Inject dc into output side of laptop power supply?

[Toel]

I have a HP omen laptop that operates on a 200w 19.5v power supply. I am currently lucky enough to live a nomadic life in a solar powered travel trailer and try to run all my devices on DC rather than use my inverter.

I have been unable to find a commercially made DC-DC power supply for the laptop so I have therefore tried to create my own. It was not difficult to set up a separate DC-DC power supply to output 19.5v at the required amperage, but because the laptop uses a third communication wire to identify the psu, it will not charge.

Please correct me if I am wrong, but it appears it would be difficult to trick the sensing wire into thinking my homemade power supply was a good fit for the laptop.

I am therefore thinking of wiring my diy 19.5v power supply in parallel to the output of the original power supply with the sensing wire still connected. In this configuration, I would NOT plug in the AC side off the original psu.

I am hoping that, if the DC side of the original power supply receives power injected from the output, it will power up the sensing wire tricking my laptop to using my DC-DC power supply.

Could this experiment end up ruining my original AC adapter?

Is there a chance it could work?

Anyone have any better solutions?

It is frustrating because the laptop clearly does not need 200w to charge but yet won’t charge unless it has the oversized PSU which is only necessary when the GPU works hard. I would be satisfied if I could just charge it via DC-DC then need to resort to AC and my inverter off I need full power.

Thanks in advance for any thoughts.

 

[Ampster]

Can you test to see if the sensing wire is a voltage source, a contact, a resistor or other signal? That would be a way to figure out if emulation was possible.

 

[Hedges]

I think my laptops draw reduced power when they fail to communicate with the supply (even though it is OEM.)
You might get reduced power operation just by feeding power.

I think communication modulated over the power wires is used. Not just a enable pin you could trick.

If you can buy a spare AC power adapter to hack, maybe you can feed power into it. But likely not. First of all, AC input is boosted to 340VDC (dangerous). The way laptop and supply are able to deliver 200W is by boosting voltage higher, so current remains low enough for the connector. Therefore, backfeed less likely to work. The AC adapter can't take your input voltage and boost it. Maybe if you drove boosted voltage, but that's just a guess.

Probably best way to go is get a small inverter to feed AC adapter. Victron makes some, for instance. Pure sine wave is most likely to work. Possibly MSW will work; depends on whether supply attempts power factor correction, and possibly high inrush current issues. (We've successfully fed 240VDC into a PFC supply at work, but MSW would be a different story.)

 

[Texas-Mark]

Maybe this thread will help

https://www.reddit.com/r/HPOmen/comments/10vf8oo

 

[stienman]

Could this experiment end up ruining my original AC adapter?

Yes, it might damage your power supply.

Is there a chance it could work?

Yes, it might work.

Anyone have any better solutions?

Connect the third wire to a 1k ohm resistor, then the resistor to the positive side of the +19.5v supply. Test. It shouldn't damage your laptop, and by most accounts this is enough for most HP products with the smart pin to turn on fully.

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Some use 100k ohm, some connect it directly.

I wouldn't connect it directly - if the laptop does use it for communication or power supply control then it will damage that pat of the laptop. You may never notice, or it may prevent the laptop for powering on again.

Using a 100k ohm is safest - worst case scenario it'l push 0.2milli amps of current through a circuit trying to pull it low, and that's easily handled by whatever circuit might be trying to pull it low.

1k is still relatively safe, with a maximum current of 20milli A, which is still very low and fairly safe.

As far as the proper way to do it, without reverse engineering a power supply, and going only on what I've experienced with my HP gaming laptop (300w power supply) and what I've read online:

The HP smart pin can perform the following functions:
- Tells the laptop how much current it can use
- Tells the laptop that the power supply is operating properly
- Allows the laptop to shut down the power supply, or to go into a low power state

This can all be accomplished through simple sensing, and so far while I've heard of people claiming it has digital signals I haven't seen evidence of it.

The resistor to +V could be sized to tell the laptop how much current the power supply is designed to supply.
The power supply can pull the pin low if it detects abnormal operation (high/low current, high/low voltage, overheating, etc)
The laptop can pull the pin low to tell the power supply it needs low or no current, and the power supply can turn off or use a much more efficient low current converter, turning off the high power converter.

So try it with a large resistor, and if it works and the laptop doesn't complain about the power supply then you've solved the problem. If the laptop complains, test different resistors until it doesn't.

 

[stienman]

Oh, also - the safest way is to use USB C to charge the laptop if your laptop supports that capability. USB C DC power adaptors (12v, 24v most commonly) are widely available and relatively inexpensive. You don't have to muck around with any of the wiring or circuitry of the power adaptor or laptop.

 

[Crowz]

I have a HP omen laptop that operates on a 200w 19.5v power supply. I am currently lucky enough to live a nomadic life in a solar powered travel trailer and try to run all my devices on DC rather than use my inverter.

I have been unable to find a commercially made DC-DC power supply for the laptop so I have therefore tried to create my own. It was not difficult to set up a separate DC-DC power supply to output 19.5v at the required amperage, but because the laptop uses a third communication wire to identify the psu, it will not charge.

Please correct me if I am wrong, but it appears it would be difficult to trick the sensing wire into thinking my homemade power supply was a good fit for the laptop.

I am therefore thinking of wiring my diy 19.5v power supply in parallel to the output of the original power supply with the sensing wire still connected. In this configuration, I would NOT plug in the AC side off the original psu.

I am hoping that, if the DC side of the original power supply receives power injected from the output, it will power up the sensing wire tricking my laptop to using my DC-DC power supply.

Could this experiment end up ruining my original AC adapter?

Is there a chance it could work?

Anyone have any better solutions?

It is frustrating because the laptop clearly does not need 200w to charge but yet won’t charge unless it has the oversized PSU which is only necessary when the GPU works hard. I would be satisfied if I could just charge it via DC-DC then need to resort to AC and my inverter off I need full power.

Thanks in advance for any thoughts.

I have one of those for my alienware notebook computer and I have one for a dell notebook computer that are dc to dc. They have cigarette lighter plugs on the ends. The alienware I bought from alienware but the dell one I bought off amazon.

 

[Symbioquine]

I don't have any experience with that laptop, but car chargers can be a decent strategy if you have sufficient 12v power. It looks like there are a few options for car chargers available. I just googled "12v car charger for hp omen" (Not sure how reputable they are though so YMMV.)

 

[Toel]

Thank you for all of the replies. I was finally able to take Steinman’s advice and try resistors between the positive and the third wire. I started with 100k, then 10k, then 1k but had no luck. I then measured the resistance between the positive wire and third wire and it was around 148k. I therefore tried a 150k resistor and now it works like a charm.