For the battery experts… Lithium??

[WiskyDan]

I just bought a battery negative cable off the shelf at Napa - it matched negative that I had in the boat.

 

[FSH 210 Sport]

How did you determine what gauge wire to use for the new negative. I assume it has to be able to handle the full load from all 3 of your system negative wires going into the shunt. I have a 195S, it has the stock negative going to the battery and then a direct run for my amp, 4 gauge 100 amp fuse, also going to the battery. Trying to figure out what gauge I would need to go from the battery to shunt.

So did some poking around to see what size battery cable is used in cars and such and what is recommended. From what I can see you’d probably be fine with #1 copper wire, in fact that is overkill for our engines, and I’d get machine wire which has lots of fine strands which makes it very flexible. The #1 wire I used for my house battery is welding cable which is very flexible.

The engines in our boats probably don’t pull more than 150 amps, check the suggested wire size at this website which makes custom battery cables. Battery Cable Size Chart | Battery & Cable Questions | 2/0 Gauge This custom battery cable shop recommends #2 for four cylinder and small six cylinder engines and #1 for large six cylinder and small V8 engines.

Once you have your shunt installed you’ll be able to see just how much your starter draws when you start your engine, and how much all of your accessory loads really are, and I’m sure quite a few people will be interested in your observed amp draws.

Here’s another wire gauge ampacity chart.

Cerrowire Resources - Ampacity Charts

Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.

www.cerrowire.com

Wire can be pushed to 200% of its rating for short periods of time, like for a starter on an engine, and to 150% for four hours with no damage to the conductor, and those overload ratings are very conservative, some utilities push the 200% rating in open air to 4 hours and the 150% in open air to 8 hours, regularly.

 

[Stealth]

Thanks @FSH 210 Sport for all the great info. I have been following a lot of your posts on batteries while I figure out my plan. What you said is the direction I was leaning in. My only concern is that I added a 4 gauge wire fused to 100 amps at the battery for an audio amp. I'm a 195S with single battery. For now I'm going to keep it that way. So in theory I'm combining the stock negative and 100 amp audio ground to one side of the shunt and sending them down just one wire on the other side. I don't draw anywhere near 100amps for the audio amp. In fact the amp itself has only a 50 amp fuse. But I don't want a fire to start on a short of some sort. I think I may go with a 2/0AWG wire for the short run which should give me about 175 amps continuous (way over kill for sure).

I'll likely swap the single battery for 100ah or 135ah LFP down the road but at the moment I haven't depleted the stock deep cycle durning normal use. The shunt data should be interesting to see just how much capacity I'm using now.

 

[FSH 210 Sport]

Thanks @FSH 210 Sport for all the great info. I have been following a lot of your posts on batteries while I figure out my plan. What you said is the direction I was leaning in. My only concern is that I added a 4 gauge wire fused to 100 amps at the battery for an audio amp. I'm a 195S with single battery. For now I'm going to keep it that way. So in theory I'm combining the stock negative and 100 amp audio ground to one side of the shunt and sending them down just one wire on the other side. I don't draw anywhere near 100amps for the audio amp. In fact the amp itself has only a 50 amp fuse. But I don't want a fire to start on a short of some sort. I think I may go with a 2/0AWG wire for the short run which should give me about 175 amps continuous (way over kill for sure).

I'll likely swap the single battery for 100ah or 135ah LFP down the road but at the moment I haven't depleted the stock deep cycle durning normal use. The shunt data should be interesting to see just how much capacity I'm using now.

The cleanest way to do your grounds is to install a buss bar and land all the grounds on the buss bar that way you only have one cable on each side of the shunt.

I get you wanting to go with 2/0 which is 195 Amps, and while I’m a fan of “overkill is underrated” that is over kill but, if you can get it in there without dramas its certainly not going to hurt anything except your wallet. Having piece of mind is priceless.

