Help with custom monitor 12 V adapter

Question

I have an electrical question about a custom adaptor I want to build.

The monitor im using: philips 258B6QUEB/00 https://www.philips.co.uk/c-p/258B6QUEB_00/brilliance-lcd-monitor-with-usb-c-dock

It uses a power brick 230 V AC to 19.5 V DC at 7.7 A.

Because I live on a boat, I want to make a power adapter that works on my boats 12 V system.

What I was thinking to buy this 12 to 19.5 V converter: https://a.aliexpress.com/_Euyf5jF

And this power cable: https://a.aliexpress.com/_EQ7mWI5

And with those in theory I can make a 12 to 19.5 V adapter right?

But the cable has 3 wires in it, one positive, one negative, and a third unknown one. Which I really don’t know what it does.

And the monitor has a USB-C connection which I know can make it more complicated.

Will this work? Or am I better of to find a car changer and modify that one?

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Fist of all thanks for the detailed response!

I must amit that in my OP I had no more (online)info then you guys, (only some unhelpful unsharp photos from ad) because I bought it through a online marketplace, and its only just now arrived.

And I did found some specs on the power supply and monitor itself(without dismantling it).

The monitor tells me on the back label, that it takes the 19.5vdc @7.7a as i expected. But has also the following warning on it: "Never remove covers unless qualified to do so, Use only AC/DC Adapter listed in the user instruction." Which is more specific than on the last part than a "normal" warning dont open label i think.

The power supply gives me also some new clues;
Model NO: TPV150-RFBN2
AC INPUT: 100-240V~, 2A 50-60Hz
DC OUTPUT:19,5V (DC icon) 7,7A 150.0W

(Mini plug scheme/diagram);
Black(-): outershell plug
White(+): inershell plug
ID PIN(N.C): innerpin plug

That makes me think that this probably is just like the DELL notebook charger case, as you referred to. Where it probably is bit like the USBC charger chip thing, where the charger works by ID handshake to verify the needed voltage and max amps.(correct me if I'm wrong)

Because of the power consumption specs (23 W) on the philips website i assumed my OP would work, but it gets clear that its not so simple as I hoped.

I want to use the monitor together a WiDi hdmi stick to connect to my Raymarine plotter, and mirror the image from the plotter and mount it in the navigatie corner inside the boat. And add it to the navigation equipment electrical group so its starts up simultaneously as the raymarine.

So as you suggested, its the easiest way to just use adaptor as intended and just kabel manage it away(room enough behind panel) and let my Victron multiplus II 3KW inverter take the load as its running anyways when I'm onboard.

Any suggestions for an 3-way AC switch with on/off/remote(signal from DC raymarine group)? To help power it up, and it's still usable as laptop monitor when DC group is off. Or have the propper name for a switch like that?(so i can find it on google)

Sorry for the bad English and probably some wrong designations, its not my native tongue.

Once again really appreciate your detailed response, and thank in advance for all the effort in the replys!

Answer 1

on a PHILIPS 276e8vjsb which has the same connector(7.4x5.0mm) its just two ground and power. unfortunately I could not find a schematic for 258B6QUEB.

If your monitor has a similar circuit, then there will be no problems.

Answer 2

You're trying to design a power supply for your monitor (which just about makes the question on-topic here), but you don't have the full specification for the existing power supply you are trying to replace, since you don't have documentation for that 3rd wire.

As already commented, that 3rd wire is likely to be similar to those in some laptop power supplies (see links below) which allow the device (in this case, your monitor) to interrogate the power supply and determine whether it is the expected model. (I don't know, and didn't see it stated in your monitor's user manual, how the monitor will behave without correct 3rd-wire communication with the power supply.)

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I will offer a "frame challenge" answer: I would not use either of those two approaches you mentioned (to make 12 V to 19.5 V boost converter from COTS modules, or try to adapt a car charger). Instead, you could either:

• Spend the (perhaps long) time reverse-engineering the monitor's mains power supply which you already have, to understand exactly how that 3rd wire is being used. Then investigate how to add that functionality to a different external DC-DC (e.g. 12 V to 19.5 V) power supply.

  That would likely involve opening & reverse-engineering parts of the power supply and perhaps the monitor too. This process may not be a sensible use of your time, especially as there is no guarantee of success at the end. You may need to buy additional equipment e.g. a logic analyser and might damage things in the process. (There are also safety risks working on a mains power supply.)

or

• Despite the power conversion inefficiencies, you could use a suitable inverter from your 12 V boat supply to mains voltage and then use the existing mains power supply for the monitor, since you know that power supply works. I recommend seriously considering this option. Although it actually removes the electronics design aspect of your problem, it is the only approach which is guaranteed to work.

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A couple of relevant links:

• On our site: 3 wires on a (bipolar) DC plug - what are they for?

• Hackaday: Hacking Dell laptop charger identification (which links to a 4-part reverse-engineering series of articles)

• Just as an example of how the 3rd wire can be used on some laptop power supplies, this reverse-engineered partial schematic shows a DS2501 1-Wire memory IC inside a Dell power supply, connected to that 3rd wire (labeled "ID"). The data contents of the memory IC are then interrogated by the laptop (in that case) to determine how to behave:

  

  (Image source: Andrea Ronešová - Notebook mains adapter DELL PA-12)

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Update based on the new information in revision 4 of the question:

The power supply gives me also some new clues;
Model NO: TPV150-RFBN2
AC INPUT: 100-240V~, 2A 50-60Hz
DC OUTPUT:19,5V (DC icon) 7,7A 150.0W

(Mini plug scheme/diagram);
Black(-): outershell plug
White(+): inershell plug
ID PIN(N.C): innerpin plug

That makes me think that this probably is just like the DELL notebook charger case, as you referred to.

I agree. The mention of "ID" fits with similar usage to the notebook power supplies which I explained.

Where it probably is bit like the USBC charger chip thing, where the charger works by ID handshake to verify the needed voltage and max amps.(correct me if I'm wrong)

The type of communication using that 3rd wire is very different to the USB-PD protocol, but that's getting into a whole different topic. At some level, I suppose you could say that both approaches are trying to confirm that the connected power source is compatible with requirements.

So as you suggested, its the easiest way to just use adaptor as intended and just kabel manage it away(room enough behind panel) and let my Victron multiplus II 3KW inverter take the load as its running anyways when I'm onboard.

Yes, that plan is my recommendation, due to the challenge of reverse-engineering the existing power supply communication otherwise (unless you really want to have that challenge).