Swapping power adapters between laptops

On May 24, 2006, at 10:40 AM, pagesbyjoy wrote:

> Well, I have both an iBook G3 and a MacBook Pro. When the iBook was
> my only
> machine, I usually just left the AC power cord (the cord that
> attaches to
> the adapter and plugs into the wall) plugged in behind my desk and,
> when I
> went mobile, removed the adapter and took it along with the small
> power plug
> attachment. Now I'm wondering if I can use either of my cords with
> both
> laptop adapters. How can I find out?

The cords are definitely interchangable between the MacBook Pro,
PowerBook, and iBook chargers. I'm sure they are the same for the
MacBook, as well.

Den 25/05/2006 kl. 0.01 skrev Walls, Bryan (MSFC-IS30) mdi:

> The cords are definitely interchangable between the MacBook Pro,
> PowerBook, and iBook chargers. I'm sure they are the same for the
> MacBook, as well.

Confirmed.

Even the cord from the transistor radio works on all of them. A very
smart way of getting a plug if you end up in a country with a
different socket, btw, as such a cord is less than 2$ :-)

Kind regards,

Kim

On 5/24/06 at 3:01 PM, Bryan.Wallsnasa.gov (Walls, Bryan (MSFC-IS30)
mdi) wrote:

> On May 24, 2006, at 10:40 AM, pagesbyjoy wrote:
>
> > Well, I have both an iBook G3 and a MacBook Pro. When the iBook was
> > my only machine, I usually just left the AC power cord (the cord
> > that attaches to the adapter and plugs into the wall) plugged in
> > behind my desk and, when I went mobile, removed the adapter and
> > took it along with the small power plug attachment. Now I'm
> > wondering if I can use either of my cords with both laptop
> > adapters. How can I find out?
>
> The cords are definitely interchangable between the MacBook Pro,
> PowerBook, and iBook chargers. I'm sure they are the same for the
> MacBook, as well.

Not completely.

Some of the older white Apple power adapters had a two-prong plug on the
AC power cord (the actual long cord, not the small plug with flip-out
prongs); all the newer ones use a three-prong cord. While the two-prong
cord will work with the newer adapters, the three-prong cord is keyed so
that it won't work with the older adapters.

To tell the difference, look at the socket on the adapter; the older
adapters have an 'indent' on both long sides of the oval-shaped socket,
while the newer adapters (like the MacBook Pro's) have an indent on one
side and are smooth on the other.


Travis Butler
tbutlermac.com

...Cats are the proof of a higher purpose to the universe.

On May 24, 2006, at 3:01 PM, Walls, Bryan (MSFC-IS30) mdi wrote:
>
> The cords are definitely interchangable between the MacBook Pro,
> PowerBook, and iBook chargers. I'm sure they are the same for the
> MacBook, as well.

While this may be true for the portable power adapters, it is not
true in general. I discovered to my dismay that the cord associated
with the adapter for a 12-inch Powerbook (DVI) cannot be used on an
Airport Express or iPod charger, despite their similar form factor.
The cord is flat on one side with a grove on the other side mating
with a projection between the contacts on the Powerbook brick.
However, the other bricks have projections on each side. So I now
travel with a small Ikea power strip rather than the cord.

Alan Forkosh Oakland, CA
aforkoshmac.com

Travis Butler (tbutlerbirch.net)wrote:

> To tell the difference, look at the socket on the adapter; the older
> adapters have an 'indent' on both long sides of the oval-shaped socket,
> while the newer adapters (like the MacBook Pro's) have an indent on one
> side and are smooth on the other.

Thanks to everybody for the feedback and especially to Travis for this
detail. I do indeed have one of the older iBooks whose adapter has two
indents, so it's good to know I can safely plug the older cord into the MBP
adapter but can't accidentally use the 3-prong plug on the older adapter.
Good design, that.

joy

On 26/5/06 18:22, Joy Freeman wrote:
> Thanks to everybody for the feedback and especially to Travis for this
> detail. I do indeed have one of the older iBooks whose adapter has two
> indents, so it's good to know I can safely plug the older cord into the MBP
> adapter but can't accidentally use the 3-prong plug on the older adapter.
> Good design, that.

This has been bugging me for a while. Can someone more knowledgeable than me
explain why this design decision is actually useful? It seems to me to be
bass-ackward. Apple have made it impossible to plug the three-wire (earthed)
cord into the older adapter; thus they have saved the plastic mushroom from
being exposed to the earth. But they do allow the newer adapter to be plugged
into the old (or any standard figure-8) two-wire cord; thus an adapter
designed to be earthed is allowed to function without being earthed.

Shouldn't this be the other way, if at all? Please help me understand.

