System Overview

Twin Inboard boats or vehicles with 240V AC

This system is specifically called out as inboard because it involves upgrading both alternators to directly charge a lithium battery bank.

Specifications:

System was designed at 24V but specification numbers would change very little at 12V

            16.2KW Hours of Lithium house batteries (90% depth of discharge)

            18KW Hours @ 100% depth of discharge (not recommended)

            4500W AC power from the Inverter/Charger for each AC line

            50A @ 120V AC shore power/AC auto transfer

            This system will also work on 30A as well

            400A house battery charging from the Inverter/Charger

            500A house battery charging directly from the engine alternators

            50A of start battery charging while from alternator through DC to DC charger

            25A of start battery charging from dedicated battery charger

How It Works:

In a twin engine boat most customers want as much power out of the alternators as possible since it’s the primary charging source when away from the dock. To maximize that power the system requires upgrading alternators to an ElectroMaax 250A GenMaax with remote rectifier. You can read more about that alternator on our product page found here.

With up to 250A of power generation available from each alternator, you will need somewhere to store all that power. That is where three 6000W Mastervolt MLI Ultra batteries comes in. These batteries are the house bank and are directly connected to the alternator output. The beauty of this system is when using the GenMaax you can pair it with the Mastervolt Alpha Pro 3 external regulator. This allows the alternator to communicate directly with the MLI Ultra batteries. If the batteries ever want to stop charging, they can automatically communicate that with the regulator and shut current off from the alternator with no risk of damage or back feeding. We feel battery to alternator communication is required when direct charging lithium from an alternator.

One callout is the Alpha Pro 3 regulator only operates on N-Type alternators. Most alternators in North America are P-Type. So, if you want to go down this path we just need to special order an N-type version for you. The good news is all ElectroMaax alternators we sell can be special ordered as N-type.

Since the house bank is being directly charged by your alternators, you will need a way to charge the start battery while under way. We recommend using lead acid start batteries for multiple reasons (outlined below). Since the system has mixed battery chemistries it is a perfect application for a DC to DC converter. We would utilize two Mac Plus line of DC to DC converters to charge each start battery bank. We program them to charge both port and starboard batteries when the engines are running. Since the Mac Plus is also on the Masterbus network you can trigger the converter to turn on only when the regulator is active, which means the alternator is running. Then when the engines are off, the converters will go into standby.

The beauty of the Mac Plus is if you wanted to trigger the charging off of voltage, or even an analog signal (like a rocker switch) you could. As you can see there are multiple ways to set up when you charge the start banks while under way.

With up to 18KW of lithium house battery being charged from 2 GenMaax alternators, this system is begging for a large inverter. As designed, we propose dual 4500W 24V inverter-charger at 240V. The system could move up to 9000W at 24V. By paralleling two 4500W Inverters, you get two lines of 120V to power 240V circuits on L1 and L2. The inverters are linked via Masterbus. This option offers 4500W on each line of inverted AC and provides 400A combined of DC current for charging the house bank.

Since there are now two battery chemistries onboard there will need to be a way to charge the lead acid start battery while on shore power. There are 2 different ways to approach this. In the diagram we recommend a 40A battery charger for the start banks, which should never get very low since they are isolated from the house loads. This allows the system to run a dedicated battery charger for lithium and lead acid while shorepower is present. The system could also be designed where you run the DC to DC charger continuously and omit the start battery AC charger. When the larger inverter charger is charging the lithium house bank the DC to DC charger would take up to 50A and charge the start batteries. If AC shorepower is limited, this is a great option and further outlines the flexibility of the DC to DC charger. The choice is yours.

The system includes the ABYC recommended ELCI (Electrical Leakage Circuit Interrupter) that acts dual purpose as an AC main breaker and leakage detector. Wiring of AC is intentionally designed simply where all shore power goes through the ELCI to feed only 2 AC main loads, House Inverter Charger and Start Battery Charger. The Inverters can handle full pass through to all AC loads on the boat, so they act as the feed to the AC panel. Therefore, the inverters are either in passthrough mode, or inverter. In systems with generators or large AC loads the inverter AC panel may be a sub panel of a larger AC panel.

The system is designed with a remote battery switch for the house bank and the start banks  (3 total). The wiring allows you to turn off these switches when away from the boat and turn them on when ready to use, so you don't have to turn off select breakers every time you leave the boat. We designed this system with an ACR (automatic charging relay), that detects charging at either bank and can close the relay in the event that a DC-DC charger fails, or act as an emergency parallel for engine cranking. This would combine both port and starboard banks if an engine battery were to fail.

You can see 3 other remote battery switches near the lithium house batteries and wonder why you need more battery switches. Those switches are part of a specialized relay bracket that sits on top of the lithium batteries joined to a Class T fuse block. Ready more about the relay brackets here. This is not a battery switch but wired directly to the battery management system of the batteries. If the batteries have a problem they will communicate to the relay and self-shut down. For that reason you still need a full house bank battery switch per ABYC. The last battery switch in the drawing is a manual switch for the inverter/charger. This could also be a remote switch but to keep costs down we recommend a manual. The reason being is this switch will almost never be turned off and is there for service work or in the event of an emergency when you need to shut power off to the inverter.

All Mastervolt products in this system are connected via ethernet (CAT 5e, RJ45) and communicate on Masterbus. Critical parameters will be displayed on the Easy View 5 monitor, and many functions can be controlled from the monitor. This monitor acts as a State of Charge DC monitor since the batteries have built in shunts, which is why you don't see any monitors in the DC panel. Also included is a Masterbus to NMEA 2000 interface box that allows critical metrics to be communicated onto your NMEA 2000 compatible MFD and from NMEA 2000 back to Masterbus. Lastly, you will see a USB interface box. This is a critical product that allows you to program the Mastervolt system to your specific needs.

In most systems we recommend lead acid batteries for starting engines, regardless of engine size.

Why Lead Acid Start Batteries?

1. Batteries will never go "offline" like a lithium batteries

2. High cranking amps for all engine sizes

3. Cost effective