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Andy Todd avatar image
Andy Todd asked

Lithium augmenting Lead Acid on a boat

I’d like to add some LiFePO4 (LFP) to my 40ft sailing boat’s system, but I need some help in determining the circuit and selecting components. Any advice is much appreciated, particularly diagrams?

I’d like to leave the current lead acid (LA) based system as much as possible the same and add some Winston cells and external BMS. This is an augmentation rather than replacement application. A key requirement is to be able to run all the essential equipment of LA if the LFP goes down and to have the ability to replace capacity in remote locations with readily available LA.

I currently have 420Ah of AGMs. I would like to add 400Ah of LFP. I would like a system that I could add more LFP if required in future.

Charging sources are a 3kW generator, 460watts of PV, shore power and a standard alternator on a 53HP Yanmar. The PV recharges the AGM’s to 100% by midday here in the Med. The PV is four 115W panels in series/parallel through two Smart MPPT 20/100’s.

The loads are a 240VAC water maker and a small AC calorifier which currently only run off shore power or the generator. The windlass (12V/85A) and bow thruster (12V/530A), a 12VDC fridge and a freezer, navigation electronics. 12VDC LED lights and light computer use.

I have a an old 1500VA Mastervolt Dakar Combi inverter/charger which I think we’ll replace… possibly with a 3000VA Victron. Which is the best model?.... pros and cons?

The reasons to add LFP are:

1.to extend the time between PV charges to account for cloudy days and

2. to run an induction hob, a kettle and power tools off the batteries through an inverter and

3. maybe the 240VAC water maker and calorifier.

Lithium Battery
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3 Answers
Trevor Bird avatar image
Trevor Bird answered ·

It sounds like you intend to have two completely separate house battery banks. I guess you could have two totally separate system and manually change over but it is an unusual design. If simply joined together the Lithium charge and discharge profile would dominate and the LA would be subject to charging voltages above their recommended levels. I have not heard of this being done before and think you should simply go to Lithium chemistry and remove the weight from the boat and enjoy the lithiums without the complication. The thought of needing replacements in remote locations may not be required as the cycle life of Lithiums is extremely high. If you have been living aboard with AGMs the lithiums will change your life. Remember that maximum discharge for AGMs is about 50% with Maximum discharge off lithiums is closer to 100% so a 400Ah lithium house bank is practically the equivalent of 800Ah of AGMs. They charge faster and hold their terminal voltage for longer during discharge and have higher round trip efficiency.

It’s time to dump the AGMs and never look back.



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pwfarnell avatar image
pwfarnell answered ·

Recently discussed with lots of detail, especially if you follow the link provided by wildebus. See

https://community.victronenergy.com/questions/119423/mix-agm-and-lifep04.html

or

https://community.victronenergy.com/questions/135279/hybrid-lithium-agm-setup.html?childToView=135340#answer-135340

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Sarah avatar image
Sarah answered ·

Having just done a AGM to Lithium upgrade I would suggest going for a single chemistry solution. Many posts will say you can do both, and you can, but I suggest keep it simple - especially on a boat! When stuff goes wrong, and it will, you want to understand why, without a lot of complexity and troubleshooting. (If you are super tech and don’t mind the extra kilos then go for it). Just my two cents ;-)

3 comments
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Andy Todd avatar image Andy Todd commented ·

Sarah and Trevor, The risk of a LFP failure during and ocean crossing or in remote locations to too great to consider ditching LA.

0 Likes 0 ·
harold avatar image harold Andy Todd commented ·
Just keep one separate LA starter battery for the Generator, at least that's my longterm goal
1 Like 1 ·
Trevor Bird avatar image Trevor Bird Andy Todd commented ·
My guess is you will have 4 x 100Ah Lithium batteries in parallel ( as I have on my Jeanneau SO42DS). It would be fairly unlucky break to have 4 batteries fail at one time. If any one failed you would simply reduce the size of the house bank.
1 Like 1 ·

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