48 Volt System

[s/v Jedi]

Originally Posted by Adelie

That also means that 4x the heat is being generated in smaller wires.

Are you trying to argue that a lower voltage is better? (hint: don’t, ends badly )

- my example uses the same size wires. Most marine wire is rated for 600V.

- when we look at generated heat, we don’t look at 3% voltage drop but to ampacity of the wire. The ampacity will be many, many times higher than what a 3% voltage drop forces you to use, so the amount of heat being generated in those circuits is completely irrelevant.

[RaymondR]

Amp flow solely creates heat. You can put 1,000,000 volts on a conductor and not create any heat whatsoever.

However any current flow whatsoever through that same piece of wire will create heat.

The amount of heat produced depends upon the amount of current flowing which depends upon the amount of resistance in the wire which can be overcome which depends upon the voltage applied and so the circle closes.

Consequently, one has two choices as to how one transmits power (amps x volts), you can increase the amps or increase the volts.

QED increasing the volts increases the power transmitted without increasing the heat produced in the wire and since heat=power losses, increasing the voltage decreases power loss.

[GrowleyMonster]

Quite simply, it's all about the amps.

For a given amount of work done in a certain amount of time, higher voltage means lower current, which gives you either:
1. lower line losses and heating,
2. ability to use smaller wire, or
3. A little of both.

Conversely, for the same amount of work done in the same amount of time, lower voltage requires greater current, which means either:
1. More wire heating and line losses,
2. Necessity for larger wire gauge, or
3. A little of both.

12 volt systems have proven their practicality. There is considerable carryover from the automotive world and due to the huge market, there are a lot of relatively inexpensive choices in stuff like alternators, motors, relays, solenoids, electronics, circuit breakers, monitoring meters and systems, and so on. Where 12v falls flat on its face is feeding very large loads, providing higher power than the customary/traditional boat stuff. EP, for instance. A case could be made over large refrigeration loads, such as central air for a large boat. The issues with heat dissapation and voltage drop and wire size with "normal" boat loads is a pain that we are already quite well used to. When you start talking about running say 30 to 100 amps for minutes or even hours, is when 12v meets its match, and higher voltages are really attractive. Or in new builds or where a complete electrical refit is needed.

Higher voltage provides the aforementioned benefits when loads are modest. Benefit enough for the increased cost of components is maybe debateable. Benefit enough for an arbitrary change to 48v, for a classically equipped yacht, doubtful. Benefit enough for a desired upgrade to high powered equipment, including possible backup EP, all electric galley, stuff like that, practically a necessity. Running large AC loads with an inverter is another case where higher voltages are attractive.

On my e-boat, even at 48 volts, I still used 2/0 copper for interconnect links, DC supply to controller, and phase wires to motor. I could have gone smaller. I preferred to reap the modest performance and efficiency gains, instead. Had I instead gone with a 96v system, I might have dropped the wire size a bit. Or maybe not. The thing is, while finding 48v replacements for everything on the boat can be a PITA and costly, there are viable sources out there. 48v home storage systems have some popularity with off-gridders and even grid connected users. Golf carts represent a huge market for various electric doodads in 48v. 48v is the most popular system voltage for small electric yachts, and that has been a big market mover for 48v equipment. low power DC/DC converters from China cost chimp change, though of course there is a small power loss in the conversion. Most marine wire used for 12v is literally more than adequate for 48v. Higher voltages are a problem, but 48v is doable, if the use case recommends 48v over 12v.

[RaymondR]

In the 1950s there were still a lot of 6 volt vehicles around and Volkswagon were one of the last to shift to 12 volt. I think the major impetus for the change was voltage problems with starter motors, particularly during cold weather.