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what's the 3rd conductor for on Dell laptop P/S?

J

jcomeau_ictx

Jan 1, 1970
0
Hi, I want to be able to run my Dell Inspiron 600m using a custom-made
external 18V battery pack at next year's Burning Man. And I can do
this, but the internal battery will not charge from it without that
3rd, inner conductor of the triaxial cable carrying some unknown
signal. I don't have an oscilloscope any more, and would rather not
have to buy one. Has anyone hacked into this and knows what's being
sent over that 3rd conductor, so I can rig a circuit to emulate it?
Googled and found nothing. Thanks -- jc
 
C

Charles Schuler

Jan 1, 1970
0
jcomeau_ictx said:
Hi, I want to be able to run my Dell Inspiron 600m using a custom-made
external 18V battery pack at next year's Burning Man. And I can do
this, but the internal battery will not charge from it without that
3rd, inner conductor of the triaxial cable carrying some unknown
signal. I don't have an oscilloscope any more, and would rather not
have to buy one. Has anyone hacked into this and knows what's being
sent over that 3rd conductor, so I can rig a circuit to emulate it?
Googled and found nothing. Thanks -- jc

I can't directly answer your question but will share something with you. If
you take apart a modern Li-Ion battery pack (for a notebook computer) you
will find several integrated circuits and lots of other stuff. Those darned
things are complicated!
 
G

Guest

Jan 1, 1970
0
all i can say us DONT mess with the charge terminal. most laptop batteries
have highly integrated charge/drain monitoring circuitry that will get
TOASTED if you try to defeat it.

u are far better off stocking up on ten or so extra correct battery packs.
or get a bonified ac adapter that inserts in same place as battery pack.

they are not just batteries anymore, they are power systems all inside the
plastic.

alternately, use a few charged 12vdc car batteries, a 12vdc to 120 vac
inverter and a standard dell 120vac adapter. yes, its ugly but you might
get a few good weeks of performance from the setup :))
 
J

jcomeau_ictx

Jan 1, 1970
0
Thanks for the advice, but I'm willing to take the risk. Carrying
around a few hundred pounds of batteries is not my idea of portable
computing... my bicycle trailer is going to be full enough with 10
gallons of water plus my camping gear.
 
M

Mike Harrison

Jan 1, 1970
0
I think I once read somewhere that the power supply contains a Dallas chip
in a transistor-style TO-92 case, that contains a serial number, to prevent
power supplies with the wrong profit margin^H^H^H^H^H^H^H^H^H^H^H^H^H
specifications from being used. Better get yourself a logic analyser, or a
DC-AC inverter.

Chris

Yes - it's a dallas chip to identify the PSU type, in particular whether or not it can supply enough
current for the device it's connected to - there are different Dell PSUs with different current
capabilities with the same plug.
These Dallas chips can be emulated fairly easily with a PIC/AVR etc. as long as you don't need the
1-wire powering facility, which you don't in this case as you have other power available.
 
G

Guest

Jan 1, 1970
0
also, a good alternative may be a correctly sized solar panel (or two) with
circuitry to charge /offsett battery drain.
 
J

jcomeau_ictx

Jan 1, 1970
0
Finally I rigged up a cable to send the signal to the microphone jack
(through a resistor of course!) of the same computer, and used it as
an o-scope with Audacity. All it does is send a few pulses, not even
remotely resembling ASCII as I was hoping. The line stays at 3.1 to
3.2VDC when there are no pulses (as seen with a VOM), and I can't tell
whether they are talking back and forth or just the P/S is sending the
pulses. I believe the computer is generating the 3.2 because the 3rd
line was at 0VDC until I plugged the power cable into the computer; so
that would presumably make it the bus master? I only bothered to
capture a few seconds because after about 8 seconds the pulses ended.
I guess it might be sending at 140Kbits rather than 14, which would
account for why I can't see any data at the 44K capture speed of the
sound
card. Well, thinking out loud... just wanted to share what little I'd
found out.
 
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