren...@gmail.com> wrote:
> In article <vilain-E6BE47....@news.individual.net>,
> Michael Vilain <vil...@NOspamcop.net> wrote:
>
> > For someone who's not so sensitive to such things, Dropbox might be OK.
> > If this technically unsophisticated user can't be trained to take care
> > of themselves and their data, they need to hire someone to make sure it
> > gets done. It would be irresponsible to do anything else.
>
> ... and anyway, her machine can be set up with rsync and cron to back
> stuff up every couple of hours. Dropbox actually sounds scary. All your
> stuff are belong to us.
I agree completely. I want my stuff on *my* servers where *I* can get it
-- or more importantly, destroy it -- whenever *I* want to.
Isaac
isw
nospam <nos...@nospam.invalid> wrote:
On a G4 mini, which can't run Leopard because it has to run some legacy
"Classic" apps. And there's no chance the user could handle SheepShaver.
Isaac
nospam
<i...@witzend.com> wrote:
> On a G4 mini, which can't run Leopard because it has to run some legacy
> "Classic" apps. And there's no chance the user could handle SheepShaver.
which ones? is there really no osx native replacement?
Tim Murray
> In article <fmoore-239A0D....@feeder.eternal-september.org>,
> Fred Moore <fmo...@gcfn.org> wrote:
>
>> Care to back your opinions up with facts? A Google search supports
>> everything Tim and I said.
>
> cites?
Simply search for "flash memory" followed by any word such as lifespan,
cycles, destructive, et al.
>
> memory circuits don't spark and nothing is vaporized.
I didn't say memory circuits spark; I said connections spark, and they do,
and then I said the flashing circuit in a thumb drive is destructive.
They call it flash because of the way they are erased, which is to drive
current -- a lot of it, actually -- through a wall of insulation. At the
particle level it's a very violent process, and it's damaged just a bit with
every read and write.
Warren Oates
isw <i...@witzend.com> wrote:
> I agree completely. I want my stuff on *my* servers where *I* can get it
> -- or more importantly, destroy it -- whenever *I* want to.
On the other hand, Wuala seems maybe secure -- your data is encrypted
before it goes, or something.
nospam
Murray <no-...@thankyou.com> wrote:
> >> Care to back your opinions up with facts? A Google search supports
> >> everything Tim and I said.
> >
> > cites?
>
> Simply search for "flash memory" followed by any word such as lifespan,
> cycles, destructive, et al.
flash memory having a limited life is not in dispute.
> > memory circuits don't spark and nothing is vaporized.
>
> I didn't say memory circuits spark; I said connections spark, and they do,
> and then I said the flashing circuit in a thumb drive is destructive.
connections do not spark unless they're poor connections.
E Z Peaces
I've been wondering for some time if flash memory could be ideal for
backup. Disks and optical media can go bad on the shelf.
For $900 extra, one can buy a Macbook Air with flash storage instead of
a disk. Apparently Apple has confidence that flash memory can be
reliable in heavy use.
Some brands of thumb drives aren't nearly as reliable as others, but the
biggest cause of data loss seems to be unplugging without first
unmounting. They're cheap enough that I would alternate backups between
two thumb drives.
Tim Murray
I'm using spark in the sense of an electron jumping from one contact to
another as it gets in range. All connections spark but one exception: When
the distance between contacts closes up so quickly that an electron does not
have time to jump.
isw
nospam <nos...@nospam.invalid> wrote:
Have you ever known somebody who was "resistant to change"?
Isaac
isw
Warren Oates <warren...@gmail.com> wrote:
> In article <isw-919C56.10235519122009@[216.168.3.50]>,
> isw <i...@witzend.com> wrote:
>
> > I agree completely. I want my stuff on *my* servers where *I* can get it
> > -- or more importantly, destroy it -- whenever *I* want to.
>
> On the other hand, Wuala seems maybe secure -- your data is encrypted
> before it goes, or something.
Or so they say...
If I think my data should be encrypted, *I* want to be the one who
choses the method, and the keys.
Isaac
isw
Tim Murray <no-...@thankyou.com> wrote:
Most of the engineers I've known (in over 40 years of being one or
managing them) would only call it a "connection" if the pieces of metal
were in actual, physical contact, with nothing separating them.
Isaac
Tim Murray
> Tim Murray <no-...@thankyou.com> wrote:
>>
>> I'm using spark in the sense of an electron jumping from one contact to
>> another as it gets in range. All connections spark but one exception: When
>> the distance between contacts closes up so quickly that an electron does
>> not have time to jump.
>
> Most of the engineers I've known (in over 40 years of being one or
> managing them) would only call it a "connection" if the pieces of metal
> were in actual, physical contact, with nothing separating them.
>
I agree. I was referring to the time just before the actual connection is
made or just after it breaks. I kinda thought the "gets in range" should have
made that clear.
Andrew Brydon
>In article <isw-AC315E.10332418122009@[216.168.3.50]>,
> isw <i...@witzend.com> wrote:
>
>> Not with Time Machine, but with "backuplist+", which does them once a
>> week.
>>
>> Pros/cons?
>
>of these can be avoided by using multiple drives for redundant backups.
>It's unlikely they'd all fail at once, so even if one was to wear out or
>get zapped or go through the laundry or something you'd still have
>others to fall back on. Get 2 or 3 (they're cheap these days) and
>rotate them.
>
I do this. As a "normal" domestic user I have a weekly backup to
extenral USB, a subset burned tp CD and taken off-site (okay, so
maybe that's not normal) but on a daily basis the likeliest to change
sub-subset is flashed to a 8Gb USB pen. Rotated if necessary. [iCal
triggers an Applescript copy command at 4am each morning, since
you weren't asking.]