- Ben

On May 26, 2006, at 10:22 AM, Joy Freeman wrote:

> Thanks to everybody for the feedback and especially to Travis for this
> detail. I do indeed have one of the older iBooks whose adapter has two
> indents, so it's good to know I can safely plug the older cord into
> the MBP
> adapter but can't accidentally use the 3-prong plug on the older
> adapter.
> Good design, that.

Since I noticed the restriction, I've wondered what function does the
3rd (grounding) prong serve when the adapter itself only has 2 wires
coming out and the non-corded plug only has 2 prongs?

Alan Forkosh Oakland, CA
aforkoshmac.com

--On May 27, 2006 11:50:52 AM -0700 Alan Forkosh <aforkoshmac.com> wrote:
> Since I noticed the restriction, I've wondered what function does the
> 3rd (grounding) prong serve when the adapter itself only has 2 wires
> coming out and the non-corded plug only has 2 prongs?

It provides an emergency ground for the transformer in the brick. Probably
a good idea as you're more likely to kick that into the water dish than the
laptop. The adapters I've seen this on have a metal stud that you slide the
cable over, that is probably what connects to the third prong.

--On May 27, 2006 11:50:52 AM -0700 Ben Rubinstein <benrcogapp.com> wrote:

> into the old (or any standard figure-8) two-wire cord; thus an adapter
> designed to be earthed is allowed to function without being earthed.
>
> Shouldn't this be the other way, if at all? Please help me understand.

This was probably done by accident. The 3rd prong on devices is not
normally used, it is an emergency ground. When an electrical component in
the device shorts it may connect to the case it's held in. At this point
the case is electrified and the electricity is seeking a shorter return to
ground than currently available. If a person touches the case and provides
a shorter path, they can be electrocuted.

The 3rd prong is attached to the case internally and if a short occurs, the
3rd prong will almost always be a better path to ground than a person
touching the case, thus saving them from electrocution.

So the device operates, but it is a safety hazard to use an ungrounded
cable on a device that expects a ground cable to be there.

Also just FYI, Ground Fault Interrupters don't use the ground cable at all.
They compare the current in the hot cable (going into a device) with the
current in the neutral (going out of the device). If they are different it
trips. This is even safer than the 3rd prong solution because it will
detect faults to any ground, not just the 3rd prong.

On May 27, 2006 at 11:50 am, BenR wrote:

Can someone more knowledgeable than me explain why this design decision is actually useful? It seems to me to be bass-ackward.

Not sure if "opinionated" counts for "knowledgeable", but here's my take on the issue, fwiw... If you have both three-prong and a non-grounded power cords, and bricks which either can, or can't, actually use that grounding connection, which is the "safer" way to do things? Have a brick which has the ability to be grounded, but is clearly not because the cord does not allow it, or a brick which looks like it is grounded, even though it has no possibility to do so, given that the internal stud is plastic, not metal?

For myself, I prefer the current design, as it forces me to know what I'm getting myself into.

As an aside, you'll note that the iPod and AirPort Express both use those fold-in 2-prong adapters, so (while I don't have one right in front of me to confirm) probably are not wired to use the ground.

On 27-mei-2006, at 20:50, Ben Rubinstein wrote:

> On 26/5/06 18:22, Joy Freeman wrote:
>> Thanks to everybody for the feedback and especially to Travis for
>> this
>> detail. I do indeed have one of the older iBooks whose adapter has
>> two
>> indents, so it's good to know I can safely plug the older cord
>> into the MBP
>> adapter but can't accidentally use the 3-prong plug on the older
>> adapter.
>> Good design, that.
>
> This has been bugging me for a while. Can someone more
> knowledgeable than me
> explain why this design decision is actually useful? It seems to
> me to be
> bass-ackward. Apple have made it impossible to plug the three-wire
> (earthed)
> cord into the older adapter; thus they have saved the plastic
> mushroom from
> being exposed to the earth. But they do allow the newer adapter to
> be plugged
> into the old (or any standard figure-8) two-wire cord; thus an adapter
> designed to be earthed is allowed to function without being earthed.
>
> Shouldn't this be the other way, if at all? Please help me
> understand.

It's the same here in the Netherlands with wall sockets. Plugs with
earth prong can be put into unearthed wall sockets, but not the other
way around (except for two-prong plugs that are connected to "doubly
isolated" devices, which are assumed to be so safe that they don't
need an earth connection). The rationale for this is that earthed
sockets were usually placed in rooms with higher electrocution
hazard, kitchens, garages, etc. Then it would be unsafe if an
unearthed device could be used in such a room. This is the official
explanation. I believe there is also a more mundane reason: when
earth plugs and sockets were introduced it would be unacceptable if
the newer devices with earth plug could not be used in houses with
only unearthed wall sokets.

Kees