switch powered by PoE? passive injector backwards?

C

cam235

Pulling my weight
Oct 5, 2016
322
164
I want to put a 5-port switch in a garden shed so I can have several cameras around there without needing to run four separate cables all the way to the house. However, the shed is unpowered, so all the power has to come from the house. Each camera uses under 3 W, so the total power requirement is not too high. I can get a standard 5-port gigabit switch under $20, but the least expensive PoE-powered switch is about 10x more expensive. So it makes sense to power the switch with an "active PoE splitter" available with 12V or 5V output.

However, I also want to send the original +48V power on to the remote cameras, so I need to get the +48V DC as well as +5V. Can a "passive PoE injector" like Gigabit Passive PoE Power Injector Compact Size 3~48V 1A | eBay also be used backwards to tap off the incoming +48V ?
 
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watch your total power draw. switch + 4 cams may well exceed the 30W PoE+ is rated for, especially if the cams fire up IR at night...
 
As usual, Nayr had the exact answer I was looking for, the 4-port PoE splitter. This is just what I had in mind: Amazon.com: UHPPOTE 10/100M 4 Ports PoE Extender Up to For Network AP IP Camera Telephone Equipment: Home Audio & Theater (apparently also available on aliexpress etc.)

Since I'm using separate IR illuminators on the house itself, out at the shed I'm just running the cameras without IR so they are each pretty low power. I measured them at only 2.2 watts each as mentioned in this post Next best thing under 100$ to Starlight Varifocal Turret (IPC-HDW5231R-Z)

It would be a different story if I had PTZ units with motors etc. but these are simple fixed lens cams, so nothing to move, glow or heat up.
 
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So to add to this, I've done this before when I wanted to run cameras off my UPS but didn't have the conduit capacity to run more cable or on a few farms that had no power in remote locations.

I found that some TrendNet POE switches had a low power consumption (onboard, not POE capacity) and basically bought a POE+ injector/splitter kit which then split out the power to power the POE switch but also ran the data over the same line. Worked quite well over the years.

In my case, the hard part was making sure you could find a POE switch that didn't require a high voltage DC input (the POE+ splitter kit I bought just broke it out, didn't give voltage adjustments so I was at the mercy of whatever came off the line. Which was right around 48V - the voltage my Trendnets needed to run at)

I think this is the model I rigged up:
TRENDnet | Products | TPE-S50 | 5-Port 10/100 Mbps PoE Switch

Edit:

I bought these on Ebay for like $20 in some cases without the power adapter as I rigged up my own system. Saved a ton of money, especially if the seller didn't include the original power supply.

I've also seen professional POE powered POE switches (last time I looked they were hardened industrial designs and very expensive, around $200 each).
 
For what it's worth, I got this 4-port PoE-powered switch:
10/100M 4 Ports PoE Extender Up to For Network AP IP Camera Telephone Equipment | eBay
and it works as expected. They also sell a 1-port version of this, called "1-port PoE extender" which can be stacked in series up to 4 units with 120m cable length on each segment. With 4 extenders in series that allows up to 600m cable run overall length from the origin, which is nearly 2000 feet. Fiber would be the natural choice for that length but you'd still need power at both ends. The PoE Extender datasheet claims it's practical to run an IP camera (with PoE draw < 6w power) at that distance.
 
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