--
Andrew Brydon
Life is just the beta-version of death
Jolly Roger
isw <i...@witzend.com> wrote:
> In article <tph-7E4F37.23571618122009@localhost>,
> Tom Harrington <t...@pcisys.no.spam.dammit.net> wrote:
>
> > In article <isw-C0CD34.21281918122009@[216.168.3.50]>,
> > isw <i...@witzend.com> wrote:
> >
> > > It's on the Mac of a barely-capable user who works with critical
> > > (financial) data (she understands the finances; just not the computer),
> > > and so absolutely cannot be trusted to do any backing up in a reliable
> > > fashion. The backup app launches at login, and runs continuously, waking
> > > up once a week to copy the folders I told it to copy.
> >
> > Sounds like a candidate for Dropbox, <http://www.dropbox.com/>.
> >
> > Have her put the files in the Dropbox folder, and the software will
> > silently mirror it to a Dropbox account (and optionally to other
> > computers) whenever it changes. She doesn't need to "do" backups,
> > they'll just happen, and if/when disaster strikes the files are easily
> > recoverable.
>
> backuplist+ works without intervention (once I set it up); I'm just
> looking for the best option for external storage. I'm leaning heavily
> towards a 2 or 4 Gig USB Thumbdrive at this time.
>
> Isaac
If it were me, for sensitive backup data, I'd probably go with a thumb
drive that can self-destruct the data if it gets into the wrong hands:
Jolly Roger
nospam <nos...@nospam.invalid> wrote:
> In article <jollyroger-657BA...@news.individual.net>,
> Jolly Roger <jolly...@pobox.com> wrote:
>
> > USB bus-powered enclosures have a design flaw: the power supplied by the
> > USB bus is barely enough for todays faster, more power-hungry drives.
That would be your opinion. My opinion is there are still drive being
sold today that require more power.
The fact that such drives come with dual Y-split USB cables lends
credence to my opinion. They require more power than one USB port can
supply. Unfortunately, I suspect some laptops may not have dual USB
buses with separate power supplies, which could result in occasional low
power situations for such drives.
> actually, recent drives use less power than older drives. usb is
> sufficient for normal operation, but not enough to spin it up.
>
> > To make matters worse, at certain times, the power delivered by USB ports
> > can fluctuate.
>
> only if the host is defective.
I disagree. Power can fluctuate if devices are aded to or removed from
the same bus. And it is my belief that power can fluctuate at other
times on a laptop where battery drain comes into play.
> > When a hard drive does not receive enough power during a
> > write, unpredictable things may occur, including data corruption on the
> > drive. Laptops are especially prone to USB bus power fluctuations.
>
> no, they're prone to not being overspeced. desktop computers have a
> much higher power budget and can easily overspec the usb ports.
Regardless, my opinion is the power delivered USB ports on laptops are
more prone to fluctuation.
> all usb hosts are required to supply 500ma, and most drives need about
> 1a to spin up the drive, but can run fine once spinning on 500ma. since
> usb hard drives are common, some computers provide more than required
> 500ma.
Unfortunately neither of us has physically monitored the power output of
each USB port on all of Apple's currently-shipping MacBook line through
all of the different phases of startup and under different usage
scenarios. So neither of us can categorically state that 500ma is
consistently delivered to all USB ports on these machines at all times.
I suspect such is not the case. I suspect this is what caused corruption
of my then-USB-connected drive multiple times in a couple months. The
same hard drive, placed into a Firewire enclosure hasn't had a single
instance of corruption since then - for the past 8 months or so.
> > I have experienced data corruption several times with a USB bus-powered
> > enclosure connected to my MacBook Pro used for Time Machine backups. I
> > can tell you from experience that finding out your Time Machine backup
> > is corrupt when you most need it is not a pleasant experience. I refuse
> > to use a USB bus-powered enclosure anymore. For me it's Firewire-only,
> > and no USB unless absolutely necessary - and then only with an external
> > power source for backups.
>
> that could be due to any number of things. i had a time machine archive
> with a desktop drive get corrupted. time machine is not all that
> reliable.
Too coincidental for my tastes - see above.
nospam
Jolly Roger <jolly...@pobox.com> wrote:
> > > USB bus-powered enclosures have a design flaw: the power supplied by the
> > > USB bus is barely enough for todays faster, more power-hungry drives.
>
> That would be your opinion. My opinion is there are still drive being
> sold today that require more power.
i didn't say there weren't. however, some new drive mechanisms use less
power than older ones. check the specs. typically, they've needed 1a to
spin up and some have reduced that requirement. that doesn't mean that
every drive on the shelf is suddenly the lower power variety.
> The fact that such drives come with dual Y-split USB cables lends
> credence to my opinion. They require more power than one USB port can
> supply. Unfortunately, I suspect some laptops may not have dual USB
> buses with separate power supplies, which could result in occasional low
> power situations for such drives.
most usb drives need more power than a single usb port can provide to
spin up the drive, thus the dual cables.
once the drive is spun up, the power requirement of a usb drive is
usually 500ma or less, which is within the capabilities of a single usb
port.
> > > To make matters worse, at certain times, the power delivered by USB ports
> > > can fluctuate.
> >
> > only if the host is defective.
>
> I disagree. Power can fluctuate if devices are aded to or removed from
> the same bus. And it is my belief that power can fluctuate at other
> times on a laptop where battery drain comes into play.
the usb spec requires that the host supply 500ma. if it doesn't, it's
not compliant. it's that simple.
> > > When a hard drive does not receive enough power during a
> > > write, unpredictable things may occur, including data corruption on the
> > > drive. Laptops are especially prone to USB bus power fluctuations.
> >
> > no, they're prone to not being overspeced. desktop computers have a
> > much higher power budget and can easily overspec the usb ports.
>
> Regardless, my opinion is the power delivered USB ports on laptops are
> more prone to fluctuation.
see above.
> > all usb hosts are required to supply 500ma, and most drives need about
> > 1a to spin up the drive, but can run fine once spinning on 500ma. since
> > usb hard drives are common, some computers provide more than required
> > 500ma.
