DC-DC converting for 48V

DIY
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1

Like many others, I’m in the process of upgrading my motorhome’s solar system from 12V to 48V. This has created a quandary that I’m seeking to resolve, the DC-DC power transfer process. As manufactured, the motorhome has four power systems, the chassis(12VDC), the house(12VDC), the house(120VAC), and the battery-bank (12VDC). There are three power transfer processes in the motorhome: from the battery-bank to the house(12VDC), from the chassis(12V-alternator) to the battery-bank (12VDC), and from the battery-bank (12VDC) to the chassis(12VDC) – i.e., the “battery boost.” My goal is to preserve all of them in my conversion to the 48VDC battery-bank, if possible. The conduit between the house and the chassis are two (1 pos & 1 neg) 2 AWG (33 mm2) cables. Note that my use of the term “battery-bank” would include the batteries, inverter, fusing, etc.

  1. Battery-bank(48VDC) to the house(120VAC) – This will be accomplished by the Quattro inverter.

  2. Battery-bank(48VDC) to the house(12VDC) – This is where the first problem lies. There are two possible solutions that I know about. The first is to keep a small 12V battery, charged with an Orion XS 12-12/50 supplied with power from an Orion-TR 48-12/30. IMO – this solution would increase maintenance issues, as the battery would add a fifth power system. My idea is to use four Orion-TR 48/12-30 to supply the necessary power. The largest power user of the house(12VDC) is starting the generator (105A for 10 seconds). This solution would appear to reduce the maintenance issues, if I’m not missing something here (many people oppose this idea). Would the surge of starting the generator negatively harm the lifespan of the Orion-TR 48/12-30? Note: The generator would need to be started on a varying frequency: Not at all in the winter or summer months (in RV campground), and in an increasing frequency (from once a week to every day) during the spring and fall months. Other than the generator, the power usage would likely be less than 30 amps at any one time.

  3. Chassis(12VDC-alternator) to the battery-bank (48VDC) – This is another problem. I’ve heard two solutions: 1) Add a 48V alternator to the motorhome, and 2) Add an Orion-TR 12/48-8 (Would this work? Would this connect to the chassis-house conduit like the Orion-TR 48/12-30?). Does anyone have any other ideas?

  4. Battery-bank (48VDC) to the chassis(12VDC) – I think this would be solved with the solution for the battery-bank(48VDC) to the house(12VDC) system which feed the chassis battery, but I’d like your thoughts on this.

2

Unfortunately you will need a small 12V battery for starting the generator. Although you measure 105A, the initial surge to get the motor turning will be much higher. This is best provided by a small battery with a float charger.

For the alternator issue: Dual alternators would be the most elegant solution. Otherwise, I would think about changing the main alternator to 48V and then dc/dc back to 12V, but with sufficient power to run all loads, lights, heaters, fans.

3

As you are aware, Victron makes very few 12v → 48 and 48–> 12v products. I’m all in favor of using 48v systems whenever possible, but in a motorhome there are two good approaches in my opinion. Either install a second alternator that outputs 48V and use Orion 48/12 converters to provide 12V DC to lights, water pumps, etc. and a second Orion 48/12 to keep the chassis batteries charged

OR

Use a 24V house bank with two or three Orion 12/24-15A to charge from alternator and multiple Orion’s 24/12 to run 12V loads and charge the chassis batteries. You could instead use a second alternator that runs at 24V.

There are bi-directional 12V-48V chargers on the market but they are expensive and finicky. In the Victron ecosystem, unless a customer is willing to install a second alternator then you’re better of using a 24V system with multiple Orions.

In the future, hopefully Victron releases more 48V converters for mobile solutions but right now the choices are limited.