Maximum DC input voltage for power?

[TheWaterbug]

Hi! I'm need to power my RPi 2 Model B over 75' of Cat5e, which means I need to crank up the DC voltage at the source to ensure ~5 V at the sink. But if I forget to crank it back down during testing, I'm worried about frying the board.

What is the maximum DC voltage that the Pi will tolerate on the power input without damage? Does the p/s circuit have any over-voltage protection?

[W. H. Heydt]

All Pis are rated for input voltage between 4.75v and 5.25v.

If you are worried about voltage drop from a long cable, extend the AC line (if you are using line power) and plug in a suitable PSU close to the Pi. Alternatively, use a significantly higher voltage and install a decent voltage regulator just before you connect to the Pi to bring the voltage down to an acceptable value.

[MarkTF]

To expand a bit, the current draw of the RPi 2B can vary about 200 mA based on CPU loading. 75' of Cat5 is close to 4 ohms round trip, so your expected voltage fluctuation is going to be on the order of (up to) 0.8 V based on processor activity. Hence, putting voltage regulation at the far end of the cable is probably not a good idea.

[TheWaterbug]

Ah yes, I had calculated 2 Ohms for 75' of 24 AWG (e.g. typical Cat5e), but I forgot that it's a round trip!

This Pi is going to run a camera board and MotionEyeOS (or something similar) so I should probably budget at least 1 A for power.

The key problem (that I didn't mention in the OP) is that this is an outdoor application, as I'm building a BeeCam for my beehive. Bringing AC power to the hive would complicate the project massively.

According to this online calculator I'd need 9 V at the source to have 5 V at the Pi. I think I have an old Radio Shack AC adapter that is switchable to 5, 7.5, 9, and 12V. I'll have to play around with it and see what happens. I'm not sure I'll have room in the tiny little box to put a regulator, so if the maximum power is 5.25 V I'll just have to be very careful

[rzusman]

What you are doing is a terrible idea!

Run 12v, and use a regulator at the Pi end. Doing anything else is just begging to end up with a dead Pi.

A voltage regulator is the size of a postage stamp - If you have room for the Pi, you have room for one.

http://www.ebay.com/itm/3-Terminal-5V-1 ... XQBwlRWEST

[davidcoton]

Run 12V to the hive, then a 12V to 5V converter. The converter doesn't have to be in the hive, a waterproof box outside but close would be fine. Just keep that last run (at 5V regulated) as short as possible.

You certainly don't want to rely on the voltage drop on the cable to reduce the source voltage. If something switches itself off, you could get instant fried Pi -- with honey, and angry bees too. (Could be the next thing after Angry Birds?)

[TheWaterbug]

What you are doing is a terrible idea!

Run 12v, and use a regulator at the Pi end. Doing anything else is just begging to end up with a dead Pi.

A voltage regulator is the size of a postage stamp - If you have room for the Pi, you have room for one.

http://www.ebay.com/itm/3-Terminal-5V-1 ... XQBwlRWEST

Thanks for the feedback. Would this work just as well, besides needing a couple of capacitors soldered to it?

http://smile.amazon.com/Addicore-Positi ... +regulator

[rzusman]

Yes, but that is a "linear" regulator, and so will get hot and require a heatsink.
The advantage to the one I linked to is that it is a "switching" regulator, and is extremely efficient, so no heatsink required.


You can figure out the dissipation of the linear regulator by:

Vin-Vout * Ipi

So, if you end up with 9v at the end of your cable, and the Pi consumes (say) 750mA, the regulator will need to get rid of 9v-5v * .75 = 3W of power. The Switching regulator is at least 80% efficient, so it only needs to get rid of .6W

[GTR2Fan]

One of these would work better for your specific purpose...

http://www.ebay.co.uk/itm/7V-24V-to-5V- ... SwcnpToC3L

[TheWaterbug]

Thanks! The buck converter doesn't ship to the US, so I bought the EZSBC version rzusman linked originally.

Meantime I'll try to figure out how to package this all when my housing shows up tomorrow.

[GTR2Fan]

It would help others to help you if you put your rough location in your forum profile.

[TheWaterbug]

Ah, fixed!

[TheWaterbug]

So I finally got around to working on this. I bought that switching regulator from ezsbc, but probably due to my crappy soldering skills, I burned it up. So I went back to using an $0.18 LM7805, 5V/1A linear regulator for now.

I hooked everything up with the POE injector and extractor on either side of a 75' length of Cat5e, with my regulator board and a USB voltage monitor between the extractor and the Pi:



With the camera attached and the Pi running MotionEye, it draws about ~0.50 A, plus or minus a few mils. At the input terminal of the voltage regulator I'm measuring about 10 V, and at the output I'm getting just under 5 V, so the regulator is dumping 5 V/0.50 A, or about 2.5 W. The back side of the PCB is pretty hot right under the regulator, but the slug of the regulator is screwed onto a ground plane, so I'm hoping it can dump enough heat to prevent it from burning out.

It's been running for 10 minutes, and I'm still getting video, so I'm hoping this means I'm good to go. If I have the inclination I might buy another one of those ezsbc linear regulators and cut down on the power I'm dissipating.

Now I have to work on the enclosure . . .

[pcmanbob]

Thanks! The buck converter doesn't ship to the US, so I bought the EZSBC version rzusman linked originally.

