Adding a battery backup to fiber ONT

Inspired by https://www.exitthefastlane.com/2012/04/how-to-use-verizon-fios-battery-backup.html

Frontier fiber Internet does not come with a battery backup unit. The XGS-PON ONT Model FOX222 has a 16V 1.5A Molex Micro-Fit 3.0 Receptacle (Dual Row, 8 Circuits),  see post on DSLReports. 

You can get a CyberPower DTC36U12V indoor UPS and CBL7PIN350MLX-004-BLK (4ft) or CBL7PIN350MLX-010-BLK (10ft) cable. I paid <$45 for UPS + cable shipped on ebay.

On UPS it has a 7 pin (TE Connectivity AMP?) connector. It takes 1 x RB1270 (7Ah) battery, but you can use a 1 x RB1290 (9Ah) battery of the same size. The UPS has 12VDC on battery output voltage and FOX222 ONT works fine with that. 

• ExpertPower EXP1290 12 Volt 9 Ah Sealed Lead Acid Battery With F2 Terminals, datasheet (this is the same battery that is commonly used in 120V UPS)

Except the ONT is configured (?) to shut down LAN when UPS is on battery (ONT optical still runs, but LAN Ethernet is shut down to conserve power). This makes the UPS useless for Internet service. Frontier customer service would not reconfigure the ONT to run on battery.

Looking at datasheet for the cable and datasheet for UPS, 7 pin UPS <> 8 pin ONT power connection.

Only 7 pins are used, with 1 (+) and 5 (-) being 12V power. I did some tests to figure out the remaining 5 pins (On Battery, Replace Battery, Battery Missing, Low Battery, Signal Return)

A/C, battery missing

pin 2 ,4 ,6 ,7 shares the same voltage

on battery

pin 3, 4 ,6 ,7 shares the same voltage

A/C

pin 2 ,3 ,4 ,6 ,7 (all signal PINs) shares the same voltage

pin 2 is on battery, pin 3 is battery missing

swapping pin 2 and pin 3 should trick on ONT to run LAN on battery (ONT won't know UPS is on battery)

Let me know if you figured out pin 4 / 6 / 7.

To make things easier without damaging the factory made cable, you can order cable assemblies (18AWG, better than factory 20 AWG power + 22 AWG signal) from Molex (free shipping)

• Micro-Fit 3.0 Female-to-Pigtail Off-the-Shelf (OTS) Cable Assembly, Dual Row, 150.00mm Length, Tin (Sn) Plating, 8 Circuits, Black
• Micro-Fit 3.0 Male-to-Pigtail Off-the-Shelf (OTS) Cable Assembly, Dual Row, 150.00mm Length, Tin (Sn) Plating, 8 Circuits, Black

when connecting the male and female pigtail, remember to swap pin 2 and pin 3. 

CBL7PIN350MLX Molex female <> Molex male cable assembly <> pigtail with pin 2/3 swapped <> Molex female cable asembly <> ONT male plug.

To connect the pigtails, you can use Wago 221 splicing connector.

I did it the hard way with

• Molex Micro-Fit 3.0 Dual Row (8 Circuits) Male & Female Receptacle Plug, w/Terminal sockets, (Pack of 1 Complete Set)  
• Molex Crimping Tool,Knoweasy Open Barrel Terminal Crimping Tool for Molex,Delphi,AMP and Tyco,Harley,PC and Computer,Automotive 24-14 AWG  

Properly crimping Molex terminals definitely takes some practice. The terminal is rated for 20-22-24 AWG but it did not work very well with 20 / 22 AWG wire, either the insulation being too thick or insulation tabs being too small. And you have only 1 pin to lose. The pins are not magnetic. 

It is probably easier and cheaper to just get a 120V UPS for ONT and not have to deal with the cabling hassle. But 12V UPS is probably more efficient for this application.

Alternatively, adding a 100 Ohm resistor to on battery signal might do the trick.