Best LiFePo4 setup for a sailboat with windmill and solar?

JohannesM

New Member
Hello everyone
I am the happy owner of a sailboat that I will be sailing full time, for the next few years. I am in the process of converting my lead battery setup to a Lithium setup.
I think I have found the right way to make it both affordable and relatively inexpensive.
If this is realistic, I will go ahead and continuously report progress here.
Before I get started, I want to hear you smart guys about / what I've overlooked? ... multiple angles on ideas often help with improvements.


Questions
In the optimal setup, the charge of LFP batteries should be controlled by current measurement and shutdown when flow goes towards 0A (0.012A).
In this setup, the charging voltage never exceeds 13.6v, but the chargers are controlled by voltage, not current.
1) Is it understood correctly that when BMS closes for LFP, then the chargers can continue to charge on start batt. - and that this setup is bulletproof?
- no overcharging of LFP
- no destruction of controllers and alternator
2) Is the insulator needed on the alternator?
3) will start batt. be sufficiently charged for me to count on it? (Volvo Penta md2030)
4) What elements have I overlooked in this setup?
5) Are there smarter ways to do this?
6) Can anyone recommend a DC / DC charger to mount on alternator (30A)

Thanks in advance ... Looks forward to your feedback

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svetz

Works in theory! Practice? That's something else
Staff member
Moderator
Welcome to the forums!

... what I've overlooked?

A few things to think about:
  • LFP should not have a float charge
  • You probably want an A/B battery switch so you don't accidentally drain the starter battery.
  • Make sure the fuses are sized for the wires, less a wire set something on fire.
  • If you're mixing lead acid with LFP, search the forums as there's a discussion about doing that which may interest you.
  • As you'll be far from land, make sure to have some spare fuses or think about circuit breakers. Also, think about how you'd bypass the BMS in a pinch.
  • A shunt is very useful, probably a clamp meter too so you can diagnose what's happening with the system.
Can't answer most of those questions... but....
1) Is it understood correctly that when BMS closes for LFP, then the chargers can continue to charge on start batt. - and that this setup is bulletproof?
- no overcharging of LFP
- no destruction of controllers and alternator
Depends on the BMS. A lot of people think of the BMSes low/high voltage cutoff protection is something you shouldn't rely on and there should be a bespoke device for that. I rely on mine, but it's in a cheapo DIY unit and not really important if it breaks.

But, if I understand the question.... when the BMS opens (breaks) the circuit due to over-voltage protection and if the charger is still on, then yes the other battery should be charged and the LFP battery not charged. Conversely, if the BMS opens the circuit to low-voltage protection then the entire load will fall to the other battery.

Not sure about the alternator, sorry....

6) Can anyone recommend a DC / DC charger to mount on alternator (30A)
Will has some recommended aware above in the solar blueprints.
 

kgol

New Member
Hello everyone
I am the happy owner of a sailboat that I will be sailing full time, for the next few years. I am in the process of converting my lead battery setup to a Lithium setup.
You will have a great time, enjoy it.
I think I have found the right way to make it both affordable and relatively inexpensive.
If this is realistic, I will go ahead and continuously report progress here.
Before I get started, I want to hear you smart guys about / what I've overlooked? ... multiple angles on ideas often help with improvements.


Questions
In the optimal setup, the charge of LFP batteries should be controlled by current measurement and shutdown when flow goes towards 0A (0.012A).
May I ask, what do you mean exactly with 0.012 A? A current of 12 mA sounds quite low to me in such a large system.
In this setup, the charging voltage never exceeds 13.6v, but the chargers are controlled by voltage, not current.
1) Is it understood correctly that when BMS closes for LFP, then the chargers can continue to charge on start batt. - and that this setup is bulletproof?
- no overcharging of LFP
- no destruction of controllers and alternator
I assume you mean 'opens' and not 'closes'? I understand that the LA battery always remains in the circuit whatever the BMS does, so the chargers and loads always see a battery. Looks good! I assume you read the Nordkyn articles?
2) Is the insulator needed on the alternator?
I think it can be left out. Its design purpose is to distribute charge current from one alternator to two lead acid banks.
3) will start batt. be sufficiently charged for me to count on it? (Volvo Penta md2030)
The MD2030 is not a very large engine so you don't need a battery in perfect shape. However, 13.4 V continuous is a bit low for charging an LA battery. Maybe taking it once in a month to 14.4 V for a few hours might help.

I'm not sure whether the BMS is designed to handle a ~800 A starting current peak.
4) What elements have I overlooked in this setup?
Your BMS appears to be wired in the positive line? Most FET-based BMSs switch the negative line, I believe. Doesn't change much, of course...
5) Are there smarter ways to do this?
6) Can anyone recommend a DC / DC charger to mount on alternator (30A)
The alternator on the MD2030 doesn't come to mind as a highly regarded piece of kit. I would not expect to get more than 20 A continuous from it. Of course, great if you can get more out of it, but I do not expect so...
Thanks in advance ... Looks forward to your feedback
You clearly did your homework, well done! Clear schematic BTW.

