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My HP Pavilion 27C Monitor and my HP Notebook 15 both have similar types of AC adapter that supplies 19 volts, but they both have that third wire in the middle, also. I am measuring 0 volts on it, on the monitor supply.

Everything works great. I am just asking for advice on what kind of circuit I need to supply whatever signal that third wire provides. Or, even better, can I just ignore it?

I'm starting with a 24 volt battery bank connected to a solar power system that varies in voltage from 23 to about 30 volts.

The goal, obviously, is to convert the Pavilion 27C monitor to run on DC so I don't incur the losses of going through both the inverter and the AC adapter. And for times when the inverter is off, like at night.

I need to design a way to use this power for this device.

I have looked at many web sites that have intricate circuits but am hoping for something simpler that can handle the voltage variations nad still put out a pure 19 volts.

In searching around I found and bought this 24-to-19 volt regulated converter. Here is the link to the converter: 24-to-19 volt converter.

enter image description here

The 19 volts seems to be very steady so far. It actually seems to tolerate the whole voltage range the solar MPPT controller puts out to the battery bank.

So maybe the power supply part is going to be OK.

But what about that third center wire? I don't know what it does or what to do with it. I don't know what the devices want from it.

My HP laptop uses the same voltage and has the same plug with the same third wire in the center, and I would like to convert it also. But I will start with the monitor.

So my question is: What do I do about that third wire? Can I simply cut into the cable and provide power to the two obvious wires that are +19 and Gnd, and just ignore the center wire? Or, if not, what can I do to make this work?

Especially for the laptop, what circuit will I need to supply that third wire with whatever the laptop is looking for?

Please help.

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closed as off-topic by Ignacio Vazquez-Abrams, Brian Carlton, laptop2d, uint128_t, Wesley Lee Apr 9 '17 at 3:43

This question appears to be off-topic. The users who voted to close gave these specific reasons:

  • "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – laptop2d, uint128_t, Wesley Lee
  • "Questions on the repair of consumer electronics, appliances, or other devices must involve specific troubleshooting steps and demonstrate a good understanding of the underlying design of the device being repaired. See also: Is asking on how to fix a faulty circuit on topic?" – Ignacio Vazquez-Abrams, Brian Carlton
If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ The screen and laptop can't tell what is powering them, they need to have the same regulation which is 19V, make sure the current that the screen an laptop is sinking is less than what the source can supply. \$\endgroup\$ – laptop2d Apr 5 '17 at 21:46
  • \$\begingroup\$ Good point. I actually have two of the 24-to-19 converters. The monitor only takes 26 Watts, so I think it should be enough. Although I am not so sure it is true they can't tell what is powering them. Maybe the screen, at least, won't care. \$\endgroup\$ – SDsolar Apr 6 '17 at 0:12
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    \$\begingroup\$ Yes you can try it but turn down brightness to avoid overheat 24-19V adapter \$\endgroup\$ – Sunnyskyguy EE75 Apr 6 '17 at 18:55
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    \$\begingroup\$ waiting for your laptop test results with dumb charger and more details of same. \$\endgroup\$ – Sunnyskyguy EE75 Apr 7 '17 at 1:40
  • \$\begingroup\$ OK, so far I am starting with the monitor. It has the same connector as a Dell.. When I cut the wire I found Black, White, Blue. With Black as negative, I am finding 18.9 Volts on each of the others. But with the power supply unplugged, I am not finding continuity between white and blue. It is like there are two power supplies. On the connector side, black is the outer shell, white is the inner shell, and blue is the wire. So I will start by putting voltage on just the shells. \$\endgroup\$ – SDsolar Apr 7 '17 at 9:01
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I have an HP laptop (EliteBook 8570) which happily powers up and charges from generic 2-wire "Universal chargers". I also used to have a laptop which would not charge and report an incompatible charger in the very same situation. I would definitely check in which situation you are before cutting the cables.

Reusing an original EEPROM IC from the PSU you have (like Ali Chen suggests) is a risky business: you'll only have one shot at every step, and missing it will leave you without a working power supply.

