FLA to LFP Battery Conversion

[Kyle Ewing]

All,

I'm looking for feedback on a conversion from FLA (Flooded Lead Acid) batteries to LFP (Lithium Iron Phosphate).  I'm considering because it's time to replace my seven year old house bank and four new golf cart batteries will cost around $600.  I estimate upgrade to LFP, including DC to DC charger and other parts, will total between $1000 and $1500 depending on the battery.  Time difference is an hour for new golf cart batteries and a day or two for LFP.

My current system has worked flawlessly for many years so I want to leave it unchanged as much as possible.  I used information from Marine How To (https://marinehowto.com/) and plan to source parts from Rod's affiliate pages.

Let me know what you think.  My goal is to avoid mistakes and help others considering the same change.

Kyle Ewing
DONNYBROOK #1010
 

[Noah]

Are you putting LiPo battery and engine FLA in existing battery box/area or will the FLA battery be located elsewhere? Reason I asked is if the existing battery space under settee bench is just for the lithium, have you determined that 300A lithium is the biggest bank that will fit there? I have been thinking about this change as well; but 300A is not very big for a house bank. If you do it this way, get the biggest DC-DC charger ( I think it is 50A) so that you can take advantage (somewhat) of lithium's ability to take a rapid high charge rate. Or, perhaps your voltage regulator has a lithium profile and eliminate the DC-DC converter. Keep us posted.

[Ted Pounds]

Are you putting LiPo battery and engine FLA in existing battery box/area or will the FLA battery be located elsewhere? Reason I asked is if the existing battery space under settee bench is just for the lithium, have you determined that 300A lithium is the biggest bank that will fit there? I have been thinking about this change as well; but 300A is not very big for a house bank. If you do it this way, get the biggest DC-DC charger ( I think it is 50A) so that you can take advantage (somewhat) of lithium's ability to take a rapid high charge rate. Or, perhaps your voltage regulator has a lithium profile and eliminate the DC-DC converter. Keep us posted.

300 Ah is plenty big for a house bank.  Keep in mind that FLA should not be discharged below 50%, meaning a 400 Ah FLA bank is really 200Ah in normal use.  While LiFePo batteries have no problem with full discharge. 

[Noah]

Yes Ted. Point well taken on 300A Lipo being usably bigger than 420A FLA.

[Kyle Ewing]

I'll put the group 27 FLA, DC2DC charger and LFP battery in the existing battery area.  There's footprint for more, but I don't want to spend more $$$ than I have to.  As Ted said, the full 300 ah can be used so it's a 50% increase in the usable capacity I have today which is fine for how I use the boat.

The Optima start battery is under the aft berth near the engine.

[Noah]

Now I am even more confused than I usually am. ;-). Do you plan to keep your engine battery under the aft bunk as well as add a group 27 FLA and 300 Lipo? Three batteries? If so, how will you charge the engine battery?

[Jim Hardesty]

Take this for what it's worth.  I remember reading or hearing someplace that some insurance companies will void policies on boats with lithium batteries.  Don't know if that is true.  But think it's worth checking.
Jim

[Kyle Ewing]

The start battery is charged with a Xantrex echo charger because the battery charger and alternator are connected to the house bank.  I'm adding the group 27 FLA so I can continue to use my charger and regulator and to have a second battery to start the engine.  My old Truecharge 40 charger and ASR-4 regulator don't have a LFP setting and it's not recommended to use the class of LFP battery I'm looking at to start an engine.

Regarding insurance, I talked to mine (Geiko/BoatUS) and they allow LFP batteries as long as they're intended for boats.  The Epoch battery I'm considering (https://www.epochbatteries.com/?rfsn=7030270.54d2cb) is marketed for marine use and is recommended by Rod Collins (Mainesail on this board).

[Noah]

Let me know if I have this correct. Both shore-power charger and alternator go to the new group 27 FLA battery. That battery then "feeds" the engine battery through an echo charger as well feeding the LiPo battery via a DC-to-Dc charger. Is this correct? Sorry to seem dense on this.

[Ted Pounds]

FWIW, I converted both our golf carts to lithium this year (Vatrer batteries). Very happy with the conversion.  No more watering.  No need to keep on the charger all the time.  No more hassle prepping for off season storage.   No need to buy another battery ever again.  You'll love the Bluetooth connected BMS (battery management system).  You can toss all your old battery monitors; it's as good or better than any of them.  On my current Gloucester 19 I added a small, 20 Ah lithium.  I went with lithium because she sits on a mooring and doesn't get charged constantly.  It only runs (LED) lights for night sailing and a USB charger.  It's easy enough to bring it ashore every now and then to recharge.

