Replace AGM with LiFePo4 Lithium Ion batteries

[La Sirena]

I should be closing on a Selene 57 next week. Woohoo! Exciting, but a little frightening at the same time.

The boat needs new batteries. It has 12 4D AGM batteries for house, engine start, and bow/stern thrusters. I'd like to replace them with lithium ion batteries, but I'm not sure they will work in this application without a major system redesign.

Question: Do LFP batteries work for engine start and thruster applications? I've talked with Battleborn, and they say their batteries do not work with high current applications. I talked with Chargex, and they say absolutely. Maybe it's a difference in the Battery Management System and battery design, or maybe it's an over enthusiastic Chargex salesman. I don't know.

Is there anyone on the forum that uses LFP batteries for engine start and/or thrusters? If so, how big is the engine/thrusters?

A mixture of AGM for start/thrusters and LFP for house is not practical without changing the way the system is wired. FYI - the current chargers are compatible with LFP, but I would need to look closely at the alternator/regulator and make some changes to avoid overheating the alternator.

 

[DavidM]

So it is one big bank of 12, 4Ds for all three needs all wired in parallel? If so you should have plenty of start current. Battleborn specifies 100 amps max for each G31, so with at least 12 batteries you will never draw 1,200 amps while starting your engine.

David

 

[Retriever]

Electric thrusters seem to be a bigger problem than starting the engine. My thrusters each draw ~ 500 amps at 24v and your Selene probably has larger thrusters. When I explored lithium a few months ago it became clear that they aren’t suitable for powering large electric thrusters and I’d need to have a separate 24v lead/AGM thruster bank even if the house batteries were lithium.

One of the challenges is defining surge loads...how much beyond the continuous rating can you go, and for how long, before the BMS intervenes.. Battleborn provides these specs but not all manufacturers do.

 

[La Sirena]

No, it is not 1 bank of 12 batteries (actually, 13 batteries, my mistake). The bow and stern thrusters and the main engine start batteries each have 2 4D batteries in series for 24V. There are 6 4D house batteries, and 1 4D for the generator, get home engine start. I'm attaching a drawing of the DC system.

 

[Alaskan Sea-Duction]

Welcome to TF. I don't have LI batteries, I have simple flood lead acid batteries.

However consider this:

1. What is the life expectancy of IL vs Flood?
2. What is the cost of IF vs Flood?

I can get 5-6 years out of my flood batteries if I take care and maintain of them.

Just a thought. Food luck in you adventures.

 

[mvweebles]

I had a similar thought - just run LFP. I did some research and calling and, as DavidM says, the capacity is additive - if one battery is limited at 100A, then you get 200A out of two, etc.

But I decided thrusters and engine start just wasn't a good use-case for LFP. So I went with a DC-DC charger between the house bank and the start/thruster batteries. House bank has a relatively slow/deep discharge; engine/thruster has a relatively fast/shallow discharge. A DC/DC charger does more than simply isolate, it provides the correct charge profile and would make for a healthier battery even if the chemistries were the same.

Peter

 

[Comodave]

We have LiFePO4 for the house. AGM for the thruster and flooded for the main and genset starting. It takes 3 chargers for our particular setup. I am going to put on a 120 amp alternator that will charge only the house bank. The other main engine alternator will charge the start batteries through ACRs.

 

[JadePanama]

We have a mix of AGM and LiFePO4. Standard Lifeline AGMs for engine start (2-8d), and two pairs of AGMs for each set of thrusters. Then use 12 LiFePO4 batters (138 AH) for the house bank. Stick with the AGMs for starting and Thrusters. They are a perfect fit for that application. The LiFePO4s are much better suited to a typical house/inverter application. Couldn't be happier with our end setup. We can run our ACs or Reverse AC Heat all night at anchor w/o a gen. When we wake up, run the gen for 3 hours and the whole bank is replenished and will last all day. Note - we are in the PNW... I am not sure that I would do the same setup for a FL boat. Very different use cases.

for details on our build i tried to document it here: Need More Power… – M/V Jade Panama'

 

[mvweebles]

We have LiFePO4 for the house. AGM for the thruster and flooded for the main and genset starting. It takes 3 chargers for our particular setup. I am going to put on a 120 amp alternator that will charge only the house bank. The other main engine alternator will charge the start batteries through ACRs.