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    \$\begingroup\$ Does your 8570 model have a 3-pin jack, or a regular two-pin? I have seen both on different HP and CPQ models. If there is a center pin, HP calls it "smart adapter". Older DELLs use serial 1-wire communication for the purpose of identification. The HP seems to have some analogish form, I am not sure. From Google sources, it looks like it is a simple resistor-based schema, 200k to 19V indicates 90W adapter. \$\endgroup\$ – Ale..chenski Apr 6 '17 at 7:40
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    \$\begingroup\$ @AliChen I've never seen a "regular two-pin" connector on an HP laptop. All laptops I've seen have a middle pin. \$\endgroup\$ – Dmitry Grigoryev Apr 6 '17 at 7:43
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    \$\begingroup\$ There are different classes of HP laptops, consumer and business. Compaq/HP have regular jacks with no center pin, although with a bit smaller outer diameter than the regular "5.5mm" power jack, so it is frequently difficult to find a fit. But you need to tell this to Tony :-) \$\endgroup\$ – Ale..chenski Apr 6 '17 at 7:58
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    \$\begingroup\$ @AliChen The OP claims he does have the center pin (which may or may not be used to disable third-party chargers), and the simplest way of knowing whether dumb chargers will work is to try. \$\endgroup\$ – Dmitry Grigoryev Apr 6 '17 at 8:16
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    \$\begingroup\$ It looks like a coaxial centre pin barrel connector in user manual phot in my answer unless it has a square metal shield, not clear. \$\endgroup\$ – Sunnyskyguy EE75 Apr 6 '17 at 15:45
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The answer for the monitor is yes. I just cut the cable and put power to it and it works.

It has the same connector as a Dell laptop: Two shells and a wire.

When I cut the cord I found Black, White, Blue.

With Black as negative, I find 18.9 Volts on each of the other two wires.

But with the power supply unplugged, I do not find DC continuity between white and blue. Nor do I find a simple resistance.

On the connector side, black is the outer shell, white is the inner shell, and blue is the wire.

So I put voltage on just the shells. Negative on black, and 19V on white.

Now the HP Pavilion 27C curved monitor works directly from DC with just the two shells connected.

The answer for the HP Notebook 15 is yes. But it was slightly different.

Same set of 3 wires: Black, White, Blue.

The plug is considerably smaller - not like the Dell-type plugs at all. I was able to verify the outer shell went to black and the inner wire went to blue, but couldn't test the inner shell without touching the wire. No big deal.

Using Black as GND, The plug-in adapter measures 19.9 Volts on White (slightly more than the monitor).
Then it measured 13.5 Volts on Blue (perhaps to indicate that it is a 45W supply?)

Back to the plug wire, I put the 19 Volts to black and white as with the monitor.

When I plugged it into the computer the screen brightened and the battery icon started the animation of charging, without showing the AC plug in the icon. When I pointed the cursor at it, the message was "95% available, (plugged in, not charging)" - which was backwards from what the icon was showing.

So I rebooted. No error message.

Now that it is up and running it is not showing the charging animation but the AC plug shows right next to the battery in the icon. Pointing to it by mouse gives "93% available (plugged in, charging). All looks normal.

So there we have it. It seems to work fine on an HP Notebook 15.

Now the sun powers my main laptop PC 24 hours a day, just like it does my ham radio set, the room lights and all the rest that is gradually being moved to DC.

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  • \$\begingroup\$ Its got to be on-topic electronics.stackexchange.com/help/on-topic This looks more like repair or just a question about integration. It would probably do better on DIY.SE \$\endgroup\$ – laptop2d Apr 9 '17 at 5:52
  • \$\begingroup\$ Why do you "need to know"? Just cut the damn thing off and try! You can always solder your wires back, and isolate with electrical tape. \$\endgroup\$ – Ale..chenski Apr 9 '17 at 6:13
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    \$\begingroup\$ There is no repair involved, @laptop2d. Nor would plumbers and sheetrock workers know more about this than EEs. Now, if we had an RV.SE or Solar.SE, maybe you would have a point. Meanwhile, there sure has been a good discussion generated here by this question. I'll tackle the laptop right after church.. \$\endgroup\$ – SDsolar Apr 9 '17 at 14:29
  • \$\begingroup\$ @SDsolar, you have exceeded my threshold of patience. I have deleted all my attempts to help you, your obtuseness makes it pointless. \$\endgroup\$ – Ale..chenski Apr 9 '17 at 18:23
  • \$\begingroup\$ OK, this project is now finished. It worked on both. I'm grateful for all the discussion. This is why I like SE; especially EE.SE \$\endgroup\$ – SDsolar Apr 10 '17 at 4:10

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