Raspberry Pi Forums

I have three Pis setup with cameras for video surveillance. The standard wall plug with the passive POE adapters like these: http://www.amazon.com/HCP05-Passive-Inj ... oe+passive have mixed results. When using 50' of 350MHz certified CAT5e, it works fine. When using 250MHz CAT6, it doesn't provide enough juice to power the USB hub on the Pi, which means no networking or KB/Mouse.

A proper PoE setup can be quite expensive, so let's see what we can build!

I challenged one of our electrical engineers to come up with a solution. The first product used linear power regulators, but the more power they had to dissipate, the hotter they got. The hotter they got, the lower the voltage to the Pi would drop, eventually low enough to go into a reboot loop about every minute or two.

The final product is cheap, incredibly easy to build and small. Head over to DigiKey.com and purchase the following:
PN: 102-1715-ND (regulator)
PN: 478-7139-1-ND (Input Capacitor)
PN: 445-8250-ND (Output Capacitor)
PN: A98076-ND (wire terminals, buy two)

Solder them to a breadboard like so:
#1: Vin(neg)-> one side of input capacitor-> ground post of regulator (pin 2)-> one side of output capacitor-> Vout(neg)
#2: Vin(pos)-> other side of input capacitor-> Vin post of regulator (pin 1)
#3: Vout(pos)-> other side of output capacitor-> Vout post of regulator (pin 3)

You should wind up with something like this:


This powers the Pi (measured on the TP1,TP2) with a solid 4.85V no matter what the load without generating any heat. This was tested with the passive PoE adapters posted above with a 12V 1A laptop power adapter through 50' of CAT5e. The layout looks like: Laptop power adapter-> passive PoE Injector-> CAT5-> passive PoE splitter-> DIY regulator-> Raspberry Pi.

Total cost is about $15 each. Should take any input voltage from 6V to 32V DC and drop it to a steady 5VDC/1A.

You can use something like this http://www.ebay.com/itm/Hot-LM2596-DC-B ... 1c367bf788 for the step down and they're adjustable so you can bump them to 5.25 volts. I'm not sure you could build one for that price

That's definitely an option, but it also uses a linear regulator which dissipates the voltage drop via heat - which is the design we originally built, but would drop below the Pi's lower limit because it couldn't dissipate the heat fast enough. My Pis are located outdoors in the Florida heat, so the switching regulator is perfect.

It would also be interesting to see the voltage over time charted out of that device. I'd be willing to wager that even though the output is adjustable, it will vary quite a bit as the regulator heats up and cools down.

EDIT: Never mind what I just posted. I misidentified the regulator in the link you posted. It is a switching regulator. That is by far the cheapest solution I've seen. It would be interesting to see how it performs.

I use them to power my PIs and they've been rock solid

The LM2596 is a switching regulator too, not a linear-type? So why should it produce much heat?

MfG, FM_81