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Center pin on power adapter plug - how does it work ?

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Externet

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On a laptop power jack,

The center pin senses/communicates something; is it
- for the power adapter to sense some feedback from a laptop or
- for the laptop to sense something from the power adapter
- or both ?

And what is the protocol/architecture/voltages of such 'data' pin under varied conditions ?

----> **broken link removed**

My Compaq has it, and most HP/CQ too
 
You need 2 pins, power and ground, but LAPTOP MFRS are getting clever. Power packs have been known to be laptop specific.

Battery packs are more complex. Cell charge equalization and temperature is needed along with a 'gas guage'.
 
Yes, 2 pins for (+) and (-) But the post is for the third pin.
Sorry, I do not know what MFRS means. This has nothing to do with battery packs :confused:
 
MFRS - Manufacturer's.

One of the things that they could do is to use the I2C bus (Inter IC Communications) and read a value from EEProm, but that might be too easy. They could also have a challenge/response set-up where the responses are different depending on what's sent sort of like remote controls with revolving codes.

The idea is to make sure the laptop gets the right battery pack and to make sure the manufacturer supplies it.
 
I think that Dells use a Dallas 1-wire EEPROM in the power supply that the laptop reads. Unless it likes what it sees, it assumes that the power supply isn't from Dell so refuses to charge.

Which would be fine if Dell used reliable connectors.
 
Hi Externet

One pin is ground, one pin is power + and what exactly the third pin is would be a function of the laptop. We can say it is a data pin but the actual data or protocol will depend on who made the system. For example I have a Dell Precision M90. It uses a 130 watt AC adapter. If I connect for example a 65 watt Dell manufacture adapter it knows the difference and is real quick to tell me. Today's laptops use smart batteries and smart AC adapters. As KISS mentions the system can monitor battery level, temperature and other parameters to adjust the rate of charge accordingly. I do not believe there is any single communication protocol but whatever a given manufacturer chooses for their specific product.

Ron
 
Hi Ron, thanks.

Very little information found about HewlettPackard/Compaq; the adapter central pin puts out DC and feeds an A>D converter in the laptop to decide if goes into charge, charge and operate or operate only as in airplane mode. The laptop schematic labels such control line as "limit signal"
Has nothing to do with the battery pack sensing at all as far as I know.
What am after is the table of voltages-to-actions. It a very elusive subject.
 
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