System Upgrade- Repost from Marine

[Kennneee]

Hi All- I didn’t get any response on the Marine Forum and hope somebody will reply here.

Hi All- I am going to upgrade the charging system on an outboard powered boat with a 30amp alternator. The existing system has a AGM Start battery and a separate AGM house battery with a BlueSea ADD A BATTERY MINI PLUS which includes a 10amp shore power charger with a built in ACR and a 3 position battery switch (OFF, ON, BOTH).
https://www.bluesea.com/products/7655/Mini_Add-A-Battery_Plus_Kit_-_65A_[North_America]

Since I plan to keep the existing AGM start battery and replace the house battery with a 100amp Lithium and add a 100watt solar panel, some changes need to be made. I have already purchased a Victron BMV712 to monitor the batteries.
I would like to keep the BlueSea shore power charger and battery switch. I intend to disconnect the House battery from the charger and use it to just keep the start battery topped off at the dock. My impression is that the best way to keep the AGM Start and Lithium battery happy would be to add a DC- DC charger to the system.
One suggestion that looks easy and makes sense is to add a Renogy DCC30s DC-DC charger with MPPT and be done. It has also been suggested to stay with all Victron components and use a Orion TR SMart 12/12-18 Isolated and a Victron Blue Solar MPPT 15 amp Solar controller. I read that the Renogy will trickle charge the start battery once the house battery is topped. Not sure if the Victorn will do this. Is there any real advantage to having the system stay all Victron? Since I am new to solar and these components I am relying on good advice that I hope I can get on this forum.
Any help appreciated. Existing system below.
Ken
Ken

 

[snoobler]

I think you're over-thinking this. Why disconnect house battery from shore power charging?

Assuming BlueSea charges at 14.6V or less and floats at 13.6V or less (for LFP health):

Just add a Victron charge controller for the solar panel to the house battery.

 

[Kennneee]

I think you're over-thinking this. Why disconnect house battery from shore power charging?

Assuming BlueSea charges at 14.6V or less and floats at 13.6V or less (for LFP health):

Just add a Victron charge controller for the solar panel to the house battery.

This is where my lack of experience with this set up gets confusing and leads to over thinking. Since the BlueSea charger has a built in ACR and is optimized for lead acid, I checked with Blueseas and BattleBorn and they both advised against using the existing set up. Would the start battery discharge into the house battery through the ACR when the house battery is low? Maybe a lobotomy would help.
Ken

 

[snoobler]

Okay. With the specs, I can see how the ACR works. The LFP would have a tendency to discharge into the AGM to float them, and they would not be isolated at start unless you did it manually, so the starter draw might exceed the BCM amp limit on the LFP.

The simple solution would be the Renogy that also has the solar controller built in. I prefer Victron, and the two Victron units might be cheaper than the Renogy.

 

[mmdb]

Making Sense of Automatic Charging Relays - Marine How To

Making Sense of the ACR WARNING: The ACR's in this article are not for use with LiFePO4 Batteries! What is an ACR? An ACR is nothing more than a fully automatic, voltage triggered, BOTH/PARALLEL switch that closes when charging voltage is present and opens when charge

marinehowto.com

 

[Kennneee]

Thanks for the help snoobler and mmdb!

 

[gtstricky]

It might be worth giving Jeff a call. He just did a short video on a similar subject that might give you some info.