Is now the time for a move to 48 volt DC systems?

Ben Stein

Ben Stein

Publisher of, passionate marine electronics enthusiast, 100-ton USCG master.

30 Responses

  1. Colin A says:

    I used to do some system design. If a boat was system heavy I would always pushed people towards 24VDC with 12VDC converters (basically for electronics). I think if all the motor loads and inverter loads (etc) are at a higher voltage, then a converter makes sense for electronics. Lot less complex then a split system and if everything over a couple amps is on 24 VDC it makes sense. We did quite a few boats this way in the 40-80′ range. At the time we ran the electronics off Newmar or BEP 20 amp converters.

    48 VDC is a bit more problematic and you will (for now) end up with two systems. The reason for this is basically pumps. 48VDC thrusters and windlass’s are now not that uncommon, but finding a potable water pump, bilge pump or marine refrigeration designed for boats is a challenge. Which then means that all your charging sources have to handle both 12 VDC and 48VDC (or have some method of bank to bank charging) .
    There are some larger DC to DC converters out there. Meanwell being a common one, and I think analytic systems offers one that can do over 50 amps marketed at commercial marine. But if you have heavy enough draws that those are required the cost to have a split system might be similar.

    So shorter thought. 48VDC will make a lot more sense when you can buy more marine equipment in that voltage, which I have a feeling will come.

    • Andy says:

      “finding a potable water pump, bilge pump or marine refrigeration designed for boats is a challenge”

      On my current boat these all run on AC anyway.

      There is a DC bilge and housewater backup pump(s), but these could well be 12VDC if no 48VDC unit is available.

  2. Mic says:

    I would love to see a marine electric systems manufacturer develop a comprehensive solution to the all electric (or mostly electric) boat. A solution that handled high power loads, inductive loads, and low power devices (electronics), and charging sources equally well with a systems approach. 48 volt systems have been on the drawing boards of automotive manufacturers for decades. And hopefully, as they become more common the builders of marine electric systems will be able to leverage those economies of scale to the advantage of the marine industry.

    • Ben Stein Ben Stein says:

      48 volt has indeed been on automaker’s drawing boards for a very long time but, except for hybrid and electric propulsion batteries, we haven’t seen it come to reality yet. I think this is in large part because of the challenges of sourcing 48 volt componentry and the sheer amount of 12 volt equipment out there. My hybrid Ford Fusion has a high voltage hybrid propulsion pack and a totally separate 12 volt system for entertainment, comfort, and control systems. I think there are real benefits to be realized from a move to higher voltage, but it’s also proved harder than many might have thought.

      -Ben S.

  3. Charles says:

    I think another large concern with the 48 V systems is safety. Working in telecommunications rooms was an eye-opener a decade ago when one of my guys dropped a screwdriver on top of a bus bar, which shattered the plexiglass cover, which meant the pliers that he dropped about 10 seconds later shorted out between the positive in the negative. I don’t know what was more traumatic watching the pliers turn red hot in about a second, or watching the red hot pliers explode into the molten metal. 48vdc on boats will increase the risk of fire, but then again maybe the move will lessen the risk of fire because no as many “undersized” wires would be used in 12v systems. Either way I think we are still 20 years away from a major change in the vast majority of vessels on the water.

    • Andy says:

      Pliers shorting a battery turn red equally well on a 12VDC battery.

      Its the current that heats them, not the voltage…

  4. Ben Ellison Ben Ellison says:

    What I’ve noticed on some high-tech boats is 48v for main DC storage and generation — or much higher voltage if electric propulsion is involved — and then both 24 and 12 volt subsystems for standard loads, like all those pumps Colin mentions. That sounds overly complex, but I can see how it makes sense given all the factors being discussed.

    Also worth noting is that virtually all the distributed power / digital switching systems I know of can handle both 12 and 24v. And also that 50v DC is apparently a threshold when it comes to safety requirements, or so I’ve heard.

    • Andy says:

      “also that 50v DC is apparently a threshold when it comes to safety requirements, or so I’ve heard.”

      Interestingly enough, in Europe the threshold for safety is 120VDC.

      That is scary high, I think.

  5. paul shard says:

    One great advantage of 48V involves charging. Carrying much greater power through the same size wires means you can have an alternator produce much more power. So a 100 amp alternator at 12V would give you 1200 watts, but at 48V you get 4800 watts from a reasonable size alternator.

    With larger Lithium battery banks arriving on more new boats it is very nice to be able to charge them up quickly with a powerful alternator.

    Paul Shard

  6. Colin A says:

    I should bring up one more item here which is engine staring and charging. I don’t think I have seen an option for anything bigger then 24V for a marine diesel starter. Which means having some lower voltage system or possibly a closed system with a super cap to handle the engine.
    There are a lot of reasons higher voltage aren’t that common yet.
    I would say if I was going to design say a 45′ motoryacht from scratch, I would go with a 24V main system that would cover engines pumps refrigeration and lightning (with 12V converter as required) then a 48VDC system that would run the thrusters, stabilizers, windlass and inverters. I would leave standard engine charging for 24VDC, and add a second alternator (possibly PTO driven for 48 VDC.) to allow for running heavy loads under engine with out a generator, I would also feed solar into the 48VDC bank. I would have a 48VDC to 24VDC charger for times when the engine was off (If this was my personal boat I would like to monitor this part for a while and then automate it later on once I was comfortable with the best possible operation) .
    I think the big question for a system like this is if you need a generator would you go for a small AC generator and battery charge or go custom and build a 48VDC generator. The other possibility is no gen if you keep HVAC loading low.

