AuxPower1U: Power Supply Selection

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.

AuxPower1U: Triggering Dell

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.

AuxPower1U: Case Selection

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.

AuxPower1U: Features

This is post 2 in the series (next: Case Selection, previous: Requirements).

In my previous post, I split all my desires into two categories: requirements and features; requirements being something mandatory while features being something that is nice to have. In reality, the line between them isn’t really as clear so you can view this just as an addition to the first post.

When it comes to features, the main externally visible functionality of my consolidated power supply box will be the ability to reset devices from the front as I currently have with ResetBox.

While this is a requirement, the exact button count is a bit more flexible since the primary function of them is to provide a quick reset of the Internet for my family when I’m not around. Considering that, the minimum would be something like this:

• Button 1: Arris SURFboard Modem
• Button 2: Mikrotik hAP ac, Mikrotik Audience, and Mikrotik hAP ax3

However, while I have other means of resetting devices, I also like buttons so my desired setup might be something like this:

• Button 1: Arris SURFboard Modem
• Button 2: Mikrotik hAP ac, Mikrotik Audience, and Mikrotik hAP ax3
• Button 3: Dell OptiPlex 3050 Micro
• Button 4: Intel NUC

Let’s add one more button to account for possible future needs, and this brings us up to a total of 5. Please note there is no requirement that the button count matches the physical layout (i.e., one button could reset two different outputs), but I like to have it setup like that nonetheless. It just simplifies configuration immensely if I keep that link.

Functionality of buttons is to remain the same as it is for ResetBox; i.e., they should handle brief touches without any action, and reset should be “hidden” behind a longer press. Also, if one keps pressing button for a long duration (e.g., more than 10 seconds), the reset should be cancelled.

I might as well try to include some monitoring for both voltage and current. This is easy enough to implement, and it would be a shame to miss such opportunity. As not to go overboard, just monitoring output lines will be sufficient since I can already see that monitoring both input and output would take a lot of board space.

In order to display that data, I would definitely like to go with OLED, albeit I can already see mounting it on the front will be a challenge no matter which case I select. Thus, I might not bother making it user-visible, but I would still like to have it on board so my development and troubleshooting can benefit from it. I trust 128x32 will do.

For real-time monitoring, I would like to have either UART, RS-232, RS-485, or CAN-bus output. Since each of those requires different components, I would need to make that decision eventually but not necessarily now. I am tentatively leaning toward CAN-bus due to its resilience; but let’s hold the final decision for now.

Lastly, having an idea of the temperature might be beneficial. While precision is not really important, there should be a sensor somewhere on the board that will give us a ballpark figure of how hot we’re running.

That’s all I really want from this project. Now, onto figuring out the details.

AuxPower1U: Requirements

This is post 1 in the series (next: Features).

As part of my home server setup, I have a few devices that have “free-floating” power supplies. For example, my modem, my wireless PoE adapters, and a few test boxes all have their power supply pushed into rack’s nooks and crannies. Even worse, since I want to have the capability to reset them, they are connected via ResetBox (or its type-C variant) making cable situation even messier. It’s way beyond time to sort that out!

In this blog series, I will go over what’s needed to design a nice 1U box that can fit all (or as many as I can) different power supplies togethe. Their outputs should be resettable by physical buttons on the device’s front. Since I actually didn’t finish the project as I’m typing this, expect the series not only to last a few months while I gather all necessary equipment but also for my “specifications” to shift slightly as I discover new things or rethink my old ways.

At first, let’s look at what power supplies we have currently:

• 12V 25W: Arris SURFboard Modem
• 22V-57V 20W: Mikrotik hAP ac
• 24-57V 30W: Mikrotik Audience
• 12-28V 40W: Mikrotik hAP ax3
• 19.5V 65W: Dell OptiPlex 3050 Micro
• 12-19V 65W: Intel NUC
• 54V 15W: Netgear GS305EPP (150W max)

If I squint hard enough, there are three distinct power supplies to use there; the first one being a simple 12V power supply for modem. Power usage will be really low on this one, so any hardware we place will run from it too.