>
> Unfortunately neither of us has physically monitored the power output of
> each USB port on all of Apple's currently-shipping MacBook line through
> all of the different phases of startup and under different usage
> scenarios. So neither of us can categorically state that 500ma is
> consistently delivered to all USB ports on these machines at all times.
you haven't measured anything, yet you are so sure it fluctuates??
apple says their computers are usb compliant, and in order to do that,
they must meet the requirements of the usb spec. one of those is 500ma
output on a port. i'm quite certain that apple has measured it.
> I suspect such is not the case. I suspect this is what caused corruption
> of my then-USB-connected drive multiple times in a couple months. The
> same hard drive, placed into a Firewire enclosure hasn't had a single
> instance of corruption since then - for the past 8 months or so.
but you never measured the voltage, so it's pure speculation that it
was the cause. it could be any number of reasons, especially if it only
happened with just one drive.
JF Mezei
to be produced on disk drives instead of plastic film: How do you
preserve movies in the long term ?
Film degrades gracefully over time. Disks go from being 100% good to
100% bad overnight.
For now, what they end up doing is copying drives to new drives every
couple of years. This not only get a new "fresh" copy out, but also
moves data only drives with current interfaces, ensuring that can still
be read.
A disk drive with the data intact, but with an interface that no system
supports today would be rather worthless. For instance, some old IBM or
Digital proprietary drives wouldn't be easy to connect to a current
computer system.
Even SCSI-1 from the 1980s would start to need additional work to find a
system capable of processing it.
Does anyone know about long term storage properties of flash drives ?
Once data is written (and only dones once to a new drive), would it last
"forever" in a vault, unconnected to anything ?
JF Mezei
> i didn't say there weren't. however, some new drive mechanisms use less
> power than older ones.
A 600 meg disk in the mid 1980s required a 10amp 115VAC circuit for each
drive, and used a 1/3HP motor to turn the disk.
Think about that the next time you turn on your ipod with 30 gigs of
storage in it.
Jolly Roger
nospam <nos...@nospam.invalid> wrote:
Yes, and it seems neither you nor I are in a position to say whether or
not all USB ports on every Mac are compliant to that requirement all of
the time.
> > > > When a hard drive does not receive enough power during a
> > > > write, unpredictable things may occur, including data corruption on the
> > > > drive. Laptops are especially prone to USB bus power fluctuations.
> > >
> > > no, they're prone to not being overspeced. desktop computers have a
> > > much higher power budget and can easily overspec the usb ports.
> >
> > Regardless, my opinion is the power delivered USB ports on laptops are
> > more prone to fluctuation.
>
> see above.
>
> > > all usb hosts are required to supply 500ma, and most drives need about
> > > 1a to spin up the drive, but can run fine once spinning on 500ma. since
> > > usb hard drives are common, some computers provide more than required
> > > 500ma.
> >
> > Unfortunately neither of us has physically monitored the power output of
> > each USB port on all of Apple's currently-shipping MacBook line through
> > all of the different phases of startup and under different usage
> > scenarios. So neither of us can categorically state that 500ma is
> > consistently delivered to all USB ports on these machines at all times.
>
> you haven't measured anything, yet you are so sure it fluctuates??
Neither have you. Are you sure it doesn't?
Common sense tells me if the battery power level in a laptop happens to
fluctuate, so will the power supplied to USB ports. Are you saying that
cannot ever happen?
> apple says their computers are usb compliant, and in order to do that,
> they must meet the requirements of the usb spec. one of those is 500ma
> output on a port. i'm quite certain that apple has measured it.
Are you certain they have measured it through all possible usage states,
not just at idle?
> > I suspect such is not the case. I suspect this is what caused corruption
> > of my then-USB-connected drive multiple times in a couple months. The
> > same hard drive, placed into a Firewire enclosure hasn't had a single
> > instance of corruption since then - for the past 8 months or so.
>
> but you never measured the voltage, so it's pure speculation that it
> was the cause. it could be any number of reasons, especially if it only
> happened with just one drive.
Of course it's speculation. And without the necessary equipment, that's
all it is going to be.
Richard Maine
...
> the usb spec requires that the host supply 500ma. if it doesn't, it's
> not compliant. it's that simple.
> apple says their computers are usb compliant, and in order to do that,
> they must meet the requirements of the usb spec. one of those is 500ma
> output on a port. i'm quite certain that apple has measured it.
Are you sure that Apple says without qualification that all their
computers are USB compliant? That sounds like speculation to me - and
speculation that doesn't match my recollections. Let's see... Well, it
isn't directly from Apple, and I'm too lazy to go chase down a
first-hand citation, but lowendmac is usually pretty reliable (certainly
far more so than random posters on usenet) and I'd suspect they would
not just invent the following.
See
<http://www.lowendmac.com/macbookpro/15in-macbook-pro-june-2007.html>
which is a profile of June 2007 15" MacBook Pro models. Note in
particular the paragraph:
"Unlike earlier models, where every USB port could provide 500 mA of
power, only a single high-powered device can be attached to the USB
ports, and software will enable one of its downstream ports to supply
500 mA of power. If a second high-powered device is attached, it will
behave like a normal bus-powered hub and only provide 100 mA per
downstream port."
--
Richard Maine | Good judgment comes from experience;
email: last name at domain . net | experience comes from bad judgment.
domain: summertriangle | -- Mark Twain
Jolly Roger
nos...@see.signature (Richard Maine) wrote:
I also doubt that the 500ma output of USB ports on a laptop is always a
continuous stream without fluctuation.
Richard Maine
> nospam wrote:
>
> > i didn't say there weren't. however, some new drive mechanisms use less
> > power than older ones.
>
> A 600 meg disk in the mid 1980s required a 10amp 115VAC circuit for each
> drive, and used a 1/3HP motor to turn the disk.
And weighed about 175 pounds and cost about $30,000 - at least one model
I recall did. I think those were the right numbers. I distinctly recall
helping our hardware guy remove one from its rack. I wasn't very smart
about how I positioned my hold on it. Once we were holding the full
weight, it seemed like the thin metal rail that I was holding it by was
cutting through my fingers. I had this horrified vision of dropping and
breaking a $30k piece of government equipment. I managed to avoid that,
but I still recall the pain.
nospam
Jolly Roger <jolly...@pobox.com> wrote:
> > the usb spec requires that the host supply 500ma. if it doesn't, it's
> > not compliant. it's that simple.
