The availability of Lithium batteries for house banks have dramatically changed the typical setup of cruising boats as we have seen a significant shift with boats having much larger battery banks, bigger solar arrays and with that a decrease in the number of generator installations.
Lithium batteries have the advantage that they can be charged significantly quicker than the more typical AGM or Gel batteries, reducing engine run time. They are also much lighter and probably most importantly, have a much greater depth of discharge (DOD) value. What does this mean?
A 200 Amp hour AGM has a DOD of 50% meaning you can only utilise 50% of that capacity (100Ah). A 200 amp hour Lithium battery has a DOD of 80% meaning you have 160Ah of usable capacity or 60% greater capacity than the AGM battery.
It's basic but important to understand that whilst the lithium batteries are very powerful and robust, they are still only going to be as good as the power that is put into them. In the most basic of analogy, batteries are simply a bucket of power. If you take more out than you put back in, then your bucket will become empty. It's important to understand that regardless of the size of the bucket, you need to be able to put the same amount back in that you use each day to keep an even state of charge. So power generation is as important and the battery type and size.
(July 2023 Specification)
Why do you we have separate start and house batteries and as different types (AGM vs Li)?
Lithium batteries are not suitable for start loads plus it is always best practice to have separate batteries for the engines. Even with flat house batteries, you can still start your engines when you need to.
1) The mastervolt lithium batteries have their own built in Battery Management System (BMS). The BMS means there is a certain level of diagnostic function with the batteries, it has the abilty to regulate the individual cells with the battery and importantly it will shut the battery down at a certain threshold, which we at Seawind set at 20% State of charge. The BMS will protect the battery at this threshold It will need to be reset and will need charge input from solar, battery charger or Yanmar alternator.
This is unlike an AGM where, if it goes below the 50% SOC, you will begin to cause long term damage.
2) The mastervolt alternators are connected to a mastervolt regulator. These regulators control the output to the batteries and will therefore not allow the batteries to become overcharged.
3) Start batteries: Should a start battery become flat, there is an emergency parallel from one start battery to the next. In addition to this, we also have a battery charger that charges from the Lithium bank to one of the start batteries in case both start batteries are flat.
The above image shows a typical Lithium installation with C-zone situated in the saloon seating area.
WIth a twin 6000 Wh lithium installation, this would equate to 920 Ah house capacity. Of this, you are able to use 80%, so 736Ah. Note, for all Seawinds, when we set the battery percentage on our lithium installs, we have the displayed State of Charge as the usable percentage. This means when you have 1% on the screen, you actually have 20% + 1% of usable capacity, so one our installations, you can run the house bank down to 0% before the BMS will shut down the system, not 20%.
The below attached file is a typical wiring diagram.
Note specifications are subject to change, and are as of a July 2023 installation.
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