backchannel - Renogy's “isolated” 60A DC-DC

[from a thread on reddit]

My 60a Renogy DC to DC charger just bit the dust…. I need an isolated version

It definitely is isolated

Renogy is sloppy with their language, reusing words that have existing meanings (cf. “Boost” for absorption, etc).

  • that product page mentions “Isolated input/output” without further comment
  • p10 of of the manual states: “The DC-DC input and output terminals are isolated, meaning that the output voltage can be kept stable without interference from the input circuit.” This is odd wording in this context but appears to refer to the completely normal ability of all DC-DC to have distinct voltages on the inputs and outputs. It’s what makes them DC-DC chargers.
  • p9 states “The DC-DC share a common negative ground
  • the wiring diagram on p10 shows both of the charger’s NEG terminals running to the chassis ground.

Common negative grounds are antithetical to the concept of isolated DC-DC chargers.

Is it conceivable that Renogy’s lowest-end 1212 series is galvanically isolated but they aren’t explicitly saying so and are encouraging non-isolating installation? Yeah, I guess. I don’t have one in front of me and can’t test continuity between the NEG terminals. There is zero chance OP could be walked through using a multimeter.

I mentioned the possibility of using a relay.

Not sure about the relay - the problem before was that my house battery was connected to my standard auxiliary battery under my passenger seat (2005 Sprinter). I had no way of knowing how low my batteries were so the house battery was overdraining the auxiliary battery until both were fucked.

What does any of that even mean?

It sounds like a poorly understood problem led to a poorly planned solution that yielded poor results.