>
> Yes, and it seems neither you nor I are in a position to say whether or
> not all USB ports on every Mac are compliant to that requirement all of
> the time.
if they want to use the logo and call it a usb 2 device, they're
required to meet certain standards.
<http://www.usb.org/developers/compliance/>
> > you haven't measured anything, yet you are so sure it fluctuates??
>
> Neither have you. Are you sure it doesn't?
>
> Common sense tells me if the battery power level in a laptop happens to
> fluctuate, so will the power supplied to USB ports. Are you saying that
> cannot ever happen?
there's a voltage regulator for changes in the battery voltage,
especially since the voltage will drop as it discharges and rise when
being charged.
nothing is perfect, so nobody can guarantee that something unusual
won't ever happen, but in normal use, there's 5v @ 500ma available on
the usb ports. that's very little compared to what the rest of the
laptop consumes so there should rarely be any problem in providing it.
> > apple says their computers are usb compliant, and in order to do that,
> > they must meet the requirements of the usb spec. one of those is 500ma
> > output on a port. i'm quite certain that apple has measured it.
>
> Are you certain they have measured it through all possible usage states,
> not just at idle?
it's a requirement to comply with the spec. here's the checklist:
<http://www.usb.org/developers/compliance/check_list/compchksys080205.pd
f>
as i said before, laptop hard drives will run on 500ma or less for
everything except spin-up. in other words, once it's spun up, there
should not be any problems due to power issues.
nospam
Maine <nos...@see.signature> wrote:
> > apple says their computers are usb compliant, and in order to do that,
> > they must meet the requirements of the usb spec. one of those is 500ma
> > output on a port. i'm quite certain that apple has measured it.
>
> Are you sure that Apple says without qualification that all their
> computers are USB compliant?
if the logo is on the box, they must meet the spec. see links in my
other post.
> which is a profile of June 2007 15" MacBook Pro models. Note in
> particular the paragraph:
>
> "Unlike earlier models, where every USB port could provide 500 mA of
> power, only a single high-powered device can be attached to the USB
> ports, and software will enable one of its downstream ports to supply
> 500 mA of power. If a second high-powered device is attached, it will
> behave like a normal bus-powered hub and only provide 100 mA per
> downstream port."
that's actually from apple's own documentation, nor does it say
anything about voltage fluctuations.
usb starts off at 100ma for a device, and if the device needs more
power it must request 500ma. that request may be denied. a good example
is a bus-powered hub, where you have 500ma (from the host) for *all* of
its ports.
nospam
Jolly Roger <jolly...@pobox.com> wrote:
> I also doubt that the 500ma output of USB ports on a laptop is always a
> continuous stream without fluctuation.
it's required. read the usb spec.
Jolly Roger
nospam <nos...@nospam.invalid> wrote:
Under all circumstance at every moment of every hour of every day of the
year, without fail? Can anyone realistically make such an assurance? I
think not.
nospam
Jolly Roger <jolly...@pobox.com> wrote:
> > > I also doubt that the 500ma output of USB ports on a laptop is always a
> > > continuous stream without fluctuation.
> >
> > it's required. read the usb spec.
>
> Under all circumstance at every moment of every hour of every day of the
> year, without fail? Can anyone realistically make such an assurance? I
> think not.
straw man. nobody can guarantee that it will *never* deviate outside
the spec.
however, in normal use, it must comply with it.
<http://www.usb.org/developers/compliance/check_list/compchksys080205.pd
f>
Can the system supply 0 to 500mA on each of its downstream ports,
regardless of whether or not the system or USB is suspended?
Can the system maintain VBUS between 4.75 at 5.25V at all of its
downstream connectors for DC loads between 0 and 500mA per
downstream port?
Does the system�s port bypassing limit the maximum voltage droop at
any of its downstream ports to 330mV, even when subjected to hot-plug
inrush currents with peaks of 7.5A or more? (As of this writing, the
highest inrush current the USB-IF has observed from a within spec
configuration is 7.40A.)
if the answer to any of those is 'no', an explanation must be provided.
in other words, it can be assumed that a usb compliant device *does*
provide 5v @ 500ma.
BreadW...@fractious.net
> In article <201220091238269346%nos...@nospam.invalid>,
> nospam <nos...@nospam.invalid> wrote:
> > you haven't measured anything, yet you are so sure it fluctuates??
>
> Common sense tells me if the battery power level in a laptop happens to
> fluctuate, so will the power supplied to USB ports. Are you saying that
> cannot ever happen?
Wow, what a tempest.
FWIW, all I said when I started with the "USB-powered 2.5 in drive"
was that I'd had power problems with an earlier model a few years
ago -- it did require the dual cables with my old PB G4.
I was skeptical of all USB-powered drives for a long time because
of that. I recently got a WD Elements 2.5" drive and it works
like an absolute charm on my MBP. Some things to note -- it
certainly uses less power, and I believe that the USB ports
on the MBP are superior to those on the old G4 -- and lastly,
I've never tried to use it while the MBP is running on battery.
I've had multiple problems with batteries on the MBP (it's on
its third one now). I'd try awfully hard to never use a
bus-powered drive on it when not plugged into the wall. But
it's awfully nice to be able to plug the drive in with a
single cable and be good to go. I hate digging under my desk to
get my larger external drives plugged in.
So, again, my original point to the OP: try a recent model
2.5" usb-powered drive. You will get vastly more storage
for way less money than you'll get with a solid-state
thumb-drive. And over the years, I've had thumb drives
flake out on me just as I've had hard drives die. These
things happen.
If it's your primary backup, make sure you have a secondary
one, too. That's all, and that goes for *any* medium.
--
Plain Bread alone for e-mail, thanks. The rest gets trashed.
