# How can PC detect AC adapter brand?

1. Mar 24, 2016

### Staff: Mentor

When I booted my laptop today, I saw a strange message for the first time.

My adapter is a Dell, so I unplugged, re-plugged, and it worked OK.

I find this behavior by manufacturers offensive, but at the same time I admire their cleverness at implementing it. Assuming that the charging port on the laptop has only $+V_{DC}$ and ground, then how do they detect the brand of adapter?

I can speculate that the power supply taps out a Morse-Code-like signal on $+V_{DC}$ when first connected (MY NAME IS DELL).

Does anyone know, in fact, how they actually do it?

2. Mar 24, 2016

### jerromyjon

Mine has been doing that intermittently for at least a year, yet it always powers the laptop, and at some random times it will charge the battery until full. The only other facet I noticed was the output wattage is stated as required to be 65 watts which I have not tested to see what my adapter supplies, and my wife's Samsung Galaxy tablet has a similar problem which only high output USB chargers will function correctly.

Last edited: Mar 24, 2016
3. Mar 24, 2016

### jim hardy

I disassembled a HP power adapter several years ago(2010)
and posted results on this thread

look for post that begins with "wow is my face ever red"...

Barrel connector has three contacts

outer barrel, power supply return
inner barrel, which is power supply positive on the Pavillion 7
center pin which is communication between computer and the SMPS power supply.
What attracted my attention to it is center pin is way too small to conduct current required by laptop.
And it doesn't affect power supply voltage as would a "remote sense" wire.
.... so what's up ?
good thing i wrote it down then, we found: "It reads 19 volts to common with a ten megohm voltmeter but only 5 volts with a 2kohm/volt meter so it's capable of only a few microamps."
Clearly it could be pulled low from either end for communication.
It is NOT remote sense. There's a computer embedded in that charger and it "talks" to computer in the laptop.
i thought at the time the computer and charger were just exchanging information as to state of CPU's battery charge and temperature of the charger , so CPU would thoughtfully not overheat charger ..

Those wires are fragile. Yanking the low voltage cord to unplug it will break one of the shields , as described in our post.
Most internet advice was "replace the wire inside the computer" which we did , to no avail.
You'll read 19 volts on center pin with a DMM which makes you think the charger is okay. A cheap analog meter reveals however that center pin is not power.
We re-soldered the broken shield wires inside the charger cable, , repaired jacket with heat-shrink and epoxied the charger back together.
We then fastened charger to a plank and made strain relief for the cable out of rubber surgical tubing . Ugly but effective.

We weren't alone. Son found our blatantly home-brewed repair to be a chick magnet at the school library ! He fixed several more of them....

4. Mar 24, 2016

### Staff: Mentor

http://assets.diylol.com/hfs/fc6/51c/5e5/resized/arte-johnson-meme-generator-verrrrry-interesting-fd236f.PNG?1406148374.jpg [Broken]

Last edited by a moderator: May 7, 2017
5. Mar 24, 2016

### jerromyjon

Commencing disassembly... resistance is futile!

6. Mar 24, 2016

### jim hardy

Veeerryyyy Interesting...

7. Mar 24, 2016

### jerromyjon

Any insight on jittery FPD cause/corrections? Alternative displays are flawless but the built-in screen gets trails through it... I'm going on the hunch that the fractured shielding could leak interference.

8. Mar 24, 2016

### jim hardy

I'm not very computer literate.....
This is my software debugger tool.

I'd look at the ends of whatever cable goes through the hinge to connect FPD to motherboard. Likely it's a thin flat flex cable. Hopefully you'll fix it with a wiggle-unplug/reinsert. Clean with alcohol while it's out. Don't use a pencil eraser, you're apt to remove its thin gold plating .

old jim

9. Mar 24, 2016

### jerromyjon

on my phone so I'm ugh but I want to remove the damaged section and resolder the intact remainder to the pcpu I hope I don't trip!

10. Mar 24, 2016

### jim hardy

Our breaks were in these two spots

share what you find ?

11. Mar 24, 2016

### meBigGuy

I'm not advocating hacking the protocol, but here it is described.

Many chargers has some level of communication, for example getting an ipad to charge at full rate requires proper loading by the charger on the USB data pins.
The USB battery charger specification has a sub-threshold protocol to define the charger capacity.
Sony has its own protocol.

For example, look at figures 1,2,3 on this datasheet: http://datasheets.maximintegrated.com/en/ds/MAX14578AE-MAX14578E.pdf

12. Mar 24, 2016

### jerromyjon

Those pesky little snakes have heads I revamped.

I figured the little blue one in the middle was good enough around the edge of the hole, the wires had what looked like "sticky" conductor clips (perhaps to hold the connections during soldering?) I just held them still in the holes after sanding them until "coppery" looking rather than silver so the solder and flux core works to get a good connection. 15 minutes until full charge!

Next, a custom PCB was made with two Dell DC jacks and an MSP430. This passes power through the board, but uses the MSP430 to send fake data to the computer. The demo shows off a 90 W adapter pretending to run at 65 W. With this working, you could power the laptop from any supply that can meet the requirements for current and voltage.

Sounds like step 2. 20v lithium ion powertool batteries for a "backup" power supply. I need an inverter?

Last edited: Mar 24, 2016
13. Mar 24, 2016

### davenn

That's so common on so much gear ..... the cable always breaks within or just outside the strain relief section
seen it over and over again

Dave

14. Mar 24, 2016

### jim hardy

I do.
Fight fire with fire, fight extortion with civil disobedience.

Congratulations on your repair , jerro....!

15. Mar 24, 2016

### jerromyjon

Thanks!

16. Mar 24, 2016

### davenn

WOW, just learnt something !!
My HP Pavilion DV6 laptop has been giving the ... "Not a HP PSU" for some time, tho it was still charging OK

and I just had a look at the plug, and as you commented it is 3 separate conductors and the centre pin was bent over,
not connecting and thus causing the error message. A little gentle adjusting and the pin is straight again

a crappy pic trying to get a close up, but hopefully good enough to show

Now depending on if they really want to get actual data from the PSU, the sense pin needs to be nothing more than connected to a
resistor to the negative rail and the computer looks for that terminal resistor ... that's the simple and easy way

Dave