Repurposing a POE network switch, possible? - Page 1
Forum section: electronics / projects

author: mapleLC
author_rank: Frequent Contributor
timestamp: February 08, 2023, 01:48:36 pm
content: I've had this idea and its growing on me because the battery bills are getting a bit muchMy wife likes those battery candles, but they are pieces of shit and don't last, eat up batteries. It got me thinking, since I have my house networked, could I run a parallel POE switch for a power only enabled network cable and pass a thin wire to power these candles?The candles are more of side quip, but the more serious question is about powering alternate/non-computer devices to from POE network switches? It seems like a ready DC source that can manage low power devices.

author: wraper
author_rank: Unknown
timestamp: February 08, 2023, 02:07:12 pm
content: You can but you will need to add step down voltage converters.

author: mapleLC
author_rank: Frequent Contributor
timestamp: February 08, 2023, 05:12:55 pm
content: Don't you have voltage regulation control at the switch?

author: langwadt
author_rank: Super Contributor
timestamp: February 08, 2023, 05:21:17 pm
content: https://www.sparkfun.com/products/18709

author: dobsonr741
author_rank: Frequent Contributor
timestamp: February 08, 2023, 07:56:21 pm
content: Awesome, we just reinvented a USB charger you probably have tens of them, unused at home. What’s the utility value of using POE and Ethernet cabling to power LED candles at home?Sorry, I had to ask.

author: mapleLC
author_rank: Frequent Contributor
timestamp: February 09, 2023, 01:33:15 am
content: Quote from: dobsonr741 on February 08, 2023, 07:56:21 pmWho are you addressing that to? If it's to myself, be less of a smart ass.To the rest of the forum not into hadtoasks:Its a technical question about POE, and what other utility might exist for it. Obviously, the story was a simple example of what I might mean by other kinds of utility.To understand what kinds of utility might be possible, I was looking towards networking/EE expertise here to understand POE's specs and more importantly whether it has a protocol that might prove problematic to work around.Any comments on this topic are welcome...

author: mapleLC
author_rank: Frequent Contributor
timestamp: February 09, 2023, 01:37:12 am
content: Quote from: langwadt on February 08, 2023, 05:21:17 pmThis is the hop I was looking to eliminate. My thinking was:Variable power sourceFixed cablingVariable power consumersIf we were to make it as atomic as possible, it's this. Running AC across the home to power increasingly less and less power hungry devices makes less sense to me. The switch as this variable power source is interesting because of all the extra capabilities beyond the "dumb use" example of the led fake candle that sorryhadtoask guy was all uptight about.

author: Someone
author_rank: Super Contributor
timestamp: February 09, 2023, 02:32:07 am
content: Quote from: mapleLC on February 09, 2023, 01:37:12 amPoE requires negotiation, so it will always need a little widget on the sink side like that example from sparkfun (and for low power devices it usually uses a keep alive load/dump). Square peg round hole.

author: calmtron
author_rank: Regular Contributor
timestamp: February 09, 2023, 02:16:41 pm
content: If I'm not misinformed standard PoE uses a fixed voltage around 48V on the device side, ie not a negotiable / variable voltage (except for cable loss compensation). You do need to tell the switch how much power (current) you intend to use.

author: wraper
author_rank: Unknown
timestamp: February 09, 2023, 09:59:40 pm
content: Standard active PoE needs negotiation. But there are also non standard versions like passive PoE. Especially common in cheaper equipment. Non standard versions may have a different voltage too.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 10, 2023, 04:25:32 am
content: Just get rechargeable batteries for them?

author: DavidKo
author_rank: Frequent Contributor
timestamp: February 10, 2023, 01:04:32 pm
content: Depends on the switch you have. Some have 24/48V capabilities (probably even passive PoE). For active PoE I usehttps://www.raspberrypi.com/products/poe-plus-hat/on my Pi and I'm happy with it - with right switch it can give you 4A.

author: mapleLC
author_rank: Frequent Contributor
timestamp: February 10, 2023, 05:13:01 pm
content: Quote from: DavidKo on February 10, 2023, 01:04:32 pmLow end voltage would be more interesting, the typical ones we see like 5v. I wonder if there is lower level control of the voltages, considering we are talking about stepping down the voltage, there is an interesting case to find out how the voltage in the switch is "decided upon" - this seems like it could be modified.

author: berke
author_rank: Frequent Contributor
timestamp: February 10, 2023, 06:14:16 pm
content: Maybe I'm missing something and I don't know what your network setup is, but if you're gonna clog a network port for wife candles, maybe you can just use the cables as DC cables and drive 5V DC or whatever the candles need from the other end directly?You could even still use some pairs for networking, it just won't be gigabit.

author: mapleLC
author_rank: Frequent Contributor
timestamp: February 11, 2023, 05:01:57 pm
content: Quote from: berke on February 10, 2023, 06:14:16 pmI know dude, I can just plug them in the wall too. Do you have any networking/POE/802.af or otherwise relevant experience that could move the thread along?