[girmann]

It looks like the diagram that you're constructing looks right, but there are a few things that you need to consider. For instance, you need compatibility between the Group 27, "DC2DC Charger", and the LiFePo batteries. None of the components of an LiFePo system work the way they do with FLA and it sounds like you know that already. I just want to throw some cautions at you and I apologize if you already know them. 
1) That DC2DC charger is not (always) your friend. These chargers can turn current on and off very quickly. These large LiFePo batteries are able to be charged at 100+A and can turn that charge current on and off in microseconds. This can play havoc with your alternator when the DC2DC goes from 50A to 0 in an instant and your Group 27 is already "floating" and not able to accept any more charge current. I believe there is a way to put in a shunt resistor at the alternator to prevent issues from occurring, but I'm not familiar with how this is done. See the issue that the Wynns had (Gone with the Wynns) on their new catamaran. Their LiFePo setup cooked both FLA batteries.
2) When the alternator is off, the charge current to the LiFePo bank is effectively limited by the characteristics of FLA Group 27 battery you put in the system. If you set the DC2DC charger to 50A, you need to make sure that the FLA battery can sustain that current drain without overheating. In your picture, the FLA looks like it's in series with the DC2DC charger. Since I don't know how that would work (without some massive diodes) I'm guessing it's actually in parallel with the house bank on/off switch and the alternator. See #1.
3) Based on Ah ratings, if you're trying to get the most life out of LiFePo batteries, they're not going to supply any more power than FLA. Most battery manufacturers should give you this information. For instance, Victron batteries can go 2500 charge cycles with 80% of their capacity when the "Depth of Discharge"(DoD) is 80%, but can go twice as long (5000 charge cycles) if the DoD is 50%. (https://www.victronenergy.com/upload/documents/Datasheet-12,8-&-25,6-Volt-lithium-iron-phosphate-batteries-Smart-EN.pdf) That 50% number looks an awful lot like the FLA number. The one big advantage is that you CAN go below 50%, and only sacrifice a little bit of longevity. This is still oodles better than FLA because if you drain FLA batteries, they may never recover. With LiFePo the batteries will continue to work for a long time (just not as long as they would have).

[Jim Hardesty]

"Capable Cruising Guide" has been doing a u-tube for a couple of years now on his experience adding LiFePo to lead acid in a real world test, living on board.  Video's are longer than most about half hour so would take a while to see them all and are mixed in with other videos, I would think it would be best to go from the oldest to latest.  I found it to be interesting and informative.

I've decided not to add LiFePo to Shamrock at this time.  I think to get the advantages of LiFePo batteries would need a number of upgrades and additions that would add to the cost and complexity.  I should say Shamrock has the OEM setup except for a new battery charger.  I'm happy enough with that, am able to spend about 3 days before needing a few hours of charging.  Hope to go back to the North Channel next summer, may change my mind before that.
Jim

[Kyle Ewing]

Thanks all for the comments.  They're prompting me to do more research to make sure I understand how it works.

Noah, you're correct about the DC2DC charger "feeding" the LFP battery.  I think of the DC-to-DC charger as a fancy Echo Charger with some differences. The DC-to-DC charger not only charges the LFP battery but also functions as a power supply, regulating voltage and current from the LFP battery to support the house loads. I'll continue to use my Echo Charger to maintain the engine start battery.

Girmann, I'm adding the group 27 battery as a bridge between my existing setup (charger, alternator) and letting the DC2DC charger handle compatibility with the new LFP battery.  I'd either have to change my wiring to charge the engine start battery first (time consuming) or replace the alternator regulator and battery charger to avoid it, then I'd still be concerned about using the LFP to start the engine.  The Epoch 300ah battery peak output is 400 amps for 3 seconds.

That's a good point about BMS shutoff protection.  I'll look into field disconnect or an alternator surge protection.

The DC-to-DC charger is connected to the FLA battery in parallel. It supplies power to the house loads at 12.8V, up to its maximum capacity of 50 amps. This prevents the FLA battery from discharging during normal operation. If current demand exceeds 50 amps (e.g., engine starting), the FLA battery supplements the current. Once the demand drops, the DC-to-DC charger replenishes the FLA battery via the parallel connection.

Regarding battery life, I use full capacity just a few times a season.  I'll get longer battery life because LFP doesn't need to be fully charged like FLA batteries.

Jim, I agree replacing existing batteries would be easiest.  If I didn't enjoy tinkering, I'd just replace the golf cart batteries.  My reason for this post is to vet my plans to avoid unpleasant surprises and costs.  I'll check out "Capable Cruising Guide".