2021/2022 Updates on 48v for main system bus

[codingparadox]

Yeah, but I already have 12V run there for a switchable line between the generator start and the house 12V for emergency backup, so it's not a big deal. I'd rather not run more space heaters than needed on the boat (the orion-trs get so hot).

[mcarling]

Originally Posted by codingparadox

I'd rather not run more space heaters than needed on the boat (the orion-trs get so hot).

Are the Orion DC-DC converters hot all the time or only when the load side is drawing current?

[codingparadox]

Originally Posted by mcarling

Are the Orion DC-DC converters hot all the time or only when the load side is drawing current?

Even with no current through it, it was warmer than ambient, when I was first setting up my system. It might have been a fluke, though. But I've kinda assumed since then that they have some nontrivial passive current through it, and I'm really trying to eliminate useless passive current on the boat. . Will be removing the bulb-backed switches for the shower pumps and replacing with non-lit ones even, since they're older non-LED ones and warm up, so pulling non-trivial power.

[mcarling]

Originally Posted by codingparadox

Even with no current through it, it was warmer than ambient, when I was first setting up my system. It might have been a fluke, though. But I've kinda assumed since then that they have some nontrivial passive current through it, and I'm really trying to eliminate useless passive current on the boat.

Thanks. If you have time, it would be an interesting test to disconnect the load side and measure the current flow across the supply side.

[mcarling]

Several posters have mentioned that marine electronics are still predominantly 12V — and NMEA 2000 is exclusively 12V. In December 2020, NMEA introduced the standard which will eventually replace NMEA 2000: it’s called OneNet. NMEA OneNet is based on IPv6 over Ethernet and the voltage is … 48V. BTW, messaging formats are unchanged from NMEA 2000, so the transition should be less painful than the transition from NMEA 0183 to NMEA 2000 (which involved thoroughly different messaging formats). I’m not aware of any NMEA OneNet products that are available yet, but they are surely coming.

[mako]

FYI, I contacted Rule in Massachusetts and they stated "Our company has never discussed a 48VDC bilge pump so I do not think it will happen in the near future."

[donradcliffe]

In regards to the maximum safe voltage, the DC limit is 60 V under dry conditions, and 30 V under wet conditions as specified in UL 1310

[seandepagnier]

i just wanted to add the shock potential for 12v is pretty low, 24v is much higher but still not too bad. By 48v (Ive been shocked by various voltages) the potential is _much_higher.

For this reason I would not want to wire an entire boat with this, but if only for a motor with limited wires it may be reasonable.

[mako]

@seandepagnier, your position is understandable. On a 33' trimaran you may not wish to load it down with a generator, air conditioners, washer/dryer, oven, induction stove, etc., in other words, your electrical requirements are modest.

However for new construction, major refits and large boats, the electrical requirements become very large. Throw in hybrid or electric drives, and you're over the edge. And the trend nowadays is to be able to run everything off of inverters, even aircon during evening hours.

I would say for 50' that a 48vdc main bus starts to make sense. At 65' absolutely. And personally if I were in the position to build a big 80'+ boat (that will never happen ) then I'd go 96v bus.

Yes, above 60volts is considered "dangerous" but we manage 240v just fine and the same mindset can be applied to direct current. I think the biggest danger comes from complacency. If you open a cabinet in your boat and see a battery sitting there then you'll naturally relax and not think twice about accidentally touching the posts. However if it is a 96v system, then that relaxed attitude could be dangerous.

[mcarling]

Originally Posted by mako

And personally if I were in the position to build a big 80'+ boat (that will never happen ) then I'd go 96v bus.

Yes, above 60volts is considered "dangerous" but we manage 240v just fine and the same mindset can be applied to direct current.

At the same voltage, DC is a greater short circuit (and hence fire) risk than AC. AC is much easier to switch off than DC because AC voltage passes through 0V 100 or 120 times per second.

On a boat too large for a 48V DC bus, I would not want a higher DC voltage running throughout. I would have 400V to 800V DC in one (two if a catamaran) compartment(s) containing the batteries, MPPT controller(s), propulsion motor controller, inverter, and (if present) shore power charger for the batteries. Everything outside that compartment(s) would be AC or (24V or 48V) DC.

I have a good understanding of the safety issues with 800,000V DC transmission lines and their switching equipment. I’m comfortable enough with 48V DC (and I’m hoping that my next boat can be almost entirely 48V DC), but I would not want 96V DC running all over a boat. In my opinion even 480Y277V is much safer than 96V DC.

[mako]

I don’t think anyone would want 96vdc running all over the boat. There is nothing to power except the inverter(s). By the time you get to that size boat then the entire vessel is A/C powered. On many commercial boats even the bilge pumps. That’s an entirely different class of electrical system.

[mcarling]

Originally Posted by mako

I don’t think anyone would want 96vdc running all over the boat. There is nothing to power except the inverter(s). By the time you get to that size boat then the entire vessel is A/C powered. On many commercial boats even the bilge pumps. That’s an entirely different class of electrical system.

I generally agree with all that — at least for vessels larger than about 120’. So why power inverters with 96V DC? The big efficiency win for the inverters comes from a DC input voltage higher than the AC output voltage. For example, the Drivetek inverters on Turanor are >99% efficient going from about 388V DC to 230V AC. There is no way get that efficiency going from 96V DC to 120V or higher AC. Going from 48V to 96V has little efficiency advantage, it’s difficult if not impossible to find MPPT controllers and inverters at 96V, and 96V DC requires the same safety precautions as 400V DC.

With 48V DC, there is substantial (and improving every year) availability of equipment. I haven’t seen anything in 96V DC except some motors.

[mako]

Concur.

My next vessel will be in the 50-65 Ft range anyway, so will likely go 48vdc.

[mcarling]

Originally Posted by mako

My next vessel will be in the 50-65 Ft range anyway, so will likely go 48vdc.

Mine also. My plan is to have it built in 2024 and fitted out in 2025, so I have about three years to decide whether mine will be 48VDC plus 230VAC or whether it will be 24VDC/48VDC plus 230VAC. It looks like the salient uncertainty is whether or not 48VDC bilge pumps will be available. If 48VDC bilge pumps will be available, then each hull will have a 48VDC LiFePO4 battery bank, MPPT controller/inverter, motor controller, and a rotating pod motor. The inverters will synchronously feed one 230VAC panel. If 48VDC bilge pumps won’t be available at decision time, then each hull will additionally have a 400W 48V->24V DC-DC controller feeding a 24V LiFePO4 battery bank which will power the bilge pumps and any other 24V loads (for example, the solenoid for the 48VDC windlass). If the bilge pumps will be 48VDC, then I’ll power them all from the 48V battery bank in the other (non-flooded) hull.

[mako]

@mcarling, you're putting an interesting configuration together, but your's is an interesting boat, a catamaran with electric drives. Here are some thoughts:
*I assume you'll have a generator onboard for powering your drives when the batteries are depleted. It will need to be large, but say it's 30kW, can you load it up adequately (min 50%) on a weekly basis for a couple of hours to keep it healthy?
*I don't like mixing up too many systems on a boat (like electric, hydraulic) and try to avoid too many voltages as well. Since you need 12v for your navigation electronics, then avoid the 24v bank.
*Two to three years from now you may be able to source 48v bilge pumps, and if you can't then you can fabricate them. Otherwise go 12v.
*Why do you need two inverters? If it's just for redundancy then keep a spare one in a small metal faraday box, with your other electronic spares.