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

[Dick Rucker]

on 1/25/04 11:50 AM, Steve Weber at kd9bo@mac.com wrote:

> Dick, if you come up with an answer, please post it to the list.  I
> have four or five power supplies that have opened at the computer end
> of the cable.  Those cables are incredibly flimsy!

They sure are!  I'm amazed that Apple blew that design decision so badly.


> 
> Xbattery indicates that my G4 powerbook battery voltage ranges from
> 16.7 to 13.9 volts, so a single 12v gell cell battery would not be
> enough.
> 
> Steve KD9BO

But if you do a search on Google for PowerBook G3 batteries for the Pismo,
you can find them ranging from 12 up towards 24 volts, so it would seem that
it is designed to cope with a variety of voltage-current sources.

Dick, KM4ML


>> I want to power my G3 Pismo PowerBook from external batteries for an
>> extended period (say, an ARES outing of 1 to 2 days).  What I have
>> determined so far is:
>> 
>> The external power adapter for the G3 is rated at 24 vdc at 1.875 amps
>> 
>> Catalog listings for replacement internal batteries for this PB seem to
>> range from 10 to 12 volts, and are quite expensive even for modest
>> capacities, relative to the gel cell batteries available at hamfests.
>> 
>> Since I have a pair of 12v, 38 AmpHr batteries that aren't being used for
>> anything else, I thought if I could rig a connector that would fit the power
>> adapter jack on the back of the PB, then I could supply it with either 12v
>> or 24v dc that way.
>> 
>> I obtained a burned-out yo-yo power adapter for a Pismo, cut off its plug to
>> the G3, and then tried to find out how it was connected.  Since the yo-yo
>> power supply was good, it showed around 24 vdc across the white center
>> conductor and the shield, with the center conductor positive.
>> 
>> The plug was another matter.  Since it had shorted and burned out right
>> where the cable entered the plug, I cut material away until I found two
>> small wires potted in a sleeve and leading to what amounts to an 1/8" stereo
>> audio plug inside a cylindrical sleeve.  The sleeve connected to the shield
>> on the cable.  The white covered wire was connected to the inner-most ring
>> of the plug, but I couldn't tell whether the black was connected to either
>> the middle ring or the tip.
>> 
>> So I took the simple-minded approach and made up a new cable with a
>> connector for either one battery, or two batteries in series, and applied
>> the positive side to the inner-most ring on the plug and the negative side
>> to the cylindrical sleeve.
>> 
>> I booted the G3 from its internal battery, then plugged in my external
>> batteries, and monitored the current drawn.  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.  So obviously, the G3 was
>> still using the internal battery and ignoring the external supply.
>> 
>> That makes me think that the black lead was connected to either the tip or
>> the middle ring and has a role to play in getting the G3 to accept power
>> from the external power jack.
>> 
>> Ideas anyone?
>> 
>> Dick, KM4ML
>> 
>> 
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> 

-- 
Richard A. "Dick" Rucker
City of Fairfax, VA