    • Andy says:

      48VDC starters are available on automotive side, depends on the engine size of course.

      Though as it is wise to have a separate starter battery with its own charging anyway, it does not really matter if the voltage is different, that much.

      But an optimal solution would be to have a PTO bolted BLDC generator with starting capability. Maybe airstarter as an ultimate backup.

    • Andy says:

      Btw, what is the reason to have 24VDC in a boat where the big loads are 48VDC?

      I think 48VDC for big loads and 12VDC for navigation, VHF, N2K etc which does not need much power makes more sense, and “only” two voltages is required.

      Actually every 24VDC boat needs 12VDC as well today, so it does not add any more complications compared to today.

      • Colin A says:

        Mostly due to things like refrigeration and pumps, but also keep wire sizing down for things like lighting. Really it would be 24VDC for everything except electronics that can’t run on 24. Ideally if you could get 48VDC refrigeration, bilge pumps, engine starters, I would just go that way.

        • Andy says:

          I would leave the engine starters out of the discussion, as they are typically separate batteries anyway, can be trickle charged from DC-DC or AC-DC charger or something.

          But for fridge, there are 48VDC units available, or could be an AC unit. Pumps can also be AC driven, and backup could very well be 12VDC.

          I just don’t see a point on _three_ DC voltages, too much complexity. 12VDC is still needed for N2K, VHF etc, so it is a good choice for backup voltage.

  7. Andy says:

    “Unfortunately, I haven’t seen large step-down transformers available.”

    How big you need?

    Schaefer C5632 takes 48VDC and outputs 240 A at 12VDC, and you can parallel many if more is needed.

    There are more options available, but maybe best is to have a 12 VDC critical load battery charged via DC-DC or AC-DC charger, latter with options for from genset, shore and/or inverter.

    • Andy says:

      Meanwell SD-1000 is maybe more handy form factor, and outputs 60A at 12VDC, and also supports multiple parallel units for more power and/or redundancy.

  8. Andy says:

    I think one point to note is the main driver for 48VDC is off grid and off grid solar especially. There 48VDC is getting more popular fast, and that is why Victron provides most all their models at 48VDC as well.

    On boats is the electric propulsion.

  9. David says:

    I now have a 38kw 48v system.
    1000ah onboard…
    Boat is now all electric off-grid.
    Not looking back…

    • Andy says:

      Can you share the details? Brand of batteries, charging, usage etc?

      • David says:

        EG4 8x48v100aH
        Signature Solar 4x450v bifacial
        Victron MPPT, charger and inverter

        Recent trip from Kemah to Hitchcock, TX 35 NM starting capacity according to the Electric Yacht monitor/computer 26.4hrs runtime
        At destination 5.5 hours later 24hrs runtime remaining with about 30% reefed jib.
        Battery bank at: 65% remaining capacity.

  10. Jon says:

    Great write up!

    We installed a hybrid 48V Victron 48/10000 Quattro System complimenting our legacy 12V system, on our boat the Elli-Yacht. Instead of fussing with DC toDC converters, we just let the legacy 12V Charger and Battery Bank serve that function…

    All of our 120/240V loads are on our 48V Inverter so the 12V System is constantly supplied/floating by being powered by our 48V system. Or, the 12V charger/power supply can be turned off to extend our power use by drawing from the 12V battery bank and replenish when we run our mains or the genset recharges the 48V LiFePO4 Battery Bank.

    Originally being a California boat, the Elli-Yacht was outfitted with all electric systems. 4 AirCon/Heat Exchangers, electric hot water and now, induction cooking. This creates significant loads that were simply out of the question on a 12/24V system which can now become common place on a 48V system.

    Here is more info on how we skinned the 48v ‘cat’. Cheap Used Valence Lithium LiFePO4 batteries + Victron 48/10000 Quattro = Off-Grid boat life (EP 8)

  11. yaarthe7 yaarthe7 says:

    Earlier today there was an article about nVidia’s new 12-pin power supply. GPUs in general are quite power hungry, and so are some CPUs. Why are we still using 12V internally in computer systems? Going to 24V or 48V would lower current requirements in cabling, and could increase efficiency in power supplies and power regulators.

    • Andy says:

      Problem is mostly the chips that run internally on very low voltages, like 1.x volts, and relatively huge currents, and DC-DC conversion has its quirks. Its a complicated issue.

  12. Ben Ellison Ben Ellison says:

    Pleased to notice that Maxwell has 48v windlass models that fit medium size boats:

    That could simplify cabling a windlass except unless you’re also powering a bow thruster up there, because 48v thrusters only seem to come in large sizes. Unless I’m missing something?

    Why am I researching windlasses? Well, our first Gizmo cruise since 2020 started with a windlass failure and a lost anchor. Damn!

    Anyone feel especially positive or negative about any windlass brands? I’m looking at Maxwell, Lofrans, Muir, and Lewmar vertical models, rope & chain gypsy plus capstan. It will be 12v but Gizmo already has 4/0 cable to bow.

  13. Chris from Balmar here. We introduced two 48V alternators and a regulator a few years ago, and are starting to see some traction in this direction. We have some early adopters that are using our 48v alts with great success on their boats.

    A few years ago, I wrote a white paper outlining the case for 48V systems:

    RV Manufacturers are embracing 48V systems, and I think in a few years we will see this in the marine market as well.


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