Your 100 amp fuse on the #4 is basically an over fuse of 5%, since your amp has its own 50 Amp fuse, you are only protecting the length of [HASH=432]#4,[/HASH] so with a 100 A fuse you are fused at 105% roughly.

Here is what I suggest you do with your current (see what I did there?) set up. Install the shunt, get your universal battery cable from the auto parts store to go from the battery to the shunt, and then attach your system grounds on the other side of the shunt being sure to put the largest cables on the bottom and the thinnest towards the top or nut part of the bolt.

Once the shunt is installed and you have installed the app on your phone, turn on each device separately to measure their draws. Then with all devices off start the engine and see how much it draws, the instantaneous amp draw should be recorded in the graphical page of the smart shunt.

By doing the two aforementioned steps you will KNOW exactly how much draw you will have on your battery and can then make educated and informed decisions about how you will proceed with your system design. Not measuring all of those loads / draws will just be a guess or an assumption.

 

[Stealth]

The cleanest way to do your grounds is to install a buss bar and land all the grounds on the buss bar that way you only have one cable on each side of the shunt.

I get you wanting to go with 2/0 which is 195 Amps, and while I’m a fan of “overkill is underrated” that is over kill but, if you can get it in there without dramas its certainly not going to hurt anything except your wallet. Having piece of mind is priceless.

Your 100 amp fuse on the #4 is basically an over fuse of 5%, since your amp has its own 50 Amp fuse, you are only protecting the length of [HASH=432]#4,[/HASH] so with a 100 A fuse you are fused at 105% roughly.

Here is what I suggest you do with your current (see what I did there?) set up. Install the shunt, get your universal battery cable from the auto parts store to go from the battery to the shunt, and then attach your system grounds on the other side of the shunt being sure to put the largest cables on the bottom and the thinnest towards the top or nut part of the bolt.

Once the shunt is installed and you have installed the app on your phone, turn on each device separately to measure their draws. Then with all devices off start the engine and see how much it draws, the instantaneous amp draw should be recorded in the graphical page of the smart shunt.

By doing the two aforementioned steps you will KNOW exactly how much draw you will have on your battery and can then make educated and informed decisions about how you will proceed with your system design. Not measuring all of those loads / draws will just be a guess or an assumption.

Thanks again, I got the shunt in this morning. An idea what settings should be used with the stock deep cell? Interesting from a quick test the audio amp uses way less power then expected. 75 watts at a loud but not max "boom boom" level.

 

[FSH 210 Sport]

Thanks again, I got the shunt in this morning. An idea what settings should be used with the stock deep cell? Interesting from a quick test the audio amp uses way less power then expected. 75 watts at a loud but not max "boom boom" level.

So I want to understand your question correctly, you are asking what the settings should be on the shunt with a flooded lead acid battery?

Thanks for the info on the amp consumption, (I’m not surprised by the low level of draw) can you please share with us the make / model and watt output of your Amp?

 

[Stealth]

So I want to understand your question correctly, you are asking what the settings should be on the shunt with a flooded lead acid battery?

Thanks for the info on the amp consumption, (I’m not surprised by the low level of draw) can you please share with us the make / model and watt output of your Amp?

Yes that is correct. This is the battery I have:

Salesforce B2B Commerce

www.fleetpride.com

I can't find a capacity but I'd guess 60-75ah. How do you determine the shunt settings for such a battery?

The amp is the Wet Sounds HTX-4. Bridged sub set to max at 300 watts, and the 4 stock recon 5s set for about 60 watts each. We don't blast music and only listen to it in the boat. No desire to make other people listen to our music.

 

[FSH 210 Sport]

Yes that is correct. This is the battery I have:

Salesforce B2B Commerce

www.fleetpride.com

I can't find a capacity but I'd guess 60-75ah. How do you determine the shunt settings for such a battery?

The amp is the Wet Sounds HTX-4. Bridged sub set to max at 300 watts, and the 4 stock recon 5s set for about 60 watts each. We don't blast music and only listen to it in the boat. No desire to make other people listen to our music.