author: Monkeh
author_rank: Super Contributor
timestamp: February 11, 2023, 06:30:42 pm
content: Quote from: mapleLC on February 11, 2023, 05:01:57 pmI can move the thread right back tohttps://www.sparkfun.com/products/18709PoE is not a variable voltage. To enable, you put a 25kohm resistor across the powered pairs, and from there on you must maintain a minimum load of around 10mA for a minimum of 60ms every 400ms, or power will be removed. A DC/DC converter will be required for any load voltage other than ~48V with relatively loose regulation. Drawing more than 15W on a port will require further negotiation.

author: Tom45
author_rank: Frequent Contributor
timestamp: February 11, 2023, 07:59:03 pm
content: There's a difference between supporting POE vs. providing power over the unused pairs in an Ethernet cable.I've seen POE voltages between 12 and 57 volts. In general there are a variety of voltages and choices of pairs to use with POE. It's a mess.An industrial POE color line scan GigE camera that I use specified 12 to 24 volts via a separate power connector, or POE. What they didn't say was that if using POE, the POE voltage must be 48 volts. Took awhile to figure out why the camera wouldn't power up with 24 volts on the POE line. They also didn't specify POE A vs B.In your case, you can bypass all of the POE negotiation and multitude of "standards" by just using a POE injector to provide power.An example:

author: dobsonr741
author_rank: Frequent Contributor
timestamp: February 11, 2023, 07:59:11 pm
content: What is the exact equipment, what standard does it support? Passive of active? Passive will give you 48V DC without asking. Active needs negotiation.There are non-standard voltages, like 24V. Vendor specific POE injectors can do even 15V. However, the voltage is one specific one, will not be able to ask 5V or 9V.The challenge I see repurposing a POE switch or injector is that the voltage is too high for the usual step down regulators - those max voltages usually stop around 36V. Safely consuming POE needs a regulator to withstand 60V.For vendor specific example:https://dl.ubnt.com/datasheets/poe/PoE_Adapters_DS.pdfFor the various standards:https://en.m.wikipedia.org/wiki/Power_over_Ethernet

author: Monkeh
author_rank: Super Contributor
timestamp: February 11, 2023, 08:02:13 pm
content: Quote from: Tom45 on February 11, 2023, 07:59:03 pmSo somewhere on the label or in the documentation it would say something like '802.3af'. This covers all these points. It's PoE (802.3af, at, or bt), or it isn't PoE.

author: ajb
author_rank: Super Contributor
timestamp: February 11, 2023, 11:38:09 pm
content: Quote from: Tom45 on February 11, 2023, 07:59:03 pmIIRC a PoE PD is required to accept A or B, per the standard, so that it will work with any PSE, which may choose to provide A or B or all four pairs.

author: nightfire
author_rank: Frequent Contributor
timestamp: February 12, 2023, 12:56:26 am
content: As POE needs usually some negotiator logic to power the port, and then generates 48 Volts, AND those 48 Volts will have to be converted somehow to the battery voltage the candles are using- surely it can be done, but in this case the "way will be the goal"- buying rechargeable batteries (and maybe make them fit in a housing under the candle in case they use those CR2032 Lithium cells) will be simpler in the long run and probably yield a better WAF (Wife acceptancy factor)There are even rechargeable Button-cell batteries, like the Varta Coinpower series, if you really want to dive deep in such applications...

author: berke
author_rank: Frequent Contributor
timestamp: February 12, 2023, 02:08:10 pm
content: Quote from: Tom45 on February 11, 2023, 07:59:03 pmWhat camera is that? I have an (ex-)Point Grey Blackfly S that I've only used with a Netgear PoE switch. The manual claims that it conforms to "IEEE 802.3af-2003".

author: Tom45
author_rank: Frequent Contributor
timestamp: February 12, 2023, 04:40:31 pm
content: Quote from: berke on February 12, 2023, 02:08:10 pmTeledyne Dalsa Genie Nano area scan cameras.

author: mapleLC
author_rank: Frequent Contributor
timestamp: February 27, 2023, 03:49:55 pm
content: Quote from: nightfire on February 12, 2023, 12:56:26 amIndeed there are simpler ways to do this, it was more of a thought experiment using the candles as a way to consider possibilities.Its not reasonable to wire a few candles, but widen the discussion and consider a POE as a low voltage system for the house in addition to standard AC. My reasoning is that there are fewer devices in your house today proportional to the number of devices that are low voltage, which historically was 0. AC started in homes with the basics, light.... then went from the first bulb to the whole house. Then 100 bulbs were consuming 60watts each, then 50 years later 10,000 leds are consuming a fraction of that power.The power system in the house no longer matches the utility, so we went from the WWW internet to new WWW... world of wall warts everywhere.