Upgrading our battery system

[Sailing Paul]

Hi everyone, I am new to the forum but have done a lot of reading on various theads. I would like to discuss my thoughts on upgrading the batteries on our 20 year old 35 ft sailing boat to LiFePO4 in order to provide more capacity when away from shore power.

Current situation. Single 85Ah SLA starter battery, 2X85Ah SLA house bank batteries. Batteries charged using a Cristec 25A AC charger and a standard 55A alternator on a Yanmar 3GM30F engine. The AC charger has a boost mode which outputs 14.5V for 6h after turning on, then drops back to 13.8V. The Yanmar alternator outputs at 14.5V +/- 0.3V. There must be an isolator somewhere to split the alternator current as the starter and house bank are not connected.

Battery loads on the house bank are the nav instruments, lights (mostly LED), fridge, water pumps and phones/tablets. No inverters, air-con or other energy intensive junk to worry about. Testing using a 60A LiFePO4 battery (with bluetooth BMS) wired up in place of the house bank indicates that approximately 40Ah per day is required. We would like about 5 days of energy before recharging on shore power.

We don't want a large scale permanent solar installation, but might buy a 100W portable/foldable panel for use at anchor and moorings with no shore power. Primarily this would be used to charge the 60Ah LiFePO4 that we use for our trolling motor with the tender.

Option 1. Remove the SLAs and replace with 2X200Ah LFP batteries. Add a new AC charger for the LFPs, disconnect the alternator from the house bank. We would need to remove the battery boxes and run cables to the new charger. The house bank would only be recharged on shore power. Primary advantage is this is very simple to implement. Disadvantage is that it is too expensive. If money was no object, this is what I would do. In a few years time if LFP battery prices continue to fall this might be a viable solution.

Option 2. Replace 1 SLA with a 200Ah LFP battery. New shore charger as before and again would only charge the LFP using shore power. We would need to add a battery combiner to link the 2 batteries. The higher voltage of the LFP should ensure this is discharged ahead of the SLA. Advantages are that this solution is cheaper, the alternator would still charge the SLA and the SLA could potentially be used to jump-start the engine. Disadvantages are lower energy storage compared with option 1 and a slightly more complicated setup.

Option 3. Similar to option 2 but a DC-DC charger (eg Victron Orion Smart 12/30) would be used in place of the new AC charger to charge the LFP. This would be connected to an output of the existing Cristec charger (would there be any issues in doing this?) and to the alternator. Clearly this option is much more complicated to set up and carries risk to the alternator and the charging of the SLAs, but if it could be made to work safely and at a reasonable price it might be a very good option. I would want the SLAs to charge ahead of the LFP, particularly so the starter SLA and I would not want to overload the alternator. What are the issues with doing this? Would extra kit be needed, eg a Sterling alternator protector?

[Fuss]

Well, I didn't read all of it ... but in the beginning, try to keep it simple as possible.
Stick with the concept that BMVs are there to shut the battery off in emergencies, not part of the daily cycles.
Alternators, AC chargers etc should charge within the BMS high and low voltage cutoff settings and be able to be switched off.
Have a decent Battery monitor like a BMV712 I think its called and learn how to program and use it correctly so you always know the state of charge.

Have a solution so your alternator does not get damaged by a BMS cutoff. Later this should not happen if you programmed everything correctly as BMS cutoffs should never happen.

Take advice from the right people on here who have experience with their own installations.


Put labels on all devices with their respective setups for Lifepo4

[Pete7]

We have been using option 3 now for 2.5 years. SLA engine battery charged by alternator and old Sterling AC charger. The DC>DC charger to LFP and FLA hybrid house bank.

DC>DC charger keeps the LFP charging down to a limit without over heating the alternator and has lithium settings or user defined if required. LFP and FLA combined means in the event of the BMS shutting down, the FLA continues to supply power for a limited period.

Just buy one LFP for now and see how you go. You can easily add more in the future if required. We manage with 220Ah of LFP and 85Ah FLA btw. Solar goes directly to hybrid bank and the low resistance of LFP means it charges up much more quickly compared to lead acid. The FLA spends all its time sitting at float twiddling its thumbs.

Pete

[bgallinger]

I switched over to LFP batteries on my Hunter 340 a couple of years ago. Here's what I did:
1) Replaced the 3x100 Ah lead-acid (house) for 3 LFP and keep one 100 Ah AGM for engine start.
2) Replaced the stock 55 Amp alternator for a Balmar 100 Amp with the Balmar MC 614 regulator.
3) Replaced old battery monitor with new Balmar SG200
4) Checked the shore charger is ok with LFP
5) Installed a Balmar Alternator Protection Module APM12

There is a mountain of info on this, so it will take considerable time to wade through it!

[Sailing Paul]

Originally Posted by Fuss

Well, I didn't read all of it ... but in the beginning, try to keep it simple as possible.
Stick with the concept that BMVs are there to shut the battery off in emergencies, not part of the daily cycles.
Alternators, AC chargers etc should charge within the BMS high and low voltage cutoff settings and be able to be switched off.
Have a decent Battery monitor like a BMV712 I think its called and learn how to program and use it correctly so you always know the state of charge.

