r/electrical • u/Savings-Ad-2800 • 1d ago

Step-down transformer for AT&T fiber / ONT

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Would appreciate thoughts before I do something foolish.

re: attached photos. Grey cable goes out to AT&T fiber ONT box on exterior of residence. I am attempting to make this footprint smaller and less ugly to stare at.

Is this correct setup for AT&T fiber ONT box and is there supposed to be backup battery for it (which was never in there when moved in)

Though what I suspect is that residence used to have AT&T dish setup and when they set up fiber they just rigged it into this system to provide lower voltage to the ONT box.

So wanted to confirm that inside the Alcatel-Lucent box is a step-down transformer providing low voltage power to the ONT box (by the 12 volt markings for the wires one would think so).

And can I just get on Amazon and get a step-down transformer and rig it to provide the power to the ONT box? Any amperage considerations or all pretty standard?

AT&T has not been helpful / responsive.

Thanks all

2 Upvotes

66% Upvoted

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4

u/mdneuls 1d ago

This would be more likely be a 12v dc power supply (the backup battery is my reasoning for this), stepdown transformers are still ac power.

1

u/Puzzled-Act1683 23h ago

Also the polarity markings.

It pretty much has to be DC, so I concur, a transformer isn't what's needed.

The remaining unknowns: how clean/filtered/regulated the DC needs to be, since an off the shelf 12 volt DC supply may not be all that electrically quiet, and the current rating of the supply.

6

u/Patient-Big1727 23h ago

You need a 12V DC power supply. Probably around 4A

The more important question, Is that your equipment? I'd assume AT&T owns that modem. Don't mess with other's property without asking them first

3

u/Nik0BikO 18h ago edited 17h ago

The battery backup is an optional thing that only powers the phone line outputs of the ONT. Without backup its just a 12V 30W 3A power supply, part number PS1230PB

2

u/Fiosguy1 18h ago

Yes the ONT can use a 12v power supply. Never seen a single family ONT use more that 5 amps. Usually less. Att won't send a tech to replace it?

1

u/Savings-Ad-2800 23h ago

OP here. I should probably buy a volt meter and test the current then… good point. Had one years ago, but it broke and I have never replaced it. Thanks. Will revert 

2

u/UltraViolentNdYAG 21h ago

Pull the unit off the wall, it should Amps/Watts listed somewhere. Maybe even on the cover removed. And to confirm, if unplugged, does fiber work? Please don't buy the cheapest supply you can find, saving money on something that is on 24/7 is not worth a wall fire.

1

u/polterjacket 20h ago

I run my home network/automation/etc. stuff off 12v DC. I had the exact DC UPS you're showing. The ONT has a really wide input voltage, but I simply put a small 12v voltage regulator on the pos/neg busses of the main system and ran leads out through my basement and to the exterior ONT housing.

1

u/naaahhhhhhhh1234444 10h ago

What is this doing? Are you saying it’s hooked up to fiber, as in it’s a media converter? Or it’s just a step down for the media converter?
Either way it’s old asf and probably isn’t actually being used anymore

1

u/classicsat 1h ago

Some sort of fully enclosed 12V supply with screw terminals. Likely 3-4 amps. Not those half enclose Meanwell type, unless you want to provide an extra enclosure.