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I need to Power an RPi from a +24VDC industrial power supply. The RPi is mounted in a DIN-rail mounting box, in which there is plenty of space. The +24VDC is quite reliable and does not vary by more than about 0.1A depending on loading.

I've looked at DC-DC converters, and it's looking like a 15w supply would be needed to give +5VDC and a max of 3A (so seems ideal) but I can only find PCB mouting types, which isn't ideal, as I need the solution to not be making a new PCB or requiring too much soldering.

There are a fair few DC-DC converters available on ebay, but I really need something that is fairly standardised. If it could be something with screw terminals for the +24VDC, and an output that you can then connect to the header to power the RPi directly, (as I believe that's possible.. you don't have to use the USB micro B port do you?) that would be ideal.

I've also seen a reference to a UBEC, no idea what it is. Would that be appropriate?

Any and all suggestions or ideas would be welcome.

Many thanks!

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    This seems to be a shopping question. ANY switch mode supply (which accepts 24V) >1A would run the Pi, slightly more if peripherals are connected. – Milliways Dec 11 '17 at 10:52
  • I'd go for a UBEC. Simply for the flexibility on input voltage. – joan Dec 11 '17 at 12:13
  • The input voltage will be completely fixed at +24vdc, so input flexibility isn't an issue. It being an off-the-shelf solution matters more.. – David_R Dec 11 '17 at 12:46
  • You may wish to check out the "Pololu 5V, 2.5A Step-Down Voltage Regulator D24V25F5", amazon.com/Pololu-Step-Down-Voltage-Regulator-D24V25F5/dp/… or pololu.com/product/2850. – bstipe Dec 12 '17 at 5:09
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You are looking for the wrong solution. A DC-DC converter not only gives a lower voltage but also has galvanic separation. They are also very expensive compared to a simple regulator. All you need is a 5volt regulator, but because your input voltage is high you should look for a switching 5V regulator. They come in 3 pin through hole like a TO-220 case but then a bit bigger.

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UBEC is just a step-down DC-DC voltage converter (Universal Battery Elimination Circuit) for flying aircraft models.

They can be switching or linear mode. If you are want to use this, make sure it is switching mode one. Otherwise you need to dissipate great power on 24V/3A (about 57W). I doubt that any linear regulator will survive this.

There are a lot of switching DC-DC step-down modules ready to use. The only problem is, that many of them are overrated on eBay by the max current they can deliver. Most of them 2A output max (even if it's written 3A or 4A), especially the cheap models. All of them need appropriate cooling with 3A output. Check if then can handle 24V input (I think you need some voltage durability reserve, at least 24V + 10-15%, e.g. 26-28V input). Or they even can catch fire.

You can connect 5V directly to the expansion header, but then you shouldn't connect any power supply through USB.

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I will recommend this, (https://www.robotshop.com/ca/en/5v-3a-step-down-voltage-regulator.html)

5V, 3A Step-down Voltage Regulator

As for the output (from this very regulator), please use the Micro USB male connector, as I have seen, directly connecting 5 volts to the motherboard of Raspberry pi can go wrong or get shorted and fry U3 regulator IC on the Raspberry pi. Details about Micro USB connectors are available on the net.

USB DIY Connector Shell (type Micro-B Plug)

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You can use a 24v switching power supply with 12v 5v entry so you can plug raspberry and also 12v equipments ....

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