I would think that due to change of chemistry (House = LFP; AGM/FLA for other), would need a DC-DC charger between House and the other AGM/FLA batteries, no?

Peter

 

[Comodave]

I would think that due to change of chemistry (House = LFP; AGM/FLA for other), would need a DC-DC charger between House and the other AGM/FLA batteries, no?

Peter

No, I have a dedicated charger for the house bank and the 120 amp alternator on one engine. The start batteries are charged by another dedicated charger and the second engine alternator through ACRs. The thruster battery has its own dedicated charger and does not get charged underway since the usage is so short.

 

[mvweebles]

No, I have a dedicated charger for the house bank and the 120 amp alternator on one engine. The start batteries are charged by another dedicated charger and the second engine alternator through ACRs. The thruster battery has its own dedicated charger and does not get charged underway since the usage is so short.

For my 36-foot Willard, the generator is in the front of the engine room so not far from the batteries for the bow thruster. I decided to share 2xG31 AGM batteries with both generator and thruster. I went with a DC-DC charger from my LFP bank, but I thought about using the 15A generator off my Northern Lights 6kw generator for the same reason - not a lot of discharge from this fairly beefy battery bank. I plan on being off-grid for extended periods so decided the best approach for me with 800W of solar was the DC-DC charger, but your solution of a small charger makes sense for most usages.

Peter

 

[Baker]

No, I have a dedicated charger for the house bank and the 120 amp alternator on one engine. The start batteries are charged by another dedicated charger and the second engine alternator through ACRs. The thruster battery has its own dedicated charger and does not get charged underway since the usage is so short.

I am considering leaving the thruster batteries "uncharged" if there is not an AC power source. Do you ever feel that they are struggling under the load without having a charge on them while underway....especially if they had to work hard to embark and get underway and then subsequently work hard to dock again....with no charge in between?

 

[Comodave]

I am considering leaving the thruster batteries "uncharged" if there is not an AC power source. Do you ever feel that they are struggling under the load without having a charge on them while underway....especially if they had to work hard to embark and get underway and then subsequently work hard to dock again....with no charge in between?

I have never had any issues with the thruster battery not being charged enough. But I usually only use the thruster for a couple of minutes at a time. I bought the next size larger than the recommended thruster so when I activate it the boat moves pretty easily. I have had it for 4 years now and have never had an issue with the battery being too low to use it. Also have never noted the thruster running slowly.

 

[Baker]

I have never had any issues with the thruster battery not being charged enough. But I usually only use the thruster for a couple of minutes at a time. I bought the next size larger than the recommended thruster so when I activate it the boat moves pretty easily. I have had it for 4 years now and have never had an issue with the battery being too low to use it. Also have never noted the thruster running slowly.

Awesome. Thanks!!!

 

[La Sirena]

Welcome to TF. I don't have LI batteries, I have simple flood lead acid batteries.

However consider this:

1. What is the life expectancy of IL vs Flood?
2. What is the cost of IF vs Flood?

I can get 5-6 years out of my flood batteries if I take care and maintain of them.

Just a thought. Food luck in you adventures.

Hi Sea-Duction! I'm considering LFP batteries for a few reasons. First, this boat has enough to maintain without checking and filling batteries spread around the boat. Second, LFP batteries will last longer, so another thing I don't have to think about replacing, probably as long as I own the boat. Third, I can charge LFP batteries quickly. I don't have solar, so I'd have to run the genny (at a low load) for a long time to fully charge lead acid batteries. Fourth, I can get a lot more amp-hours of capacity in the same space with LFP than with lead acid. In the long run, LFP batteries may be a little more expensive, but there are a lot of benefits to LFP.

 

[La Sirena]

Electric thrusters seem to be a bigger problem than starting the engine. My thrusters each draw ~ 500 amps at 24v and your Selene probably has larger thrusters. When I explored lithium a few months ago it became clear that they aren’t suitable for powering large electric thrusters and I’d need to have a separate 24v lead/AGM thruster bank even if the house batteries were lithium.

One of the challenges is defining surge loads...how much beyond the continuous rating can you go, and for how long, before the BMS intervenes.. Battleborn provides these specs but not all manufacturers do.

Hi Retriever. You're boat is beautiful! I considered a Nordhavn 50 (Wild Rumpus) that sold a few months ago. In the end we'll be full time cruisers and wanted something a little bigger. But I'm sure there will be many times I'll regret not getting the N50.