Let me see what I can come up with…you do need to know the Ah of the battery though.

 

[Stealth]

Let me see what I can come up with…you do need to know the Ah of the battery though.

I'm still trying to find the exact number. I have guessed 60ah to be on the safe side for now.

 

[FSH 210 Sport]

I'm still trying to find the exact number. I have guessed 60ah to be on the safe side for now.

Okay, cannot find the Ah listing from Deka, but, I found a reserve min calculator to Ah calculator, looks like 130 reserve minutes is 54 Ah. Which seems about right since this is a starting battery not a deep cycle battery. The best I have seen from a group 24 FLA deep cycle battery is 72Ah, which I find HIGHLY dubious.

Reserve capacity to amp hours

Convert reserve capacity to amp hours

www.convert-formula.com

I have a call into Battle Born to have them give me the settings for this battery.

In the mean time, check to see if there is a lead acid battery set up in the drop down settings in the device, I’d be surprised if there isn’t a pre programmed setting in the shunt.

 

[FSH 210 Sport]

Here’s the manual, go to section 7 for the Peukert setting and other settings related to your battery.

https://www.victronenergy.com/upload/documents/SmartShunt/9172-Manual_BMV_and_SmartShunt-pdf-en.pdf

 

[WiskyDan]

Battle Born is running a 15% off flash sale..........very happy with mine.

Battle Born Batteries | Reliable Lithium-Ion Batteries

At Battle Born Batteries, we specialize in top of the line LiFePO4 lithium-ion batteries. Get out there, stay out there!

battlebornbatteries.com

 

[WiskyDan]

I'm still trying to find the exact number. I have guessed 60ah to be on the safe side for now.

@FSH 210 Sport helped me this morning with an issue where my SmartShunt app showed no charging in progress when I had my battery hooked up to my 10amp Noco Genius charger. The negative from your battery charger has to be connected to the “To System Minus” side of the shunt. I initially had my battery charger negative connected to the negative post on the battery and the shunt app showed no change in voltage or charge percentage. Once I moved the battery charger negative to the correct position the shunt the app data started reading properly.

 

[SamN44]

I'm a glutton for punishment after the failure I had using a cheap deep cycle lifepo4. Is there any reason why this "dual purpose" battery wouldn't work for a single battery setup in our 190? Amazon.com

I'm willing to spend some money for a single lithium if it will work with our stator setup. The flooded lead acid battery I bought just isn't powerful enough for me to run our 12v cooler and stereo with a small amplifier floating all day and I don't want the weight or wiring of a dual battery setup. The stereo distorts on the ride home from a lack of amps. Anyone willing to educate me? The problem with the cheap deep cycle lifepo4 I used was that the BMS would cut all power from battery while the boat was running at full charge and the boat would surge and the stereo and electronics would freak out without a battery in the circuit.

 

[FSH 210 Sport]

I'm a glutton for punishment after the failure I had using a cheap deep cycle lifepo4. Is there any reason why this "dual purpose" battery wouldn't work for a single battery setup in our 190? Amazon.com

I'm willing to spend some money for a single lithium if it will work with our stator setup. The flooded lead acid battery I bought just isn't powerful enough for me to run our 12v cooler and stereo with a small amplifier floating all day and I don't want the weight or wiring of a dual battery setup. The stereo distorts on the ride home from a lack of amps. Anyone willing to educate me? The problem with the cheap deep cycle lifepo4 I used was that the BMS would cut all power from battery while the boat was running at full charge and the boat would surge and the stereo and electronics would freak out without a battery in the circuit.

Summary; There are three main advantages to LFP batteries, performance, longevity and half the weight of a lead acid battery. The longevity is what makes LFP batteries cheaper by far than even the most inexpensive FLA battery over their service life, quality LFP batteries have a minimum of a 10 year warranty most are 11 years, and if the battery doesn’t work correctly then you don’t get the performance either. So unless you are willing to spend the money on a quality LFP battery stick with an inexpensive FLA battery or an inexpensive AGM battery.

