Marine

Is now the time for a transfer to 48 volt DC programs?


48 volt and 12 volt battery banks

For so long as I’ve been overlaying marine know-how, I’ve heard constant speak of a transfer to the next voltage than the defacto 12-volt customary. 48 volts is usually cited because the candy spot between effectivity, security, and diminished weight. However, why make a change? 12-volt has served boats properly for a very long time, why change? Let’s check out the explanations for a change and maybe some causes to maneuver cautiously.

There’s little doubt that increased voltage comes with some benefits. These benefits embody smaller wires, much less voltage drop, and for a lot of gadgets, higher effectivity working at the next voltage.

The quantity of vitality a load requires is measured in watts. Watts equals volts instances amps. For instance, let’s take a look at a 600-watt load. At 12 volts you have to 50 amps of present to get 600 watts (12*50=600). At 48 volts it’s solely 12.5 amps to get 600 watts (48*12.5=600).

Wire sizing chart courtesy Blue Sea Programs

Since wire sizes are decided by the variety of amps they carry, lowering the amperage reduces the wire dimension. For instance, at 3% voltage drop over a 25 foot circuit size we would wish 4 AWG wire at 12 volts and 50 amps. Our similar load at 48 volts would require 12.5 amps and therefore solely an 8 AWG wire. For those who run to your native West Marine to buy the wire, 4 AWG will value $3.39 per foot in comparison with $1.39 per foot for 8 AWG.

As you may see within the desk above, Victron’s suggestions for battery cable dimension differ significantly relying on the battery financial institution voltage. A 12-volt, 3,000-watt inverter would require both 1/0 or 2/0 battery cables, relying on the space from the batteries to the inverter. Victron recommends two optimistic and two unfavorable cables. 1/0 cable weighs over just below half a pound per foot and a couple of/0 is simply over half a pound. 1/0 is $6.89 a foot and a foot of two/0 will set you again $8.89. Since you have to optimistic and unfavorable, that’s one aspect or the opposite of two kilos a foot and both $27.56 or $35.56 per foot..

Now, contemplate a 48-volt inverter. Leaping to a 48-volt system cuts the cabling wants down fairly dramatically. Check out the cabling wants in case your battery cable run is lower than 5 meters. As an alternative of 4 1/0 cables at 2 kilos and $27.56 a foot, you want 2 2 AWG cables at half a pound and a complete of $8.88 a foot.

Vitron MultiPlus-II inverter spec sheet

However, battery cables aren’t the entire story of 48 volts. The Victron MultiPlus-II inverter spec sheet exhibits the rising efficiencies of upper DC voltage models. The three,000 watt inverter is on the market in 12, 24, and 48 volts at 93%, 94%, and 95% effectivity. A 2% distinction in effectivity could not sound like a lot, nevertheless it’s lowering your complete vitality misplaced by 29%. Lastly, utilizing increased voltage battery banks means smaller photo voltaic cost controllers. 1,000 watts of photo voltaic at 12 volts would wish MPPTs with a capability of 80 plus amps. The identical 1,000 watts at 48 volts solely requires 20 amps of MPPT capability. Which means, smaller, cheaper, and cooler working cost converters.

48 volt concerns

Thus far, we’ve solely talked about the advantages of shifting to 48-volts. However, there are some causes for warning. FIrst, I believe we’re a protracted methods from having the ability to convert a complete boat to 48 volts with out a 12-volt system.

I’ve heard folks make the case that it’s easy to make use of voltage converters when 12-volt energy is required. Sadly, I haven’t seen massive step-down transformers out there. The biggest I can discover is the Newmar 48-12-35I which helps 35 amp intermittent masses however solely a 20 amp steady load. The 20 amp steady ranking matches the most important models out there from Victron or Mastervolt.

Sizing a converter would possibly appear to be so simple as simply including up the hundreds and guaranteeing you’re underneath the utmost of the converter. However, that’s not the entire story. DC motors require rather more energy to begin than they do to function steadily. For instance, I measured a small, freshwater pump on my take a look at bench. When the motor is working it attracts round 3 amps. However, at startup, the inrush is over 12 amps. Actually, the very best measurement I noticed (however didn’t get an image of) was almost 14 amps. That’s a 4 to 5-fold enhance over regular working. As you may see within the snippet from Newmar’s instruction handbook, they don’t suggest their converters be used with inductive or motor masses.

Inrush masses grow to be very troublesome (or unimaginable) to fulfill as the scale of the hundreds goes up. The specs above are for a Maxwell RC6 windlass. Maxwell’s specs record the RC6 for a 15-25 foot boat. At 12 volts the 500-watt motor attracts 42 amps. Inrush might be 3-5 instances that or properly over 100 amps. There’s no 48-volt to 12-volt DC-to-DC converter within the marine market that may deal with that load.

Hybrid options

The image of the battery financial institution firstly of this text is from an upcoming article on a ship with a really fashionable method to energy and air con. The boat has each 12-volt batteries to service conventional home wants and a 48-volt battery financial institution devoted to a 48-volt inverter. Proper now this looks like the one sensible method to introducing increased voltage DC programs on boats.

And not using a 12-volt home system, every little thing not out there in 12-volt fashions must be supported by a converter. This will result in vital challenges find the appropriately sized fashions and vital expense. As talked about, that’s not all the time doable. 24-volt elements are pretty broadly out there, however usually at a major premium. Almost each 24-volt boat I work on additionally has at the very least a small 12-volt system for navigation electronics. The NMEA 2000 spec requires 12-volt energy to the bus. Many digital elements will run on 10-30 volts of energy however there are additionally lots that solely function on 10-16 volts.

The truth is that the price of converters and specialised elements will dwarf any financial savings from diminished wire sizes or higher efficiencies. Thus, I imagine, the most suitable choice to seize the advantages of upper voltage is through a hybrid method.

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