Upgrading our battery system

[Sailing Paul]

Originally Posted by 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.

Thanks for the detailed description. Low voltage cutoff is an area I had not propery considered. My initial approach would be just to regularly monitor battery capacity as part of our hourly log entries.

I am not sure what the peak draw is. I have never seen the fridge draw more than 5A. Lights are easy enough to quantify, but the big unknown at present is the autopilot. I need to look at the manual for that, unfortunately it is on the boat, 2 hours away. Hopefully get down to it again soon.

I was a little concerned about going for a 30A DC-DC charger. Might I be overworking the 55A alternator with that if/when we have to motor all day and the LFP bank is flat? I was considering the Victron 18A version so as not too push the alternator too far. A 30A DC-DC would be useful though if I could get away with it.

If you turn off a DC-DC charger when it is pouring amps at full tilt into a battery, would that not lead to an alternator voltage spike and fried diodes, just as if the BMS shut off? Or do the DC-DC chargers offer some protection against this?

[CaptainRivet]

The voltage spike comes from the alternator but because you have a lead contected there is no spike as its high resistance prevent from that.
The low voltage cutoff you need as automated system protection, also in case of a desaster. Most system cause issues at the pontoon when on shorepower and not supervised. Discharge your LFP to low and its dead.
Normally the BMS takes care of that but these 5$ BMS in the budget drop ins i don't trust a second...its also an installation requirement to have the LCV.
Thats why the smart battery protect is handy, leave the boat and with a fingertip the LFP has no load connected.
I would connect the bilge pump to the starter in your case.

Do you have a badly ventilated engine room or motor long with low rpm like 1500. If yes the 18A is ok, if not i would use the 30A. The 55A hitachi is a tough cookie :-), well and if worse comes to worth a 85AH alternator is below 200 Euro.
18A is just really low (5A AP, Colling box, lights...) you bassically have no charge left for the LFP. as main charge source you should have 30A DC2DC.

Main peak draw would be an anchor windlass?
Autopilot expect 5A draw continuous, total peak draw below 30A i would expect so 100A BP is enough.

[CaptainRivet]

Originally Posted by Sailing Paul

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

The DC2DC charger takes care of that, the FLA is practically bypassed and only presents a dump load to the DC2DC in case the LFP disconnects under load. The power comes directly from the alternator or FLA shore charger.

[Pete7]

Originally Posted by CaptainRivet

The DC2DC charger takes care of that, the FLA is practically bypassed and only presents a dump load to the DC2DC in case the LFP disconnects under load. The power comes directly from the alternator or FLA shore charger.

Indeed, the FLA just sits there at a high state of charge. Since its flooded, I can top it up 2 or 3 times a year as well. Since its a deep cycle battery well "ish" it doesn't give up energy like an AGM, so quite gently when connecting a LFP battery at storage voltage say 13.2v with the FLA at 13.5, hence only a few amps flow across to the LFP before tapering off and they are again in equilibrium.

Pete

[donradcliffe]

The windlass load is an important point. You need a power supply good for 150 amps to run your windlass, and most drop in LFP battery BMS top out at 100. That is why I would choose two 100ahr LFPs in parallel rather than one 200 ahr. You could also address the issue by wiring the windlass to the FLA.

[dan104]

I just got through doing this project, I had 4x6v 225AH floating and 2x 200ah AMG & a 60AH starter AMG.


I swapped out the 4 flA with 4 x 100AH LFP and added in Clark's BBMS which manages the charging of both from the common sources (I have solar, wind, shore and a 120A alternator on my Beta).


I recommend toy take a look at Clark's whole series on this problem on youtube, he covers charging, alternator problems and burnout. (You would not believe what happens to the alternator when the LFP batteries BMS figures it is full and turns off. If your lucky it just blows the alternator and does not start a fire).

https://www.youtube.com/watch?v=Xp6ssk4Guuc&t=5s

I was going to go the DC-DC charger but unseeing the BBMS I did not need it so if any body ants to buy my Victron one I am open.

[mcon12000]

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.

Mine is hybrid as well 24v main Lifepo4 bank 7200w and 1200w LA. The LA services all 12v loads like lights and Navigation and is kept twiddling its thumbs by dual 24/12 30amp DC to DC Charger. Balmar 120 in terminated to the 12v LA so no protection required and dual Victron 50 amp Buck Boost charge the 24v Lifepo4 bank. Engine starts off the same Victron LA battery (Beta 38).

[dan104]

Here is rough view of how it is wired


The light wires are sensor lines



The contractor is a high powered switch, it lets the Bank manager disconnect the power going to the LP when charge reaches desired amount. The Alternator's power is them dumped into the remaining lead, not shown is temp sensor switch located on the ALT to cut field when temp get too hot (At idle the alt is making a bunch of power that LP will suck as fast as it can but the alt built in fan will not cool to reach that level so the switch cuts it off till things cool down and then it back to work (bunch of temp switches cost less than $10.)


Again all this knowledge came from Clark @ temprest

[dan104]

Oh and the current sensor came from Clark's BBMS as part of the kit

[George_SD]

Just as a data point reference. The system below gives us unlimited time on anchor, provided we don't run into 2 or more days with no sun.

1x 100wxsolar panel in horizontal orientation, permanent mount on the rail
3x Group 29 Deep Cycle 100ah batteries (2 house, 1 engine)
1x Renogy Wonderer PWM 10A controller

Our boat is all LED, I don't run really any electronics on anchor except charging phones, tablets, portable VHF radio charger.

Folding and flexible solar panels are usually not as efficient, but you can buy 2x100w and they will provide all the power you need.

Alternator charging is secondary and while it contributes while the engine is running, I see it as a wasteful and dirty way to charge. It's there as a backup. Going solar was by far the best move. We never have to worry about running the engine for power or that if engine dies that we will be without electronics/navionics.