48 V DC power for fiber ISPs

You have between a handful and a few dozen cabinets, each with a small DC plant nobody has opened in three years, and the batteries are the part that fails first.

The pattern we see

The pattern is consistent: the network grew faster than the power documentation. Nobody has a current inventory of which rectifier is in which cabinet, the VRLA strings went in at different dates, and the first sign of trouble is a node dropping on a grid dip that should have been survivable. When you ask the OEM, the answer is a new plant — for cabinets whose rectifiers are fine.

What this actually requires

An inventory of what is actually installed, cabinet by cabinet: rectifier, controller, firmware version, string age.
A straight answer on whether the existing shelf can charge lithium, before buying any battery.
Replacement modules for the cabinets that do fail, without replacing the whole plant.
A migration you can do node by node as budget allows, not as one capital project.

How we approach it

We start with the sites you are least worried about, not the most. A pilot on a non-critical node, with the old VRLA string kept on site for thirty days so the change is reversible, tells you more than a specification does — and gives you a documented result to take to whoever signs the budget.

What is actually inside a node cabinet

A fiber node cabinet is not a small central office. It is normally one shelf with a handful of rectifier modules, a controller, a VRLA string and DC distribution — and the three parts age on completely different clocks. The rectifiers usually outlive everything; the string is the consumable; the controller is the piece that quietly decides what you are allowed to install next, because its generation and firmware version gate whether the plant can charge anything other than lead-acid. That is why replacing a battery and replacing a plant are different projects, and why an OEM quoting the second when you asked about the first is not necessarily wrong — just answering a different question.

The three numbers to collect per cabinet, before buying anything

Rectifier part number from the module label. Controller model and its firmware version, read from the display menu rather than assumed from the model. String age and rated Ah. With those three per cabinet you can sort the estate into the cabinets that take lithium as they stand, the ones that need a controller upgrade first, and the ones where the honest answer is to keep VRLA until the plant is replaced for other reasons. Without them, every quotation you receive is a guess wearing a price tag.

Equipment and guides for this segment

Common questions about this family

Can I retrofit lithium into a node cabinet without touching the rectifier?

Sometimes, and that is exactly what has to be established before you buy. The rectifier module often stays; what changes is the configuration held in the controller — charge setpoint, temperature compensation, equalize, charge current limit and low-voltage disconnect. Whether those are reachable depends on the controller generation and its firmware version, which is why we ask for the controller photo and not just the module label.

We have thirty cabinets and no power engineer. Where do we start?

With an inventory, not with a purchase. Rectifier part number, controller model and firmware, string age and Ah, cabinet by cabinet. That sorts the estate into three groups and turns a fleet-wide question into a handful of specific ones. Our compatibility audit produces exactly that sheet, signed, at USD 450 per site — free for the first ten accounts.