Have a solution so your alternator does not get damaged by a BMS cutoff. Later this should not happen if you programmed everything correctly as BMS cutoffs should never happen.

Take advice from the right people on here who have experience with their own installations.


Put labels on all devices with their respective setups for Lifepo4

Great tips thanks. Do you have anything in place to avoid or alert you to LFP running to low and the BMS disconnecting?

[Sailing Paul]

Originally Posted by bgallinger

I switched over to LFP batteries on my Hunter 340 a couple of years ago. Here's what I did:
1) Replaced the 3x100 Ah lead-acid (house) for 3 LFP and keep one 100 Ah AGM for engine start.
2) Replaced the stock 55 Amp alternator for a Balmar 100 Amp with the Balmar MC 614 regulator.
3) Replaced old battery monitor with new Balmar SG200
4) Checked the shore charger is ok with LFP
5) Installed a Balmar Alternator Protection Module APM12

There is a mountain of info on this, so it will take considerable time to wade through it!

Replacing the alterator is option 4! We may get there, but I want to proceed in incremental steps and if we can manage without tinkering with or replacing the alternator, so much the better.

There is actually an option 0, which I am using at present. I turn off our house bank and connect a 60Ah LFP direcly to the house circuit by running a cable into the engine room. The LFP has a bluetooth BMS so I can monitor the state of charge. This gives the house bank a rest and saves it from discharging too far. No way to recharge the LFP without shore power yet, so needs thinking about. I need to tidy up the cabling and make it more idiot proof - the idiot here being me.

I am thinking about a 100W foldable solar panel next with maybe a Victron SmartSolar MPPT 75/10.

I note that Victron do a smart 18A DC-DC charger. That would seem reasonably safe with our alternator. I am still wondering whether I could hook that up to the AC charger in the first instance to provide a high quality 18A LFP charger. No reason why it would need to connect to an alternator is there?

[Sailing Paul]

Originally Posted by Pete7

We have been using option 3 now for 2.5 years. SLA engine battery charged by alternator and old Sterling AC charger. The DC>DC charger to LFP and FLA hybrid house bank.

DC>DC charger keeps the LFP charging down to a limit without over heating the alternator and has lithium settings or user defined if required. LFP and FLA combined means in the event of the BMS shutting down, the FLA continues to supply power for a limited period.

Just buy one LFP for now and see how you go. You can easily add more in the future if required. We manage with 220Ah of LFP and 85Ah FLA btw. Solar goes directly to hybrid bank and the low resistance of LFP means it charges up much more quickly compared to lead acid. The FLA spends all its time sitting at float twiddling its thumbs.

Pete

Interesting. How have you combined the FLA and LFP? Is it alternator straight to FLA with DC-DC to the LFP or something different? FLA twiddling its thumbs is what I have in mind, using it only if the LFP fails in some way.

[Fuss]

Originally Posted by Sailing Paul

Great tips thanks. Do you have anything in place to avoid or alert you to LFP running to low and the BMS disconnecting?

The Bmv712 beeps when the voltage is low if all is setup correctly.
What you want to design is a balanced system for your use…
Use over a week not a day… this could mean, less solar, more alternator, more hydro alternator.
You know you have it balanced when you don’t look at the bmv712 so much.

[Pete7]

Originally Posted by Sailing Paul

Interesting. How have you combined the FLA and LFP? Is it alternator straight to FLA with DC-DC to the LFP or something different? FLA twiddling its thumbs is what I have in mind, using it only if the LFP fails in some way.

Paul, this is the latest design, but you get the idea. We would have to pretty much drain the LFP, or have both BMSs shut down for the FLA to supply.

Pete

[Sailing Paul]

That is really interesting thanks. Lots of questions, but here are a few if I may:

What is the blue Victron box in the middle (not the DC-DC or the MPPT)?

I cannot see a dedicated LFP charger. It looks as though these are charged from the DC-DC charger, taking power from the 40A shore supply and/or alternator. Is that correct? It is what I was thinking of doing rather than have a dedicated LFP charger.

You have different capacity LFPs in parallel. Is that OK? How does the charger manage this?

Why do you have an FLA battery?

When switched on, the LFPs are connected to the FLA such that current can flow between them and the FLA is charged with the DC-DC, which is presumably set to LiFePO4 characteristics. Are there any issues here? How does the DC-DC charger cope with this?

Your shunts are connected to the positive terminals. I thought the recommendation was to connect to negative, although I am not sure why it would matter.

[Pete7]

Originally Posted by Sailing Paul

That is really interesting thanks. Lots of questions, but here are a few if I may:

What is the blue Victron box in the middle (not the DC-DC or the MPPT)?

Its Victron Power In. With 4 bolts and a quick conversion becomes a rather neat fuse box with bus bars all in one unit.

I cannot see a dedicated LFP charger. It looks as though these are charged from the DC-DC charger, taking power from the 40A shore supply and/or alternator. Is that correct? It is what I was thinking of doing rather than have a dedicated LFP charger.

Yes that's correct. We already had the 40A shore supply charger and its only a back up rather than the main charging source which is solar. Therefore decided to carry on using it.

