Backup Routing when power to phones lost

My PBX runs on 12v and is backed up using auto battery. Most phones (48v) are AC powered and only have short term backup. My calls come into a ring group and go to IVR if not answered. I would like to designate an analog phone set connected to my FXS card up to ring when one or all the connections to the ring group phones are lost.

How would I go about creating something like this?

Let me understand, the power supply in the PC is used to charge the battery?

This is really a bad idea. You are overcharging the battery and at some point will boil off the water. In the process you will really toxic gas into your office.

Batteries under constant load will have a designated float voltage to operate at. The rectifier (AC to DC) converter output should be set to this value.

You can also get 12V to 48V DC to DC converts. You can probably also find a PoE switch with a 12V input.

Lastly this all sounds like a lot of effort and you still need to properly fuse the loads on the battery.

It would be much better to get a UPS with an external battery connector (I got a liebert 2kw on Craig’s list for $40 the other day) and connector your external batteries to that.

Also inside the batteries need to be in a vented spill catch for fire code.

“You can also get 12V to 48V DC to DC converts. You can probably also find a PoE switch with a 12V input.” Interesting, haven’t seen one like that (12v in 48v out).

“UPS with external battery connector.” Interesting. At this point all I have running AC is cable modem and phones I am looking for a 12v cable modem.

Rest of the suggestions are really good for someone who is considering a 12v solution and doesn’t understand such things.

Back to the problem at hand, ideas on how to set up an analog backup extension that normally doesn’t ring when the digital phones are connected but does when the connections are lost.


2 Linksys switches: 12V
1 Wireless Router: 12V
1 PBX with mobile power supply: 12V
1 Blue Sea 5 fuse block & cover
1 3-stage smart 12V charger
1 185amp/hr auto battery & case

Cable modem: AC
POE power block 48V: AC

Critical phones have adapters powered
along with desktop by local backup power.

Features: High efficiency native 12 volt.
Low cost relative to duration of backup ($300)
Only power system failure points are battery and charger which are easily replaceable.

You are possibly better of with a -48 DC volt backup system, This is what the Telcos use and you will find that ebay carries many telco grade routers, switches etc. that will use that power bus, also 48v drop in PC psu’s, chargers et all at very reasonable prices.

I disagree with Dicko, a -48 solution is not energy efficient with that small a solution, you have have a BDFB and most people don’t intuitively work on positive ground systems.

With that charger you are creating the unsafe condition I described. It has no forward current sensing ability so it can easily overcharge the battery. Best case destroyed battery. Worst case is a building full of toxic gaseous acid.

Years ago I set an equalize voltage wrong on a -48 rectifier. There were 8 batteries in the rack powering a channel bank connected to a T1. Got a call from that office that people were not feeling well and it smelled funny. Got over to the office and it was filled with acrid acid smell. I had boiled all the electrolyte out. With only front door and fixed windows I was forced to call fire department. They show up in the hazmat garb and use the huge yellow vent tubes to clear the office. I was standing watching all this when my boss pulled up. I just looked at him and said “this won’t be making on the resume”. Luckily no one was injured.

Anyway, I think powering the phones off the 12v plant is the proper solution. The failover phone is hokey.

Here is a link for $13.00 to a 12v boost converter. you could the power any of the cheap -48v PoE switches.

Let me know what you think.

hehe, let me forward that to AT&T and Verizon, they and their antecedents have obviously been doing it wrong for 160 years :wink: One month of physics or electronics 101 would have prevented such simple mistakes, it’s just ohm’s law, Anybody here know what ohm’s law is? The good old chargers used metal oxide rectifiers, which self limited the charge, for the last 30 years they use microelecronics to to do it just as well or even better.

OK, enough from the techno geek oldies, One pragmatic solution is to get a cheap UPS and extend the wires from the short order internal 12v nicad selaed battery to and external deep charge marine battery, (obviously it needs to be on a piece of wood) you might be surprised as to how well that will perform, monitored charging, and many hours of backup power, it does take a few hours or days to recharge an exhausted battery though.

That’s what I do at home. Have an old Ferrups from Best with 8 batteries. 30 amps @118V for 18 hours.

I also have an exterior generator inlet plug and a manual transfer switch.

Also I said for this dudes application that the -48 would be overkill. If you look at the pictures of the channel banks I put in the hotel they are powered from a 4 slot Lucent rectifier.

Excellent, but a manual transfer switch? Through another 100 bucks at your solution

Caterpillar has a an upgrade kit to fast start their big diesels with 12 gauge shotgun shells (also probably overkill)

I have heard but never seen one of those. At the data center the big Megawatt generators have block heaters, pre oilers and are at full power in about 30 seconds. They have two, two UPS, two utility feeds from two sides of the building. It’s the NAP for the area with L3, Qwest, Time Warner, Global Crossing (RIP) etc having their Internet POP’s there. The main fiber trunks go to Chicago West and DC East. It’s an impressive facility. The DMDM OC-192 has 8 Lambda’s on each pair so that would be 45mbps1928 = 6.9 terabits per pair if I have my decimal point in the right place.

Anyway, back down to earth, that’s a great value in a xfer switch. I am going to order one right now.

Happy Fourth

And to you also, anecdotally, for historical reasons, japan’s grid is 60Hz 120 volts in the south and the older 100volt 50 HZ in the north (go figure why :slight_smile: ), the two systems are connected with a big Toshiba Plant in the middle, I have been there, it also is rather impressive.

( a few more than 8 batteries ther :slight_smile: )

@dicko: that grid frequency’s difference originates from the very initial different generators provided to Japan by differents companies (AEG 1895 vs GE 1896), main info here. It’s so impressive to see how decision taken in a far past can have a huge impact still today, read here.

@SkykingOH you probably would love to read the book “Tubes” by Andrew Blum (a journey to the center of the Internet), Chapter 7 “Where the data sleeps” is the one to go. I read an Uncorrected Proof copy back in 2012 and it was very interesting.