Meantime I'll try to figure out how to package this all when my housing shows up tomorrow.

form ebay.com shipped from china world wide

http://www.ebay.com/itm/New-6-24V-12V-2 ... SwZ1BXeHCv
just one of over 2000 listings

[DavidSturzenbecher]

TheWaterbug,

I haven't seen that camera module before. Have I been living under a rock?

[TheWaterbug]

TheWaterbug,

I haven't seen that camera module before. Have I been living under a rock?

It's the Arducam module with a CS-mount lens. I believe it's a standard Pi camera module behind the lens.

[W. H. Heydt]

TheWaterbug,

I haven't seen that camera module before. Have I been living under a rock?

It's the Arducam module with a CS-mount lens. I believe it's a standard Pi camera module behind the lens.

Ah... I'm kind of hoping that they'll do that modification to the new, 8MP, cameras. Kind of wish they'd use a C-mount, though. I have a bunch of C-mount lenses that go with my 16mm cine camera. (Be fun to use the 102mm F2.7 with a Pi...)

[TheWaterbug]

I put it in a box. I used a simple gasketed food container, similar to these, but available singly from my local Japanese dollar store:



POE comes in through a waterproof RJ45 coupling. I put the both washers on one side of the coupler, around the mating with the enclosure, because I don't need to seal the inside jack:





I used DAP silicone to seal the inside and outside of the lens against the hole I drilled into the top lid, and then afterwards realized that now I can't adjust the focus. :



But this is just a proof of concept. I can try to scrape off the silicone and figure out another way to seal it.

I'll post some images tomorrow when it's light out.

[TheWaterbug]

So my BeeCam is running, but I have the focus point set incorrectly, and there's no way to adjust it on the camera any more. :rolleyes:. The camera also has a surprisingly short depth of field:



I'll either have to reposition the camera or move the hive a bit, depending on which is more work.

What issues would I have viewing through another piece of glass? I'm thinking I should buy another lens (that's not siliconed into a food box lid) and try an enclosure that's just a box with a window, and shoot through that.

And then I need to figure out a way to transcode and re-serve the video stream from a Mac inside my house. If I have more than a few viewers I'm thinking the Pi won't have enough CPU and/or BW to serve them all. I'd rather run one stream back up to my house and then use a beefier computer to transcode to something more efficient, and then serve clients from there.

[TheWaterbug]

So I finally got around to working on this. I bought that switching regulator from ezsbc, but probably due to my crappy soldering skills, I burned it up. So I went back to using an $0.18 LM7805, 5V/1A linear regulator for now.

I had to bring my BeeCam inside to replace the lens and change the lens mount, because it is definitely _not_ waterproof!



It's sitting in a bag of rice right now, which is actually doing a pretty decent job. It'll have water spots, but it'll be dry.

I have another camera/lens assembly, so I put that in behind a standard 35 mm UV filter with silicone:



I still haven't figured out the public streaming bit, but I used ffmpeg to save a 60 second video:



It's working well, but yes, that regulator gets hot as hell.

While I had it inside I only had about 3' of Cat5e between the 12V supply and the regulator assembly, so it was dumping 7W. I had put the regulator board into a prototyping box, and it was too hot for me to touch. It even shut down a few times. It didn't do that during nearly a week when it was out in the field, over 100' of cable, so the 2V/1W reduction over the cable must have been just enough to prevent it shutting down. So I must be right on the margin.

My ezsbc linear regulators should arrive any day, so assuming I don't blow them up (again) I should have fixed the heat problem.

I also replaced MotionEye with RaspberryIPCamera because it outputs h.264 over RTSP, which reduces the network traffic by about 90%. But that might increase the power consumption, because it's doing GPU compression/encoding. I forgot to measure the current before I put it back out in the field.

[paulhothersall]

a little late to this thread, but this is what PoE (along with the bastard relation of 24v DC) was made for.

A TP-Link PoE that drops out a clean regulated 5V-2A is like $13 from amazon.

[TheWaterbug]

a little late to this thread, but this is what PoE (along with the bastard relation of 24v DC) was made for.

A TP-Link PoE that drops out a clean regulated 5V-2A is like $13 from amazon.

LOL! I didn't know these existed. I thought they were all unregulated. Here's one for $14.70 with an output selector switch for 12 V, 9 V, or 5 V.

Had I known I'd have just bought one of these. Still, I have the ezsbc regulators already in the mail, and the TP-Link splitter is a bit large for a camera enclosure, so I still may roll my own for BeeCam2. I'm thinking of wiring the 12 V out from the RJ45 jack into an unused GPIO pin and putting the regulator module output hole onto the 5 V GPIO pin, if I can make the pin numbering work. That would keep it all within the footprint of the Pi, keep it all on one cable, and get rid of the micro-USB cable, which further reduces the effective footprint.

Does anyone know if RJ45 pins 4,5,7, and 8 are truly N/C? It looks that way on the PCB drawing, but I want to be sure!

[davidcoton]

I'm thinking of wiring the 12 V out from the RJ45 jack into an unused GPIO pin and putting the regulator module output hole onto the 5 V GPIO pin

I don't think there are any unused GPIO pins (you may not be using them, but they are still connected on board), and they are NOT safe for 12V.

Also, connecting power via the GPIO header (rather than microUSB) bypasses the polyfuse, so you will lose any protection against a fault in your regulator.