ev-gavia avatar image
ev-gavia asked

48V to 12V isolated charger?

Hello, for a boat, I'm searching for a way to use a 48V system (used for propulsion) to charge 12V batteries used for house loads.

  • The charging device needs to have isolation between the 48V and 12V legs
  • The charging device needs to have programmable charging parameters for the 12V batteries (battleborn LFP)

The Orion-Tr series of converters are not smart and just output a steady voltage, since they are converters only, so they won't work for this use case

The Orion Smart charger/converters only support 12V/24V and not 48V.

I could use a MPPT solar charge controller but I'm not sure that they are actually isolated.
I do see the "SmartSolar MPPT RS 450|100 & 450|200 - Isolated" but I think it is overkill, and too big for the space available for the device.

Any ideas of a victron product that would work? Are the usual victron solar charge controllers isolated?


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2 Answers
JohnC avatar image
JohnC answered ·

Hi @ev_gavia

I don't think the normal mppts are isolated, and Victron don't really have a single unit of any type to handle 48>12V. I use a 48/12 Isolated Orion to do similar. Output V is adjusted with a tiny screwdriver through a hole in the casing, It's a flat setting, but very stable once set. The Orion has a remote port though, and I switch mine with a Multiplus Assistant.

So I went for a look back through your previous posts to try and find what you're using, and found your electric boat proposal. What you could consider using is a shunt with a relay output on the 12V side (like the BMV) to switch the Orion after it reaches (say) a set V or SOC. And you'd find a BMV configured as a dc-load on your main batts will be very useful in seeing your system as a whole.

I think you could make this work well with your Battleborns. Depending on your 12V loads you may need more than one Orion though.

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ev-gavia avatar image
ev-gavia answered ·

JohnC, thanks very much for your detailed thoughts. After considering the options available we've decided to get an AC 12V battery charger (Victron Energy Blue Smart IP67 12-Volt 17 amp Battery Charger (Bluetooth) 120V) and use that to charge the two Battleborns; the AC charger will draw from the Multiplus Inverter back on the 48V side.

I think the advantages of this are

  1. A programmable charger that can have a specific LFP profile (vs the Orion constant voltage solution)
  2. AC power for the charger is flexible, we can pull power from the Multiplus or charge directly from shore power (or in the shop if we pull the 12V batteries out)
  3. Simpler and easier to troubleshoot?

I can keep the Orion converter onboard as an emergency backup to power the 12V system critical house loads (radio, lights) if the 12V batteries fail.

The drawbacks of using the AC charger are lowered efficiency (yet this charger claims 93% efficiency, which I guess is pretty good?), and there might be some others I haven't thought of.

I suppose the AC charger is "isolated" (maintaining isolation between 12V and 48V system) since there is no shared negative reference ground between the two DC systems? But I'm beyond my DC understanding.

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