Hi.

We're required to get a backup power solution (battery not solar) for a site.

The site currently has 2 x 2 crs125-24g-1s-rm & 2 x passive POE injectors. (Passive POE Injectors are powered by 1 x 24v 2.5amp power supply)

Previously we've used a Mecer UPS and a 12v 105amp lead acid battery for a similar installation.

The problem is that solution is very bulky and it seems so unfortunate to go [AC Input | 12v DC]-> UPS [AC Output] -> DC power supply

Any other suggestions for a "low cost" but more about size of installation?

Get an APC UPS that just plugs right in, and install the UPS package on your router. Then you can access some nifty features like power monitoring and automatic shutdown.

Running the devices directly off a battery plant would be better. Ideally with redundant battery chargers to protect you in case a battery charger fails. Easier if all the devices can operate off the same voltage. And there is no switching time upon AC power failure - only the battery chargers stop charging the battery or batteries.

Note: Important to understand the safety about working with a large battery. The short circuit current available from even a car battery is substantial. Get a metal wrist watch across it, and you are apt to lose your hand. Proper wiring and fusing is a safety must. FYI, as part of my job, I deal with large 48 volt battery plants. The largest are 3,600 AH at 48 volts (that's about five tons of battery). I have seen the end result of a 1/4 inch stainless steel bolt that was turned into a flashbulb - and that was only across 180AH at 48 volts.

You can purchase modules designed for just such a use: UPS with battery charging and monitoring, with DC input (from your PSU) and direct battery power when the PSU/mains fails. For instance the DRU-24V10ACZ for 24V: http://www.farnell.com/datasheets/3182601.pdf

That one seems to cost around £35; quite cheap for a ready made solution. Just add batteries and a 28V PSU.

You can purchase modules designed for just such a use: UPS with battery charging and monitoring, with DC input (from your PSU) and direct battery power when the PSU/mains fails. For instance the DRU-24V10ACZ for 24V: http://www.farnell.com/datasheets/3182601.pdf

That one seems to cost around £35; quite cheap for a ready made solution. Just add batteries and a 28V PSU.

Interesting

Is there such a thing but with ethernet inputs/outputs to go in between regular injectors and devices? Would make things a bit simpler

Or ideally something with multiple ports that can do passive 24/48v (switchable) to power multiple devices

Is there such a thing but with ethernet inputs/outputs to go in between regular injectors and devices? Would make things a bit simpler

Use your existing POE injectors, but power if from a 24 volt battery plant. Use the same thing to power the routers. Much easier than any sort of UPS.

Is there such a thing but with ethernet inputs/outputs to go in between regular injectors and devices? Would make things a bit simpler

Use your existing POE injectors, but power if from a 24 volt battery plant. Use the same thing to power the routers. Much easier than any sort of UPS.

I'm confused

The injector needs 120/240v input which converts down to 24v (many devices we use are 48v though)
The injector has an ethernet output to the radio, that's where the power is. So where does the device go? I imagine it goes between the injector and the radio, ergo it would make more sense to have ethernet in/out and the battery connected there as well. So that if the injector loses power from the mains, the battery supplies power instead right?

The injector needs 120/240v input which converts down to 24v (many devices we use are 48v though)

I guess @k6ccc was talking about RBGPOE (or some other passive injector) which takes some DC power through power jack and puts it on the UTP wires. In this case one uses DC battery power directly, no conversion takes place ever. Prerequisite is equipment which works on voltage supplied by battery pack - whatever voltage battery pack provides, 24V is a pretty good compromise between battery size/price (2 standard 12V lead-acid batteries) and current (=cable loss) through UTP cable. If your gear works off 48V DC, then use appropriate battery pack and charging electronics.

The original poster said that he has two CRS125 routers and two passive POE injectors running on 24 volts. My original and followup suggestions was to run both the routers and the POE injectors off the same 24 volt battery plant.

The original poster said that he has two CRS125 routers and two passive POE injectors running on 24 volts. My original and followup suggestions was to run both the routers and the POE injectors off the same 24 volt battery plant.

How do you ideally split current between 4 devices (2xCRS, 2xPoE injectors) ?
With some sort of 1xinput/4xoutput fuse box ? Just plugging-in 4 cables into 1 terminal block ?

The original poster said that he has two CRS125 routers and two passive POE injectors running on 24 volts. My original and followup suggestions was to run both the routers and the POE injectors off the same 24 volt battery plant.

How do you ideally split current between 4 devices (2xCRS, 2xPoE injectors) ?
With some sort of 1xinput/4xoutput fuse box ? Just plugging-in 4 cables into 1 terminal block ?

Yes, in reference to my original post talking about battery safety, you ABSOLUTELY should fuse each load individually. Fuse panels for low voltage DC are readily available from your local auto parts store, home improvement store, electronics store, electronics parts supplier, even Amazon.

Note: The commonly used ATC type fuses that are used in most cars these days are normally rated for 32 volts DC. Therefore, that style of fuses can be used for a 24 volt system. They should NOT be used for a 48 volt system.

I use this:

https://www.townet.it/portfolio-items/4095/

look at the specs..