Are you posting responses that are easy for others to follow?
http://www.greenend.org.uk/rjk/2000/06/14/quoting
Jolly Roger
nospam <nos...@nospam.invalid> wrote:
> In article <jollyroger-144F5...@news.individual.net>,
> Jolly Roger <jolly...@pobox.com> wrote:
>
> > > > I also doubt that the 500ma output of USB ports on a laptop is always a
> > > > continuous stream without fluctuation.
> > >
> > > it's required. read the usb spec.
> >
> > Under all circumstance at every moment of every hour of every day of the
> > year, without fail? Can anyone realistically make such an assurance? I
> > think not.
>
> straw man. nobody can guarantee that it will *never* deviate outside
> the spec.
And that has been my point all along. Thanks.
nospam
Jolly Roger <jolly...@pobox.com> wrote:
> > > > > I also doubt that the 500ma output of USB ports on a laptop is always
> > > > > a
> > > > > continuous stream without fluctuation.
> > > >
> > > > it's required. read the usb spec.
> > >
> > > Under all circumstance at every moment of every hour of every day of the
> > > year, without fail? Can anyone realistically make such an assurance? I
> > > think not.
> >
> > straw man. nobody can guarantee that it will *never* deviate outside
> > the spec.
>
> And that has been my point all along. Thanks.
you seem to think it happens with regularity. it doesn't.
Jolly Roger
nospam <nos...@nospam.invalid> wrote:
I never said that at all. It's a potential problem with any USB
bus-powered enclosure though, IMO.
Tim Murray
> Even SCSI-1 from the 1980s would start to need additional work to
> find a system capable of processing it.
Maybe I should get into the business. I can still use SCSI-1.
TaliesinSoft
(in article <0001HW.C754F711...@nntp.charter.net>):
> Maybe I should get into the business. I can still use SCSI-1.
As a somewhat amusing aside, I remember reading, and this was likely in the
mid 1980s, that the expected verbalization of SCSI was expected to be "sexy"
and not "scuzzy".
--
James Leo Ryan --- Austin, Texas --- talies...@me.com
Tom Stiller
TaliesinSoft <talies...@me.com> wrote:
> On Mon, 21 Dec 2009 08:57:37 -0600, Tim Murray wrote
> (in article <0001HW.C754F711...@nntp.charter.net>):
>
> > Maybe I should get into the business. I can still use SCSI-1.
>
> As a somewhat amusing aside, I remember reading, and this was likely in the
> mid 1980s, that the expected verbalization of SCSI was expected to be "sexy"
> and not "scuzzy".
And, following the naming conventions at the time, the Mac SE/30 should
have been called the Mac SEX.
--
Tom Stiller
PGP fingerprint = 5108 DDB2 9761 EDE5 E7E3 7BDA 71ED 6496 99C0 C7CF
isw
> On Mon, 21 Dec 2009 08:57:37 -0600, Tim Murray wrote
> (in article <0001HW.C754F711...@nntp.charter.net>):
>
> > Maybe I should get into the business. I can still use SCSI-1.
>
> As a somewhat amusing aside, I remember reading, and this was likely in the
> mid 1980s, that the expected verbalization of SCSI was expected to be "sexy"
> and not "scuzzy".
Well, SCSI's prototype was SASI; "sassy".
Isaac
E Z Peaces
has time to jump.
Plugging in a USB device could produce a static discharge of tens of
thousands of volts. I'd be concerned that the device was designed not
to be damaged by static. I wouldn't worry about damage from the 5V supply.
The big problem with contacts comes not from closing but from opening
with an inductive load. There, the available voltage can be
theoretically infinite. A car starter uses a solenoid so that a spring
can break the arc quickly.
Tim Murray
> Tim Murray wrote:
>> isw wrote:
>>> Tim Murray <no-...@thankyou.com> wrote:
>>>> I'm using spark in the sense of an electron jumping from one contact to
>>>> another as it gets in range. All connections spark but one exception:
>>>> When the distance between contacts closes up so quickly that an
>>>> electron does not have time to jump.
>>> Most of the engineers I've known (in over 40 years of being one or
>>> managing them) would only call it a "connection" if the pieces of metal
>>> were in actual, physical contact, with nothing separating them.
>>>
>>
>> I agree. I was referring to the time just before the actual connection is
>> made or just after it breaks. I kinda thought the "gets in range" should
>> have made that clear.
>>
> I've been trying to imagine plugging in a USB device before en electron
> has time to jump.
Superman could do it.
> Plugging in a USB device could produce a static discharge of tens of
> thousands of volts. I'd be concerned that the device was designed not to
> be damaged by static. I wouldn't worry about damage from the 5V supply.
>
> The big problem with contacts comes not from closing but from opening with
> an inductive load. There, the available voltage can be theoretically
> infinite. A car starter uses a solenoid so that a spring can break the
> arc quickly.
All I was trying to explain was that all connections -- okay, the "act" of
making the connection--even if quick and low power, generate some tiny spark.
Alan Browne
> The big problem with contacts comes not from closing but from opening
> with an inductive load. There, the available voltage can be
> theoretically infinite. A car starter uses a solenoid so that a spring
> can break the arc quickly.
The primary reason a car uses a solenoid is because the current is much
too high to route via the ignition switch in the car. The cabling would
be very thick, and the path so long as to make winter starting a problem
in places where it's quite cold.
Richard Maine
Not to speak of the fact that you probably wouldn't want that much juice
running through the steering column to the ignition switch. Hey,
accidents where one impales oneself on the steeing column are already a
bad enough issue. Imagine adding electrocution to the mix.
E Z Peaces
That's why the solenoid isn't in the steering column.
The Picker PC 7150 is an automotive relay designed to switch 300 amps
10,000 times. That should be ample current for a starter motor. This
relay is a little plug-in cube like a headlight relay. The coil draws
only 130 ma.
By contrast, even when a starter solenoid has no mechanical function,
its coil draws about 3 amps. It's built heavily to switch off an
inductive load. Hmmm... how about using an ordinary relay with diode
protection?
