I have an old, but good, Dell XPS 17 (L702X) laptop that I would like to use as a personal NAS. I would disassemble the entire thing and place it in a new enclosure, likely one I make myself (because I like diy stuff). I would ditch the screen, speakers and probably the WiFi card. I want to use a 2.5" SSD for the OS, and two 3.5" HDDs for storage.
The problem is the power draw from the 3.5" drives. I suspect that the power into the laptop is sufficient especially considering all of the things I’ll be ditching. From what I’ve read online the copper on the PCB might not be able to handle the power draw from the larger drives.
So I’d like to tap directly into the power from the power converter just after the plug from the computer. The output from the power adapter is 19.5v 6.7a so I would need two DC to DC Step Down converters (buck converters), one to reduce the input to 12v and another to 5v. From the converters id connect to SATA power cables.
Does this sound like a suitable solution? Am I missing anything? Thanks for the read and for any responses.
If you’re willing to spend a bit of cash, have you considered finding a cheapo ATX power supply and doing some minor surgery?
I made a custom HDD enclosure and had to figure out how to power them. I tried thinking of all sorts of clever solutions, but ultimately giving a buddy ten bucks for an old disused PSU was the best option. Snip off all the wires you don’t need and you have a relatively clean PSU that will power all the HDDs you can ever throw at it.
I did consider using an off the shelf power supply. The problem with that is I can’t find a power supply that would also be able to power the rest of the components. The laptop requires 19.5v. I cant find a regular PC power supply that outputs more that 12v. Even if i did find one it would need to be adjusted to 19.5v somehow. I really don’t want to have to use a full size power supply (or its guts) and the regular power supply for the laptop.
If you aren’t using it for anything else, can’t you steal 5V from the USB ports? That way a single 12V power brick or wall wart would provide the rest and you could get one with plenty of headroom since power supplies don’t like to be pushed that much.
If you do go with cheap buck converters, I would test them a bit first. The voltage under load will likely sag a bit compared to no load. Maybe run an old case fan or two as you dial it in. I’ve had decent luck with buck converters and much less luck with cheap boost converters.
You can also get a laptop car charger and connect it between the laptop and the power brick to trick the Dell into thinking it has a legit charger. That’s what I do to charge my Dell with solar. I’d imagine a PSU with a solid 12V rail would have no problem powering one of those. Definitely more than one way to go about things.
Using a buck converter with the laptop DC input sounds like a good idea. I’d recommend getting one of these:
I found that this type is one of the only step down converters that actually delivers a good amount of power. Even though the smaller ones (like the LM2596) are advertised as “3A” you can just barely get 12V -> 1.5A @ 5V out of them. I’ve used these as a battery charger from 20V to 12V and it was able to deliver 75 watts (6A)!
You can find these by searching for “step down CC CV”. They are $2.50-$5.00
I’d get a powerful enough 12V DC-DC converter and hooked it to 19V rail in the laptop as others have suggested. HDDs need more amps when spinning the platters up so pick a converter than can handle some amps.
5V you could steal off USB, or better yet, get your hands on a schematic for your laptop, trace back where the 5V is created and solder in there, before any fuses or switches. Less voltage drop and no current limiting, if there is one for USB ports.
Or just get another DC-DC converter to step down 19V to 5V.
I hadn’t really considered finding a voltage source already on the board. I’ll browse around for a diagram of my motherboard. If I cant find one I guess I could probe it with my multi meter.
I was about to pull the trigger on a few step down converter that use the LM2596 chip. The listing says they are updated chips that can handle up to 5A but would be best to only go as high as 4.5A. I thought this would be fine since the spec sheet for the HDD in looking at (WD Red NAS) says the peak current is 1.85A. I will have two connected so I’d need max 3.7A. Derkades, and Vader, you have me wondering if I should buy converters that can handle more amps just in case.
I only have two SATA ports on the board anyway. I have an ODD port that Ill attach a 2.5" SSD to for the OS.
I have seen a teeny PCI card with sata ports on it that would fit where my WiFi card would go. But I don’t think I need them or want to mess with it right now.