You have different capacity LFPs in parallel. Is that OK? How does the charger manage this?

Yes its fine, charging sources don't know any different. The batteries have identical BMSs which helps, just need to be aware that if a similar amount of current is drawn from both batteries, the % SOC will be slightly different. We only use the %SOC for a quick glance, battery cell voltage is a better measure of what is going on

Why do you have an FLA battery?

I the event of a BMS shutdown or both of them, the FLA will keep the lights, VHF and chart plotter running for some time whilst we sort it out. Handy if you are entering a strange harbour at night

When switched on, the LFPs are connected to the FLA such that current can flow between them and the FLA is charged with the DC-DC, which is presumably set to LiFePO4 characteristics. Are there any issues here? How does the DC-DC charger cope with this?

In practice we sometimes see 6A flowing from the FLA to the LFP when first connected, because the FLA has been sat on float at 100% and the LFP at about 60%. This doesn't last long until the voltages equalise. We have two profiles in the Victron Orion. One for storage keeping the FLA charged so 14.8v Absorption and 13.5v float. Another profile for when we are on board which much lower settings.

Your shunts are connected to the positive terminals. I thought the recommendation was to connect to negative, although I am not sure why it would matter.

Most shunts are indeed for the negative side of the circuit. However, Sterling Power allow either pos or neg. 16 years ago it was easier to put the first one in the engine / battery pos side.

Pete.

[SV Confianza]

We use a stay alive / high amp relay to parallel the LFP and FLA batteries when charging from the alternator. Much simpler than using a dc to dc charger. Since the start battery just needs to be topped up, it just sees float voltage when charging.

Wrote up the whole setup here.

[CaptainRivet]

Originally Posted by SV Confianza

We use a stay alive / high amp relay to parallel the LFP and FLA batteries when charging from the alternator. Much simpler than using a dc to dc charger. Since the start battery just needs to be topped up, it just sees float voltage when charging.

Wrote up the whole setup here.

That ONLY works if your alternator has an internal properly working temp controls which his 55A defintily doesn't have.
A relay is not the right choice here because it can fry closed and most importantly allow the flow of reverse current which you don't want to happen with FLA and LI.

it will be correct to use a splitting diode like Victron ArgoFet (again only if the alternator has proper internal or external temp control) which also has the advantage of a voltage drop so you are not overcharging the LFP with the too high float voltage of an FLA.

[CaptainRivet]

i Suggest to do the follow:
get a 200A LFP and keep one FLA starter

1) connect your alternator and SLA shorepower charger to the FLA
2) get a 30A DC2DC charger (renorgy or the triple expensive Victron) and connect the input of the DC2DC charger to the FLA.

3) on the terminal of the LFP goes a class T or NH fuse (nothing else!) with the rating needed for your cable size (speced for your loads and taking voltage drop into consideration)
4) get a Victron BMV712 battery monitor and a 100A Victron smart Battery protect. directly after the class T or NH fuse of 3) connect the shunt of the BMV712.

5) directly on the output of the shunt connect 2 wires

a) main load wire: short after connection insert a fuse with rating for the cable, after fuse connect the Victron smart battery protect. That is programmable SSD relay when to cut load in an LCV=low voltage cut off situation, i would put it at 12V (3V per cell) but you can also use 11.6V (2.8V per cell). on the output you connect the main loads cable. if the main loads exceed 100A get the BP220 = 220A Smart Battery protect but i highly doubt you need that.

b) main charge wire: short after connection insert a fuse with rating for the main cable. now connect the output of the DC2DC charger to the output of that fuse. the relay output of the BMV 712 use the NO (normally open relay) output and connect it to the remote on/off of the DC2DC charger.
6) now program the relay of the BMV712 to stay close till Voltage is above 14,4 or 14,6V (depending which voltage the manufacturer of your Lithium write in their manual) so called HVC=High voltage cutoff. its important to do it this way, as if the remote cable get interrupted due to any reason the charger is off.
7) now program the DC2DC charger so it charges the LFP when the shorecharger or alternator are running but stays off when both are disconnected and also are not draining your FLA. This will be a bit trail and error till you have the correct setting, start with the defaults.
your LFP BMS should do the cut offs but above is additional security needed and also gives you the opportunity to control that.

Done is your little system.


I would spend the extra money and get the Smart Batterie protect so the BP has bluetooth and with your phone and victron connect app you can connect and disconnect your loads with a tip of a finger. you don't need to buy a new shore charger, it charges the FLA and that the LFP.
yes a little bit inefficent but its a small system and small capacity so thats worth living with this instead getting a new shore charger.
if you descide to get a new shore charger it should have a remote (so the BMV712 can turn it off) and a trickle charge for the FLA, the victron smart Phönix 30/1/1 is your choice then. connect the remote in parallel to your DC2DC and also the charger output in parallel to the main charge cable fuse.

[Sailing Paul]

Originally Posted by Pete7

Pete.

Thanks for the tip on the Victron Power In. That might prove useful at some point.

How do you avoid gassing your FLA when charging the LFP? Do you keep the voltage down and not fully charge the LFP?