A few thoughts:
- Instead of switching the battery with the FET inside the BMS, I would use a mechanical relay driven by your BMS. FETs are rather sensitive to overloading and thus not very suited for inductive loads (windlasses) and high startup currents (inverters). If a FET fails, they fail almost always in short circuit, that is, the BMS will be unable to disconnect the battery when it has to. Most BMSs cannot detect a FET failure, so it presents a hidden failure. I believe this is unacceptable in a system for a sailboat, where you cannot easily evacuate in case something goes south. A good relay costs a bit of money (~100$) but you can use a cheaper BMS as you only have to switch the relay. Downside is that the relay consumes some current, however its voltage drop is lower than a FET's. Be sure to get a relay with a coil economizer and from a decent brand (Tyco Kilovac comes to mind). As the current does not go through your BMS anymore, the SOC gauge of your BMS will not work anymore, however.

- With the eye on increasing safety, I would keep a separate start battery and use a second, yet small (~20 Ah) LA battery in parallel with the LFP (instead of the starter battery, as in you current scheme). The engine is only connected to that start battery, and the LA/LFP setup is charged using a B2B from the starter battery. Second, I would use an 'off-1-2' switch (not 'off-1-2-both') that allows to put all loads on your starter or on your LA/LFP setup. If something goes wrong, you start the engine and switch all loads to the starter, which is kept charged by the engine (the loads will drop out for a short moment as you turn the switch, though). That way you always have a backup that you can safely engage - even if you are tired - in just a few seconds.

- The 250 A fuse at the battery, be sure that it does not blow before one of the 125 A ones blows. Take care that the 250 A one has the same (or a slower) speed than the 125 A ones. If the 250 A one blows first, you'll get loads and chargers without a battery attached.

Success with your project!
 
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paul12345

Solar Addict
LFP should not have a float charge
Hey @svetz could you elaborate on this please? LFP have a float phase, for example from 28.4V down to 27V (in default Victron settings). But you just mean no power is supplied during that period? Do lead acid batteries require some charge supplied during “float”?
 

svetz

Works in theory! Practice? That's something else
Staff member
Moderator

paul12345

Solar Addict
Thanks; I guess I assumed correctly. So "float" is sort of a misnomer for lead-acid batteries since the charger is still connected, whereas in LFP that phase is actually floating.
 

JohannesM

New Member
Hi @svetz and @kgol

First, I want to say thank you for your feedback. it is a great help as it sets the mind in motion.
I have closely read your comments and made a new design.

1) I have replaced the BMS with a model that can control external relays
2) maintained with seperate starter battery

I would like to hear your thoughts on the new design?
Is there anything I have overlooked?


Existing setup:
1620044576242.png





New setup:

1620044636694.png
 

svetz

Works in theory! Practice? That's something else
Staff member
Moderator
Here are my first thoughts:
  • If your BMS low voltage cutoff is set to 10V, you won't get the longevity out of them you might expect (see the battery FAQ), but you might be able to raise the high voltage cutoff (check with your battery vendor).
  • Not quite sure what the voltage/control is for the BMS to switch between Lead-acid and LFP. Have you confirmed it'll work in both charge and discharge modes?
  • As the three 125 amp devices would blow the 250 amp fuse, be sure to have a few spares or replace with a circuit breaker.
  • The size of the fuse should be to protect the wire, the wire should be sized to supply the desired amps.
Hope that helps!
 

CarlN

New Member
I think you'll be better off if you use "marine" equipment where ever possible. I don't think it will cost you more and will be much more reliable in the salt air of a boat.

I'd suggest the following:

Use a Balmar 614 alternator regulator with a temperature sensor on the alternator. Alternators get very hot trying to charge lithium banks. It can destroy them. The Balmar will monitor the alternator temperature and reduce the charge rate before the alternator gets so hot that it burns up.

I would have both the alternator and the charger charge the house batteries and get rid of the isolator -- replacing it with a Victron 30 amp DC-DC charger between the house bank and the start battery. You're start battery needs to be charged at more than 13.6V - more like 14.4V. Start batteries don't need much charging because starting an engine requires a lot of amps but very few AH.

I don't understand the 80AH House battery but it also won't charge correctly either at 13.6v. I would just get rid of it.

I would consider replacing the chargers and the inverter with a Victron 2000 watt Multi Inverter/Charger. These are very high quality marine equipment with a five year warranty. This will give you 70 amp charging. Or spend a little more and get the 3000 watt Multi with 120 amp charging.

Finally, I would connect a Sterling alternator Protector to your alternator. This is a 2nd layer of protection for your alternator diodes in case the BMS shuts down while the engine is running.

Here is a fairly technical piece by one of the country's best marine electrical guys about putting lithium into boats. Well worth reading: https://marinehowto.com/lifepo4-batteries-on-boats/
 
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