I’m thinking about using 15V velbus power line to power raspberry pi (OpenHAB). Obviously with voltage regulator 15V->5V. Has anyone done that? I don’t want to get into any power supply problems, but RPI takes only a few watts.
I assume (after some search) it’s safe to have multiple power supplies on the velbus network running in parallel.
Edit: Voltage changed, I thought Velbus runs on 24V
Hi
Happy new year to you.
FYI
Velbus bus power must be
15v +/- 3v
In theory, as long as you prep the correct sized PSU, you should be fine.
However
I supply Odroid C4 machine’s, which are happy to run on anything from 5V to 17v, which is perfect for hanging directly from the Velbus PSU.
In parallel, no absolutely not.
But mainly due to the nature of PSUs, unless you buy ones that are happy to be wired that way.
If you mean, running multiple PSUs on a large Velbus network, then yes, but !!!
Each Segment of the larger network must isolate the +Vcc from each other.
Continuing only the
between each segment.
For example
If you are thinking of using your Three Phase supply and balancing the supply by breaking your installation into three sections.
Each section can have it’s own 15V PSU or pair of 15V PSUs with a new power supply manager, that will bond the supplies or create redundant backup (could just as easily be a battery)
There is a drawing on my downloads page that shows two segments
I’m happy to draw something for three phrase
Thank you very much!!! As always to class explanation! I was not aware of the isolation requirement. What’s the model of the new power supply manager? Is it available on the market?
My Velbus power is in four separately powered sections. Like MDAR says, each section is joined at ground but the positive power is broken (must not be connected between the sections). I use several of the Meanwell din-rail power supplies. You must use the 15V model (like this 30 Watt one but there are larger 60W models too if you need it) and for keeping velbus voltage high you can adjust them up to 18V… but no higher… DO NOT try to run velbus at 24v. Many older velbus modules will not like more than 18v as they have linear power supplies internally that may run hot at higher voltages.
My reason for doing this in four pieces rather than having one big power supply is because my Velbus run is quite long (about 900m) and the voltage drop from the ends to where the power supply connects would be too great otherwise. I did initially have three sections but even with that section’s voltage turned up to 18 volts a relay (VMB1RLYNO) at the furthest away point kept failing to work (and it’s diagnostic LEDS were flashing to indicate low voltage)… the voltage at that point was down to just over 11 volts… the other seven volts was lost in the cable length.
If you are going to put your Pi right next to the Velbus power supply then voltage drop may not be a problem but if you want to put the Pi somewhere else on the bus then be aware it will cause a significant voltage drop that may make Velbus modules unreliable (ie.if voltage a any modules drops below 12 volts).
Another very important thing… be sure to use a suitable switch-mode power supply for your Pi. DO NOT TRY TO USE LINEAR REGULATORS LIKE 7805 type power supplies as these will run extremely hot and draw too much power. Switch mode supplies are much more compact and efficient. You need to keep the current drawn from the Velbus supply as low as possible. To provide 1A for a Pi they will draw much less than 1A from the Velbus 18v rail. The more current they draw from Velbus, the greater the voltage drop issue.
If you want screw terminals (or even simpler, a USB socket) for your Pi supply then something like this sort of thing would work well…
Still make sure to use a short and sturdy USB cable though. Long or flimsy power cables can drop your 5V Pi supply to 4.8V or less and then the Pi becomes unreliable.
Are you OK to solder the power connections yourself? If so then two more suitable examples would be like these…
The first example needs to be adjusted to 5.2V BEFORE you connect the pi. This PSU is a good size that makes it fairly easy to connect to.
The second example is very small and is fixed at 5 volts and it’s connections are so small they are a bit fiddly but will work fine if your soldering is tidy and you keep the cable to the pi fairly short.
If you want to browse then Robotshop also has a good selection of alternative DC-DC power supplies…
Yes, you can run multiple of these DC-DC PSUs from your Velbus supply, even all along your velbus cable but watch for the voltage drop if you have any of these far from the Velbus 15/18V PSU. If in doubt, check voltage on the Velbus +/- lines at the connection point with a multimeter and do bear in mind that the pi will draw more current (and so cause a bigger voltage drop) if/when it is very busy.
Lastly - consider the nature of the Pi model you are using. Pi Zero takes very little power but Pi4 or Pi5 will draw power sometimes in quite big short peaks that could cause sudden voltage drops on your Velbus. Pi4 or Pi5 can easily draw 10W or more for short intervals when fully loaded.
Wow, you’re amazing! Thank you for sharing the knowledge!
I’m using these:
But the Odroid C4’s are easier… they can be plugged straight into the Velbus power (hoping for the redundant option coming soon) - similar like my 12V tablets…
Thanks again! I already bought RPI a while ago and Odroid is not fully open source (important factor for me), so I’ll get a voltage regulator.
A lot of good stuff already said. MDAR, thanks for making me aware of ODROID. I guess you use it for Home Assistant or something of that sort? It seems a bit more expensive than Pi and a bit less open. Pi has a much larger user base. So is the input voltage the only reason why you use ODROID?
I have a few thoughts.
PSU should never be wired in parallel unless they are made for that purpose. Most are not. The reason being their output voltages don’t match perfectly so one PSU will provide all the power while the other will sit idle, overloading the one that does provide the power. Even worse, some PSU may even short circuit each other. I always like to give some explanation, I know some people may be quite happy with the “NO!” without the why, but that’s me…
There is a more wasteful but simple option for powering the Pi. A 7805 3-pin voltage regulator. I’d never choose to do this. But I just wanted to offer the option. It will dissipate twice as much power as it is providing to the Pi and put a bigger load on the Velbus PSU. Some Pi models may use ALL of its available power when using the 7805. If the Pi draws 2 A, the 7805 will draw 2A… at 15 V = 30 W! I thought I’d throw it in as an option because it may be sufficient and it is certainly a lot simpler and more reliable. Make sure to adequately cool the 7805.You will need the 60W PSU for Velbus.
Why do I throw this in? I don’t know your case in every detail, it may be what you need.
I’d never do that. I’d rather go for independent power and it is cheap enough:
Another less likely option, but giving you a UPS: VELBUS is based on CANbus automotive, it is built to run on “12 Volt” battery power. So you can always run it from a 12 Volt battery with a charger for the battery 
That is where the 15V +/- 3V comes from. I’d use LiIon, not lead acid. LiIon will give you more voltage. Lead acid is stone age tech, Tesla is the first to finally part from it. The reason for EVs still having lead acid 12 Volt is purely because of all the automotive stuff made to run off a 12 V Lead Acid. Including the chargers. It will go away over time.
Thanks again! I hang my head in shame - I checked what I actually bought 3 months ago with the RPI that I plan to use as OpenHAB server. And guess what? There is a DIN mounted 5V 4A (20W) power supply waiting to be installed. I think I need to install more, buy less…
The bottom line: RPI will be powered from a dedicated 20W 5V unit (LINK). CUI PSK-20D-5-DIN to be precise.
Anyway I learned a lot about Velbus power from my pointless question 
You can always use our 5V Dinrail power supply to power the RPi.
https://www.velleman.eu/products/view/?id=467918
Best Regards,
Velbus Team