Paul Sture
> On Mon, 21 Dec 2009 08:57:37 -0600, Tim Murray wrote
> (in article <0001HW.C754F711...@nntp.charter.net>):
>
> > Maybe I should get into the business. I can still use SCSI-1.
>
> As a somewhat amusing aside, I remember reading, and this was likely in the
> mid 1980s, that the expected verbalization of SCSI was expected to be "sexy"
> and not "scuzzy".
First time I've heard that one, but I can attest that the following is
true:
"SCSI is not magic. There are fundamental technical reasons why it is
necessary to sacrifice a young goat to your SCSI chain now and then."
John Woods (1960-?)
P.S. If you don't have any goats handy, chickens will often do.
--
Paul Sture
Paul Sture
nos...@see.signature (Richard Maine) wrote:
> JF Mezei <jfmezei...@vaxination.ca> wrote:
>
> > nospam wrote:
> >
> > > i didn't say there weren't. however, some new drive mechanisms use less
> > > power than older ones.
> >
> > A 600 meg disk in the mid 1980s required a 10amp 115VAC circuit for each
> > drive, and used a 1/3HP motor to turn the disk.
The 250MB disk drives I was using in the early 1980s had a mechanism to
fire each one up in sequence so that during startup the main circuit
breaker didn't flip.
> And weighed about 175 pounds and cost about $30,000 - at least one model
> I recall did. I think those were the right numbers. I distinctly recall
> helping our hardware guy remove one from its rack. I wasn't very smart
> about how I positioned my hold on it. Once we were holding the full
> weight, it seemed like the thin metal rail that I was holding it by was
> cutting through my fingers. I had this horrified vision of dropping and
> breaking a $30k piece of government equipment. I managed to avoid that,
> but I still recall the pain.
I don't recall how much those 250MB disk drives weighed but they were
washing machine sized rather than rackable. Two gorilla sized guys were
needed to get them upstairs. They did this stuff for a living and still
turned the air blue with their curses.
--
Paul Sture
Fred Moore
E Z Peaces <ca...@invalid.invalid> wrote:
> Tim Murray wrote:
> > I agree. I was referring to the time just before the actual connection is
> > made or just after it breaks. I kinda thought the "gets in range" should
> > have made that clear.
> >
> I've been trying to imagine plugging in a USB device before en electron
> has time to jump.
Sorry, Grasshopper, that's _way_ too Zen a concept for this group. You
want alt.zen.comp.ohm. ;)
Alan Browne
> Alan Browne<alan....@FreelunchVideotron.ca> wrote:
>
>> On 09-12-21 13:52 , E Z Peaces wrote:
>>
>>> The big problem with contacts comes not from closing but from opening
>>> with an inductive load. There, the available voltage can be
>>> theoretically infinite. A car starter uses a solenoid so that a spring
>>> can break the arc quickly.
>>
>> The primary reason a car uses a solenoid is because the current is much
>> too high to route via the ignition switch in the car. The cabling would
>> be very thick, and the path so long as to make winter starting a problem
>> in places where it's quite cold.
>
> Not to speak of the fact that you probably wouldn't want that much juice
> running through the steering column to the ignition switch. Hey,
> accidents where one impales oneself on the steeing column are already a
> bad enough issue. Imagine adding electrocution to the mix.
12 V can't kill you.
Autos are transitioning to 42 VDC - in several years 12VDC will be a
memory. And 42VDC was chosen, amongst other reasons, as it is too low V
to harm anyone.
Alan Browne
> Alan Browne wrote:
>> On 09-12-21 13:52 , E Z Peaces wrote:
>>
>>> The big problem with contacts comes not from closing but from opening
>>> with an inductive load. There, the available voltage can be
>>> theoretically infinite. A car starter uses a solenoid so that a spring
>>> can break the arc quickly.
>>
>> The primary reason a car uses a solenoid is because the current is
>> much too high to route via the ignition switch in the car. The cabling
>> would be very thick, and the path so long as to make winter starting a
>> problem in places where it's quite cold.
>
> That's why the solenoid isn't in the steering column.
The solenoid is placed as close between the battery and the starter as
possible to reduce power loss in the cables (and keep required cable
diameter to a reasonable size). Likewise, most (all?) starters use the
engine block as the return ("ground") side which is also connected to
the battery with as short a cable as possible.
This is also why you boost a car with the return ("negative") lead
connected to the engine block, not to the dead battery. (+ lead to the
batter, typically).
>
> The Picker PC 7150 is an automotive relay designed to switch 300 amps
> 10,000 times. That should be ample current for a starter motor. This
> relay is a little plug-in cube like a headlight relay. The coil draws
> only 130 ma.
>
> By contrast, even when a starter solenoid has no mechanical function,
> its coil draws about 3 amps. It's built heavily to switch off an
> inductive load. Hmmm... how about using an ordinary relay with diode
> protection?
Should work. As far as I can tell the only difference between a
solenoid and a relay is that a relay is a "switch" like device being
pulled onto the coil core thus making contact with a spring pulling it
off when deactivated; a solenoid moves the core in the coil (piston
like) to make contact and also has a spring to pull it back. I don't
know if there is a diode in there.
E Z Peaces
> On 09-12-21 22:40 , E Z Peaces wrote:
>> Alan Browne wrote:
>>> On 09-12-21 13:52 , E Z Peaces wrote:
>>>
>>>> The big problem with contacts comes not from closing but from opening
>>>> with an inductive load. There, the available voltage can be
>>>> theoretically infinite. A car starter uses a solenoid so that a spring
>>>> can break the arc quickly.
>>>
>>> The primary reason a car uses a solenoid is because the current is
>>> much too high to route via the ignition switch in the car. The cabling
>>> would be very thick, and the path so long as to make winter starting a
>>> problem in places where it's quite cold.
>>
>> That's why the solenoid isn't in the steering column.
