Changing a lead acid to LFP setup on sailboat - Help needed?

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Johannes Madsen

May 3, 2021, 8:13:04 AMMay 3
to electrodacus
Hi every one 

I am the lucky owner on a saliboat , which me and my family will be sailing full time the next year.
Today there are a good working lead acid battery setup. but I have decided to upgrade with a LFP system.

I have attached drawings of my existing setup and the setup I plan to install.
BMS and cells are already ordered, so I need your clever thoughts about the best way to design my setup.
I will try to use my existing components. but If it is total crap, I will change them! - please advise me.

I have for sure forgot something but here are my questions:

Altornater must be protected when charging on the LFP cells - how do I dimension my DC / DC charger? (can it be made easier?) 

I can not "turn off" my charging units, so I plan to connect a GEL battery in parallel on the LFP bank. 
      - Is this a passable road? Is it okay to let SBMS connect / disconnect the LFP bank?          - Which relays should I use (is limited by 50mA in control current from SBMS)? 
      - How big should my consumer battery be (as small as possible)? 
 Inverter draws 3000W peak (continuously max 1500W) and approx. 12v / 30A in alm. consumption 
      - How should relays and shunts be dimensioned? 
When the LiFePo4 batteries are fully charged and BMS switches off - what happens to the power from the generator, wind turbine, solar panels and possibly shore power (ProCharge Ultra)?
     - Does this solution work with a consumer battery? 

Is there anything else I need to be aware of?

I look forward to your thoughts - Thanks you

Existing setup.jpg
New LFP_LA setup.jpg

Dacian Todea

May 3, 2021, 12:29:48 PMMay 3
to electrodacus

Please check the SBMS0 user manual page 5
You will see there that current shunts are on the positive side of the battery. 
You can not parallel LiFePO4 to any other battery.
SBMS0 needs to have remote ON/OFF control over all charge sources and separately over all loads.
For the small DC loads you can use a Victron BP65 that will be controlled by the SBMS0 EXT IO3 set as type 2

Dave McCampbell

May 4, 2021, 12:07:00 AMMay 4
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Johannes.  We also have a boat, 44' cat, on which we have just finished installing a LiFePO4 house bank with a lot of help from these folks.  We have been out out cruising 14 years now, 6 with a Gel house bank.   It is important to get all this right before going cruising, especially since you might not be able to get an immediate replacement if something goes wrong, and you certainly don't want the lights to go out at sea.     

In addition to studying Dacian's ED manual, I recommend you have a look at our installation and especially the links at the end to the Beginners' Guide/Summary of Functions, Types and Features and our separate ElectroDacus page.  there are lots of equipment options, but it all starts with proper system design.  It is important to get all this right before going cruising, especially since you might not be able to get an immediate replacement if something goes wrong.   Here is the link: 

Here are a few questions that will need answering.  Have you ordered your LiFePO4 cells or BMS yet?  If so what?  I don't see any solar on your drawings, and that is by far the most useful charging source in the tropics.  What will your approx daily amphr usage be?    How big is your boat and how much room for solar?  Do you have a dual buss electrical system already?  Will you be spending most time at anchor or in a marina?   

Keep reading and asking questions and you will get there.

Chris Card

May 4, 2021, 3:21:51 AMMay 4
to electrodacus

Do you really need to change your working lead acid bank to lithium, or might a better idea be to keep the lead acid batteries and add lithium cells in parallel?

If you’ve not already seen it, this is a good video on the subject:

Richard Lussier

May 4, 2021, 10:38:39 AMMay 4
to electrodacus
Hi, I also have a sailboat with SBMS0 setup for a second year now. 
I use a seperate AGM starting battery on an Atomic 4 engine and an alternator. 
I use a synopoly 300a 12v LIFEPO4 house bank. I charge my house bank with solar (420W) thru DSSR20. 
I use a shore power supply also a Meanwell RSP-750-15, and if i want to use the alternator to charge (very seldom since it is not energy efficient), I link the starting AGM and the LIFEPO4 battery with a VSR, and a DC-DC converter Renogy DCC1212. 
My load is controlled by a Victron BP100. Simple setup. I live on the boat, with a fridge and mostly only need solar to power the boat. Cooking is thru propane and alcool, and a microwave over used few minutes a day.

Johannes Madsen

May 6, 2021, 4:16:33 PM (12 days ago) May 6
to electrodacus

I have already been inspired by your questions.

I have ordered 8 LiFePO4 cells (202Ah) and plan to do a 12v 2x4cell, 404Ah (s4)
I already have a SBMS0 Ian testing it on 4 x 0,6ah cells :-)

My situation is, that I am living I Denmark and my boat is in Croatia. We will go there from july and be sailing for a year.
Our boat is new for us.. so I do not yet know/remember the hole setup - it is a 40f Bavaria from 2000

I try to plan the LFP setup from home, and bring all the parts with us in July... that is a bit of a 

On my boat I have:
- shore power (50A)
- wind generator (silent wind, 400W)
- solarpanels (4x150W panels)
- alternator (not known - but isolator is 70A)

- I will try to eliminate the house LA battery 
( the idea about parallel LFP and LA battery seems however appealing)

After thinking my plan now is to:
- Control shore power with a SSR relay controlled by SBMS0

- Control solarpanels by cutting connection betwine panels and controller (silent wind hybrid 1000) with a Victron battery protection 65A
- Control windgenerator by adding a SSR by SBMS0 (making the manual break remote controlled on the Silent wind hybrid 1000)
Problems here is:
This control overcharging, but not protection against low voltage. 
(after talking with Dacian, we agree that the load from break on windgenerator is so little, that it have no real effekt on LFP.

Load busbar will be managed by a Victron BP220

- Alternator
Protected by a DC/DC charger (20/40 depending on alternator max current
Keep a seperat start battery (GEL) only charged by the alternator - conected by an isolator.

Low voltage protection:
I will connect a relay just before the load busbar, controlled by SBMS0 (Victron BP220)

Here is an updated drawing!

what is your thoughts about this?

- what about the dimensions of the fuses?
New LFP_LA setup 2.0.jpg

Dacian Todea

May 6, 2021, 4:47:45 PM (12 days ago) May 6
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Please check page 3 of the user manual
The shunt is not connected at all like you have done in your diagram and doing so will damage the SBMS0.
Shunts are connected is series with battery current shunt (ADC1n/ADC1p) first connected directly to battery+ and then in series with that the PV shunt (PVn/PVp). 

Johannes Madsen

May 11, 2021, 3:17:31 PM (7 days ago) May 11
to electrodacus

I have now made the changes to the setup. I can see what you mean.

Please let me know if anything seems suspicious. 

Thanks you
New LFP_LA setup 2.1.jpg

Johannes Madsen

May 11, 2021, 3:58:12 PM (7 days ago) May 11
to electrodacus
I have one question.

in this setup, all loads are only controlled by the Victron BP 220A.

what happens if the inverter is running with fx 1000W and the BMS shouts off the loads.... will it do any damage, when it switch on the loads again? - provided the inverter is still connected with a 1000W load?

Dacian Todea

May 11, 2021, 4:06:07 PM (7 days ago) May 11
to electrodacus
Problem with the inverter is not the Load on his output but the fact that inverter has large capacity electrolytic capacitors than when discharged will act as a short circuit so the BP220 can be damaged and is best the inverter to be connected after the 160A fuse before the BP220 and then use the remote ON/OFF in order to control the inverter.
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