I’m not sure if you are the member I am thinking about, but there was a guy who had a similar problem as you do, and I thought I responded to that guy as well, regardless, the inexpensive LFP batteries can have issues like this, it is the BMS that causes issues.

The next thing you need to do is install a Victron Energy Smart Shunt / battery monitor so you KNOW what the state of charge is in your battery and how much draw your devices have. ANYthing less is just a guess.

You may not “want” the weight of a dual battery set up, but it is in fact what you are probably going to need based on your description, but, with LFP batteries the weight of two will be less than one FLA or AGM battery. Speaking of weight, to get the same performance out of a lead acid battery, you would need five times the weight of lead acid batteries to get the same performance as a LFP battery.

Again, without knowing what the energy demands are it is impossible to determine the sizing of your batteries for you purpose. The 12V cooler, which is an awesome device to have, probably draws around 5 amps, but, it should not be constant all day, unless stuff was put in there that was not pre cooled. The other thing that just came to mind is, do you have an onboard charger that you plug in after every outing? This is crucial in getting any decent performance out of your lead acid battery, or LFP battery.

So, my suggestion to you would be to go to a two battery set up, have a dedicated lead acid / FLA start battery and a LFP house battery. The lead acid battery will give the alternator some place to put some current while running even when fully charged as the alternator puts out 14.4 volts. Install a BEP marine two battery switch with DVSR, and hook the DVSR hot wire up to your fuel pump hot wire for automatic and trouble free operation, you will need to do this with the LFP house battery otherwise the DVSR will always be closed due to its 13.6 resting voltage. A group 24 LFP house battery would probably be enough power for your house needs while on the water, but why not put in a 100ah if you can.

A single Dakota Lithium group 24 dual purpose LFP battery would probably work for a single battery operation for your boat, again, put in a Victron shunt so you know what is going on with your battery. Some folks are running two LFP batteries with the aforementioned BEP marine battery switch and either running the DVSR hot wire to a relay off the key switch, rocker switch, or the most elegant is running it off of the fuel pump hot wire. The big advantage for you with dual LFP batteries is that two group 24 LFP batteries will be slightly less weight than a single FLA battery, and you will have at least twice the storage capacity if not three.

While I mentioned the Dakota Lithium dual purpose battery as it is a rated starting battery, I will only recommend Battle Born batteries. One member here installed two group 27/31 Battle Born 100Ah batteries in his boat, one for starting and one for the house, even though the BB are not rated as a starting battery, the draw of the starters on our engines is well within the performance envelope of the BB battery and that member reported to me that he has had great results with that set up.

 

[SamN44]

Summary; There are three main advantages to LFP batteries, performance, longevity and half the weight of a lead acid battery. The longevity is what makes LFP batteries cheaper by far than even the most inexpensive FLA battery over their service life, quality LFP batteries have a minimum of a 10 year warranty most are 11 years, and if the battery doesn’t work correctly then you don’t get the performance either. So unless you are willing to spend the money on a quality LFP battery stick with an inexpensive FLA battery or an inexpensive AGM battery.

I’m not sure if you are the member I am thinking about, but there was a guy who had a similar problem as you do, and I thought I responded to that guy as well, regardless, the inexpensive LFP batteries can have issues like this, it is the BMS that causes issues.

The next thing you need to do is install a Victron Energy Smart Shunt / battery monitor so you KNOW what the state of charge is in your battery and how much draw your devices have. ANYthing less is just a guess.

You may not “want” the weight of a dual battery set up, but it is in fact what you are probably going to need based on your description, but, with LFP batteries the weight of two will be less than one FLA or AGM battery. Speaking of weight, to get the same performance out of a lead acid battery, you would need five times the weight of lead acid batteries to get the same performance as a LFP battery.