>
> The solenoid is placed as close between the battery and the starter as
> possible to reduce power loss in the cables (and keep required cable
> diameter to a reasonable size). Likewise, most (all?) starters use the
> engine block as the return ("ground") side which is also connected to
> the battery with as short a cable as possible.
On Ford pickups I've seen, it's on the fender near the battery. If it
were on the starter motor, the cable length would be about the same.
>
> This is also why you boost a car with the return ("negative") lead
> connected to the engine block, not to the dead battery. (+ lead to the
> batter, typically).
If it weren't for safety, I'd clip to the battery to be sure of a good
connection.
>>
>> The Picker PC 7150 is an automotive relay designed to switch 300 amps
>> 10,000 times. That should be ample current for a starter motor. This
>> relay is a little plug-in cube like a headlight relay. The coil draws
>> only 130 ma.
>>
>> By contrast, even when a starter solenoid has no mechanical function,
>> its coil draws about 3 amps. It's built heavily to switch off an
>> inductive load. Hmmm... how about using an ordinary relay with diode
>> protection?
>
> Should work. As far as I can tell the only difference between a
> solenoid and a relay is that a relay is a "switch" like device being
> pulled onto the coil core thus making contact with a spring pulling it
> off when deactivated; a solenoid moves the core in the coil (piston
> like) to make contact and also has a spring to pull it back. I don't
> know if there is a diode in there.
Technically, it's a solenoid if it mechanically engages the gear of the
starter motor. In that case, it must be attached to the starter motor.
If it has no mechanical function, it's really just a contactor, but on
vehicles they are commonly called solenoids anyway. A contactor is a
relay built to control motors.
Nick Naym
Moore at fmo...@gcfn.org wrote on 12/22/09 11:38 AM:
> In article <hgog6c$l8j$1...@news.eternal-september.org>,
> E Z Peaces <ca...@invalid.invalid> wrote:
>> Tim Murray wrote:
...
...
>> I've been trying to imagine plugging in a USB device before en electron
>> has time to jump.
>
> Sorry, Grasshopper, that's _way_ too Zen a concept for this group. You
> want alt.zen.comp.ohm. ;)
ROTF!
--
iMac (24", 2.8 GHz Intel Core 2 Duo, 2GB RAM, 320 GB HDD) � OS X (10.5.8)
Nick Naym
alan....@FreelunchVideotron.ca wrote on 12/22/09 3:04 PM:
With enough current, _any_ voltage can kill you.
Nick Naym
Michelle Steiner at mich...@michelle.org wrote on 12/22/09 4:28 PM:
> In article <uNudnVj6g7z1u6zW...@giganews.com>,
> Alan Browne <alan....@FreelunchVideotron.ca> wrote:
>
>> 12 V can't kill you.
>
> It's not the voltage that kills; it's the amperage.
It's both.
Tom Stiller
Don't forget, E=I*R. For a given resistance, you don't get either
voltage or current without the other.
JF Mezei
> The human body, being mostly water with dissolved electrolytes, has a
> fairly low R.
Remember that we are ugly bags of mostly water :-)
(does this qualify as topic drift ?)
Richard Maine
Tom Stiller
Michelle Steiner <mich...@michelle.org> wrote:
> In article <tom_stiller-8683...@news.individual.net>,
> Tom Stiller <tom_s...@yahoo.com> wrote:
>
> > With enough current, _any_ voltage can kill you.
> >
> > Don't forget, E=I*R. For a given resistance, you don't get either
> > voltage or current without the other.
>
> The human body, being mostly water with dissolved electrolytes, has a
> fairly low R.
That doesn't change the fact that one can't get enough current with
_any_ voltage.
J.J. O'Shea
(in article <paul.nospam-0F5D...@pbook.sture.ch>):
If you're talking about the old CDC disk packs and disk drives like these
<http://www.bitsavers.org/pdf/cdc/discs/brochures/ProductLine_May73.pdf> I
can say that the 300 MB disk packs weighed 25 pounds each (and cost US$10,000
when new...) and the drives for them weighed in excess of 500 pounds and
were, yes, the size of a washing machine. A big washing machine. The first
place I worked for had three CDC 9790 units. We did not move them unless we
had to, and when we did, we got out the trolley and a couple guys from Motor
Maintenance. The damn things did move all by themselves when in operation
unless their feet were properly set. This tended to cause head crashes,
resulting in our needing to replace the disk pack ($10k, remember) and all 20
of the read-write heads at $512 each, plus recalibrating the drive with a
$25k engineering disk pack... and if any of the replacement heads weren't
properly set, the engineering pack might crash, requiring the replacement of
a all 20 heads _and_ getting a new engineering pack. That got old real fast
and we replaced them with 250 MB fixed disks which lived in one of the racks.
And, of course, we had to get out the trolley and the boys from Motor Maint
to move the silly things back to where they were supposed to be...
At about the same time I had sitting on my desk at home a Mac 128 updated to
Plusdom to which was attached a 40 MB drive. My Mac had 4 whole MB of RAM
(the $1.5 million supermini had 5.5 MB...) and a 32 bit CPU running at 8 MHz
(the supermini was 24 bit, yes, really, 24 bit, running at 5 MHz...) so my
home machine had a fairly significant fraction of the total storage available
to the supermini and was faster and had better graphics as well. (The
supermini had VT-100 class green screens, except for the control room, where
there were 19" colour screens for the system control staff...)
Of course, the smallest capacity thumb drive I still have has more capacity
than the disk pack, (512 MB...) and I can get a brand new 4 GB thumb drive
for under $15, probably for under $10 if I try.
--
email to oshea dot j dot j at gmail dot com.
Fred Moore
E Z Peaces <ca...@invalid.invalid> wrote:
> Technically, it's a solenoid if it mechanically engages the gear of the
> starter motor. In that case, it must be attached to the starter motor.
> If it has no mechanical function, it's really just a contactor, but on
> vehicles they are commonly called solenoids anyway. A contactor is a
> relay built to control motors.
Well, according to the dictionary which comes with the Mac a solenoid is
'a cylindrical coil of wire acting as a magnet when carrying electric'.
