[Ham-Mac] Using external battery to power a PowerBook

[David Allred]

>I want to power my G3 Pismo PowerBook from external
>batteries for an extended period (say, an ARES outing of 1
>to 2 days).

>Regardless of whether I had one battery, or two batteries
>in series, the current drawn by the G3 when the external
>power cable was attached was about 25 mA.
>
>Ideas anyone?
>
>Dick, KM4ML
>


Dick:

When I got my new 15" Aluminum PowerBook, with it's new
smaller power connector, I wanted to know if I could cut
the cable in half, put on my own connectors on the cable,
and use my older Apple 24 Volt adapters. Further, why
couldn't I use any 24 Volt source?

Answer: You CAN stuff anything from 15 to 24 VDC directly
into your PowerBook, but you don't want to do it.

Here's what I know about getting DC into PowerBooks:

The following applies to current PowerBooks using the newer
smaller three-circuit plug inside a shell. Older larger
three-circuit plug power connectors are similar. Way old
PowerBooks are two circuit and much simpler.

The PowerBook power connector plug is
Tip-Ring-Sleeve-Shell. If the shell were not in the way,
you would see a plug similar to an eighth-inch stereo plug
(Tip-Left, Ring-Right, Sleeve-Common).

As used for the PowerBook, the plug is wired:

Tip - not connected Ring - Ground Sleeve - +24 VDC Shell -
Power Adapter Identifier

Here's where it gets tricky. The voltage on the shell tells
the PowerBook power manager circuit what to expect from the
adapter that is plugged into the power jack.

The reason your PowerBook wouldn't suck current is likely
due to the absence of the PS ID voltage on the shell of the
connector. The PMU gets no information so it never turns on
the external power input.

This ID voltage on the shell is expected to be in the range
of 0.79 to 3.25 VDC and will identify the power adapter as
a 65W, 45W, or Aircraft Adapter. And, no, it's not a linear
relationship.

Most of the details for the sense circuit functionality can
be seen in Apple Developer Documentation Technical Q&A
QA1266: Power Adapter Sensing for the 17" PowerBook
<http://developer.apple.com/qa/qa2001/qa1266.html>.

This TechNote has schematics of the PMU (power management
unit) sense input and wiring for the sense output circuits
on the 65W, 45W, and Aircraft adapters.

Apple rates their power adapters by "Wattage." This isn't
very useful to us, but makes it simpler to specify which of
their adapters will work with which PowerBook.

The full list of Adapters can be seen at the Apple support
site <http://kbase.info.apple.com>. Search for Article
16168: PowerBook and iBook: AC Adapter, Battery, and
Charger Identification.

After looking at the circuitry in the PowerBook and the
power adapters, I decided that I could design a circuit
that would mimic a 65W, or 45W adapter. But after
considering over-voltage and static protection for the
PowerBook inputs, I opted NOT to make my own input cable
system.

What I DID do was get a DC-DC adapter. This is not as power
efficient as a direct DC Voltage input, but it gets around
the sense circuit construction and will run the PowerBook
AND charge the battery from a 12 Volt input. I use it for
auto, aircraft, and can plug it into my 12 V bus in the
radio room.

The DC-DC adapter I selected is actually dual input and
accepts AC 100 - 230 V, 50 - 60 HZ, and DC 11.75 - 16 VDC.
It's a bit pricey, but means that I need only one adapter
when traveling. It also has a tap for low current output
adapters for cell phones and PDAs. I might try that output
for HT charging...

My adapter is the Juice from iGo <http://www.igo.com/> and
is identical, other than the case, to one from another Mac
accessory provider. (I saw it in the Apple Store in
Cupertino, but I didn't write down make and model.)

For more DC-DC adapters, go to Made-for-Mac at the Apple
site <http://guide.apple.com>, and search for "powerbook
power adapter."


Dick, If you do decide to "roll your own," let us know how
it turns out.

73, David N1EXQ


     |  J. David Allred
     |
     |  P H O T O N
     |
     |  allred@photoninc.com
     |  Photon, Inc.
     |  617-661-9046
     |  www.photoninc.com