I'm not going to argue with Rod. The issue is the margin of safety. I use the house bank for the windlass (don't have electric winches). The 3 batteries each have a max current surge (peak) discharge of 350a (3 seconds) for a total of 1050a. The inrush for the windlass is well below that threshold. Additionally, my alternator feeds the house bank and is typically running when the windlass is used providing an additional ~80a of current.Thanks @dlochner for the tip on BEP Pro installer.
I actually don't have the Epoch but rather a WattCycle 314AH Mini as recommended by @Maine Sail. My wiring scheme is set up to avoid potentially large "in-rush" current which, as described by Rod as potential problems for the BMS system of Lithium battery banks. This places the loads with the potential for "in rush" current onto the Start Battery. In particular the "in-rush" is not the same as "continuous" or even the "peak discharge current." The in-rush current last only for less than a second but can play heck on the BMS system. Here is the link to his discussion. Hopefully @Maine Sail will comment not only on the proposed diagram, but the topic of in-rush current. Maybe I'm overly concerned with this.
The following exerpts are from Rod's primer on Drop-In Lithium batteries and considerations in their proper care and use.
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From:
Drop-In LiFePo4- Be an Educated Consumer
DC Motor In-rush
The reason most drop in batteries cannot be used for starting is the in-rush current. The in-rush of large DC motors looks like a dead short to the FET’s. Imagine sitting there and intentionally shorting your battery multiple times each day…..That is what starting your motor, running a windlass, electric winch or Bow thruster looks like to the FET’s. There are LFP batteries that can be used for starting but they are very expensive at this point in time.
Starting a 40HP Westerkeke takes=640A!!!!
Know your loads before you buy!
The critical load data you need to know is the in-rush current for all DC Motors .This includes a windlass, electric winches or a bow thruster. You also want know your inverters Pre-charge in-rush. Unfortunately most DC Clamp meters cannot properly capture DC in-rush current. We own three DC clamp meters that claim to do in-rush but all except the Fluke meters fail miserably. The image below is one of our Fluke 376 meters capturing the in-rush current for a Lewmar V2 Windlass. This customer ruined his FET BMS (seen in an image above in this article) by using his “direct from China” drop-in battery to power his windlass. Warranty? Ha-ha now that’s funny….
The image above is a prime example of how drop-in battery bank went wrong for this customer. he wanted to lighten the load in the bow of his sailboat so he installed a single drop-in battery to power his windlass.What he failed to understand was the BMS’s current handling rating . In just a few short weeks he destroyed his drop-in battery with his windlass when he failed to account for what the peak in-rush current handling of the BMS., Warranty? Not covered!
In your case, because the alternator feeds the start battery it is better to use that battery for the windlass and winch. If I were to have that arrangement on my boat, I would have a large start battery because the drain on the battery will be relatively high and recharging with the Hitachi alternator will be slow. (See Rod's article on Automotive alternators.) In particular a small AGM battery could easily be left in a partial state of charge for longer periods of time which is fatal for those batteries. FLA batteries would only fair slightly better.
Wattcycle does not provide a Max surge (peak, instantaneous) discharge rating for the 314ah batteries. As a result, using them for a windlass or winch might risk the kind of damage to the BMS that Rod mentions, but we don't know because WC didn't specify the max surge current. Bear this in mind if you should find yourself in the position of having to run everything off the house battery due to a start battery failure.