I just noticed on the electrical drawing I attached to an earlier post that there is a 300A fuse in line with the bow and stern thrusters. I'd need to measure the current draw with the thrusters on. Maybe the 300A breaker is a slow blow. The BMS on a battery may be more quicker reacting. You don't want to be in a situation where the thrusters stop working because the BMS caused the batteries to disconnect.

 

[La Sirena]

I had a similar thought - just run LFP. I did some research and calling and, as DavidM says, the capacity is additive - if one battery is limited at 100A, then you get 200A out of two, etc.

But I decided thrusters and engine start just wasn't a good use-case for LFP. So I went with a DC-DC charger between the house bank and the start/thruster batteries. House bank has a relatively slow/deep discharge; engine/thruster has a relatively fast/shallow discharge. A DC/DC charger does more than simply isolate, it provides the correct charge profile and would make for a healthier battery even if the chemistries were the same.

Peter

I think I'm coming to the same conclusion. Stick with AGM on the thrusters and starters, and go with LFP on the house batteries. It looks like I have a convenient place to put a DC to DC charger that will allow me to charge the LFP batteries with the correct profile, and continue to charge the AGM batteries with the AGM charging profile. I'll need to consult with someone that knows more than I do. This could be a costly mistake if not done right.

I am excited about increasing my house bank capacity significantly, reducing the charge time of the house bank, and loading up the 16kW generator.

 

[contingensea]

Thoughts

Your question of changing energy storage chemistries is not uncommon nowadays. The topic comes up on many of the forums I follow, e.g. AGLCA, MTOA, etc..

Changing between like chemistries, FLA, AGM, Carbon Foam is a relatively simple process. Moving to Lithium Iron Phosphate (LiFePO4) is not for the faint of heart, at least that is what I have learned over the last couple of years.

Whether you’re somewhere between a DIY’r or having deep pockets, understanding the integration of LiFePO4 into a vessels energy system is worthwhile for the owner.

Here is recent article, written by Jim Healy, titled “Lithium Chemistry Batteries on Boats” that he posted on April 22, 2021 on his web site: http://gilwellbear.wordpress.com
Jim writes an engineering column in the MTOA monthly news letter and is a frequent contributor to the the MTOA and AGLCA Forums. Jim is also involved with ABYC.

There are many very good resources on the web for educating one’s self on the pluses and minuses of LiFePO4 in boat applications.

Here are a few:
MTOA
http://greatloop.org
Pacific Yacht Systems YouTube videos by Jeff Cote

I should be closing on a Selene 57 next week. Woohoo! Exciting, but a little frightening at the same time.

The boat needs new batteries. It has 12 4D AGM batteries for house, engine start, and bow/stern thrusters. I'd like to replace them with lithium ion batteries, but I'm not sure they will work in this application without a major system redesign.

Question: Do LFP batteries work for engine start and thruster applications? I've talked with Battleborn, and they say their batteries do not work with high current applications. I talked with Chargex, and they say absolutely. Maybe it's a difference in the Battery Management System and battery design, or maybe it's an over enthusiastic Chargex salesman. I don't know.

Is there anyone on the forum that uses LFP batteries for engine start and/or thrusters? If so, how big is the engine/thrusters?

A mixture of AGM for start/thrusters and LFP for house is not practical without changing the way the system is wired. FYI - the current chargers are compatible with LFP, but I would need to look closely at the alternator/regulator and make some changes to avoid overheating the alternator.

 

[stone beach]

In electric cars size / weight / output is an important factor, I can see why they need to use Li batteries.

This is not the case on a boat, certainly not on a trawler.

Why swop simple cheap lead acid technology for something that needs a built in management system which (in case you dont know) will turn the battery off if it is not "happy".

My chrystal ball tells me that in a couple of years time this forum will be full of posts about Li battery problems.

 

[jim.johnson3570]

No, it is not 1 bank of 12 batteries (actually, 13 batteries, my mistake). The bow and stern thrusters and the main engine start batteries each have 2 4D batteries in series for 24V. There are 6 4D house batteries, and 1 4D for the generator, get home engine start. I'm attaching a drawing of the DC system.

You could always go with your Lithium batteries and keep the bow-thruster separate with it's own smaller charger. I did the same thing recently with my new Victron Inverter and Lithium bank and then had a smaller charger for the (2) AGM 8D start batteries and even a small charger for the Group 31 AGM for the generator start.