This is post 5 in the series (next: Cooling, previous: Dell Trigger).

When it comes to power supplies for embedded electronics, it’s really hard to beat Meanwell. They are easily available, they have a wide selection, and they are reasonably priced. Thus, my search for power supply started with the first Meanwell catalog I found.

After testing the Dell trigger board, my power supply setup crystallized to 48/55V (for my routers), 15/20V for computers, and lastly (optionally) 12V for a modem. Why do I say “optionally”? Well, the option of using a buck regulator for the modem is always open. Since I have my case dimensions predetermined, the choice on whether to use 2 or 3 power supplies will be mostly driven by their dimensions.

As 1U severely restricts the height, my choice fell onto four power supply families:

• LRS-100-XX
• RSP-150-XX
• RSP-320-XX
• UHP-200-XX

I wanted to get as small as possible (can I fit 3?), a reasonable amount of power at each voltage (100W+, especially for 15V needed by computers), a reasonably small ripple (less than 200mA, if possible), tight voltage tolerance (1%, ideally), high efficiency (90%+ desired), and lastly robust overload controls (ideally with auto-recovery). Looking at the catalog, I placed the following power supplies on the short list:

After tinkering with a couple of combinations, including using power supplies from different families, I decided on a homogenous UHP-200-XX setup. They have ridiculously low profile, high power, and high efficiency. On the downside, they do have a bit of a ripple and their cost is quite a hit.

Another setup I could go with would still have UHP-200-15, but combined with LRS-50-12 and LRS-100-48. The downside of this approach would be a bit of a crowded central setup and less robust power supply.

The three power supplies I ended up with are UHP-200-12, UHP-200-15, and UHP-200-55. While the last one might be a surprise since I was leaning more toward 48V, the 55V version has unusually wide adjustment range (45-58V). This means it covers both 48V and 55V thus allowing me some flexibility.

If you look into their datasheet carefully, one will notice that these power supplies require quite a big heatsink. But alas, we cannot solve everything today; there needs to be something for a future me to deal with too. For now, I need to order these three before I change my mind again.

This is post 4 in the series (next: Power Supply Selection, previous: Case Selection).

One action item mentioned way back in the first post, was discovering if a Dell Optiplex 3050 Micro can handle voltages lower than its specified 19.5V. However, you cannot just check that by plugging in any old power supply. No Sir, you need to have a 19V charger blessed by gods and naked virgins who dedicated their life to making sure your Dell equipment is not using impure power like those other peasant computers do.

However, since I am unworthy of such service, I decided to see about bypassing the same for three reasons. The firs2024t one is that it makes my life so much easier if I can use any old charger in case my current charger dies. Secondly, it really messes with my goal of consolidating power supplies if I need to take special care of Dell.

Before I went onto deciphering the charger protocol myself, I decided to check if someone had already done the work. And, wouldn’t you believe it, someone did. Even better, the author provided all the information one might need. The only thing I had to do was to make a PCB. So make a PCB I did.

The final board consists just of a resistor in series with the EEPROM data line and a zener diode for overvoltage protection between the data and ground. The value of the resistor is not really important but original charger uses 330 so that’s what I went with. Zener is also not critical so I went with 5.1V one I had laying around - go, mini-MELF, go!

The main part is a 1-wire EEPROM memory, either DS2501 or DS2502. And yes, you can program that EEPROM yourself, but there is actually a source of preprogrammed memory on AliExpress. That is way easier than dealing with 12V pulses programming this memory requires. There are some reports suggesting you can use DS2431 (with much simpler programming model) but buying preprogrammed stuff was easier.

As for the Dell connector, I was originally planning to cut the existing cable but Amazon had some pigtails available so I opted to use them and keep my original charger for emergencies. On the barrel connector side I found that a DC 2.1x5.5mm connector intended for panel mounting has spacing that fits a 1.6mm PCB perfectly.

With PCB and all parts ordered, the only remaining work was to assemble, wrap it in heat shrink, and finally test whether 3050 is properly charging at 15V. Will it? Well, it will!

Based on the old method of “try and see what happens”, I could power on my Dell starting as low as 13V. While that was the lowest voltage it booted on but I found it would ocassionally “stutter” a bit. However, when I bumped it to 14V, all looked the same as when running at the official 19.5V. For all practical purposes, you can view the Dell Optiplex 3050 Micro voltage range as 14-20V.

And yes, all standard disclaimers apply, especially given that it’s a test sample of one. For this use case, I only care about my setup, so this is sufficient. However, I am willing to bet that pretty much all other similar Dell machines behave the same.

In any case, this smalll board enables me to emulate Dell charger at lower voltage, thus allowing use of 15V power supply. This gives me access to a more common voltage in embeeded electronics (way more common than 20V that’s usual for laptops) and it also proves that both my NUC and Dell can both drink power from the same faucet.

This is post 3 in the series (next: Dell Trigger, previous: Features).

Quite often, I like to start my projects with a case selection. Since I have quite a few hardware projects under my belt, I also have a fair idea of how much space things are going to take. Despite this, in reality, I sort-of overlap the selection of case with the selection of the largest components; in this case, power supplies. I will cover power supplies in a future blog post; suffice it to say that I determined 200 mm of case depth would suffice.

Based on that, I wanted a 19" 1U rack case with a depth of 200-250mm. The width and height were fully determined by the 1U factor, while the depth was selected as not to interfere with other components. For power supply health, I also wanted to have some cooling slots.

Representative of a cheap case was AliExpress Lang Lang coming in at only $32. It’s made of aluminium, has slots, and gets offered in depths of 200mm (1), 250mm (4), and 300mm (3). However, the specification is a bit unclear as to the rear panel. One picture makes it seem as though it’s predrilled, but on another, it seems to be one-piece. I find this case to be as close as it gets match to my requirements.

Even cheaper variant is AliExpress Tokban at $28. It has no slots, but that’s not an issue since drilling aluminium is not an issue. And it already has power supply input cutout, so that’s a bonus. On the negative side, its dimensions seem to be higher than 1U would allow. There is a high possibility this is just a typo. Also, considering I need 2 AC inputs, I’m missing a second cutout.

All other cases I found on AliExpress were just a variant of these two.

My other source is always DigiKey and I started my search by filtering on basic case properties.

The cheapest case I found comes at $34 in form of Bud Industries PRM-14460. This one is 200 mm deep and already has some mounting options inside. I am not as worried about structural stability since it will sit on top of UPS, but structural supports inside do fragment the internal space a bit.

Another interesting case is Hammond RM1U1908VBK, but I try not to even look at it too hard due to its high price of $158. Yes, it’s built better than any other case in this list, but the premium cost doesn’t justify it for this project. That said, for some other projects, this might be a really nice option, so I’m placing it as an alternative here.

At this time, I am leaning toward a plastic option with Bud Industries PRM-14460 since plastic seems the most promising material to mount an OLED screen. If mounting stuff inside proves to be much of a challenge, my backup option is AliExpress Lang Lang since it allows for more freedom when it comes to mounting and it also has a deeper 250mm option.