Again, without knowing what the energy demands are it is impossible to determine the sizing of your batteries for you purpose. The 12V cooler, which is an awesome device to have, probably draws around 5 amps, but, it should not be constant all day, unless stuff was put in there that was not pre cooled. The other thing that just came to mind is, do you have an onboard charger that you plug in after every outing? This is crucial in getting any decent performance out of your lead acid battery, or LFP battery.

So, my suggestion to you would be to go to a two battery set up, have a dedicated lead acid / FLA start battery and a LFP house battery. The lead acid battery will give the alternator some place to put some current while running even when fully charged as the alternator puts out 14.4 volts. Install a BEP marine two battery switch with DVSR, and hook the DVSR hot wire up to your fuel pump hot wire for automatic and trouble free operation, you will need to do this with the LFP house battery otherwise the DVSR will always be closed due to its 13.6 resting voltage. A group 24 LFP house battery would probably be enough power for your house needs while on the water, but why not put in a 100ah if you can.

A single Dakota Lithium group 24 dual purpose LFP battery would probably work for a single battery operation for your boat, again, put in a Victron shunt so you know what is going on with your battery. Some folks are running two LFP batteries with the aforementioned BEP marine battery switch and either running the DVSR hot wire to a relay off the key switch, rocker switch, or the most elegant is running it off of the fuel pump hot wire. The big advantage for you with dual LFP batteries is that two group 24 LFP batteries will be slightly less weight than a single FLA battery, and you will have at least twice the storage capacity if not three.

While I mentioned the Dakota Lithium dual purpose battery as it is a rated starting battery, I will only recommend Battle Born batteries. One member here installed two group 27/31 Battle Born 100Ah batteries in his boat, one for starting and one for the house, even though the BB are not rated as a starting battery, the draw of the starters on our engines is well within the performance envelope of the BB battery and that member reported to me that he has had great results with that set up.

Thank you for taking the time to write such a thorough response. I do keep the FLA on a charger when not in use, but it's only around 65AH (1/2 useable). Reliable, but very anemic for the cooler, tunes, and our inflatable pump.

My understanding is that: on a lead acid battery as state of charge increases, resistance also increases, so the battery acts as a buffer between the voltage from the stator and the electronics. The battery is always in the circuit and there is no BMS to protect the battery.

With the lithium batteries, they absorb charge much more readily until they are fully charged, act as a buffer between the stator and the electronics until full, and then (from my experience), removes itself from the circuit because the BMS goes into protection mode from the stator voltage (15V+). From my research, it seems like there has to be a shunt to divert excess voltage to keep the battery from overcharging or going into protection mode on a stator (like a DC/DC charger for a house battery), which I think you are describing with the DSVR system for the house battery like you mentioned. On our 190 it's just a single hookup with no DSVR system.

I know the stator is the problem, and that outboards with real alternators run fine. Does any lithium have a BMS with some sort of internal shunt to keep it from going into protection mode after receiving a full charge from the stator? Alternatively, does a product exist that would act as voltage regulator between the starter battery and the stator?

I should just do the smart thing and get an add-a-battery kit and 2x AGM's, but I have enjoyed learning from your and others writings and feel as if I may be missing something small that would make a single lithium battery work for everything.

 

[FSH 210 Sport]

You are welcome!

First, automotive style alternators, VMA (variable magnetic flux/alternators) do have major issues with LFP batteries due to their low resistance. This causes them to run at 100% duty cycle and they are only designed to run at about 10-20% duty cycle, and will burn up as a result.

The alternators in our boats are PMA (permanent magnet alternators), their output is always at 100% and the excess voltage is shunted to ground via the regulator, and it regulates voltage to 14.4 volts DC. These charging systems are a great marriage with lfp batteries.

The stator is just the stationary winding part of the alternator, the part that spins on the crankshaft is the rotor and holds the permanent magnets that spin the magnetic field across the windings of the stator which induces voltage into that winding. This voltage is AC and goes to the rectifier where it is rectified into DC voltage and then the DC voltage is regulated. This is all the same unit, so you do not need to add anything else.

