Technical centre

The questions we are actually asked, answered the way we would answer them on the phone. No brochure language, no invented compatibility, and the arithmetic shown where it matters.

15 engineering guides

• Is the Emerson R48-2900U the same as the Vertiv R48-2900U?

  Short answer: yes, it is the same hardware lineage, and the reason you cannot find it is a company name change — not obsolescence.

• Can I mix R4850G2 and R4875G1 modules in the same shelf?

  They fit the same slot, which is exactly why this question comes up. Fitting and working correctly are different things.

• What float voltage do I set for lithium on a Flatpack2?

  The parameter list is short. Getting it wrong is what turns a lithium retrofit into a warranty argument.

• Can I put a 51.2 V rack battery in my −48 V telecom plant?

  The honest answer is: probably not without validating it first — and the reason is arithmetic, not commercial preference.

• How do I disable temperature compensation on a NetSure controller?

  This is one of the two settings that most often makes a lithium retrofit misbehave. It is also one of the quickest to fix — if the firmware lets you.

• Is the Eltek Flatpack2 discontinued?

  No. And the reason so many people believe otherwise is worth understanding, because the same mistake makes buyers replace plants that did not need replacing.

• Where do I set the low-voltage disconnect on a lithium retrofit?

  This setting decides which device opens first when a site runs the bank down. Get the order wrong and the BMS becomes your load-shedding mechanism, which is not what it is for.

• What paperwork does a telecom lithium battery need to ship?

  Two documents and one rule. The documents are routine; the rule is the one that quietly rewrites your warranty process.

• How do I identify my 48 V DC plant?

  Everyone photographs the module. Almost nobody photographs the controller — and the controller is what decides what you are allowed to install next.

• Does my controller need a firmware update before a lithium retrofit?

  This is the question that decides whether a site is a two-hour job or a project, and it is almost never asked before the battery is ordered.

• How does a lithium BMS talk to a telecom DC plant?

  There are two very different projects hiding behind the phrase "the battery talks to the plant", and the quotation rarely says which one you are buying.

• How do I size a lithium bank to replace my VRLA string?

  The most expensive mistake in a lithium retrofit is the cheapest to make: ordering the same number of amp-hours that is written on the old string.

• Does the grounding scheme change when I retrofit a −48V plant to lithium?

  Nothing about lithium requires touching the ground point. What actually changes is that a second monitor — the BMS — is now watching the same wiring.

• Can I reuse the old breaker when I swap VRLA for lithium?

  The breaker bolted to the old VRLA string was sized for a battery that is about to leave the cabinet. Reusing it without checking is a guess wearing a rating label.

• Can a VRLA string and a lithium string run in parallel during a migration?

  "Keep the old string as backup" and "keep both strings electrically connected" sound like the same plan. They are not, and the difference is the float voltage.

These guides describe general engineering practice on −48 V DC plants and the parameters that drive compatibility. They are not a substitute for the datasheet of your specific battery and the manual of your specific controller — and every parameter here has to be confirmed against both before anyone changes a live plant.