To the second power supply, I had to give a bit more thought. Without question, it has to run of the UPS but its target voltage is a bit of an unknown. Currently, I am running my hAP ac and Audience from a 20V type-C power supply, and Audience doesn’t seem to love it as any minor transient causes reset. And yes, officially Audience doesn’t run that low, but I got lucky, I guess. Previously, I was running my WiFi routers on 48V and both were fine with that; so there are my two daya points. Considering other devices, I was leaning toward selecting 24V as a second power supply.

However, that leaves my NetGear PoE switch a bit of a loner and outside of The Box. For it, I would need to provide a proper 55V PoE power supply or at least 48V if stars align. The downside of this approach is that it leaves my Mikrotik hAP ax3 either on 12V or for the last, non-UPS power supply. But the upside is that it allows for a bit of future-proofing.

That leaves 2 non-UPS computers. Why are they not using UPS? Well, in my setup, UPS power is really limited and is reserved for only two categories: my main server and my Internet delivery devices (modem, router, WiFi APs). Anything else just needs to handle a power loss. These two computers fall into “anything else” category.

Intel NUC, we can already see, is flexible with a power supply specification. When it comes to standard industrial voltages, it can handle both 12V and 15V inputs. However, it Dell bretheren officially are not that flexible. While there is a possibility my 3050 micro would work on 15V, anything higher is a no-go. And since Dell authenticates its chargers, to figure this out, I’d need to trick it first into accepting such voltage - all of which smells like another sub-project. :)

If Dell doesn’t want to cooperate, the only way forward would be to use one of many buck modules intended for RVs that brings 24V to 19V. I would really like to avoid this, if possible, because the last thing I need is yet another power supply. However, it’s good to have options. And yes, ideally, I would find a 19V power supply; but I have a feeling that finding one that can be properly mounted inside a 1U case is not going to happen.

This brings us to the following rough power supply distribution (with a bit of derating on power specification):

• 12V 150W (100W if I kick out Mikrotik hAP ax3 from my network):

  • 25W: Arris SURFboard Modem
  • 25W: Control boards
  • 40W: Mikrotik hAP ax3

• 15V/19V/24V 200W (150W should be realistically more than fine):

  • 65W: Dell OptiPlex 3050 Micro
  • 65W: Intel NUC

• 48V/55V 100W (going higher than this might be good for the future PoE devices):

  • 20W: Mikrotik hAP ac
  • 30W: Mikrotik Audience
  • 15W: Netgear GS30s5EPP

There is an alternative at a bit lower voltage:

• 12V 75W

  • 25W: Arris SURFboard Modem
  • 25W: Control boards

• 15V/19V/24V 200W (150W should be realistically more than fine):

  • 65W: Dell OptiPlex 3050 Micro
  • 65W: Intel NUC

• 24V 150W

  • 20W: Mikrotik hAP ac
  • 30W: Mikrotik Audience
  • 40W: Mikrotik hAP ax3

• Out-of-scope

  • 15W: Netgear GS30s5EPP

I am strongly leaning toward option 1, but option 2 is a good alternative. And yes, Mikrotik is not as power hungry as it seems above; I’ve never seen it reach its maximum power usage. However, since I really love my network, I use those numbers to bring an additional margin to the dimensioning process. If I find a nice power supply that’s slightly below what I need, I will get it and not worry about it. But, before I get to that, this fudged accounting provides more visibility into what brings the most value.

For various protection circuits, I’, going to rely onto power supplies to protect themselves. Thus, at minimum, I expect any selected power supply to have over-voltage, over-current, short-circuit, and over-temperature protection built-in.

When it comes to controlling this, I would say that ability to reset my Modem and WiFi is a must. And these can be two buttons as I want to be able to separately restart modem. For the hAP ax3, I don’t care as much since it has “under test” status in my network at this time. But let’s argue that it needs to be a separate button. At this time, I do control each of my computers inside the rack via smart plug so moving them into The Box, I might want to see a button for each, but I wouldn’t really mind if both go down at the same time. This brings the total number of reset buttons to somewhere between a minimum of three and a maximum of seven.

Lastly, this blog post leaves us with the following action items I will probably get around to solving:

• Chck can Netgear GS305EPP work on 48V
• Make trigger board for Dell
• Check does Dell Optiplex 3050 Micro work on 15V