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Context: We live full-time in an RV (a travel trailer) while traveling around the US. We have 300Ah of 12V Lithium batteries, a 3,000W inverter and 600W of solar. Although we have an inverter, it has a parasitic draw of ~35W (~3A). We camp off-grid ~90% of the time with no hookups - just sunshine and fresh air!

We currently have two laptops which draw power from USB-C - we're using 12V adapters to power these. We need to upgrade to a more powerful laptop (for video editing), and that will obviously have higher power demands. One contender is a Dell laptop that uses a 240W 110VAC power adapter to produce 19.5VDC @ 12.3A. Given our intended usage, I can foresee extended periods of the laptop running at maximum capacity - high CPU/GPU usage, etc.

I'd like to power this directly from DC power if possible. We're already doing this for an Intel NUC using a DC boost converter. However, 240W is a lot more power than the NUC is drawing!

Questions:

  1. Do the Dell power adapters have any fancy electronics (e.g. negotiation like USB-C PD) or do they just output a steady 19.5VDC? Is this something I should be weary of on other brands as well?

  2. Any other reason why I can't just use a DC-DC boost converter and the right sized barrel connector to charge the laptop? The wires could all be short and high gauge - no worries there.

  3. Any recommendations on a high-quality, high-efficiency DC boost converter that could accept a fluctuating input (typically 13.0-14.4VDC) and output a constant 19.5VDC?

The alternative would be a small, dedicated inverter just for the laptop, but I'd rather not do DC-AC-DC conversion at all (given the implicit inefficiency) if not required.

PS - yes, we may need more solar anyway...!

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  • \$\begingroup\$ dell power adapters have a data pin in the center of the connector that is used for communicating with the laptop \$\endgroup\$ – jsotola Sep 26 at 0:36
  • \$\begingroup\$ Eurgh, that's what I was afraid of! Just had a bit of a look online and it doesn't seem like that's easily mimicked. Will the laptop just refuse to power off a supply without that, or just accept a reduced power? \$\endgroup\$ – Matt Knight Sep 26 at 0:43
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    \$\begingroup\$ i think that it will power up, but will not charge the battery \$\endgroup\$ – jsotola Sep 26 at 0:48
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In theory, you should be able to use a simple DC-DC converter to generate the 19.5 Vdc from your 12V battery bank.

Where you may run into problems is that many Dell computers have a 3rd conductor in the DC power cable that allows the computer to determine what size of power supply is connected. It does this so that it can throttle back the current consumption if a too-small power supply is connected.

On all of the Dell laptops and power supplies that I have worked on, the mechanism is a Dallas One-Wire memory chip inside the power supply. This connects to the laptop via a 3rd conductor in the power cable and connector.

You can usually see this by examining the plug that goes into the laptop. The plugs with the 3 conductors are a coaxial plug with a shell on both the outside and inside of the large-diameter barrel and a quite-small center pin in the middle of the plug. That center pin is the data line and the two shells are the DC power connections.

The easiest way to do what you want to do is to obtain another power supply and scavenge the DC power cable that feeds the laptop as well as the One-Wire chip from inside the power supply.

There is a plethora of DC-DC up-converters available with the power requirements that you require. Amazon or Digikey or even eBay will sell you something appropriate.

If you are finding it difficult to obtain a donor power supply to scavenge parts from, you can use your existing power supply. Simply splice directly into the laptop power cable coming out of the power supply. There would be three conductors: two large conductors for DC+ & DC- as well as a much smaller conductor for the data line. Simply splice into the two DC lines and you will be good to go. Be sure not to cut or short the data line.

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