Alernative ways to power a Pi

[stderr]

Usually they have 2x32W florescent bulbs in a fixture, We're talking small closet.

You still haven't explained why you need to use a pi. Would an arduino work? You might be able to use batteries in such a case. It's also not clear if you are going to be hooked up to the PoE network why PoE isn't ideal. But the real question is, you are saying that these closets are filled with electronic networking gear but there are no power plugs at all? How is the network gear powered?

[Jim Manley]

Solar power (photovoltaic) panels convert _solar_ wavelength photons into electron flow, which are from primarily toward the red end of the visible spectrum due to the physics of the materials used in the panels. Fluorescent lights actually generate mostly UV internally in the bulbs, and the phosphorescent coating on the inside of the bulbs absorbs the UV photons and re-emits the energy almost exclusively in the blue end of the visible spectrum. You may be starting to see the problem with trying to use solar power panels that need to see mostly red-spectrum photons being provided photons largely from the blue end of the spectrum ...

Then, there's the horribly inefficient process of converting from electron flow to photons and back to electron flow (somewhere in the low single digits of percentage, even with the best equipment), not to mention the high cost of the equipment, even if it were 100% efficient.

As for the inductive current measuring meters using the wrap-around clamps, the amount of current induced in the clamp sensor is minuscule, which just happens to also be highly desirable due to the Heisenberg Uncertainty Principle. The process of measuring a quantity changes the quantity, thereby affecting the measurement ... oops

If you do go the battery route, be very careful that you use charging equipment appropriate to the battery technology selected. What works for lead-acid (auto/marine/etc.) batteries is generally not appropriate for Nickel-Cadmium (NiCd), Nickel-Methal Hydride (NiMH), Lithium-ion (Li-ion), or Lithium-Polymer (Li-Poly) battery technologies, and vice-versa between any of those technologies.

[W. H. Heydt]

At that price, installing outlets would be the cheaper alternative...even at the price the OP cited.

I want the name of your electrical contractor

OP cited $1000 to put in the needed outlets...a dozen or more, as I recall. At $70 for a battery per installation, that hits $1000 pretty fast.

[CarlRJ]

OP cited $1000 to put in the needed outlets...a dozen or more, as I recall. At $70 for a battery per installation, that hits $1000 pretty fast.

I got the impression the OP was quoting $1000 per closet for putting in outlets. Presumably the closets are not all in a neat row (else you'd just have one big closet), but scattered all through multiple buildings.

[justinm001]

Running power is last resort and would cost about $1000 per location with about 50 locations. These closets are designed to not have power for compliance reasons and would be a huge pain if needed. We service about once per year and looking for a permanent solution.

These are network closets with cat3 and cat6 wiring only for voice/data. No switches or anything powered in the room other than a switch and 4ft flourecent light. All our switches and phone systems are in a secured room, then all cables go here in each floor and then are spread across the floor. We have power conduit in these and could induction tap but can't add an outlet.

[W. H. Heydt]

Running power is last resort and would cost about $1000 per location with about 50 locations. These closets are designed to not have power for compliance reasons and would be a huge pain if needed. We service about once per year and looking for a permanent solution.

The *permanent* solution is to get outlets wired in. Yes, it's going to cost. But at least it isn't some Rube Goldberg wierdness.

...other than a switch and 4ft flourecent light.

When you say "switch" you mean the light switch? You can't wire power from the switch box. Assuming it's a standard--small--junction box. Why not replace the switch with a switch-and-outlet module that fits in the same space?

We have power conduit in these and could induction tap but can't add an outlet.

[/quote]
Can't add an outlet? Or *won't* add an outlet? It sounds to me like you have a classic case of "penny wise and pound foolish" going here.

[davidcoton]

When you say "switch" you mean the light switch? You can't wire power from the switch box. Assuming it's a standard--small--junction box. Why not replace the switch with a switch-and-outlet module that fits in the same space?

I'm not sure how US systems are wired, but usually it is poor practice to mix lighting and power (sockets) on the same circuit. Fine if only a Pi is plugged in, tricky when something beefier gets substituted. Lighting circuits are not designed for power distribution. Also, there is a way of wiring light switches, widely used in Europe, which means that only the line ("hot") side of the supply appears at the switch, so a socket cannot be connected.

While I would be investigating the "compliance reasons" for not having power sockets in the closets (which is something I have not come across in the UK), and also the apparently extreme quote for socket installation, this does seem one case in which POE is a reasonable solution. As long as a nearby outlet can source power to a spare network point, the cabling is all in place and power can be extracted in the closet. It does mean that there is something else, somewhere else to go wrong, but it is likely to be more reliable than attempting to get power from fluorescent lights via solar panels (64W in, light output a fraction of that (25%?), light captured a fraction, probably <1%, conversion efficiency <10%, power output negligible, less than a Pi needs) or non-contact induction (extracting sufficient power could adversely affect the downstream load.)

Just consider, if any such technique could work, it would be at least as widely available as POE.

[CarlRJ]

... These closets are designed to not have power for compliance reasons and would be a huge pain if needed. ...

Why not replace the switch with a switch-and-outlet module that fits in the same space?
...
Can't add an outlet? Or *won't* add an outlet? It sounds to me like you have a classic case of "penny wise and pound foolish" going here.

I'm sensing the key phrase is "compliance reasons". Physically hacking the room itself - adding a power outlet/etc. or your suggestion of replacing the wall switch with one including an outlet - would not fall within some existing agreement or regulation, and would thus require going several levels further up the chain of command to get things approved, inspected, and signed off upon. While methods that don't require hacking the room itself (batteries, solar, induction) don't technically violate whatever paperwork. We're looking for an engineering solution, but perhaps engineering isn't all that's in play here.

From an engineering standpoint, installing a separate new outlet is the most solid answer (albeit at high cost), your suggestion of replacing the wall switch with a switch-plus-socket is the pragmatic answer (inexpensive yet could still meet building codes), PoE would run the Pi's great and hands-off if you can inject power from upstream in every situation, a stack of marine batteries would get the desired hands-off/no-room-modifications solution with the overhead of having to revisit at regular intervals, and most of the other possibilities get increasingly sketchy/unrealistic (solar cells powered off fluorescent lights, etc.).