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

[Dick Rucker]

on 1/26/04 6:15 PM, David Allred at allred@photoninc.com wrote:


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

I'm beginning to think you are right, but I still am intrigued by the notion
of avoiding the DC-to-AC-to-DC conversion process and the attendant
inefficiencies and RF noise that might accompany it.
 
> 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).

Arrgh!  The shell on the plug that I modified to do the job the wrong way is
not easily reclaimable.  It's true that an ordinary 1/8" audio stereo plug
will work just fine, but its the shell that's hard to replicate.
 
> 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.

Thanks for the info and the pointer to Tech QA1266.  What I don't understand
now is where the voltage sense and battery charging circuitry is located in
Apple's yo-yo style power adapter.  There are only two wires coming from the
yo-yo's 110 vac to 24 vdc converter:  white with +24 vdc on it and the
shield wire which completes that circuit.  There are two wires that come out
of the plug, plus one for the shell.  Where is the circuitry that lies in
between physically?  I sure didn't see it inside the power plug that I tore
apart to get the shell.

> 
> 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.

That's probably what I will do, once I get over the urge to roll my own
solution.


> 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.)

The Juice adapter looks attractive:  $120 list, but available for $85 from
Amazon.com.  One thing that concerns me:  There were two consumer reviews at
Amazon.com, and both warned that the connector assembly used to plug into
the G3's external power jack is unreliable.  One said his broke off after 4
uses.

Comments?

Dick