This goes without saying, which is why I have to say it: Any power supply modifications can cause injury and/or property damage. Please leave these modifications to professionals and fully understand what you are doing before you start a project like this.
Most of Dell's products don't seem to have car chargers. They also use proprietary connectors and circuits to tell the computer if it is using a 'Dell Certified' power supply. After doing a lot of searching, I found one person who took apart a dead Dell power supply and repurposed the circuit used to tell the computer the brand and wattage of the power supply. Since this circuit runs off of the DC voltage that provides charging power to the laptop, it made sense to me that I could connect any power supply of proper voltage and amperage to the DC power wire between the power brick and the laptop, and that this would provide power to this proprietary circuit inside the power brick as well as charge my laptop.
I'm waiting on some connectors to come in so I can clean it up a bit and make it a bit more travel friendly, but it works great. I am able to plug a car charger into a cigarette lighter socket connected to my solar charge controller and charge my laptop. The charger I bought takes 12-16 VDC input which means I can use any power source in this range and of sufficient amperage (it has a 10A fuse, so somewhere less than that at minimum). It also has a USB charger built in, and I was able to charge my laptop and dumb phone at the same time while it barely got warm in one small spot. I figured that was pretty good considering the warm temperatures in my shed (somewhere in the 80's F). I'm slowly moving things in my life over to solar and minimizing my overall power consumption, and this cheap modification worked as well as I could have hoped!
I put warnings in my post in the link and will touch on it again here: I don't know if plugging in both power sources will cause one or both to fail or other issues, but it sounds like a bad idea that I wouldn't recommend. I won't make any recommendations on which power supply to use because this is not for beginners and if you can't choose a power supply then I don't want anyone blaming me for any problems that can arise. This is a fairly straightforward modification where you connect the DC power of a car charger to the DC wire of the AC charger; positive to positive and negative to negative. Please use due diligence and properly test your car charger for compatibility with the power needs of your laptop before making any connections.
One other quick note I have for anyone looking to power a computer or home office directly from DC - many computer monitors out there use a power brick very similar to laptops; ~19V and often under 30 watts power consumption. It should be fairly easy to convert one of these monitors over to car or solar power with the right power brick. It should be pretty easy to make a small office in a tiny house, RV, or other off-grid situation using off the shelf parts any perhaps a little modification.
I think it is a bit insane to convert DC to AC just to go back to DC to power devices. Some chargers don't play nice with some inverters and it is rather inefficient. With this cheap mod I am able to use AC or DC to charge my laptop; be it a house, a car, solar, or whatever I can find that works with either of these two power supplies. I have also been testing out a desktop computer on solar using a power supply made for the task. You can do a search for Pico PSU or check out what they have over here at mini-box.com. I have the M3-ATX which is a bit overkill for the computer it is powering, but I have used it for years in different projects and it is very small and efficient. The low power segment of the computer market has been rapidly changing, and the amount of work you can do per watt of energy used has increased greatly. I would definitely recommend anyone interested in this to look into the options I have listed or other devices similar to the Raspberry Pi for some affordable methods of working with computers that don't use much energy.
you definitely want to be careful with the laptop charger.
It will matter a lot where Dell put the charge controller circuitry for the battery.
I'm sure the overtemp protection is inside the battery itself, so fire shouldn't be a problem.
However, I wouldn't be surprised if that brick is doing the constant current/ constant voltage switching that Lithium batteries need in order to have such a long life.
(also called "intelligent charging")
If that's the case and you just throw it it on a relatively constant voltage supply (like a car or a DC solar system) you could dramatically shorten the service life of your battery
I just wanted to touch back on this topic with a small update. I pulled the slow hard drive and installed an SSD for better performance and lower power consumption. While I was in there I saw the internal battery which has a nominal voltage of 11.1V (typical of similar devices), and 12.6V charging voltage. I installed Linux and the information there told me it was charging at 12.59 volts, which is close enough for me. I am not terribly with Windows, so there may be a way to get this information in Windows, but it was readily available to me in Linux by clicking on the power icon on the panel. There was also a charge rating listed, when the battery was at 80% the charge was at ~25 watts, at 95% it was at ~7 watts, and at 98% it was at ~3.5 watts. I just glanced at it while it was charging to see these numbers.
It is pretty common for laptops to have an input voltage of 19V +/- 5% or something similar. Obviously these voltages are purposely higher than the voltages used by the motherboard and the battery so the internal power supply can control the power with enough overhead for the margin of error given for the external power brick. Again, this is not a modification someone should do if they do not completely understand what they are doing, but it does work and I have charged my laptop a few times with my small PV power system this way with no issues. This is definitely an option for someone looking to go solar. Minimizing your energy needs and avoiding unnecessary energy loads and power conversions will reduce the cost and bulk of equipment required to provide your energy needs with off grid renewable energy systems.
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