Many cars have 2 solenoids--one to close the circuit and one to throw
the Bendix gear between the flywheel and the starter motor cog wheel.
Some cars combine these functions to save money in the design.
Fred Moore
Alan Browne <alan....@FreelunchVideotron.ca> wrote:
> 12 V can't kill you.
With respect, Alan, yes it can if properly applied. It's just that a low
voltage is less likely to produce the current necessary to disrupt cell
function (permanently).
> Autos are transitioning to 42 VDC - in several years 12VDC will be a
> memory. And 42VDC was chosen, amongst other reasons, as it is too low V
> to harm anyone.
Having been zapped by voltages in the 40s numerous times while working
on telephones, let me say it can HURT and it can be deadly (I'm writing
to you from beyond the grave), though house current is worse.
High-voltage RF is probably the worst. The high frequency of RF allows
it to penetrate the skin and disrupt cell function more easily. Ask a
celluar biologist for the specifics.
48v (4x12) is what the telephone central office uses to ring your phone
(in the US and Canada) because the backup system is 48v. My
understanding is that 48v was chosen as a standard because it could
produce enough current to ring several of the old solenoid/bell ringers
in parallel and could easily be produced with the available lead-acid
batteries when the power went down. That's why it's a good idea to
maintain a wired landline in case of emergency power outages.
Nick Naym
Stiller at tom_s...@yahoo.com wrote on 12/22/09 11:01 PM:
You can grab the terminals of a megavolt voltage source and (assuming
nominal body resistance -- e.g., a few kilohms) still not be injured.
Nick Naym
Michelle Steiner at mich...@michelle.org wrote on 12/23/09 12:33 AM:
> In article <017a1ca4$0$3201$c3e...@news.astraweb.com>,
> JF Mezei <jfmezei...@vaxination.ca> wrote:
>
>>> The human body, being mostly water with dissolved electrolytes, has a
>>> fairly low R.
>>
>> Remember that we are ugly bags of mostly water :-)
>
> You may be ugly.
Bessie Braddock: "Winston,...you are disgustingly drunk."
Winston Churchill: "Bessie,...you are disgustingly ugly. But tomorrow I
shall be sober..."
Nick Naym
Stiller at tom_s...@yahoo.com wrote on 12/23/09 7:13 AM:
> In article <michelle-371A8A...@news.eternal-september.org>,
> Michelle Steiner <mich...@michelle.org> wrote:
>
>> In article <tom_stiller-8683...@news.individual.net>,
>> Tom Stiller <tom_s...@yahoo.com> wrote:
>>
>>> With enough current, _any_ voltage can kill you.
>>>
>>> Don't forget, E=I*R. For a given resistance, you don't get either
>>> voltage or current without the other.
>>
>> The human body, being mostly water with dissolved electrolytes, has a
>> fairly low R.
>
> That doesn't change the fact that one can't get enough current with
> _any_ voltage.
???
isw
Absolutely NOT true -- unless you define "killed" as not being a sort of
"injury". A million volts across, say, ten thousand ohms, will cause
about one hundred amperes to flow through your body. Then, when the heat
from that has damaged your skin (which is where all that resistance is),
the current will go up-- way up.
Kids, don't try this at home -- or any place else, for that matter.
Isaac
Alan Browne
> In article<uNudnVj6g7z1u6zW...@giganews.com>,
> Alan Browne<alan....@FreelunchVideotron.ca> wrote:
>
>
>
In order to move current, you need voltage to push it against resistance.
If you could get 12V right across the heart, it would hardly notice
anything at all even if the same system were conducting power somewhere
else at high current. IOW, the current follows the path of least
resistance, not most. And the human body is generally a poor conductor.
Defibrillators operate in the range of 200 - 1000 volts (direct against
the heart at the low range, outside the body at the high range).
And that's to _save_ your life, not end it. To be sure this has to be
applied correctly and for the right reasons.
Alan Browne
> In article<tom_stiller-8683...@news.individual.net>,
> Tom Stiller<tom_s...@yahoo.com> wrote:
>
>> With enough current, _any_ voltage can kill you.
>>
>> Don't forget, E=I*R. For a given resistance, you don't get either
>> voltage or current without the other.
>
> fairly low R.
>
See my other post.
Nick Naym
wrote on 12/23/09 12:34 PM:
Isaac, the question is not the voltage of the source, but the actual voltage
that is applied to the load. The two differ by the internal impedance of the
source.
isw
I'm perfectly aware of that. If the internal impedance is high, then it
hardly qualifies as a "megavolt source", since you can never actually
get that out of it for any useful purpose -- such as touching it 8^}
More properly, a source such as what you are describing probably should
be called a "quasi-constant current source", since over quite a large
range of load resistance, the voltage will adjust as necessary to cause
a constant current to flow. Do the numbers on a megavolt source behind a
hundred million ohms (the "internal impedance" as you say); over what
range of load resistances will the current be within one percent of ten
milliamps?
Isaac
isw
Nick Naym <nicknaym@[remove_this].gmail.com> wrote:
> In article tom_stiller-2DEC...@news.individual.net, Tom
> Stiller at tom_s...@yahoo.com wrote on 12/23/09 7:13 AM:
>
> > In article <michelle-371A8A...@news.eternal-september.org>,
> > Michelle Steiner <mich...@michelle.org> wrote:
> >
> >> In article <tom_stiller-8683...@news.individual.net>,
> >> Tom Stiller <tom_s...@yahoo.com> wrote:
> >>
> >>> With enough current, _any_ voltage can kill you.
> >>>
> >>> Don't forget, E=I*R. For a given resistance, you don't get either
> >>> voltage or current without the other.
> >>
> >> The human body, being mostly water with dissolved electrolytes, has a
> >> fairly low R.
> >
> > That doesn't change the fact that one can't get enough current with
> > _any_ voltage.
It's lucky you are still alive. For extra credit, explain why power line
technicians wear all that protective gear, when they work on live
high-tension lines.
Isaac