backchannel - shore power alongside a DCC50S

[this backchannel post was inspired by a reddit thread]

• OP has a Renogy DCC50S, a type of combo DC-DC/MPPT charger.
• has portable panels that will not be used in the scenario
• has access to shore power in stretches that last “a few days”
• is considering the Renogy 20A AC charger for shore power charging
• which suggests the bank is LiFePO4 (Reno does not make a wall charger for lead, AFAIK)

unsuitablility of the Reno for this use case

IMO the Renogy charger is not well-suited for this purpose. The charging voltage is too high (14.5v) and the manual suggests the charger will hold it there indefinitely. It has alligator clip leads which will either be insecure, require removal after use, or be cut off.

the traditional approach

The traditional tool for use with shore power is a converter, which is intended both to charge the bank and to support loads.

The Reno is ~$110. In that ballpark one can get a multistage converter designed for such use, more powerful, more configurable, and more robustly built. (example, not necessarily a recommendation).

For the described use case (on shore power a few days) I might:

1. use it in constant-voltage mode (13.0v - 13.2v?¹) to hold an SoC baseline while running loads for the majority of the stay, then
2. the morning of departure turn on staged charging to pump Ah into the bank. The Absorption voltage of the model linked above is 14.4v, still too high IMO. But it wouldn’t be sitting at that voltage for days and might not even reach it depending on how long it’s in charge mode.

using a “dumb” converter

But we already have 50A² of alternator charging that we will be able to leverage when driving away. IMO one smart charger is sufficient for most use cases.

So let’s consider a different approach:

1. use it in constant-voltage mode (13.0v - 13.2v?) to hold an SoC baseline while running loads for the majority of the stay, then
2. drive away charging at 50A

untraditional approaches

12v power supply

Costs might be reduced further by using a 12v power supply dialed into the target voltage instead of a bespoke converter.

24v power supply feeding MPPT

If for some reason we did want to have staged charging at the site we could still do it inexpensively: shore power -> 24v³ power supply -> DCC50S PV inputs

Mine is set up that way. A small MPPT is used for portables occasionally and for shore power support during the build and the one time to date I had access to shore power.

1. I don’t know what SoC OP wants or how his system will behave; it would require a bit of experimentation.. I have played with voltages in that range to good effect. ↩

2. portables will not be deployed while driving so the full 50A will be available ↩

3. set to ~22v, as the DCC has a 25v input limit. Maybe a 30A PS? ↩