The problem is that the inexpensive LFP batteries have crappy bms in them, and that is the main source of your problem.

LFP batteries charge 5 times as fast as FLA batteries due to their low resistance btw.

While Blue Sea makes a VSR etc.. I prefer the BEP marine switch, it is way more compact and simple to install.

Go here and read this thread; Conversion to LiFePo batteries There is a lot of great info there about lfp batteries, charging, and use in our boats.

Myself, I would not feel comfortable with a single battery, I like, no, demand, having a dedicated start battery, and I carry a jump pack.

The smart thing, imho provided that you can afford it, would be to set yourself up with the fla start battery and the lfp house battery as I described above. You will never be wanting for battery capacity @WiskyDan can chime in with his results.

Don’t mean to be curt with this response but I’m a bit short on time and wanted to respond to you before I head out.

 

[SamN44]

After much research and testing, I have simply combined a 12v lead acid starting battery and the 100ah 12v lifepo4 I already have in parallel. My boat, without DSVR, now behaves exactly how I have wanted.

A Youtube video from an electrical engineer piqued my interest and explains why it works:

For anyone who hasn't read my previous posts, the problem I had with lifepo4 only was the lifepo4 bms shutting the battery off at full charge which causes the electronics to go crazy from the voltage spike. My goal was to add ample energy storage for my stereo amp, inflatable pump, and 12v cooler. Keeping a lead acid in between creates a voltage buffer that never removes itself from the electrical circuit.

The different chemistries, for my boat without DSVR, behaves incredibly well together. The lifepo4 does the majority of the work while chilling on the lake with the motor off and floats the lead acid at a nice float voltage. During testing, I charged both to full on the trailer and let them sit together for 2 weeks. The result was that the lifepo4 spends some energy to keep the (new) lead acid voltage up and they equalize around 13.2v with very little parasitic draw between the two. This keeps the lead acid at a happy float voltage and the lifepo4 around 70% which is great for storage.

I will update if I experience any problems, but after 5 long outings, this is now my full time setup. The engineer in the video I linked sells a custom bank manager for charging this setup, but I found it unnecessary for how we use the boat. Emily & Clark's Adventure - BankManager™

 

[FSH 210 Sport]

After much research and testing, I have simply combined a 12v lead acid starting battery and the 100ah 12v lifepo4 I already have in parallel. My boat, without DSVR, now behaves exactly how I have wanted.

A Youtube video from an electrical engineer piqued my interest and explains why it works:

For anyone who hasn't read my previous posts, the problem I had with lifepo4 only was the lifepo4 bms shutting the battery off at full charge which causes the electronics to go crazy from the voltage spike. My goal was to add ample energy storage for my stereo amp, inflatable pump, and 12v cooler. Keeping a lead acid in between creates a voltage buffer that never removes itself from the electrical circuit.

The different chemistries, for my boat without DSVR, behaves incredibly well together. The lifepo4 does the majority of the work while chilling on the lake with the motor off and floats the lead acid at a nice float voltage. During testing, I charged both to full on the trailer and let them sit together for 2 weeks. The result was that the lifepo4 spends some energy to keep the (new) lead acid voltage up and they equalize around 13.2v with very little parasitic draw between the two. This keeps the lead acid at a happy float voltage and the lifepo4 around 70% which is great for storage.

I will update if I experience any problems, but after 5 long outings, this is now my full time setup. The engineer in the video I linked sells a custom bank manager for charging this setup, but I found it unnecessary for how we use the boat. Emily & Clark's Adventure - BankManager™

After watching that video It’s hard to know where to begin … Know what’s worse than no information? Bad information

