Twin Outboards

We call this a Twin Outboard system but it's ideal for any twin engine system where your alternators are feeding dedicated start batteries. It's appealing to many customers that don't want to change alternators or start batteries, but still want a house battery upgrade.

Specifications:

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

• 10.8KW Hours of Lithium house batteries (90% depth of discharge)
  • 12KW Hours @ 100% depth of discharge (not recommended)
• 3500W AC power from the Inverter/Charger
• 30A @ 120V AC shore power/AC auto transfer
  • This system can handle 50A @ 120V as well
• 200A house battery charging from the Inverter/Charger
• 25A of start battery charging from dedicated battery charger
• 100A house battery charging off the engine alternators

How It Works:

This system allows you to upgrade your house battery bank to lithium while keeping everything related to your engines the same. That way you get the benefit of a deep discharging house bank, larger inverter to feed your AC devices, all while keeping your engine, alternators, and engine batteries the same.

To ensure you get charge off the engines there is a DC to DC converter between each start battery and the house bank. DC to DC converters are also known as DC to DC chargers and in this case they aren't converting voltage but converting charging profile. The system is designed so when the AGM start batteries are above 13.5V the DC to DC chargers turn on and take power from the start batteries and convert it to a lithium charging profile and charge the house bank. The converters in the diagram are rated at 50A so with both engines running that would be 100A of charge going into the house bank. If your alternators can handle more power, you can simply add more DC to DC converters in parallel to get more house charge. One additional benefit of the DC to DC chargers in this system, is by limiting the charge to 50A per engine you can use this system on a boat with smaller alternators without the risk of damaging them or having them temperature compensate. To ensure both start batteries stay charged while underway we recommend an ACR (automatic charging relay) be placed between both start battery banks. This is cheap insurance in case one engine battery has low voltage the ACR can be triggered to act as an emergency parallel switch.

Since there are now two battery chemistries onboard there will need to be a dedicated AC charger for the lead acid start batteries and one for the lithium house bank. To keep in mind system pricing we recommend a small 25A 2 bank battery charger for the start batteries, which should never get very low since they are isolated from the house loads. We recommend that the system be programmed to shut off the DC to DC chargers when the start battery charger is charging. This prevents the DC to DC chargers from taking power from the start battery charger while at the dock and allows the start batteries to be prioritized so they top up quickly. We only recommend this since there is a large 200A battery charger dedicated to the lithium house bank, so there is no reason to steal power from the start batteries while shore power is present.

For efficiency when you only need 1 inverter on a boat we recommend an inverter charger. In this case a 3500W inverter charger that also provides 200A of DC charging to the lithium house bank. That is plenty of charging for a house bank this size and would charge this near empty bank back to full in around 4 hours. If you install this system with a 30A shore power service we recommend de-rating the inverter charge down to around 22A AC to allow for the start battery charger to pull 4A AC off of shore power. This de-rating is purely to prevent tripping shore power pedestal breakers while you are away from the dock. If being installed with a 50A pedestal no de-rating is needed.

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 Inverter can handle full pass through to all AC loads on the boat so the inverter acts as the feed to the AC panel. Therefore the inverter is either in passthrough mode, or inverter. 

The system is designed with a remote battery switch for the house bank and each start battery (3 total). The wiring allows you to turn off these switches when away from the boat and turn them off when ready to use so you don't have to turn off select breakers every time you leave the boat. You can see 2 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. 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. Many alternators are not designed for the high charge acceptance of lithium and can be damaged when direct charging lithium

2. High cranking amps for all engine sizes

3. Cost effective

Bill of Materials*

*Contains only major components in the application diagram, does not have all required circuit protection devices, wiring, connectors, & bus bars