First there are what I will call several lies of omission. The first is about the function of the built in BMS on a quality LFP battery, such as the Battle Born battery pictured, the BMS protects the LFP battery from the things that could damage it, low voltage, high voltage, excessive charge and discharge rates, charging when it’s either too cold or too hot. The video would have the viewer believe that the LFP battery is susceptible to some bad things but not others. Next would be the natural discharge rate of FLA and LFP batteries, FLA batteries have a much higher natural discharge rate than a LFP battery does, you now see this with your estimated (unless you installed the smart shunt mentioned previously) 70% state of charge on your LFP battery, whereas if the batteries were isolated your LFP battery would still be at 100% instead of 70%. You said that there is very little parasitic loss and go on to state that after two weeks the LFP battery is at 70%?!! That’s a 60% discharge rate per month whereas if the LFP battery was isolated it would be 1% or less. Another reason there is such a high discharge rate on your LFP battery is that is maintaining a higher resting voltage on the FLA battery is because the FLA battery only has a fully charged resting voltage of 12.5 volts due to the potential difference caused by the chemical reaction between the plates and the electrolyte (diluted sulphuric acid).
This another one of the key advantages of LFP batteries, the ability to leave a fully charged LFP sit for a year and it will still be at 90% state of charge or more whereas a FLA battery will be at 50% under ideal conditions lower than 50% in less than ideal conditions. Then there is the charge time, the video host mentions once about LFP batteries and their low resistance and rapid discharging into a FLA battery but fails to mention that LFP batteries charge 5 times faster than FLA. Also, there is a reason that battery chargers leave the maintenance voltage at 12.6 volts on lead acid batteries to keep from boiling off the electrolyte. The maintenance voltage on a lfp battery charger is 13.6. So by leaving the lfp battery tied to the FLA battery it is constantly being over charged.

Another is the weight, typically for a given Ah size of a battery LFP is one half the weight of a LFP battery, and when looking at energy storage LFP batteries are 1/5 the weight of lead acid batteries. The video host mentions once about life cycles about lead acid batteries but fails to mention that LFP batteries have 10 times the life cycles, and LFP batteries can be discharged 80% to a 20% state of charge with no impact to its 5000 cycles, and discharged 90% to a 10% state of charge with minimal impact to its life cycles. Take a lead acid battery to 80% discharge on a regular basis and you’ll be replacing that battery very soon. I severely doubt the claim of the hosts FLA batteries lasting 15 years, let alone without doing equalization charges, which is ironic as he mentions LFP battery cell balancing, another of the BMS’s functions.

Cost, the video host says LFP batteries are more expensive than FLA batteries, true in up front cost, BUT, over the batteries’ life span LFP batteries are a fraction the cost of FLA. The fully charged resting voltage of a BB LFP battery is not 13.2 it’s 13.6 and as mentioned above, smart chargers in a lfp charging profile maintain 13.6 volts.



Then there’s the peukert effect difference between FLA and LFP batteries and that has to do with discharge efficiency, LFP batteries of a given size have at minimum 2 times the storage capacity (KWh) and greater than 2 times as the rate of discharge increases.

All of these aspects are covered in the Conversion to LiFePo batteries thread.

From a reliability standpoint you now have your batteries tied together and therefore do not have a dedicated start battery, that’s not something I’d want on my boat. That’s the whole point of having a DVSR, to have an isolated dedicated start battery and then once the start battery is charged enough it closes and begins charging the house battery.

As I stated previously the BMS on your LFP battery is more than likely what was causing your issues previously, so it appears to me that the problem of a poor LFP battery BMS was solved by tying it to a FLA battery.

I appreciate the amount of time and effort you put in on this post but do yourself a favor and put in some sort of DVSR / VSR set up and energize the DVSR with a hot from your fuel pump and keep the batteries isolated when you’re floating and take advantage of the energy storage capability ( and the other advantages of LFP batteries) of your LFP battery and your FLA start battery will be there to start your engine when called on to do so. This will also allow you to charge the start and house batteries independently as they should be with the two different chemistries.

 

[Jdz1]

Great info in this thread thanks to all who contributed. Could someone post of a picture of the DVSR spliced into the fuel pump/12v run? Or maybe link a thread that has pictures of this mod?

Thanks again!!